Review of the Status of Chinook Salmon ( Oncorhynchus tshawytscha) from Washington, Oregon, California, and Idaho under the U. S. Endangered Species Act Prepared by the West Coast Chinook Salmon Biological Review Team 17 Dec 1997 The Biological Review Team ( BRT) for chinook salmon included, from NMFS Northwest Fisheries Science Center: Peggy Busby, Dr. Stewart Grant, Dr. Robert Iwamoto, Dr. Robert Kope, Dr. Conrad Mahnken, Gene Matthews, Dr. James Myers, Philip Roni, Dr. Michael Schiewe, David Teel, Dr. Thomas Wainwright, F. William Waknitz, Dr. Robin Waples, and Dr. John Williams; NMFS Southwest Region: Gregory Bryant and Craig Wingert; NMFS Southwest Region ( Tiburon Laboratory): Dr. Steve Lindley, and Dr. Peter Adams; NMFS Alaska Fisheries Science Center ( Auke Bay Laboratory): Alex Wertheimer; and from the USGS National Biological Service: Dr. Reginald Reisenbichler. iii CONTENTS List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxvii Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 The " Species" Question . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Background of Chinook Salmon under the ESA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Summary of Information Presented by the Petitioners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Distinct Population Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Population Abundance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Causes of Decline for Chinook Salmon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Information Relating to the Species Question . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 General Biology of Chinook Salmon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Ecological Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Geological Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Ecoregions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Coastal Range (# 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Puget Lowland (# 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Willamette Valley (# 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Cascades (# 4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Sierra Nevada (# 5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Southern and Central California Plains and Hills (# 6) . . . . . . . . . . . . . . . . . . . 23 Central California Valley (# 7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Eastern Cascades Slopes and Foothills (# 9) . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Columbia Basin (# 10) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Blue Mountains (# 11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Snake River Basin/ High Desert (# 12) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Northern Rockies (# 15) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Marine Habitat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Chinook Salmon Life History and Ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Juvenile Life History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Ocean Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Size and Age at Maturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Run Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Straying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Fecundity and Egg Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Other Life History Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Regional Variation in Life History Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 iv Puget Sound to the Strait of Juan de Fuca . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Washington and Oregon coasts ( Hoko River to Cape Blanco) . . . . . . . . . . . . . 55 California and southern Oregon coast ( south of Cape Blanco) . . . . . . . . . . . . . 56 California Central Valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Columbia River ocean type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Lower Columbia River ( to the Cascade Crest) . . . . . . . . . . . . . . . . . . 63 Upper Willamette River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Columbia River ( east of the Cascade Crest) . . . . . . . . . . . . . . . . . . . . 69 Columbia River Stream Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Genetic Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Statistical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Previous Genetic Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Pacific Northwest overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Yukon and British Columbia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Washington . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Columbia River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 California and Oregon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Levels of Genetic Differentiation among Populations . . . . . . . . . . . . . . . . . . . . . . . . . . 92 New Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Regional patterns of genetic variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 British Columbia, Washington, Oregon, and California . . . . . . . . . . . . . . . . . 103 Columbia and Snake Rivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Discussion and Conclusions on ESU Determinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Evolutionary Significance of Life History Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Major Chinook Salmon Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 California Central Valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Coastal basins and Puget Sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Columbia River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 ESU Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 1) Sacramento River Winter Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 2) Central Valley Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 3) Central Valley Fall Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 4) Southern Oregon and California Coastal ESU . . . . . . . . . . . . . . . . . . . . . 119 5) Upper Klamath and Trinity Rivers ESU . . . . . . . . . . . . . . . . . . . . . . . . . 120 6) Oregon Coast ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 7) Washington Coast ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 8) Puget Sound ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 9) Lower Columbia River ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 10) Upper Willamette River ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 11) Mid Columbia River Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . 124 12) Upper Columbia River Summer and Fall Run ESU . . . . . . . . . . . . . . . . 124 13) Upper Columbia River Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . 125 v 14) Snake River Fall Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 15) Snake River Spring and Summer Run ESU . . . . . . . . . . . . . . . . . . . . . . 127 Relationship to State Conservation Management Units . . . . . . . . . . . . . . . . . . . . . . . 127 Relationship to ESU Boundaries for other Anadromous Pacific Salmonids . . . . . . . . . 131 Artificial Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Overview of Artificial Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Asia and Oceania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Russia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 New Zealand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 North America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 British Columbia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Columbia River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Scale of Hatchery Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Introduction of Non Native Chinook Salmon into Hatcheries . . . . . . . . . . . . . . . . . . . 149 West Coast Artificial Propagation Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 1) Sacramento River Winter Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 2) Central Valley Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 3) Central Valley Fall Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 4) Southern Oregon and California Coast ESU . . . . . . . . . . . . . . . . . . . . . . 153 5) Upper Klamath and Trinity Rivers ESU . . . . . . . . . . . . . . . . . . . . . . . . . 155 6) Oregon Coast ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 7) Washington Coast ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 8) Puget Sound ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 9) Lower Columbia River ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 10) Upper Willamette River ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 11) Mid Columbia River Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . 165 12) Upper Columbia Summer and Fall Run ESU . . . . . . . . . . . . . . . . . . . . . 167 13) Upper Columbia River Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . 170 14) Snake River Fall Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 15) Snake River Spring and Summer Run ESU . . . . . . . . . . . . . . . . . . . . . . 173 Assessment of Risk Extinction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Absolute Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Historical Abundance and Carrying Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Trends in Abundance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Naturally spawning hatchery fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Habitat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 Regional perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Factors Causing Variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Threats to Genetic Integrity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Recent Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Other Risk Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 vi Previous Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Data Evaluations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Quantitative methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Data types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Computed statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 Analysis of Biological Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Central Valley Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 1) Sacramento River Winter Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 2) Central Valley Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 3) Central Valley Fall Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 Southern Coastal Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 4) Southern Oregon and California Coastal ESU . . . . . . . . . . . . . . . . . . . . . 201 5) Upper Klamath and Trinity River ESU . . . . . . . . . . . . . . . . . . . . . . . . . . 206 Oregon and Washington Coastal Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 6) Oregon Coast ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 7) Washington Coast ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 8) Puget Sound ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 Lower Columbia River Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 9) Lower Columbia River ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 10) Upper Willamette River ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 Upper Columbia and Snake Rivers Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 11) Middle Columbia River Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . 230 12) Upper Columbia River Summer and Fall Run ESU . . . . . . . . . . . . . . . . 234 13) Upper Columbia River Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . 238 14) Snake River Fall Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 15) Snake River Spring and Summer Run ESU . . . . . . . . . . . . . . . . . . . . . . 241 Discussion and Conclusion on ESU Risk Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 1) Sacramento River Winter Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 2) Central Valley Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 3) Central Valley Fall Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 4) Southern Oregon and California Coastal ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 5) Upper Klamath and Trinity Rivers ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 6) Oregon Coast ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 7) Washington Coast ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 8) Puget Sound ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 9) Lower Columbia River ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 10) Upper Willamette River ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 11) Middle Columbia River Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 12) Upper Columbia River Summer and Fall Run ESU . . . . . . . . . . . . . . . . . . . . . . 253 13) Upper Columbia River Spring Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 14) Snake River Fall Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 15) Snake River Spring and Summer Run ESU . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 Citations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Appendix A: Age at Smoltification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 vii Appendix B: Age at Maturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 Appendix C: Reproductive Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 Appendix D: Hatchery Releases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 Appendix E: Abundance Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 Appendix F: The Risk Matrix Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 viii ix List of Figures x xi xii xiii List of Tables xiv EXECUTIVE SUMMARY In 1994, the National Marine Fisheries Service ( NMFS) received a petition ( PRO salmon 1994) requesting the listing of four populations of chinook salmon ( Oncorhynchus tshawytscha) in Puget Sound as threatened or endangered species under the federal Endangered Species Act ( ESA). In response to this petition and the more general concerns for the status of Pacific salmon throughout the region, NMFS announced that it would initiate ESA status reviews for all species and populations of anadromous salmonids in the states of Washington, Idaho, Oregon, and California. Subsequently, NMFS received a petition ( ONRC and Nawa 1995) to list all chinook salmon south of British Columbia under the ESA.

The ESA allows the listing of " distinct population segments" of vertebrates as well as named species and subspecies. The policy of the NMFS on this issue for anadromous Pacific salmonids is that a population will be considered " distinct" for purposes of the ESA if it represents an evolutionarily significant unit ( ESU) of the species as a whole. To be considered an ESU, a population or group of populations must 1) be substantially reproductively isolated from other populations, and 2) contribute substantially to the ecological or genetic diversity of the biological species. Once an ESU is identified, a variety of factors related to population abundance are considered in determining whether a listing is warranted.

West Coast Chinook Salmon ESUs Previous status reviews conducted by the NMFS have identified three ESUs of chinook salmon in the Columbia River: Snake River fall run ( Waples et al. 1991), Snake River spring and summer run ( Matthews and Waples 1991), and mid Columbia River summer and fall run chinook salmon ( Waknitz et al. 1995). In addition, prior to development of the ESU policy, the NMFS recognized Sacramento River winter chinook salmon as a " distinct population segment" under the ESA ( NMFS 1987). In reviewing the biological and ecological information concerning west coast chinook salmon, the Biological Review Team ( BRT) identified 11 additional ESUs for chinook salmon from Washington, Oregon, and California. Genetic data ( from protein electrophoresis and DNA analysis) and tagging information were key factors considered for the reproductive isolation criterion, supplemented by inferences about barriers to migration created by natural features. Life history differences were another important consideration in the designation of ESUs. The BRT utilized the classification system developed by Healey ( 1983, 1991) to describe the two races of chinook salmon: 1) ocean type populations which typically migrate to seawater in their first year of life and spend most of their oceanic life in coastal waters, and 2) stream type populations which migrate to sea as yearlings and often make extensive oceanic migrations. Genetic differences, as measured by variation in allozymes, indicate that the oceanand stream type races represent two major ( and presumably monophyletic) evolutionary lineages. A number of additional factors were considered to be important in evaluations of ecological/ genetic diversity, with data on life history characteristics ( especially ocean distribution, time of freshwater entry, age at smoltification and at maturation) and geographic, hydrological, and environmental characteristics being particularly informative. xvi Chinook Salmon ESUs 1) Sacramento River Winter Run ESU This ESU includes the Upper Sacramento River below Keswick Dam. Historically, winter run populations existed in the Upper Sacramento, Pit, McCloud, and Calaveras Rivers. Winter run chinook salmon were distinguished from other chinook salmon populations in the Sacramento River Basin based on their unique run timing and genetic characteristics. Adult winter run chinook salmon enter the Sacramento River from November to June and spawn from late April to mid August, with a peak from May to June. No other chinook salmon population has a similar life history pattern. In general, winter run chinook salmon exhibit an ocean type lifehistory strategy, and remain near the coasts of California and Oregon during their marine residence. Winter run chinook salmon also mature at a relatively young age ( 2 3 years old). DNA analysis indicates substantial genetic differences between winter run and other chinook salmon temporal runs in the Sacramento River.

2) Central Valley Spring Run ESU This ESU contains the Sacramento River Basin and includes chinook salmon entering the Sacramento River from March to July and spawning from late August through early October, with a peak in September. Spring run fish in the Sacramento River exhibit an ocean type life history, emigrating as fry, subyearlings, and yearlings. Marine coded wire tag ( CWT) recoveries are primarily from fisheries off the California and Oregon coast. Differences in adult size, fecundity, and smolt size were also observed between spring and fall run chinook salmon in the Sacramento River. DNA analyses indicates moderate differences between the spring, fall, and late fall runs in the Sacramento River.

3) Central Valley Fall Run ESU This ESU contains the Sacramento and San Joaquin River Basins and includes fall and late fall run chinook salmon. These populations enter the Sacramento and San Joaquin Rivers from July through March and spawn from October through March. Fish in this ESU are oceantype chinook salmon, emigrating predominantly as fry and subyearlings, remaining off the California coast during their ocean migration. Fall run chinook salmon in the Sacramento and San Joaquin River Basins are physically and genetically distinguishable from coastal forms. xvii 4) Southern Oregon and California Coastal ESU This ESU includes native spring and fall runs of chinook salmon south of Cape Blanco, Oregon. Historically, the range may have extended to the Ventura River in California, but currently does not extend south of San Francisco Bay, California. Also included in this ESU are populations in the Klamath River Basin from the mouth upriver to the confluence of the Trinity and Klamath Rivers. Chinook salmon in this ESU exhibit an ocean type life history, with marine distribution predominantly off the California and Oregon coasts. In contrast, populations north of Cape Blanco ( ESU 5) migrate in a northerly direction, travelling as far north as British Columbia and Alaska. The Cape Blanco region is a major biogeographic boundary for numerous species. Fall run populations predominate in this ESU, with the exception of the Rogue River Basin where there is a substantial spring run. The status of naturally spawning chinook salmon in San Francisco Bay was not determined by the BRT due to a lack of information. Furthermore, the BRT was unable to document the existence of extant naturally spawning chinook salmon populations south of San Francisco Bay. Ecologically, the majority of the river systems in this ESU are relatively small and heavily influenced by a maritime climate.

5) Upper Klamath and Trinity Rivers ESU This ESU includes fall and spring run chinook salmon in the Klamath and Trinity River Basin upstream of the confluence of the Klamath and Trinity Rivers. Historically, spring run chinook salmon were probably the predominant run. This ESU still retains several distinct springrun populations, albeit at much reduced abundance levels. As with all chinook salmon populations south of the Columbia River, fish from this ESU exhibit an ocean type life history; however, genetically and physically, these fish are quite distinct from coastal ( ESU 4 and 6) and Central Valley chinook salmon ( ESU 1, 2, and 3). Marine recoveries of CWTs indicate that both the fall and spring runs have a coastal distribution off the California and Oregon coasts.

6) Oregon Coast ESU This ESU contains coastal basins north of, and including, the Elk River, Oregon, to the mouth of the Columbia River. This ESU includes fall, summer, and spring runs of chinook salmon, with fall run fish predominating in this ESU. With the exception of the Umpqua River Basin, the majority of streams in the ESU are relatively short. The marine distribution, age structure, and genetic characteristics of fish from this ESU are very different from neighboring ESUs ( ESU 4 and 9), although somewhat similar to that of fish from the Washington Coast ( ESU 7). xviii 7) Washington Coast ESU This ESU contains coastal basins north of the mouth of the Columbia River to, but not including, the Elwha River. This ESU includes fall, summer, and spring runs of chinook. These fish exhibit an ocean type life history ( as do all coastal stocks in Washington, Oregon, and California), but their marine distribution and age structure differs considerably from fish in the Puget Sound ( ESU 8) and Lower Columbia River ( ESU 9) ESUs. Fish in this ESU generally mature at 3, 4, and 5 years old and migrate in a northerly direction to British Columbian and Alaskan coastal waters.

8) Puget Sound ESU This ESU contains coastal basins of the eastern part of the Strait of Juan de Fuca, Hood Canal, and Puget Sound. This includes the Elwha River and extends to the Nooksack River Basin and the U. S. Canadian Border. Spring, summer, and fall run chinook salmon are included in this ESU. Puget Sound chinook salmon tend to mature at ages 3 and 4, and are not recovered in Alaskan waters to the same extent as fish from the Washington coast ( ESU 7). The genetic and life history characteristics of Puget Sound chinook salmon are very distinct from the adjacent Washington Coast ESU ( ESU 7); however, the Elwha River chinook salmon were somewhat intermediate between the two ESUs.

9) Lower Columbia River ESU This ESU contains tributaries to the Columbia River from the mouth of the Columbia River to, but not including, the Klickitat River. This includes natural fall and spring run chinook salmon, with the exception of spring run chinook salmon in the Willamette River Basin above Willamette Falls ( see ESU 10). Chinook salmon in this ESU were genetically distinct from their neighboring ESUs, and exhibited distinctive life history traits ( age at maturation) and oceanmigration distribution.

10) Upper Willamette River ESU This ESU contains the Willamette River Basin above the Willamette Falls. The ESU includes natural spring run chinook salmon, but excludes fall run chinook salmon that were introduced above the Willamette Falls. These fish exhibit an ocean type life history, and are very distinct from adjacent ESUs genetically, in their age structure, and in marine distribution. Furthermore, the geography and ecology of the Willamette Valley is considerably different from surrounding areas. Historically, migratory access above Willamette Falls was only possible during a narrow temporal window, which provided a powerful isolating mechanism for upper Willamette River spring run stocks. xix 11) Mid Columbia River Spring Run ESU This ESU includes tributaries to the Columbia River from the Klickitat River Basin upstream to include the Yakima River Basin, excluding the Snake River Basin. This ESU includes natural spring run chinook salmon that exhibit a stream type life history. Genetically and morphologically, this ESU is very distinct from ocean type spring run chinook salmon which exist in the Lower Columbia River ESU, and fall run ( ocean type) fish which cohabit the same rivers as fish belonging to this ESU. Streams in this region drain desert areas east of the Cascades ( Columbia Basin Ecoregion) and are ecologically differentiated from the colder, less productive, glacial streams of the upper Columbia River Spring Run ESU and from the generally higher elevation streams of the Snake River.

12) Upper Columbia River Summer and Fall Run ESU This ESU contains tributaries to the Columbia River upstream of the confluence of the Snake and Columbia Rivers to the Chief Joseph Dam. It includes fall and summer run ( oceantype chinook salmon, with the exception of chinook salmon which spawn in the Marion Drain, an irrigation collection canal to the Yakima River ( see Status Review). Summer run fish in this ESU were heavily influenced by the Grand Coulee Fish Maintenance Project ( 1939 43), whereby fish returning to spawn in the upper Columbia River were trapped at the Rock Island Dam, downstream of the Wenatchee River. Some of these fish were released into enclosed sections of the Wenatchee and Entiat Rivers to spawn naturally, while others were spawned in hatcheries. The result of this project was the mixing of multiple populations into one relatively homogenous group.

13) Upper Columbia River Spring Run ESU This ESU includes tributaries to the Columbia River upstream from the Yakima River to the Chief Joseph Dam. It includes spring run chinook salmon in the Wenatchee, Entiat, and Methow River Basins. These fish all exhibit a stream type life history. Although slight genetic differences exist between this ESU and the other ESUs containing stream type fish ( see ESU 11 and 15), ecological differences in spawning and rearing habitats between these stream type ESUs were important in establishing the ESU boundaries. Fish in this ESU were also influenced by the Grand Coulee Fish Maintenance Project ( 1939 43). The result of this project was the mixing of multiple populations into one relatively homogenous group.

14) Snake River Fall Run ESU This ESU contains tributaries to the Columbia River from the Dalles Dam to the confluence of the Snake and Columbia Rivers, including the Snake River Basin. It includes all native populations of fall run chinook salmon in the mainstem Snake River and the following xx subbasins: Deschutes, John Day, Tucannon, Grand Ronde, Imnaha, Salmon, and Clearwater Rivers. Previously, this ESU had only included fall run chinook salmon from the Snake River Basin, but based on new information presented in this review the ESU was expanded to include the Columbia River populations listed above. Fish from this ESU exhibit an ocean type life history. Genetic and ocean migration differences contrast fish from this ESU with those from ESU 12. The BRT also noted ecological differences between the Snake River Basin and the upper Columbia River ( above the confluence of the Snake River).

15) Snake River Spring and Summer Run ESU This ESU includes tributaries to the Snake River upstream of the Snake and Columbia Rivers' confluence. It includes all natural populations of spring and summer run chinook salmon in the mainstem Snake River and the following subbasins: Tucannon River, Grand Ronde River, Imnaha River, and Salmon River. Although genetic differences between this and other streamtype ESUs ( ESU 11 and 13) are moderate, ecological differences in spawning and rearing habitat were substantial enough to warrant the establishment of distinct ESUs. Genetically and behaviorally, these fish are very different from the ocean type fall run fish that exist in the Snake River Basin.

Assessment of Extinction Risk The ESA ( section 3) defines the term " endangered species" as " any species which is in danger of extinction throughout all or a significant portion of its range." The term " threatened species" is defined as " any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range." According to the ESA, the determination as to whether a species is threatened or endangered should be made on the basis of the best scientific information available regarding its current status, after taking into consideration conservation measures that are proposed or are in place.

For the purposes of this review, the BRT did not evaluate likely or possible effects of conservation measures and therefore did not make recommendations as to whether identified ESUs should be listed as threatened or endangered species. The BRT did, however, draw scientific conclusions about the risk of extinction faced by ESUs under the assumption that present conditions will continue.

With respect to the 11 newly identified ESUs, the BRT concluded that two ( Sacramento River Spring Run and Upper Columbia River Spring Run) are at risk of extinction, primarily due to seriously depressed abundance. Five ESUs ( Central Valley Fall Run, Southern Oregon and California Coast, Puget Sound, Lower Columbia River, and Upper Willamette River) are at risk of becoming endangered, due to a variety of factors. Only four ESUs ( Upper Klamath and Trinity xxi Rivers, Oregon Coast, Washington Coast, and Middle Columbia River Spring Run) are not at risk of extinction or endangerment.

Chinook Salmon ESUs 1) Sacramento River Winter Run ESU Historically, the winter run was abundant and comprised populations in the McCloud, Pit, Little Sacramento, and Calaveras Rivers. Presently, the ESU has been reduced to a single spawning population confined to the mainstem Sacramento River below Keswick Dam. Since counting began in 1967, the population has been declining at an average rate of 18% per year, or roughly 50% per generation. This ESU is currently listed as endangered under the California Endangered Species Act and was listed as threatened in 1989 and reclassified as endangered in 1994 under the U. S. Endangered Species Act.

2) Central Valley Spring Run ESU Spring run chinook salmon were once the predominant run in the Central Valley. Dam construction and habitat degradation has eliminated spring run populations from the entire San Joaquin River Basin and from many tributaries to the Sacramento River Basin. Abundance has declined dramatically from historical levels, and much of the present day production is from artificial propagation. There are only a few naturally spawning populations remaining and these all have relatively low abundances (< 1000). Furthermore, there is concern that the hatchery propagated spring run fish have been inadvertently hybridized with fall run fish. Hatchery release practices result in high levels of straying and an increased potential for hatchery strays spawning with native fish. The majority of the BRT concluded that this ESU was at risk of extinction in the foreseeable future.

3) Central Valley Fall Run ESU Total abundance in this ESU is relatively high, perhaps near historical levels. However, the status of populations in the San Joaquin River Basin are extremely depressed. Spawning and rearing habitat quality throughout the ESU are severely impacted by agricultural and municipal water use activities. Returns to the hatcheries account for 20% of the spawning escapement, and hatchery strays spawning in the wild may account for an further 30% of the spawning escapement. The exchange of stocks between Central Valley hatcheries may have resulted in considerable loss of among population genetic diversity. Furthermore, naturally spawning populations that are least influenced by hatchery strays are experiencing generally negative trends in abundance. Finally, relatively high ocean and freshwater harvest rates may threaten the sustainability of xxii naturally spawning populations. The majority of the BRT felt that this ESU is likely to become at risk of extinction in the foreseeable future.

4) Southern Oregon and California Coastal ESU Populations in this ESU have generally experienced declines in abundance from historical levels, with the exception of populations in the Rogue River. Spring run populations outside of the Rogue River have undergone severe declines. There is an almost complete lack of data for coastal rivers south of the Klamath River, and many rivers which historically sustained large populations of fall run chinook salmon contain severely reduced populations or their populations have been extirpated. The BRT unanimously concluded that this ESU was likely to become at risk of extinction in the foreseeable future.

5) Upper Klamath and Trinity Rivers ESU Fall run populations in this ESU are at relatively high abundances, near historical levels, and trends are generally stable. Hatchery production contributes significantly to total escapement. In contrast, spring run abundance is at only 10% of historical levels, and much of the present production is hatchery derived. Dam construction eliminated much of the historical spring run spawning and rearing habitat and was responsible, in part, for the extirpation of at least seven spring run populations. Due to the disparity in risk status between spring and fall runs, the BRT had considerable difficulty in evaluating the status of this ESU. The majority of the BRT concluded that this ESU, as a whole, was not presently at significant risk of extinction, but there was substantial concern for the status of spring run populations.

6) Oregon Coast ESU Total abundance in this ESU is relatively high. Long term trends for populations are generally upward, although a number of populations are experiencing severe short term trends in abundance. Spring run populations are generally in better condition in this ESU than in other coastal ESUs. Hatchery production appears to be a relatively minor component of total escapement. The BRT unanimously concluded that chinook salmon in this ESU are not in danger of extinction nor are they likely to become so in the foreseeable future.

7) Washington Coast ESU Long term trends for most populations in this ESU have been upward; however, several smaller populations are experiencing sharply downward trends. Fall run populations are predominant and tended to be at a lower risk than spring or summer runs. Hatchery production is significant in the southern portion of this ESU, whereas the majority of the populations in the xxiii northern portion of the ESU have minimal hatchery influence. The BRT unanimously concluded that chinook salmon in this ESU are not in danger of extinction nor are they likely to become so in the foreseeable future.

8) Puget Sound ESU Total abundance in the ESU is relatively high; however, much of this production is hatchery derived. Both long and short term trends in abundance are predominantly downward, and several populations are exhibiting severe short term declines. Spring run chinook salmon populations throughout this ESU are all depressed. The BRT was concerned that the high level of hatchery production is masking more severe underlying trends in abundance. In many areas, spawning and rearing habitats were severely degraded and migratory access restricted or eliminated. A majority of the BRT concluded that this ESU is likely to become endangered in the foreseeable future.

9) Lower Columbia River ESU Abundance in this ESU is relatively high; however, the majority of the fish appear to be hatchery produced. The chinook salmon fall run in the Lewis River appears to be the only healthy naturally produced population in this ESU. Long and short term trends in abundance are mostly negative, some severely so. The numbers of naturally spawning spring runs are very low, in fact, the BRT was unable to identify any healthy native spring run populations. The pervasive influence of hatchery fish in almost every river in this ESU and the degradation of freshwater habitat suggested that many naturally spawning populations are not able to replace themselves. The majority of the BRT concluded that this ESU is likely to become endangered in the foreseeable future.

10) Upper Willamette River ESU Total abundance in this ESU is relatively high ( 20,000 30,000 adults) and stable; however, approximately 10% of escapement spawns naturally, and of the natural spawners more than half are first generation hatchery strays. The introduction of non native fall run chinook salmon above Willamette Falls is viewed as a potential risk to the genetic integrity of this ESU. Furthermore, exchanges of fish between hatcheries in this ESU has most likely lead to the homogenization of populations within the ESU, although this ESU is still quite distinct from adjacent ESUs. The majority of the historical spawning habitat is now inaccessible, and the remaining habitat is quite limited and degraded. The majority of the BRT concluded that this ESU is likely to become endangered in the foreseeable future. xxiv 11) Mid Columbia River Spring Run ESU Total abundance in the ESU has declined considerably from historical levels, but appears to be relatively stable during recent years. Natural production accounts for most of the escapement in the Yakima and Deschutes River Basins. Habitat degradation, especially due to agricultural practices, affects most of the rivers in this ESU. The majority of the BRT concluded that chinook salmon in this ESU are not in danger of extinction nor are they likely to become so in the foreseeable future.

12) Upper Columbia River Summer and Fall Run ESU Total abundance in this ESU is quite high, although naturally spawning chinook salmon in the Hanford Reach are responsible for the vast majority of the production. The BRT was concerned about the recent decline in summer run populations in this ESU, and the apparent increase in the contribution of hatchery return to total escapement. It was unclear if, under current conditions, the naturally spawning summer run chinook salmon populations are selfsustaining In an earlier review, this ESU was determined to be neither at risk of extinction nor likely to become so, and its status was not reviewed in detail here.

13) Upper Columbia River Spring Run ESU Recent total abundance in this ESU is quite low, and escapements from 1994 96 were the lowest in 60 years. At least 6 populations of spring run chinook salmon in the ESU have been extirpated, and almost all remaining naturally spawning populations have fewer than 100 spawners. Hydrosystem development has blocked access to much historical habitat and directly impeded adult and smolt migrations. The majority of the BRT concluded that this ESU is currently at risk of extinction.

14) Snake River Fall Run ESU Historically the Snake River component of this ESU was the predominant source of production. Currently the five year average for Snake River fall run chinook salmon is about 500 adults ( compared with 72,000 in the 1930s and 1940s). The abundance of naturally spawning fish in the Deschutes River has averaged about 6,000 fish ( 1990 96). There is some uncertainty as to the origins of fish spawning in the lower Deschutes River, and their relationship to fish in the upper Deschutes River ( above Sherars Falls). Extirpated populations in the John Day, Umatilla, and Walla Walla Rivers are believed to have belonged to this ESU. Hydrosystem development blocks access to most of the historical spawning habitat in the Snake River portion of this ESU, as well as affecting migration corridors. Snake River fall run chinook salmon are currently listed as a threatened species under the U. S. ESA. The BRT concluded that the newly defined ESU xxv ( which includes the Deschutes River population) is likely to become in danger of extinction in the foreseeable future.

15) Snake River Spring and Summer Run ESU Recent abundance of the naturally spawning population for this ESU has averaged about 2,500 fish, compared to historical levels of approximately 1.5 million. Both long and short term trends are negative for all populations. A number of populations have been extirpated in this ESU, primarily due to dam construction. This ESU is presently listed as a threatened species under the U. S. ESA and was not reviewed further in this document. xxvi xxvii ACKNOWLEDGMENTS The status review for west coast chinook salmon was conducted by a team of scientists from the National Marine Fisheries Service ( NMFS) and the U. S. Geological Survey ( USGS). The members of the biological review team ( BRT) contributed a substantial amount of time and effort to this process. The BRT included: Peggy Busby, Dr. Stewart Grant, Dr. Robert Iwamoto, Dr. Robert Kope, Dr. Conrad Mahnken, Gene Matthews, Dr. James Myers, Philip Roni, Dr. Michael Schiewe, David Teel, Dr. Thomas Wainwright, F. William Waknitz, Dr. Robin Waples, and Dr. John Williams of NMFS Northwest Fisheries Science Center; Gregory Bryant and Craig Wingert of NMFS Southwest Region; Dr. Peter Adams and Dr. Steve Lindley from NMFS Southwest F. S. C. ( Tiburon Laboratory); Alex Wertheimer of NMFS Alaska Fisheries Science Center ( Auke Bay Laboratory); and Dr. Reg Reisenbichler from the USGS Biological Resource Division. Their review was dependent on information submitted directly to NMFS, which was presented at one of the Biological and Technical Committee meetings, provided in response to queries by NMFS or previously published in reports or the scientific literature. A number of state, federal, and tribal agencies actively provided information and critical review during the status review process. The authors wish to acknowledge in particular the efforts of Lisa Seeb and Penny Crane of the Alaska Department of Fish and Game; Alan Baracco, Colleen Harvey, Bill Loudermilk, Debra McKee, Mike Wallace, Dave McLeod, Larry Preston, and Wade Sinnen from the California Department of Fish and Game; Kathryn Kostow and Jay Nicholas of the Oregon Department of Fish and Wildlife; Susan Bishop, formerly of the Northwest Indian Fisheries Commission; Duane Anderson and Gary Christofferson of StreamNet; Jim Craig and Doug Olsen from U. S. Fish and Wildlife Service; Jerry Boberg and Al Olsen of the U. S. Forest Service; and Anne Marshall, Carol Smith, Bill Tweit, and Bob Woodard of the Washington Department of Fish and Wildlife.

The authors also wish to thank the external reviewers, Dr. T. Bjornn, Dr. R. Hankin, Dr. E. Taylor, and Dr. F. Utter, who provided considerable insight and clarity to the complex issues concerning chinook salmon. Additional thanks to Judith Larsen, Tod McCoy, Sue Joerger, Kathleen Jewett, and JoAnne Butzerin for their editorial and technical writing skills. xxviii 1 The use of the term " spring run" to describe the chinook salmon returning to the Dungeness River has been discontinued by state, tribal, and federal agencies. It has been replaced with the term " native," but in this report the term " spring run" has been retained for the purpose of maintaining consistency with older references to the stock. INTRODUCTION On 14 March 1994, the National Marine Fisheries Service ( NMFS) was petitioned by the Professional Resources Organization Salmon ( PRO Salmon) to list spring run populations of chinook salmon ( Oncorhynchus tshawytscha) in the North Fork and South Fork Nooksack River, the Dungeness River1, and the White River ( Fig. 1) as threatened or endangered species under the Endangered Species Act ( ESA) either singly, or in some combination ( PRO Salmon 1994). At about the same time, NMFS also received petitions to list additional populations of other Pacific salmon species in the Puget Sound area. In response to these petitions and the more general concerns for the status of Pacific salmon throughout the region, NMFS announced on 12 September 1994 that it would initiate ESA status reviews for all species of anadromous salmonids in Washington, Oregon, California, and Idaho ( NMFS 1994d). This proactive approach was intended to facilitate more timely, consistent, and comprehensive evaluations of the ESA status of Pacific salmonids than would be possible through a long series of reviews of individual populations. Subsequent to this announcement, NMFS was petitioned on 1 February 1995 by the Oregon Natural Resources Council ( ONRC) and Siskiyou Project Staff Ecologist Dr. Richard K. Nawa to list 197 stocks of chinook salmon either separately or in some combination.

This document reports results of the comprehensive ESA status review of chinook salmon from Washington, Oregon, California, and Idaho. To provide a context for evaluating these populations of chinook salmon, biological and ecological information for chinook salmon in British Columbia, Alaska, and Asia were also considered. This review thus encompasses, but is not restricted to, the populations identified in the PRO Salmon and ONRC Nawa petitions.

Because the ESA stipulates that listing determinations should be made on the basis of the best scientific information available, NMFS formed a team of scientists with diverse backgrounds in salmon biology to conduct this review. This Biological Review Team ( BRT) for chinook salmon included: Peggy Busby, Dr. Stewart Grant, Dr. Robert Iwamoto, Dr. Robert Kope, Dr. Conrad Mahnken, Gene Matthews, Dr. James Myers, Philip Roni, Dr. Michael Schiewe, David Teel, Dr. Thomas Wainwright, F. William Waknitz, Dr. Robin Waples, and Dr. John Williams of NMFS Northwest Fisheries Science Center; Gregory Bryant and Craig Wingert of NMFS Southwest Region; Dr. Steve Lindley and Dr. Peter Adams from NMFS Southwest Region ( Tiburon Laboratory); Alex Wertheimer of NMFS Alaska Fisheries Science Center ( Auke Bay Laboratory); and Dr. Reg Reisenbichler from the USGS Biological Resource Division. NMFS received scientific and technical information from Pacific Salmon Biological and Technical Committees ( PSBTCs) convened in Washington, Oregon, and California. Meetings of the PSBTC were not held in Idaho because all chinook salmon populations in Idaho 2 Figure 1. Map showing major rivers and other key geographic features discussed. 3 are already listed under the ESA. The BRT discussed and evaluated scientific information gathered at the PSBTC meetings, and also reviewed information submitted to the ESA administrative record for chinook salmon, including specific comments by co managing agencies on a draft version of this document ( CDFG 1997b, HVTC 1997, IDFG 1997, LIBC 1997, NWIFC 1997a, ODFW 1997a, and WDFW 1997a, YTFP 1997a).

In determining whether a listing under the ESA is warranted, two key questions must be addressed:

1) Is the entity in question a " species" as defined by the ESA? 2) If so, is the " species" threatened or endangered?

These two questions are addressed in separate sections of this report. If it is determined that a listing( s) is warranted, then NMFS is required by law ( 1973 ESA Sec. 4( a)( 1)) to identify one or more of the following factors responsible for the species' threatened or endangered status: 1) destruction or modification of habitat, 2) overutilization by humans, 3) disease or predation, 4) inadequacy of existing regulatory mechanisms, or 5) other natural or human factors. This status review does not formally address factors for decline; except insofar as they provide information about the degree of risk faced by the species in the future if current conditions continue. A separate document identifies factors for decline of chinook salmon from Washington, Oregon, California, and Idaho, and is presented subsequent to any proposed listing recommendation.

The " Species" Question As amended in 1978, the ESA allows listing of " distinct population segments" of vertebrates as well as named species and subspecies. However, the ESA provides no specific guidance for determining what constitutes a distinct population, and the resulting ambiguity has led to the use of a variety of criteria in listing decisions over the past decade. To clarify the issue for Pacific salmon, NMFS published a policy document describing how the agency will apply the definition of " species" in the ESA to anadromous salmonid species, including sea run cutthroat trout and steelhead ( NMFS 1991). A more detailed discussion of this topic appeared in the NMFS " Definition of Species" paper ( Waples 1991b). The NMFS policy stipulates that a salmon population ( or group of populations) will be considered " distinct" for purposes of the ESA if it represents an evolutionarily significant unit ( ESU) of the biological species. An ESU is defined as a population that 1) is substantially reproductively isolated from conspecific populations and 2) represents an important component of the evolutionary legacy of the species.

The term " evolutionary legacy" is used in the sense of " inheritance," that is, something received from the past and carried forward into the future. Specifically, the evolutionary legacy of a species is the genetic variability that is a product of past evolutionary events and that represents 4 the reservoir upon which future evolutionary potential depends. Conservation of these genetic resources should help to ensure that the dynamic process of evolution will not be unduly constrained in the future.

The NMFS policy identifies a number of types of evidence that should be considered in the species determination. For each of the criteria, the NMFS policy advocates a holistic approach that considers all types of available information as well as their strengths and limitations. Isolation does not have to be absolute, but it must be strong enough to permit evolutionarily important differences to accrue in different population units. Important types of information to consider include natural rates of straying and recolonization, evaluations of the efficacy of natural barriers, and measurements of genetic differences between populations. Data from protein electrophoresis or deoxyribonucleic acid ( DNA) analyses can be particularly useful for this criterion because they reflect levels of gene flow that have occurred over evolutionary time scales.

The key question with respect to the second ESU criterion is, if the population became extinct, would this represent a significant loss to the ecological/ genetic diversity of the species? Again, a variety of types of information should be considered. Phenotypic and life history traits such as size, fecundity, migration patterns, and age and time of spawning may reflect local adaptations of evolutionary importance, but interpretation of these traits is complicated by their sensitivity to environmental conditions. Data from protein electrophoresis or DNA analyses provide valuable insight into the process of genetic differentiation among populations but little direct information regarding the extent of adaptive genetic differences. Habitat differences suggest the possibility for local adaptations but do not prove that such adaptations exist.

Background of Chinook Salmon under the ESA On 7 November 1985, NMFS received a petition from the American Fisheries Society ( AFS) to list the winter run chinook salmon in the Sacramento River as a threatened species under the federal ESA. NMFS initially announced its decision not to list this population as threatened or endangered on 27 February 1987 ( NMFS 1987). Subsequently, the winter run chinook salmon population experienced a further decline, and an emergency listing to list the population as threatened was made on 4 August 1989 ( NMFS 1989); the listing was extended on 2 April 1990 ( NMFS 1990a). A final rule to list the Sacramento River winter run chinook salmon as threatened was made on 5 November 1990 ( NMFS 1990b). The winter run continued to decline and was subsequently listed as endangered 4 January 1994 ( NMFS 1994b).

On 7 June 1990, NMFS received a petition from Oregon Trout and five co petitioners to list Snake River spring run chinook salmon, Snake River summer run chinook salmon, and Snake River fall run chinook salmon under the ESA. A final rule was announced on 22 April 1992 ( NMFS 1992), which determined that Snake River chinook salmon should be listed as threatened under the ESA. Furthermore, it was determined that the spring and summer run 5 2 Mid Columbia was used by the petitioners to refer to the Columbia River Basin between Priest Rapids and Chief Joseph Dams. populations collectively constituted a separate ESU from the fall run chinook salmon under the ESA. As a result of record low adult returns in 1994 and projected returns for 1995, an emergency interim rule was announced 18 August 1994 to reclassify the Snake River spring/ summer run and Snake River fall run as endangered ( NMFS 1994c); however, both Snake River chinook salmon ESUs were subsequently classified ( 17 April 1995) in a final ruling as being threatened ( NMFS 1995a).

A petition for the listing of summer run chinook salmon in the mid Columbia River2 was submitted to NMFS on 3 June 1993, by the American Rivers and ten co petitioners. On 23 September 1994, NMFS determined that the mid Columbia River summer run chinook salmon stocks petitioned did not constitute an ESU, but belonged to a larger fall and summer run chinook salmon ESU located along the mainstem Columbia River between the Chief Joseph and McNary Dams ( NMFS 1994a). NMFS concluded that this ESU did not warrant a listing of endangered or threatened.

Summary of Information Presented by the Petitioners This section briefly summarizes information presented by the petitioners ( Professional Resources Organization ( PRO) Salmon 1994, Oregon National Resources Council ( ONRC) and Nawa 1995) to support their arguments that specific chinook salmon stocks in Washington, Oregon, Idaho, and California qualify as threatened or endangered species under the ESA. Previous ESA petitions for chinook salmon under the ESA have been evaluated and summarized in elsewhere ( NMFS 1987, Matthews and Waples 1991, Waples et al. 1991b, Waknitz et al. 1995).

Distinct Population Segments The PRO Salmon ( 1994) petition requested that NMFS evaluate four stocks of chinook salmon in Washington state for listing as threatened or endangered under the ESA: the North Fork Nooksack River spring run, South Fork Nooksack River spring run, Dungeness River spring run, and White River spring run. The petitioners presented several alternative groupings of these stocks into one or more ESUs, which might also include stocks not specifically mentioned in their petition. The ONRC and Nawa ( 1995) petition listed 197 " stocks" in Washington, Oregon, California, and Idaho to be considered for listing as threatened or endangered, either separately or in one or more ESUs. The authors specifically included non native stocks, such as Clearwater River spring run chinook salmon, which contains components of other spring run stocks from the 6 Snake River spring and summer run ESU. They argued that if an ESU that contains the original components of a mixed stock is identified and listed as threatened or endangered, then the mixed stock should be included in the ESU.

ONRC and Nawa suggested several alternative scenarios for chinook salmon, specifically, to list:

° chinook salmon and their critical habitat as an ESU in Washington, Oregon, California, and Idaho; or ° spring, summer, fall, and winter chinook salmon and their critical habitat as four distinct ESUs; or ° ESUs which comprise one or more of the 197 stocks of chinook salmon ( listed in the petition), the four stocks previously petitioned by PRO Salmon in addition to stocks which belong to the four existing chinook salmon ESUs identified by NMFS, and their critical habitat; or ° each of the 197 stocks of chinook salmon ( listed in the petition) and the 4 stocks previously petitioned by PRO Salmon as separate ESUs, in addition to the 4 existing chinook salmon ESUs identified by NMFS; or ° regional ESUs: ( a) spring and summer run chinook salmon in Washington, Oregon, California, and Idaho; ( b) coastal fall chinook salmon that spawn in rivers and creeks south of Cape Blanco, Oregon ( excluding Rogue River fall chinook salmon); ( c) Columbia River fall chinook salmon, which spawn in tributaries below McNary Dam; ( d) Puget Sound fall and summer/ fall chinook salmon ( including Sooes River fall chinook salmon on the Washington Coast); and ( e) fall chinook salmon from the Central Valley of California ( including " wild" fall chinook salmon that spawn in small tributaries to San Francisco Bay) and their critical habitat.

Population Abundance Both the PRO Salmon ( 1994) and ONRC and Nawa ( 1995) petitions cited extensive information to document the decline of specific chinook salmon stocks. PRO Salmon ( 1994) cited the work of Nehlsen et al. ( 1991), who considered the four stocks of chinook salmon in the petition to be at a high or moderate risk of extinction, and WDF et al. ( 1993), who identified the status of the four stocks as " critical," based on " chronically low" escapement or redd counts. The spring run on the White River had declined from 5,432 in 1942 to a low of 66 in 1977, and return numbers have averaged less than 200 fish from 1978 91 ( PRO Salmon 1994). Escapement estimates for the North Fork Nooksack River spring run are less accurate because of unfavorable 7 river conditions for sampling. Spawner/ redd surveys nevertheless indicate a considerable decrease in stock size.

ONRC and Nawa ( 1995) surveyed and categorized 417 stocks of chinook salmon, of which they considered 67 ( 16.1%) to be extinct, 21 ( 5.0%) nearly extinct, 95 ( 22.8%) declining, 75 ( 18.0%) composite production [ in which the hatchery contribution exceeds natural production], and a further 37 ( 8.9%) of unknown status. Using information from a number of sources, the petitioners presented overall and regional estimates of the decline of chinook salmon stocks. Nehlsen et al. ( 1991) listed 64 stocks of chinook salmon that they determined to be at a high or moderate risk of extinction or of special concern. WDF et al. ( 1993) determined the status of 40 of the 108 ( 37.0%) chinook salmon stocks in Washington State to be " critical" or " depressed." The Wilderness Society ( 1993) reported that 63% of spring and summer run chinook salmon stocks in Washington, Oregon, California, and Idaho were considered to be extinct, with a further 24% being endangered or threatened. Similarly, among fall chinook salmon stocks, 19% were extinct, and 25% endangered or threatened.

On a regional basis, the Central Valley of California had the highest percentage of extinct stocks ( 40%), with only one wild stock classified as not declining according to ONRC and Nawa ( 1995). Stocks within the coastal basins south of Cape Blanco, Oregon had also experienced a similar decrease in abundance, with 67% of the stocks classified as extinct, nearly extinct, or declining. Within the Columbia River Basin, chinook salmon stocks below McNary Dam ( River Kilometer [ RKm] 470) have been heavily influenced by artificial propagation, and only six wild stocks were identified that were not declining. According to ONRC and Nawa, the Columbia River chinook salmon stocks above McNary Dam have experienced the second highest level of extinction ( 28%), with 44% of the stocks being classified as declining. In the Snake River, the petitioners identified 13 stocks ( 28%) as being extinct and 22 stocks ( 47%) to be in decline. No wild stocks were found that were not declining. Among chinook salmon stocks in Puget Sound, 50% of the spring run stocks were extinct. Only coastal stocks north of Cape Blanco, Oregon were not found to be seriously declining. ONRC and Nawa ( 1995) presented individual stock historical abundance information for many of the 417 stocks surveyed. This information further documented many of the regional declines noted above.

Causes of Decline for Chinook Salmon The petitioners identified several factors which they believe have either singly or in combination resulted in the chinook salmon stock declines in abundance described above. Because the petitions cover such a wide geographic area, encompassing several terrestrial and marine ecological regions, and because the populations surveyed have been impacted by varying anthropogenic factors, only a very generalized review of this topic will be given. 8 3 The term dams includes the physical presence of mainstem dams, the operation of the hydropower system, reservoir storage, and water withdrawal associated with dams.

4 Logging activities include tree cutting, road building, and splash damming ( historically). PRO Salmon ( 1994) and ONRC and Nawa ( 1995) both cited references indicating that habitat degradation is the major cause for the decline in the petitioned chinook salmon stocks. The influence of dams3 was most commonly implicated by ONRC and Nawa ( 1995) as being responsible for the decline or extinction of chinook salmon stocks. Of the stock extinctions surveyed in the coastwide region, 76% were dam related. This was most noticeable in the Central Valley, California where 100% of the extinctions surveyed were dam related ( Campbell and Moyle 1990). Furthermore, 48 of the spring and summer run stocks found to be in decline were affected by dams. Two of the four chinook salmon stocks petitioned by PRO Salmon ( 1994) were impacted to some extent by dam operation, but logging4 and agricultural land use/ water diversion ( including diking) also figured as major factors in all four stocks. The Nooksack Technical Group ( 1987) indicated that sedimentation from logging activities had seriously impacted the quality of the spawning habitats in both the North and South Forks of the Nooksack River. PRO Salmon ( 1994) considered water diversion for agricultural use to be a major contributor to the decline of the Dungeness River spring run. Overall, ONRC and Nawa ( 1995) estimated that logging was responsible, in part, for 60% of the declines and 6% of the extinctions among the stocks surveyed. Similarly, agriculture, water withdrawal, mining and urbanization factors were implicated in 58% of the declines and 9% of the extinctions among the 417 stocks surveyed. Both petitioners also presented evidence that the exploitation rates on the stocks were sufficiently high to have seriously depleted stocks or been partially responsible for the extinction of stocks ( Dosewallips, Duckabush, and Mokelumne Rivers spring run chinook salmon ( ONRC and Nawa 1995)).

The other major concern of the petitioners was the impact of introduced and/ or artificially propagated fish on indigenous stocks. Potentially deleterious impacts of artificial propagation presented by ONRC and Nawa ( 1995) include: interbreeding of fall and spring runs in California due to habitat alterations ( Campbell and Moyle 1990), interspecies hybridization between chinook and coho salmon ( Oncorhynchus kisutch Walbaum) ( Bartley et al. 1990), competition between hatchery and native stocks, interbreeding between hatchery and native chinook salmon stocks, disease introductions by artificially propagated fish, and the unsustainability of hatchery stocks in general. Finally, ONRC and Nawa ( 1995) suggested the " inadequacy of existing regulatory mechanisms" was a general reason for the overall decline in abundance of chinook salmon. 9 INFORMATION RELATING TO THE SPECIES QUESTION In this section, we summarize biological and environmental information and consider the relevancy of each in determining the nature and extent of West Coast chinook salmon ESUs. ESU boundaries were determined by the BRT on the basis of the team's professional opinion of the degree to which environmental and biological attributes exhibited significant changes with respect to the reproductive isolation and ecological/ genetic diversity of West Coast chinook salmon.

General Biology of Chinook Salmon Chinook salmon, also commonly referred to as king, spring, quinnat, Sacramento, California, or tyee salmon, is the largest of the Pacific salmon ( Netboy 1958). The species distribution historically ranged from the Ventura River in California to Point Hope, Alaska in North America, and in northeastern Asia from Hokkaido, Japan to the Anadyr River in Russia ( Healey 1991). Additionally, chinook salmon have been reported in the Mackenzie River area of northern Canada ( McPhail and Lindsey 1970). Of the Pacific salmon, chinook salmon exhibit arguably the most diverse and complex life history strategies Healey ( 1986) described 16 age categories for chinook salmon, 7 total ages with 3 possible freshwater ages. This level of complexity is roughly comparable to sockeye salmon ( O. nerka), although sockeye salmon have a more extended freshwater residence period and utilize different freshwater habitats ( Miller and Brannon 1982, Burgner 1991). Two generalized freshwater life history types were initially described by Gilbert ( 1912): " stream type" chinook salmon reside in freshwater for a year or more following emergence, whereas " ocean type" chinook salmon migrate to the ocean within their first year. Healey ( 1983, 1991) has promoted the use of broader definitions for " ocean type" and " stream type" to describe two distinct races of chinook salmon. This racial approach incorporates life history traits, geographic distribution, and genetic differentiation and provides a valuable frame of reference for comparisons of chinook salmon populations. For this reason, the BRT has adopted the broader " racial" definitions of ocean and stream type for this review.

The generalized life history of Pacific salmon involves incubation, hatching, and emergence in freshwater, migration to the ocean, and subsequent initiation of maturation and return to freshwater for completion of maturation and spawning ( Fig. 2). Juvenile rearing in freshwater can be minimal or extended. Additionally, some male chinook salmon mature in freshwater, thereby foregoing emigration to the ocean. The timing and duration of each of these stages is related to genetic and environmental determinants and their interactions to varying degrees. Salmon exhibit a high degree of variability in life history traits; however, there is considerable debate as to what degree this variability is the result of local adaptation or the general plasticity of the salmonid genome ( Ricker 1972, Healey 1991, Taylor 1991). 10 11 Several types of biological evidence were considered in evaluating the contribution of West Coast chinook salmon to ecological/ genetic diversity of the biological species under the ESA. Life history traits examined for naturally spawning chinook salmon populations included smolt size and outmigration timing, age and size at spawning, river entry timing, spawn timing, fecundity, and ocean migration. These traits are believed to have both a genetic and environmental basis, and similarities among populations could indicate either a shared genetic heritage or similar responses to shared environmental conditions.

The analysis of life history trait information is complicated by several factors. Data collected from different locations during different years are confounded by spatial and temporal environmental variability. This variability creates considerable " noise," which may be as large as differences between geographically distant populations, and may mask subtle regional patterns. High interannual variability also complicates the comparison of results from studies conducted during different time periods. For chinook salmon, for which a single broodyear may return from the ocean over a 5 or 6 year period, variations in ocean productivity due to events such as the 1983 El Niño ( Johnson 1988b) may bias estimates of age distribution, age size relationships, and/ or age and size related fecundity estimates. Furthermore, it may be difficult to distinguish between fish from different runs emigrating from, or returning to, the same river system. Direct comparisons of chinook salmon life history traits between stocks under controlled conditions are limited in number, and the extent to which inference can be made to wild populations is uncertain.

A third confounding complication is that the expression of life history traits may be altered by anthropogenic activities such as land use practices ( Hartman et al. 1984, Holtby 1987), harvest ( Ricker 1981), or artificial propagation ( Steward and Bjornn 1990, Flagg et al. 1995b). To help limit any bias introduced by artificial propagation, life history trait comparisons in this status review have focused on naturally spawning populations. However, because of the widespread practice of off station plants of hatchery reared fry and smolts, many studies of naturally spawning populations may have inadvertently included first generation hatchery fish or fish whose ancestors have been hatchery reared. Life history trait information from hatchery populations was used only when insufficient information from naturally spawning populations was available, as in the case of ocean migration patterns. As with environmental variability, the effects of anthropogenic activities may confound the expression of life history traits and are difficult to factor out.

Because of these potential sources of variability, we felt that statistical analyses of lifehistory trait variability would not be particularly informative. Instead, data were collected from as many sources as possible from each system to give some indication of the mean and range in character traits. Older data sets were especially sought to provide insight into chinook salmon population characteristics prior to the proliferation of hatchery programs, which have produced fish with relatively high juvenile survival and growth rates and modified saltwater entry dates.

Ecological Features 12 Geological Events The geologic events of the last 20,000 years have provided mechanisms for genetic isolation, colonization, and population interbreeding. In determining ESU boundaries it is useful to understand the factors that may have shaped present day chinook salmon population distributions. Much of the present distribution of aquatic and terrestrial species in western North America is a legacy of the volcanic, tectonic, and glacial forces that have shaped this region. Events such as headwater transfer or stream capture have altered the flow of major rivers and the aquatic species that inhabit them. The Cordilleran ice sheet was the last major glacial event to affect the distribution of chinook salmon. At its height some 10,000 15,000 years ago, vast areas of Southeast Alaska, British Columbia, Washington, and Idaho were covered with ice ( McPhail and Lindsey 1970). This created a discontinuous distribution of chinook salmon stocks. Two major ice free refugia existed: Beringia, composed of the Bering land bridge connecting Eastern Siberia and Western Alaska; and Cascadia, composed of the lands south of the mid Columbia River drainage ( McPhail and Lindsey 1970). An additional ice free refuge existed on the coast of the Olympic Peninsula in the area of the Chehalis River. The drop in sea level during the glacial periods may have created minor refugia along the coast of Vancouver Island or the present day Queen Charlotte Islands ( McPhail and Lindsey 1986). As the ice sheet receded, the colonization of newly exposed freshwater habitat began from the two refugia.

Chinook salmon colonization during the postglacial period ( approximately beginning 10,000 years ago) occurred through a number of possible pathways. Straying adults could invade coastal river systems, as could salmon that moved farther upriver to headwaters exposed by the receding glaciers. Ice dams and land expansion after the retreat of glacial ice sheets caused rivers to alter course and change watersheds. Watershed capture has resulted in the exchange of aquatic organisms between several major river systems. Parts of the present day Fraser River drainage flowed into the Columbia River via the Okanogan River and Shuswap Creek during the last deglaciation ( McPhail and Lindsey 1986). Species that moved into the Upper Fraser River from the Columbia River also gained access to southeastern Alaskan coastal rivers. The Stikine, Skeena, and Nass Rivers at various times drained east into the Fraser River Basin relative to their current westerly flow to the Gulf of Alaska ( McPhail and Lindsey 1986). Similarly, the Alsek River in Alaska, which also flows to the Gulf of Alaska, drained what is now part of the Yukon River headwaters ( Lindsey and McPhail 1986). Presently, the headwaters of the Taku, Stikine, and Yukon Rivers lie within 50 miles of one another. Chinook salmon populations from Beringia also had access to the Mackenzie River in Canada during the deglaciation, which may explain recurring reports of chinook salmon in that river system ( McPhail and Lindsey 1970).

Ecoregions 13 The fidelity with which chinook salmon return to their natal stream implies a close association between a specific stock and its freshwater environment. The selective pressures of different freshwater environments may be responsible for differences in life history strategies among stocks. Miller and Brannon ( 1982) hypothesized that local temperature regimes are the major factor influencing life history traits. If the boundaries of distinct freshwater habitats coincide with differences in life histories it would suggest a certain degree of local adaptation. Therefore, identifying distinct freshwater, terrestrial, and climatic regions may be useful in identifying chinook salmon ESUs. The Environmental Protection Agency ( EPA) has established a system of ecoregion designations based on soil content, topography, climate, potential vegetation, and land use ( Omernik 1987). These ecoregions are similar to the physiographic provinces determined by the Pacific Northwest River Basins Commission ( PNRBC 1969) for the Pacific Northwest. Historically, the distribution of chinook salmon in Washington, Oregon, California, and Idaho would have included 13 of the present day EPA ecoregions ( Fig. 3). Similarly, there is a strong relationship between ecoregions and freshwater fish assemblages ( Hughes et al. 1987). We have retained the ecoregion names and numbers used by Omernik ( 1987) and included physiographic information presented by PNRBC ( 1969), present day water use information ( USGS 1993), river flow information ( Hydrosphere Products, Inc. 1993), and climate data from the U. S. Department of Commerce ( 1968) into the appropriate ecoregion description ( Omernik and Gallant 1986, Omernik 1987). Additional information for British Columbia ( Environment Canada 1977, 1991) and Alaska ( Hydrosphere Products, Inc. 1993) is included for comparative purposes. The following ecoregions are wholly or partially contained within the historical natural range of chinook salmon in Washington, Oregon, California, and Idaho.

Coastal Range (# 1)

Extending from the Olympic Peninsula through the Coast Range proper and down to the Klamath Mountains and the San Francisco Bay area, this region is influenced by medium to high rainfall levels due to the interaction between marine weather systems and the mountainous nature of the region. Topographically, the region averages about 500 m in elevation, with mountain tops under 1,200 m. These mountains are generally rugged with steep canyons. Between the ocean and the mountains lies a narrow coastal plain composed of sand, silt, and gravel. Tributary streams are short and have a steep gradient; therefore, surface runoff is rapid and water storage is relatively short term during periods of no recharge. These rivers are especially prone to low flows during times of drought. Regional rainfall averages 200 240 cm per year ( Fig. 4), with generally lower levels along the southern Oregon coast. Average annual river flows for most rivers in this region are among the highest found on the West Coast when adjusted for watershed area ( Fig. 5). River flows peak during winter rain storms common in December and January ( Fig. 6). Snow melt adds to the surface runoff in the spring, providing a second flow peak, and 14 Figure 3. U. S. Environmental Protection Agency ecoregions for California, Idaho, Oregon, and Washington ( Omernik and Gallant 198, Omernik 1987). Regions are based on land use, climate, topography, potential natural vegetation, and soils. Ecoregions with number designations are described in the text. 15 Figure 4. Average annual precipitation ( cm) for selected areas of Washington, Oregon, California, and Idaho ( U. S. Dep. Commerce 1968). 16 Figure 5. Average annual flow per area ( m ³ seconds( s) 1km 2) for selected river basins in Alaska, British Columbia, Washington, Oregon, California, and Idaho. Values were calculated as the average annual flow for each gauging station divided by the reported gauged area. Based on USGS streamflow data ( Hydrosphere Data Products, Inc. 1993) and Inland Water Directorate streamflow data ( Environment Canada 1991) ( modified from Weitkamp et al. 1995). 17 Figure 6. Timing of annual peak flow ( by month) for selected river basins in Alaska, British Columbia, Washington, Oregon, California, and Idaho. If two peaks in flow occur, the higher of the two peaks is represented. Based on USGS streamflow data ( Hydrosphere Data Products, Inc. 1993) and Inland Water Directorate streamflow data ( Environment Canada 1991) ( modified from Weitkamp et al. 1995). 18 there are long periods when the river flows are maintained at least 50% of peak flow ( Fig. 7). During July or August there is usually no precipitation; this period may expand to 2 or 3 months every few years. River flows are correspondingly at their lowest ( Fig. 8) and temperatures at their highest during August and September ( Fig. 9). Oregon coastal rivers have the largest relative difference in minimum and maximum flows, where minimum flows are 2 5% of the maximum flows.

The region is heavily forested primarily with Sitka spruce, western hemlock, and western red cedar. Forest undergrowth is composed of numerous types of shrubs and herbaceous plants.

Puget Lowland (# 2)

Situated between the Coast Range and Cascade Range Ecoregion, this region experiences reduced rainfalls ( 50 120 cm) from the rainshadow effect of the Coast Mountains. The area is generally flat with high hills ( 600 m) at the southern margin of the ecoregion. Soils are composed of alluvial and lacustrine deposits. These deposits are glacial in origin north of Centralia, Washington. This area tends to have large groundwater resources, with groundwater from the bordering mountain ranges helping sustain river flows during drought periods. Peak river flow varies from December to June depending on the contribution of snowpack to surface runoff for each river system. Rivers tend to have sustained flows ( 5 to 8 months of flows at 50% of the peak or more), and low flows are generally 10 20% or more of the peak flows.

Douglas fir represent the primary subclimax forest species, with other coniferous species ( lodgepole, western white, and ponderosa pines) locally abundant. Prairie, swamp, and oak, birch, or alder woodlands are also common. The land is heavily forested, and wood cutting activities ( including road building, etc.) contribute to soil erosion, river siltation, and river flow and temperature alteration.

The region is heavily urbanized, and domestic and industrial wastes impact local water systems. Urban run off and sewage treatment influence water quality west of the Cascade Mountains, with the exception of the Olympic Peninsula coastal and northern Puget Sound rivers. Glacial sediment also influences water quality, especially in the Skagit, North Fork Nooksack, Nisqually, and Puyallup/ White River Basins.

Willamette Valley (# 3)

Adjoining the southern border of the Puget Sound Lowland Ecoregion at the Lewis River, this region was not glacially influenced. A rainshadow effect, similar to the one influencing the Puget Sound Lowlands, limits rainfall to about 120 cm per year. River flows peak in December and January and are sustained for 6 or 7 months of the year. Low flows occur in August and September, although the volume is generally 20% of the peak flow. 19 Figu re 7. Duration of high flows ( number of months when flow is equal to or exceeds 50% of peak monthly flow) for selected river basins in Alaska, British Columbia, Washington, Oregon, California, and Idaho. Based on USGS streamflow data ( Hydrosphere Data Products, Inc. 1993) and Inland Water Directorate streamflow data ( Environment Canada 1991) ( modified from Weitkamp et al. 1995). 20 Figure 8. Timing of annual low flow ( by month) for selected river basins in Alaska, British Columbia, Washington, Oregon, California, and Idaho. If two peaks in flow occur, ( Hydrosphere Data Products, Inc. 1993) and Inland Water Directorate streamflow data ( Environment Canada 1991) ( modified from Weitkamp et al. 1995). 21 Figure 9. Annual maximum monthly stream temperatures ( 0C) for selected river basins in Alaska, British Columbia, Washington, California, Oregon, and Idaho. Based on USGS streamflow data ( Hydrosphere Data Products, Inc. 1993) and Inland Water Directorate temperature data ( Environment Canada 1991) ( modified from Weitkamp et al. 1995). 22 Much of the land has been converted to agricultural use, with Douglas fir and Oregon white oak stands present in less developed areas. Irrigation is commonly employed, and stream flows, especially in the southern portion of this region, can be significantly affected. Agricultural and livestock practices contribute to soil erosion and fertilizer/ manure deposition into stream systems.

Water quality is impacted by agricultural and urban activities. Many water quality problems are exacerbated by low water flows and high temperatures during the summer. Pulp and paper mill discharges of dioxin into the Columbia and Willamette Rivers were cited as another water quality concern, although this situation has been much more serious in the past ( USGS 1993).

Cascades (# 4)

This region is composed of the Cascade Range in Washington and Oregon and the Olympic Mountains in Washington state. Peaks above 3,000 m are distributed throughout the region. The crest of the Cascade Range ( averaging 1,500 m) captures much of the ocean moisture moving eastward in addition to providing a biological barrier. Rainfalls can average 280 cm per year ( up to 380 cm in the Olympic Mountains), much of which is in the form of heavy snowpack. Intensive rainstorms, those depositing more than 2.5 cm per hour, are rare. Rainfall is generally spread over the year with the majority occurring between October and March. Except where porous rock substrate exists, there is little capacity for long term groundwater storage. In these porous rock areas, streams receive 75 95% of their average discharge as groundwater, and are able to maintain their flows during dry periods. Surface water flow originating in the Cascades and Olympic Mountains influences river flows throughout this region.

Currently the area is primarily forested with Douglas fir, noble fir, and Pacific silver fir ( all subclimax species), whereas western hemlock and red cedar are common climax species. At higher elevations, these trees are replaced by Englemann spruce, whitebark pine, and mountain hemlock. Forest undergrowth tends to be dense on the western slopes of this region and rather sparse on the eastern slopes. Heavy rainfall, combined with woodcutting activities, has resulted in increased soil erosion.

Sierra Nevada (# 5)

To the south of the Cascades Ecoregion lies a similar mountainous ecoregion, comprised of portions of the Klamath, Sierra, Trinity, and Siskiyou Mountains. Annual rainfall varies considerably, from 40 cm to over 150 cm, depending on elevation and the degree of rainshadowing. Most of the rain comes in the winter months, with summers being hot and dry. Topographically, the region rises to over 2,000 m with an average elevation of 1,000 m. This region contains the headwaters for the Rogue, Klamath, and Sacramento Rivers. Peak flows 23 occur in February, with low flows in August, September, or October. As a result of water diversion and impoundment activities, flows are now more evenly apportioned throughout the year. This has occurred primarily through irrigation/ flood mitigation related reductions in peak flows and less so through increased spillage during the historical time of minimum flows.

Douglas fir is the predominant tree species, but mixed coniferous oak stands are common. Soils tend to be unstable, and timber harvest or livestock grazing can result in severe erosion. Hydraulic placer mining has had a considerable impact on stream quality and hillslope stability.

Southern and Central California Plains and Hills (# 6)

To the east and in the rainshadow of the Coastal Mountain range, the tablelands and hills of this region have generally low levels of annual rainfall ( 40 100 cm). Tributary rivers to the Sacramento and San Joaquin Rivers flow through this region. Vegetation is composed of California oaks and manzanita chaparral with extensive needlegrass steppe. Livestock grazing in the open woodlands is the predominant land use.

Central California Valley (# 7)

The Sacramento and San Joaquin Rivers are the key features of the Central California Valley Ecoregion. The broad flat lands that border the river naturally support needlegrass and marshgrasses, although much of the region has been extensively converted to agricultural use. The annual rainfall for the region is 40 80 cm. The Sacramento and San Joaquin Rivers peak in February with a 6 month period of high flows (> 50% of peak flow). Low flows occur in September and October. Changes in the hydrology of tributaries and irrigation withdrawals from the mainstem rivers have drastically altered the flow characteristics of these rivers over the course of the last 100 years. An estimated 90% of the surface water withdrawals were used for irrigation in 1990 ( USGS 1990). The maintenance of livestock and cultivation, irrigation, and chemical treatment of crop land has resulted in increases in fecal coliform, dissolved nitrate, nitrite, phosphorus, and sulfate concentration levels ( USGS 1993). Industrial and mining runoff from sites, such as the copper mines near Spring Creek in the Sacramento River Basin, also impact water quality in the immediate area.

Eastern Cascades Slopes and Foothills (# 9)

This ecoregion marks the transition between the high rainfall areas of the Cascades Ecoregion and the drier basin ecoregions to the east. The area receives 30 cm to 60 cm of rainfall per year. Streamflow is intermittent, especially during the summer dry season. Surface and groundwater contributes to flows in the Yakima, Deschutes, Klickitat, and White Salmon Rivers. 24 Ponderosa and lodgepole pine are common throughout the region, with little forest undergrowth. Soils tend to be volcanic, young, and highly erodible. Primary land uses are timber harvest and mixed grazing/ timber areas. Agriculture is limited to valleys and irrigation is commonly employed.

Columbia Basin (# 10)

This ecoregion is typified by irregular plains, tablelands, and high hills/ low mountains. The plateau spans from the Cascade Mountains to the Blue Mountains in the south and southeast. Much of the basin is covered with glacial and alluvial deposits. The loose surface substrate is prone to erosion. There is little rainfall and the majority of the water discharge comes from the mountains that border the basin. Because tributaries to the mid and upper Columbia River receive much of their water from snowmelt, peak river flows are in May and June, except for the Deschutes, John Day, and Umatilla Rivers, which peak in April. Peak flows are not as sustained as on the coast, generally lasting 2 3 months. Annual rainfalls of 20 60 cm support sagebrush and wheatlands. Most smaller streams are ephemeral, partially due to irrigation withdrawals ( Omernik and Gallant 1986). The Columbia Plateau experiences a prolonged drought of 1 to 3 months every year, with longer events occurring frequently. Low river flows occur during the late summer and early fall, August October, when irrigation demand is heavy. Nitrates, sulfites, and pesticides commonly associated with crop irrigation are found in most of the rivers in the Columbia River Basin. Heavy metal contamination from Canadian mining operations has been detected at several downstream sites on the Columbia River ( USGS 1993).

Sagebrush and wheatgrass constitute the primary natural vegetation for this region. Much of the land has been converted to dryland wheat agriculture, with smaller irrigated areas supporting the cultivation of peas and potatoes. Irrigation and agriculture have changed the flow and course of smaller rivers and streams ( Omernik and Gallant 1986).

Blue Mountains (# 11)

The Blue, Wallowa, Ochoco, Strawberry, and Aldrich Mountains are contained in this ecoregion. The mountains are a mix of older sedimentary and younger volcanic peaks. Mountainous regions contain ponderosa pine, grand fir and Douglas fir, and Englemann spruce stands. Rainfall varies from 25 50 cm in the lowlands, and as much as 100 cm in the mountains, most of which falls as snow. The aquifers that develop in these mountains feed into numerous river systems: the John Day, Umatilla, and Walla Walla Rivers, which flow into the Columbia River, and the Tucannon, Grande Ronde and Imnaha Rivers, which flow into the Snake River. Peak flows occur from April to June, but only last 2 to 4 months; however, flood events historically have occurred from December through February as rain on snow events ( WDFW 1997a). Minimum flows occur predominantly in August or September, except in the mountains where flows are at a minimum in January and February. 25 Lowlands contain sagebrush, wheatgrass, and bluegrass. Land use activities correspond to vegetation, with timber harvest more prevalent in the mountains and grazing prevalent in the lowlands. Both of these activities have led to considerable localized stream side erosion.

Snake River Basin/ High Desert (# 12)

This region spans southeastern Oregon, southern Idaho, northeastern California, and northern Nevada. Passage of chinook salmon into most of the region has been blocked by dams, but the region still exerts a considerable influence on downstream habitat. This area is geologically very new and contains extensive areas of lava and other volcanic material. The rock substrate is very permeable, streams tend to lose much of their flow through percolation and evaporation, and only the larger rivers that lie below the water table contain substantial flows year round. Rainfalls are generally less than 30 cm annually, but may be as high as 60 cm on the borders of the ecoregion. Extended dry intervals are very common in the Snake River Plateau.

Sagebrush and wheatgrass are prevalent with much of the area utilized as rangeland. Agriculture ( potatoes, corn, grains) is sustained where water resources are available. Rivers in the southern half of Idaho are affected by agricultural and urban development. Irrigation return flows, livestock grazing, and urban activities were associated with high nutrient concentrations in the Boise and Snake Rivers ( USGS 1993).

Northern Rockies (# 15)

Forming the northeast boundary of the Columbia Basin Ecoregion, this region is a mosaic of mountain crestlines ( up to 2,500 m) and valleys. Rainfall varies accordingly from 50 to 150 cm or more per year, some of which falls in intense local storms. Winter snowpack is the major contributor to the streamflows; river flows peak with the spring melt in May or June lasting only 2 3 months. One and 2 month drought periods are fairly common; however, longer periods are quite rare, especially in the higher mountains, where drought periods of even 1 month are rare ( once in 5 years). Low flows correspond with low periods of precipitation in August and September except in the higher elevations, where winter temperatures limit flow. In many areas, soil and subsoil development have created important areas for water storage. Seepage is an important water source for major rivers in this area. The Salmon and Clearwater Rivers drain the southern portion of this region and are the only major tributaries to which chinook salmon still have access. The Spokane, Kootenai, and Pend Oreille Rivers drain into the Columbia River from the eastern and northern portions of this ecoregion; however, runs that historically existed on these rivers have been eliminated by impassable dams ( Fulton 1968).

Forests are dominated by conifers: western white pine, lodgepole pine, western red cedar, western hemlock, western larch, Englemann spruce, subalpine fir, and Douglas fir. Prairie and mixed forest/ grassland are also common. Forestry is the primary land use activity, although 26 mining and grazing activities are commonplace. Water systems in the northern half of Idaho, the Coeur d'Alene and Clearwater Rivers, are impacted by mining and logging operations; however, containment ponds appear to limit metal concentrations downstream ( USGS 1993).

Marine Habitat The marine habitat can be subdivided into three general regions   estuary, coastal, and ocean. Chinook salmon with different life history strategies use these regions to different extents; therefore, changes in the conditions in one region may selectively affect some populations more than others.

Ocean type chinook salmon reside in estuaries for longer periods as fry and fingerlings than do with yearling, stream type, chinook salmon smolts ( Reimers 1973, Kjelson et al. 1982, Healey 1991). The diet of outmigrating ocean type chinook salmon varies geographically and seasonally, and feeding appears to be opportunistic ( Healey 1991). Aquatic insect larvae and adults, Daphnia, amphipods ( Eogammarus and Corophium spp.), and Neomysis have been identified as important food items ( Kjelson et al. 1982, Healey 1991). Rivers with well developed estuaries are able to sustain larger ocean type populations than those without ( Levy and Northcote 1982). Juvenile chinook salmon growth in estuaries is often superior to river based growth ( Rich 1920a, Reimers 1971, Schluchter and Lichatowich 1977). Stream type chinook salmon move quickly through the estuary, into coastal waters, and ultimately to the open ocean ( Healey 1983, Healey 1991). Very limited data are available concerning the ocean migration of stream type chinook salmon; they apparently move quickly offshore and into the central North Pacific, where they make up a disproportionately high percentage of the commercial catch relative to ocean type fish ( Healey 1983, Myers et al. 1987). The Stikine, King Salmon, and Chilkat Rivers are notable exceptions to this general stream type migration pattern. Apparently, a portion of fish from these stocks remain in the coastal waters of southeast Alaska throughout their lives ( ADFG 1997). In contrast, throughout their ocean residence ocean type chinook salmon inhabit coastal waters, where coded wire tag ( CWT) marked fish are recovered in substantial numbers ( Healey and Groot 1987).

The utilization of estuaries by ocean type chinook salmon makes them more susceptible to changes in the productivity of that environment than stream type chinook salmon. Estuaries may be " overgrazed" when large numbers of ocean type juveniles enter the estuary en masse ( Reimers 1973, Healey 1991). The potential also exists for large scale hatchery releases of fry and fingerling ocean type chinook salmon to overwhelm the production capacity of estuaries ( Lichatowich and McIntyre 1987). The loss of coastal wetlands to urban or agricultural development may more directly impact ocean type populations. Dahl ( 1990) reported that California has lost 94% of its wetlands. Furthermore, an estimated 80 90% of the undiked tidal marshlands in the Sacramento River Delta area, the major nursery area for Central Valley chinook salmon stocks, has been lost ( Nichols et al 1986, Lewis 1992). A similar reduction has been 27 reported in Washington and Oregon wetlands: a 70% loss in the Puget Sound, 50% in Willapa Bay, and 85% in Coos Bay ( Refalt 1985).

The ocean migrations of chinook salmon extend well into the North Pacific Ocean. The productivity of various ocean regions has been correlated with the degree of wind driven upwelling ( Bakun 1973, 1975). Under normal conditions this upwelling decreases along the coast from California to Washington and British Columbia ( Bakun 1973). Changes in wind directions related to sea level pressure ( SLP) systems, most notably the Aleutian low pressure ( ALP) or Central North Pacific ( CNP) pressure indices, can greatly alter upwelling patterns ( Ware and Thompson 1991, Beamish and Bouillon 1993). Upwelling brings cold, nutrient rich waters to the surface, resulting in an increase in plankton and ultimately salmon production ( Beamish and Bouillon 1993). Strong ALP measurements ( high pressure readings) tend to result in minimal upwelling in the North Pacific. Similarly, atmospheric pressure systems in the Central Pacific can alter trade wind patterns to bring warmer water up along the California coast; this occurrence is better known as an El Niño. El Niño events suppress coastal upwelling off the Washington, Oregon, and California coasts and tend to bring warmer water and warm water species northward ( McLain 1984). One difference between El Niño events and ALP events is that the northerly flow of warm waters associated with El Niño events may stimulate ocean productivity off Alaska ( McLain 1984). Ocean migratory pattern differences between and within ocean and stream type chinook salmon stocks may be responsible for fluctuations in abundance. Moreover, the evolution of life history strategies has, in part, been a response to long term geographic and seasonal differences in marine productivity and estuary availability.

Chinook Salmon Life History and Ecology Juvenile Life History The most significant process in the juvenile life history of chinook salmon is smoltification, the physiological and morphological transition from a freshwater to marine existence. The emigration from river to ocean is thought to have evolved as a consequence of differences in food resources and survival probabilities in the two environments ( Gross 1987). Salmon juvenile lifehistory patterns are usually deduced by examining the developmental pattern of circuli on juvenile and adult fish scales ( Gilbert 1912, Rich 1920a, Koo and Isarnkura 1967). Within the ocean type ( subyearling) and stream type ( yearling) migrant designations, several subtypes have been described ( Gilbert 1912, Reimers 1973, Schluchter and Lichatowich 1977, Fraser et al. 1982). Ocean type juveniles enter saltwater during one of three distinct phases. " Immediate" fry migrate to the ocean soon after yolk resorption at 30 45 mm in length ( Lister et al. 1971, Healey 1991). In most river systems, however, fry migrants, which migrate at 60 150 days post hatching, and fingerling migrants, which migrate in the late summer or autumn of their first year, represent the majority of ocean type emigrants. When environmental conditions are not conducive to 28 subyearling emigration, ocean type chinook salmon may remain in freshwater for their entire first year. Stream type chinook salmon migrate during their second or, more rarely, their third spring. Under natural conditions stream type chinook salmon appear to be unable to smolt as subyearlings. The underlying biological bases for differences in juvenile life history appear to be both environmental and genetic ( Randall et al. 1987). Distance of migration to the marine environment, stream stability, stream flow and temperature regimes, stream and estuary productivity, and general weather regimes have been implicated in the evolution and expression of specific emigration timing.

The success of different juvenile life history strategies is linked to the coordinated expression of other traits. Gilbert ( 1912) noted that ocean type fish exhibited a faster growth rate relative to stream type fish. The growth difference between ocean and stream type juveniles has also been observed by other researchers ( Carl and Healey 1984, Cheng et al. 1987, Taylor 1990a). Some of this difference may be related to differences in rearing environment, although under standardized conditions there was still a significant growth difference between ocean and streamtype juveniles ( Taylor 1990b). Clarke et al. ( 1992) demonstrated that the growth of stream type juveniles was strongly associated with photoperiod, while ocean type juvenile growth appeared to be independent of photoperiod. Juvenile life history appears to be a heritable trait. Hybridization experiments indicated that the stream type smoltification and growth pattern are recessive relative to the ocean type pattern ( Clarke et al. 1992). Juvenile stream type chinook salmon have also been shown to be more aggressive than ocean types. This may be a territorial defense mechanism for resource limited freshwater systems ( Taylor and Larkin 1986, Taylor 1988, Taylor 1990b). Morphometric differences, such as larger and more colorful fins, observed in some stream type populations may be related to social displays that maintain territories ( Carl and Healey 1984, Taylor and Larkin 1986). Thus, the timing of parr smolt transition appears to be associated with the expression of a number of other traits in order to maximize individual survival.

Juvenile stream and ocean type chinook salmon have adapted to different ecological niches. Ocean type chinook salmon tend to utilize estuaries and coastal areas more extensively for juvenile rearing. In general, the younger ( smaller) juveniles are at the time of emigrating to the estuary, the longer they reside there ( Kjelson et al. 1982, Levy and Northcote 1982, Healey 1991). There is also an apparent positive relationship between rivers with large estuary systems and the number of fry migrants ( Fraser et al. 1982). Brackish water areas in estuaries also moderate physiological stress during parr smolt transition. The development of the ocean type life history strategy may have been a response to the limited carrying capacity of smaller stream systems and glacially scoured, unproductive watersheds, or a means of avoiding the impact of seasonal floods in the lower portion of many watersheds ( Miller and Brannon 1982). In the Sacramento River and coastal California rivers, subyearling emigration is related to the avoidance of high summer water temperatures ( Calkins et al. 1940, Gard 1995). Ocean type chinook salmon may also use seasonal flood cycles as a cue to volitionally begin downstream emigration ( Healey 1991). Migratory behavior in ocean type chinook salmon juveniles is also positively correlated with water flow ( Taylor 1990a). 29 Stream type juveniles are much more dependent on freshwater stream ecosystems because of their extended residence in these areas. A stream type life history may be adapted to those watersheds, or parts of watersheds, that are more consistently productive and less susceptible to dramatic changes in water flow, or which have environmental conditions that would severely limit the success of subyearling smolts ( Miller and Brannon 1982, Healey 1991). Stream type chinook salmon juveniles exhibit downstream dispersal and utilize a variety of habitats during their freshwater residence. This dispersal appears to be related to resource allocation and migration to overwintering habitat and is not associated with saltwater osmoregulatory competence ( Hillman et al. 1987, Levings and Lauzier 1989, Taylor 1990a, Healey 1991). For example, the migration of subyearling juvenile spring run chinook salmon in the Wenatchee River ( a stream type population) may be due to competition with hatchery releases or the interspecific interaction between steelhead and chinook salmon juveniles ( Hillman and Chapman 1989). There was a tendency for juveniles to move into deeper water, farther from the bank shelter, as they grew older. If suitable overwintering habitat, such as large cobble, is not available then the fish will tend to migrate downstream ( Bjornn 1971, Bustard and Narver 1975, Hillman et al. 1987). At the time of saltwater entry, stream type ( yearling) smolts are much larger, averaging 73 134 mm depending on the river system, than their ocean type ( subyearling) counterparts and are therefore able to move offshore relatively quickly ( Healey 1991).

The variability in the time of emigration to the marine environment among stocks of chinook salmon, combined with geographic and yearly differences in freshwater productivity, make comparisons of the sizes of smolts among different stocks difficult. Size data may be confounded by the presence within a watershed of multiple native stocks that exhibit different lifehistory strategies. The possible inclusion of hatchery reared fish in smolt samples is a further confounding factor. Smolt size, therefore, was not emphasized among the life history traits used to determine ESU boundaries.

Ocean and stream type chinook salmon populations exhibit a geographical distribution that further underscores the ecological adaptation of these two races. Chinook salmon stocks in Asia, Alaska, and Canada north of the 55th parallel, and in the headwaters ( upper elevations) of the Fraser River and the Columbia River Basins, exhibit a stream type life history: emigrating to sea in their second or third spring and generally entering freshwater several months prior to spawning ( Healey 1991). A notable exception to this trend includes populations in the Situk River and several Yakutat foreland River Basins in Alaska, which emigrate primarily as subyearlings ( Johnson et al 1992a, ADFG 1997). Ocean type chinook salmon are predominant in coastal regions south of 55 E N, in Puget Sound, in the lower reaches of the Fraser and Columbia Rivers, and in California's Central Valley ( Gilbert 1912, Rich 1920a, Healey 1983, Taylor 1990b). One analysis of principal components influencing life history type ( distance to the sea, daylight hours during the growing season and air temperature) accounted for 96% of the total observed variation in age at smoltification ( Taylor 1990a). However, the abrupt change between streamand ocean type life histories at 55 E N occurs in the absence of a similarly abrupt change in environmental conditions ( Healey 1983) and may be related to patterns of colonization following deglaciation ( Taylor 1990b). 30 Stream type life histories are most commonly associated with early timed runs of fish ( Rich 1920a, Healey 1983). This is partially because the headwater regions south of 55 E N are only accessible during peak spring stream flows, additionally, temperatures in more northerly streams and headwater areas are much colder than in other areas and require early deposition of eggs to allow for proper developmental timing. Overall, juvenile smoltification strategies are one expression of a more complicated, genetically based life history adaptation to ecological conditions ( Taylor 1990a, Clarke et al. 1992). Differences in juvenile life history strategies among chinook salmon stocks were a useful component in helping to determine boundaries between ESUs.

Ocean Distribution Coastwide, chinook salmon remain at sea from 1 to 6 years ( more commonly 2 to 4 years), with the exception of a small proportion of yearling males which mature in freshwater or return after 2 or 3 months in salt water ( Rutter 1904, Gilbert 1912, Rich 1920a, Mullan et al. 1992). Differences in the ocean distribution of specific stocks may be indicative of resource partitioning and may be important to the success of the species as a whole. Current migratory patterns may have evolved as a balance between the relative benefits of accessing specific feeding grounds and the energy expenditure necessary to reach them. If the migratory pattern for each population is, in part, genetically based, then the efficiency with which subsequent generations reach and return from their traditional feeding grounds will be increased.

The vast majority of CWT marked chinook salmon come from hatchery populations; therefore, the migratory routes of many wild fish stocks must be inferred from their corresponding hatchery populations. Furthermore, CWT ocean recoveries are obtained through commercial and sport fishery samples; therefore, the relative intensity of each fishery can bias the interpretation of the oceanic distribution of each stock. Comparisons of oceanic distributions across years can also be influenced by changes in fishing regulations and ocean conditions ( such as during an El Niño). Confounding effects were considered in the interpretation of CWT recoveries, and small differences in CWT ocean recoveries between stocks were not considered as a distinguishing factor.

The genetic basis for ocean distribution has been supported by a number of different studies involving the monitoring of CWT marked fish caught in the ocean fisheries. The relative influence of genetic vs. environmental factors on migratory pattern can be deduced from transplantation studies. Transplanted Elwha River chinook salmon continued to follow their traditional migratory pattern after being reared and released at a site 150 km to the east, except that the actual route had also been shifted 150 km eastward ( Brannon and Hershberger 1984). Additionally, hybrids between the Elwha River and Green River ( University of Washington) stocks exhibited an intermediate ocean migration pattern. Transplantation studies with coastal stocks in Oregon have yielded similar results ( Nicholas and Hankin 1988). Chinook salmon 31 whose natal stream lies south of Cape Blanco tend to migrate to the south, while those to the north of Cape Blanco tend to migrate in a northerly direction. Transplants of south migrating stocks to release sites north of Cape Blanco do not alter the basic southerly direction of ocean migration ( Nicholas and Hankin 1988). Recoveries of CWT marked fish from ocean fisheries indicate that fish stocks follow predicable ocean migration patterns, and that these are based on " ancestral" feeding routes ( Brannon and Setter 1987).

Ocean and stream type chinook salmon are recovered differentially in coastal and midocean fisheries, indicating divergent migratory routes ( Healey 1983, 1991). Ocean type chinook salmon tend to migrate along the coast, while stream type chinook salmon are found far from the coast in the central North Pacific ( Healey 1983, 1991; Myers et al. 1984). Studies of CWTmarked prerecruit (< 71 cm) fish in the marine fisheries off of Southeastern Alaska indicated that differences in migration speed, timing, and growth were related to the life history, age, and general geographic origin of the stocks ( Orsi and Jaenicke 1996). The causal basis for this difference in migration pattern is unknown, but may be related to poor coastal feeding conditions during past glacial events for the more northerly ( stream type) populations.

The freshwater component of the adult returning migratory process is also under a significant genetic influence. In one experiment, " upriver bright" chinook salmon were captured, spawned, and the subsequent progeny reared and released from a downriver site ( McIsaac and Quinn 1988). A significant fraction of the returning adults from the " upriver bright" progeny group bypassed their rearing site and returned to their " traditional" spawning ground 370 km further upriver. The high degree of fidelity with which chinook salmon return to their natal stream has been shown in a number of studies ( Rich and Holmes 1928, Quinn and Fresh 1984, McIsaac and Quinn 1988). Returning to the " home stream" provides a mechanism for local adaptation and reproductive isolation.

Ocean migration patterns represent an important form of resource partitioning and are important to the evolutionary success of the species; therefore, differences in ocean migratory pattern were an important consideration in the determination of ESU boundaries.

Size and Age at Maturation The age at which chinook salmon begin sexual maturation and undertake their homeward migration is dependent on a number of different factors. Age, body size and composition, and fecundity traits in salmonids have all been shown to be partially under genetic control ( Ricker 1972) and genetically and phenotypically correlated ( Gall 1975). Because of genetic correlations between these traits, natural selection on one or more of these traits may affect the expression of other traits. The confounding effects of correlated traits make it difficult to identify specific selective ( ecologically important) criteria that influence size and age at maturity. 32 5 J. D. Hubble, Biologist, Yakama Tribal Fisheries, P. O. Box 151, Toppenish, WA 98948. Pers. Commun., April 1996. Adult body size in chinook salmon does not appear to be strongly correlated to latitude; however, there appears to be a slight negative correlation between adult body size and length of migration ( Roni and Quinn 1995). The relationship between size and length of migration may also reflect the earlier timing of river entry and the cessation of feeding for chinook salmon stocks that migrate to the upper reaches of river systems. Juvenile life history has an apparent influence on the size of returning spawners. Ocean type fish that have been at sea from 1 to 2 years are generally larger than their respective stream type counterparts ( Roni and Quinn 1995). This may reflect the more productive feeding conditions that exist in the marine environment and/ or the additional 3 to 5 months that ocean type fish remain in the marine environment before beginning their spawning migration.

Body size, which is correlated with age, may be an important factor in migration and redd construction success. Beacham and Murray ( 1987) reported a correlation between body size and large (< 100 km2 watershed area) and small river size in chum salmon ( O. keta). Roni and Quinn ( 1995) reported that under high density conditions on the spawning ground, natural selection may produce stocks with exceptionally large sized returning adults. Spawning aggregations may select for large body size in males due to competition between males for females and the " attractiveness" of large males to females ( Foote 1990). Large body size may be advantageous for females because of the success of larger fish in establishing, digging, and protecting their redds ( Healey and Heard 1984). Competition for redd sites, stream flow, and gravel conditions are also thought to influence adult size in coho salmon ( Holtby and Healey 1986).

An alternative strategy for chinook salmon is for males to mature at an early age. " Minijack or " jack" chinook salmon males mature in their first or second ocean years, respectively. Early maturation among male chinook salmon was first described by Rutter ( 1904). Early maturation offers a reduced risk of mortality, but younger ( smaller) males may be at a competitive disadvantage in securing a mate ( Gross 1987). The incidence of jack males has underlying genetic determinants and appears to be, in part, a response to favorable growing conditions. A variant of this life history strategy is maturation without emigrating to the ocean. Rich ( 1920a) estimated that 10 12% of the juvenile males on the McCloud River were maturing without leaving the river. Mullan et al. ( 1992) found that early maturing resident males were common in both hatchery and wild populations in the Wenatchee River. Non migrating mature males have also been observed in the Snake River Basin ( Gebhards 1960, Burck 1967, Sankovich and Keefe 1996), Methow and Yakima Rivers ( Hubble5), and the Deschutes River. Resident males have been observed among some stream and ocean type chinook salmon stocks in the Fraser River above Hell's Gate, which would have historically been a potential barrier to small migrating early maturing males, but not among lower river or coastal populations ( Taylor 1989, Foote et al. 1991). The location and physical characteristics of each river may determine the expression of this life history trait. It is 33 unlikely that small jack males would be physically able to undertake the arduous return migration to many upriver areas ( Mullan et al. 1992) or that sufficient time exists for the completion of the smolt emigration and return migration. Nonmigrating early maturing males may have a good chance of mating success, especially during poor return years when there may be a shortage of large males on the spawning grounds. The modification of smoltification, a major physiological process, to produce early maturing males in a population is indicative of the importance of this life history trait to the reproductive success of specific populations.

The heritability of body size and age has been more extensively studied in chinook salmon than have other traits. Crosses between different aged parents have demonstrated that the ages of maturity for parents and progeny were strongly correlated ( Ellis and Noble 1961, Donaldson and Bonham 1970, Hershberger and Iwamoto 1984, Withler et al. 1987, Hankin et al. 1993). The expression of early maturation in chinook salmon was found to have a significant genetic component; moreover, different stocks exhibited different levels of early maturation in response to environmental changes ( Heath et al. 1994). The positive response of chinook salmon to selective breeding experiments is indicative of a significant genetic component to body size ( Donaldson and Menasveta 1961). Chinook salmon stocks exhibit considerable variability in size and age of maturation, and at least some portion of this variation is genetically determined.

From an evolutionary standpoint, the potential increases in size, fecundity, and egg size gained from remaining on the marine feeding grounds an additional year must be weighed against the chances of mortality during that year ( Healey and Heard 1984, Healey 1986). The specific conditions that exist in each river must also influence, in part, the expression of these characteristics. The size and age of spawning chinook salmon in any given population may have a significant impact on their survival, and trends in size and age were utilized in determining ESU boundaries. However, the large environmental influence ( on a regional and annual basis) on chinook salmon size and age, as well as possible biases resulting from different fishery harvest techniques and the inclusion of hatchery reared fish, would suggest that available size and age data be used with caution.