Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water Quality Standards Temperature Criteria Draft Discussion Paper and Literature Summary Revised December 2002 Publication Number 00 10 070 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water Quality Standards Temperature Criteria Draft Discussion Paper and Literature Summary Prepared by: Water Quality Program Washington State Department of Ecology Watershed Management Section Olympia, Washington 98504 Revised December 2002 Publication Number 00 10 070 For additional copies of this document contact:

Department of Ecology Publications Distribution Center P. O. Box 47600 Olympia, WA 98504 7600 Telephone: ( 360) 407 7472 If you have special accommodation needs or require this document in an alternative format, please call Mark Hicks at ( 360) 407 6477. The TTY number is 711 or 1 800 833 6388. Email can be sent to mhic461@ ecy. wa. gov. Evaluating Standards for Protecting Aquatic Life in Page i Washington's Surface Water quality Standards Table of Contents Part I: Background and Project History ..................................................................................................... 1 1. Background ............................................................................................................................ 1 2. Current Temperature Requirements ....................................................................................... 1 3. Organization of this Review Document ................................................................................. 2 Part II: The Effect of Temperature on the ................................................................................................... 3 Freshwater Aquatic Life of Washington ......................................................................................... 3 1. The Goal of this Technical Review........................................................................................ 3 2. Summary of Thermal Requirements and Recommended Threshold Values.......................... 3 a) Native Char ( Bull Trout and Dolly Varden) ...................................................................... 4 b) Salmon and Trout .............................................................................................................. 4 c) Warm Water Aquatic Life.................................................................................................. 5 d) Special Provisions to Prevent Acute Effects...................................................................... 6 3. Methodology and Considerations in Establishing Temperature Recommendations.............. 6 a) The Multiple Lines of Evidence ( MLE) Methodology...................................................... 6 b) General Thoughts and Observations................................................................................ 10 i) Adjusting Laboratory Data for Application to Natural Waters ........................................ 10 ii) Minimum Temperature Thresholds ................................................................................. 15 iii) Protection of Untested Species....................................................................................... 16 4. Temperature Requirements of Char, Salmon, and Trout Species ........................................ 17 a) Native Char Temperature Requirements.......................................................................... 17 i) General Life History Information:.................................................................................... 17 ii) Spawning Requirements.................................................................................................. 19 iii) Juvenile Rearing............................................................................................................. 23 iv) Migratory Adult and Sub Adult Char Populations......................................................... 28 v) Lethality to Adults and Juveniles .................................................................................... 30 b) Salmon and Trout ............................................................................................................ 33 i) General Life History Information..................................................................................... 33 ii) Spawning Requirements.................................................................................................. 38 iii) Juvenile Rearing............................................................................................................. 52 iv) Juvenile Winter Holding................................................................................................. 80 v) Adult Migration ............................................................................................................... 81 vi) Lethality to Adults and Juveniles ................................................................................... 91 c) Temperature Influenced Fish Diseases .......................................................................... 108 d) Smoltification and Sea Water Adaptation ..................................................................... 115 e) Miscellaneous Indigenous Species ................................................................................ 120 i) Sensitive Amphibians ..................................................................................................... 121 ii) Other Sensitive Fish Species ......................................................................................... 123 iii) Stream Macroinvertebrates........................................................................................... 125 f) Miscellaneous Indigenous Fish Species ......................................................................... 128 g) Summary of Temperature Requirements for Indigenous Aquatic Life ......................... 131 i) Cold Water Species ........................................................................................................ 131 ii) Warm water Species ...................................................................................................... 133 5. References Reviewed ......................................................................................................... 138 Part III: Ambient Temperatures of Washington's Streams and Rivers..................................................... 175 Proposal for Applying Char Protection ....................................................................................... 183 Page ii Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards Abstract Maintaining proper temperatures in our natural waterways is vital to the long term health of fish and other aquatic life. In response to critiques over the adequacy of Washington's existing temperature criteria for freshwaters, the Washington State Department of Ecology performed a comprehensive review of the available technical literature on the temperature requirements of our native fish and aquatic life. This document summarizes the findings of that review.

Part I of this document provides a brief history of the review effort. Part II of this document reviews the scientific literature and establishes technical recommendations for protecting the state's freshwater aquatic species. Based on previous reviews of the literature it was determined that freshwater species can be reasonably placed into four groups having similar sensitivity to temperature. These four groups, identified by key species, serve as the foundation for this review:

1) Native Char ( bull trout and Dolly Varden); 2) Salmon, Steelhead, Cutthroat Trout, and Coastal Rainbow Trout; 3) Interior non Anadromous Redband Trout ( eastern Washington species); and 4) Warm Water Fish Species ( e. g., dace, shiner, sucker, etc.).

Technical evaluations provide recommendations for temperature thresholds that protect the key life stages of adult migration and holding, spawning, incubation, juvenile rearing, and smoltification. Recommendations are also made to avoid significant increases in the risks of warm water fish diseases and parasites.

Recommendations are also presented that may be instructive in trying to avoid detrimental effects from discrete site specific human actions that may cause:

1) Thermal blockages to migration, 2) Short term ( 7 day duration) lethality, and 3) Near instantaneous ( 1 2 seconds) lethality.

The temperature thresholds identified in this paper are ones which Ecology has high confidence represents the upper threshold temperatures that provide full protection for the species. As temperatures rise above these values, negative impacts to the health of fish and other aquatic life will rapidly escalate to levels detrimental to the health of aquatic communities. The metric used to express the technical recommendations ( a 7 day average of the daily maximum temperatures) was chosen to better match the laboratory and field research results to an exposure period that reflects the risk of harm to aquatic species. The result of this process is the recommendation of temperature limits that better reflect the thermal requirements and limitations of the state's indigenous freshwater fish and aquatic life. There are still some notable areas where more research would improve confidence in specific recommendations ( particularly for warm water species and for interior redband trout). It is clear however, that implementation of the temperature thresholds identified in Evaluating Standards for Protecting Aquatic Life in Page iii Washington's Surface Water quality Standards part II of this paper, wherever attainable would eliminate human warming of water temperature as a source of impairment to our native aquatic communities.

Part III of this document examines temperature data from rivers and streams around Washington. The information provided in this section can be used to assess the potential implications of selecting specific temperature values for use as state criteria. Evaluating Standards for Protecting Aquatic Life in Page 1 Washington's Surface Water quality Standards Part I Background and Project History 1. Background The Washington State Department of Ecology administers the state's surface water quality standards ( Chapter 173 201A WAC). These regulations establish minimum requirements for the quality of water that must be maintained in lakes, rivers, streams, and marine waters. This is done to ensure that all the beneficial uses associated with these waterbodies are protected. Examples of protected beneficial uses include: aquatic life and wildlife habitat, fishing, shellfish collection, swimming, boating, aesthetic enjoyment, and domestic and industrial water supplies.

As part of a public review of its water quality standards, the Department of Ecology convened a technical work group to evaluate the water quality criteria established to protect freshwater aquatic communities. One of the recommendations of the work group was that Ecology should re evaluate the state's existing temperature criteria.

2. Current Temperature Requirements The existing state surface water quality standards contain three separate single daily maximum temperature criteria limits that can be applied to rivers:

Class AA  16 ° C Class A  18 ° C Class B  21 ° C Lake Class  Temperatures are to be maintained at natural levels.

Class AA and Class A provide two different levels of protection for the same set of beneficial uses, and are intended to protect salmonid spawning, rearing, and migration. Class AA is predominately applied to forested upland areas, but Class A waters are designated broadly throughout the state. Class B, is designed only to protect salmonid rearing and migration, and was not intended to fully protect spawning. There are only a small number waterbodies in the state that have been assigned the Class B designation. With each class, the criteria are applied as the highest single daily maximum measurement of temperature occurring in the waterbody. Page 2 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards 3. Organization of this Review Document Part I: Provides a brief background discussion on the effort to revise the state's existing water quality criteria for temperature in freshwater systems.

Part II: Reviews available scientific research on the effects of temperature on aquatic life, with a particular focus on species occurring in Washington.

Part III: Summarizes the patterns of temperature in Washington's rivers using available continuous monitoring data. Evaluating Standards for Protecting Aquatic Life in Page 3 Washington's Surface Water quality Standards Part II The Effect of Temperature on the Freshwater Aquatic Life of Washington Prepared by: Mark Hicks, Senior Analyst Water Quality Standards Washington Department of Ecology ( 360) 407 6477 mhic461@ ecy. wa. gov 1. The Goal of this Technical Review The primary goal of this paper is to identify temperature thresholds that if met would have a high probability of fully protecting Washington's freshwater aquatic communities. Full protection includes the reasonable prevention of both lethal and sublethal effects that may detrimentally affect the health, fecundity, and the ultimate wellbeing of naturally balanced indigenous populations. This review uses the available technical literature to determine temperature regimes that will fully protect the individual life history stages of key species. This information is then combined into stream wide temperature recommendations that will protect entire communities of aquatic life.

The following summarizes the findings pertaining to the protection of our state's native fish species. The technical recommendations are based on grouping together species having the same or nearly the same temperature requirements. This both simplifies the resulting recommendations and acknowledges that these species commonly occur together in the state's streams, rivers, and lakes. This approach results in establishing temperature threshold values for four different species groupings: 1) native char, 2) salmon and coastal trout, 3) non anadromous interior redband trout, and 4) warm water fish species.

2. Summary of Thermal Requirements and Recommended Threshold Values Page 4 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards a) Native Char ( Bull Trout and Dolly Varden)

Char require colder waters to be fully supported than the other fishes native to Washington. Char do not begin spawning until temperatures drop to 7 9 ° C, and subsequent egg incubation is harmed by continuous daily average water temperatures above 5 6 ° C. The same waters that are used for spawning are also used for tributary rearing by juvenile char. Tributary rearing waters that provide full support for char are best described by summer maximum temperatures at or below 13 15 ° C or average ( 7 day) daily maximum temperatures below about 12.5 14 ° C.

At age 2 3, char often move to lower more main stem waters to rear. This may be a pattern that more effectively uses the larger prey bases of larger stream and rivers, or just acts to disperse the populations in order to use wider resource areas. In any case, it is common to find char in waters where the summer maximum temperatures would appear unsuitable based on research focused on young juveniles and non migratory ( resident) populations. It appears that char will move into and out of these waters in a manner that avoids ( or in response to) warm water temperatures. The temperatures noted in association with the movement varies but generally appears to be above those identified as necessary to fully protect the rearing of young juveniles. At this time, information is not available to either identify the historic patterns in specific Washington streams or identify with confidence temperature criteria appropriate for this migratory life stage.

b) Salmon and Trout Salmon and trout both have similar spawning and incubation requirements. In evaluating the temperature requirements of salmon and trout it is important, however, to remember that salmon begin spawning in the fall as temperatures are cooling and trout begin spawning in the spring as temperatures are warming. For simplicity, the following discussion follows the pattern of fall spawning fish:

In the weeks immediately preceding spawning, temperatures above 14 16 ° C can reduce the health of the eggs and sperm in adult fish. Constant temperatures in the range of 8 10 ° C and daily maximum temperature below 13 15 ° C are necessary to ensure that fertilized eggs have high survival success and the embryos develop into healthy emergent fry. Once the fry emerge, juvenile rearing will be fully supported in natural streams where the average temperatures do not exceed 13 15 ° C, and maximum temperatures do not exceed approximately 17 19 ° C. Once the fish have reached a critical size, they will begin the process of changing from parr to smolts. This is the critical physiologic process that allows these freshwater juveniles to adapt their systems for life in marine waters. Average temperatures greater than 15 16 ° C appear capable of stopping the process altogether, and average temperatures below 12 13 ° C appear necessary to fully support smoltification ( particularly for the spring out migration of steelhead). In early spring, overlapping the period of out migration of many anadromous salmonids, adult smelt will be moving upstream to spawn. These fish have been found to have very low temperature thresholds. Evaluating Standards for Protecting Aquatic Life in Page 5 Washington's Surface Water quality Standards While the information on these fish is somewhat limited, it appears that spawning success can be impaired by maximum temperatures above about 12 13 ° C, and adult mortality has been noted in association with water temperatures as low as 16 ° C. After a period of growth in the ocean, salmon and steelhead will begin their migrations back up to their natal streams to spawn. Migration can be impaired by experiencing average temperatures above about 15 ° C and maximum temperatures above about 18 20 ° C. Temperatures above 21 22 ° C have frequently blocked the migration of anadromous fish altogether; particularly where the fish have come from cooler waters. For both the rearing of juvenile fish and the migration of adult fish, warm water diseases can reduce survival. Average temperatures above 13 14 ° C and periods of maximum temperatures above about 17 18 ° C have been found to increase the risks of losses associated with warm water fish diseases and parasites. Extreme temperatures can be lethal to salmon and trout with exposure periods from a couple of seconds to a couple of hours. Single daily peak temperature of 24 25 ° C are capable of killing salmonids that have not been well acclimated to warm waters in advance of the exposure, and plumes of water warmer than 32 33 ° C can be lethal to passing fish in only 1 2 seconds regardless of their prior acclimation temperature.

The information reviewed for revising the state's temperature criteria generally suggests that non anadromous interior forms of rainbow trout ( often described as the subspecies of redband trout that occurs on the eastside of the Cascade mountains in Washington) have higher optimal temperature ranges than other subspecies of rainbow trout. However, the information was rather inconsistent on this point, and caution is warranted before allowing any significant departure from the temperature ranges determined healthy for the majority of the state's salmon and trout. It is recommended therefore that temperatures at the upper end of the range determined to fully protect salmon and trout in general be viewed as the warmest temperatures that will protect these interior redband trout. The available information suggests that acutely lethal temperatures are very similar for all subspecies and stocks of trout, and thus no sound basis exists for assuming that these fish would be better capable of resisting short term spikes of temperature into the lethal range.

c) Warm Water Aquatic Life A warm water fish community in Washington would be characterized by the presence of redside shiner; tui chub; margined, mottled, or piute sculpin; longnose or speckled dace, sucker, and northern pikeminnow. These fish are known to exist in our warmest waters, where they often out compete introduced populations of rainbow trout. Insufficient information exists to develop individual water quality recommendations for these species, so it is recommended that they be considered broadly as a community. There is very little experiential data available that can be used to establish the fully protective upper temperature range for our warm water species in general, so these recommendations may need to be revisited periodically to determine if changes are warranted. Establishing criteria to protect our temperature tolerant non salmonid fish species will also provide protection for desirable introduced warm water sport fish species such as bass and crappie. In general, Washington's indigenous warm water fish communities can sometimes thrive in waters that have summer Page 6 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards maximum temperatures as high as 25 27 ° C; although, most appear to prefer waters below 20 ° C d) Special Provisions to Prevent Acute Effects The previous technical recommendations are designed to protect waterbodies in recognition of the way that temperatures change in nature over hours, days, and weeks. Discrete human actions, such as point source discharges, are capable of altering these normal temperature regimes and thus may require special consideration. For example, scheduled or emergency bypasses for maintenance at an industrial facility may require asking questions like: a) How much can temperature be raised for a single day or week?, or b) How hot can a discharge be within an authorized mixing zone? These questions require a departure from consideration of what are healthy stream conditions and instead must focus on what is tolerable for a discrete location and a limited duration of time. To assist in answering these inevitable questions, recommendations have been made for avoiding acute ( short term) lethality and barriers to migration.

For evaluating the effects of discrete human actions, a 7 day average of the daily maximum temperatures greater than 22 ° C or a 1 day maximum greater than 23 ° C should be considered lethal to cold water fish species such as salmonids. Discharge plume temperatures should be maintained such that fish could not be entrained ( based on plume time of travel) for more than 2 seconds at temperatures above 33 ° C to avoid creating areas that will cause near instantaneous lethality. Barriers to migration should be assumed to exist anytime daily maximum water temperatures are greater than 22 ° C and the adjacent down stream water temperatures are 3 ° C or more cooler.

3. Methodology and Considerations in Establishing Temperature Recommendations This chapter discusses the methodology used and some of the underlying thoughts and concerns that went into establishing the temperature threshold recommendations contained in this paper.

a) The Multiple Lines of Evidence ( MLE) Methodology Scientific information comes in a wide variety of forms. These include:

  Laboratory testing where the temperature is held constant,   Laboratory testing where the temperature is made to fluctuate at a set rate,   Controlled field studies using either natural or artificial channels,   Field studies where environmental variables such as shade are altered, and Evaluating Standards for Protecting Aquatic Life in Page 7 Washington's Surface Water quality Standards   Field observational studies where the patterns of fish are observed in the wild.

All of these sources of information provide valuable insights, but it can be a challenging task to try and compare and contrast such different types of research. This has led many researchers to simplify their approach and select only a single type of research. This simplification, while understandable, can result in a loss of understanding. More importantly, however, it can result in a lost opportunity to demonstrate how well all of these very different types of studies correspond to one another. The key to using a diversity of information types is to convert the results into a common metric.

The multiple lines of evidence ( MLE) approach used in this paper was developed as a means to use all of the available scientific information to support sound decision making. The MLE methodology was developed to provide a method for making recommendations that are transparent to the reviewer and that can be predictably modified when new information becomes available. The basic approach is rather simple. All the scientific information is sorted first by the life stage ( e. g., spawning, rearing, migration, etc.) or by some discrete environmental risk ( e. g., lethality, smoltification, disease, etc.). The information is then sorted into different categories of study types. The following provides a simplified example of how this information can be categorized into independent lines of evidence ( ILOE) for the life stage of juvenile rearing:

Study types ( ILOE): Constant temperature laboratory testing of growth Fluctuating temperature laboratory testing of growth Controlled field studies on growth Studies on the distribution and health status of natural populations Laboratory studies examining competition and predation Field studies examining competition and predation For each line of evidence the study conclusion are standardized into a standardized exposure metric and summarized as the range of individual study results. Depending upon the line of evidence, this range may be either the absolute range or the dominant range ( e. g., 90th percentile of distribution of study results).

The standard metric for this temperature analysis is a 7 day average of the daily maximum temperatures ( 7DADMax). This metric was chosen primarily because:

1. Sublethal chronic biologic reactions generally take more than a week's exposure to become meaningful; 2. Small daily maximum temperature fluctuations beyond some " healthy" target level will not be biologically meaningful, but if a single daily maximum metric were chosen and then not attained such fluctuations would have regulatory repercussions; and 3. It is not as defensible to use weekly averages of the daily average temperatures alone because fluctuations about the mean temperature can be highly variable and extreme fluctuations will erase or diminish the benefits of otherwise healthy average temperatures. Page 8 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards To make the conversions to a standard metric, this analysis relies upon the conversion equations provided by Dunham et al. ( 2000) that are based on data from 752 stream sites located in the Western United States; particularly the Northwest. For converting the temperature research results for protecting bull trout and Dolly Varden ( Washington's most cold water loving fish species), it is assumed that their habitat will have very stable temperatures. This analysis uses the assumption that summer average diel fluctuations are less than 2 ° C in char habitat. This is consistent with the state's information showing that colder streams ( 7DADMax < 15C) have median average fluctuations of 2.1 ° C ( 90% between 1.1 3.6 ° C). It is also consistent with the commonly held belief that many of these waters are kept thermally stable due to a higher reliance on input from groundwater. For salmon and trout waters, the conversion is based on assuming that the summer average diel fluctuations are from 4 6 ° C. This is consistent with the state's data showing that warmer streams ( 7DADMax 15 19 ° C) have median average fluctuations of 1.2 5.3 ° C ( 90 percentile range   median 2.6 ° C). It also recognizes that the waterbodies used by salmon and trout have the most variable temperature regimes overall. The following table shows the adjustment calculations that were used to convert temperatures to a common metric. Evaluating Standards for Protecting Aquatic Life in Page 9 Washington's Surface Water quality Standards Table 3.1. Conversion equations for standardizing duration of exposure scenarios. These are used to convert study results to the standard metric of a 7 day average of the daily maximum temperatures.

The metric adjustment step was also used where appropriate to put bounds on the potential correct estimate on each line of evidence. This bounding process was used where there was reasonable uncertainty about the duration of exposure that best represented the line of evidence and the related biological response. For example, growth studies are generally conducted for a relatively long period of time ( e. g., 30 90 days), but significant changes in growth between different test temperatures are commonly obvious after the first week or two. Thus there is uncertainly whether the results of these tests should be applied as if they are summer average exposures or weekly average exposures. In the face of this uncertainty, conversions are made for both possible cases. The range produced by using these two adjustment factors creates a range within which the most probable correct answer would be expected to occur.

The results of this MLE process are presented in tabular form, and a range is produced by independently averaging both the lower and upper range values for each line of evidence. This creates a range within which the best estimate should be found. The midpoint of this range is considered to be the overall best estimate, unless overriding concerns with any particular line of evidence suggest another conclusion is warranted. In such a case, the suspect line of evidence is noted and either dropped entirely from the final range calculation, or is used as a basis for conditioning the recommendation. Table 3.2 shows a simplified example based on protecting the juvenile rearing life stage of salmon and trout. Convert from: To a 7DADMax ( ° C) Summer Average of the Diel Ranges ( ° C) In Char Spawning Habitat: Summer max Subtract 0.55 0 2 Summer mean Add 2.00 0 2 Weekly mean ( highest) Add 0.93 0 2 Daily mean ( highest) Add 0.62 0 2 In Salmon and Trout Habitat: Summer max Subtract 0.95 4 6 Summer mean Add 4.64 4 6 Weekly mean ( highest) Add 3.18 4 6 Daily mean ( highest) Add 2.60 4 6 Page 10 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards Table 3.2. Juvenile rearing of salmon and trout:

Line of Evidence ( LOE) 7DADMax ( ° C) Midpoint Comments Regarding LOE Laboratory Growth Studies at Constant Temperatures x z y Based on well controlled laboratory tests. Laboratory Growth Studies at Fluctuating Temperatures x z y Field Studies on Growth x z y Predation and Competition x z y Ranges Identified as Protective x z y Basis for estimates and intended metrics unclear. Comparing Discrete Test Regimes x z y Laboratory Temperature Preferences x z y Swimming Performance and Scope for Activity x z y Field Distribution of Healthy Populations x z y This estimate relies on the general upper range considered healthy, and temperatures above which coldwater species begin to loose dominance Summary Statistics and Final Estimated Range: Ave( x) Ave( z) Midpoint Based on previous draft reviews of the temperature requirements of Washington's native fish, it was determined the differences in thermal thresholds between species were generally slight. Only division into three species groupings ( guilds) appears warranted ( Hicks, 1998, 2000). Therefore, the multiple lines of evidence procedure was conducted separately in this current review only for the guilds of: 1) Char, 2) Salmon and trout, and 3) Warm water species.

b) General Thoughts and Observations i) Adjusting Laboratory Data for Application to Natural Waters Laboratory tests do not represent the full range of conditions that an organism will face in the natural environment. In most laboratory tests fish are exposed to a constant temperature environment, while in natural waters the temperature continuously fluctuates during each day, between days, and in seasonal trends of spring warming and fall cooling. In natural waters, fish must actively maintain position and seek food and shelter in the currents of rivers, succeed in the face of inter and intra species competition for both food and shelter, avoid predation, and resist disease. In laboratory studies, however, the fish are often in test chambers without substantial currents, fed food in pellet form, treated to prevent disease, and Evaluating Standards for Protecting Aquatic Life in Page 11 Washington's Surface Water quality Standards seldom need to compete or avoid predation. On the other hand, in laboratory tests, fish are often crowded into very small unnatural spaces, even Styrofoam cups, forced to perform using electrical stimulation or prodding, subjected to laminar artificial flows, and often fed unusual rations with large time intervals of starvation.

Because of the differences between laboratory conditions and the environmental conditions that fish face in the natural world, we must use caution in how we apply laboratory derived data in setting ambient water criteria. We must ensure that the temperature regimes used in the laboratory tests are considered in any application to natural streams.

Growth Studies:

Most of the research on optimal growth temperatures is conducted with water kept at a constant temperature. Water quality standards, however, must apply to naturally fluctuating thermal environments. Since temperature directly effects the metabolism of the fish, a fish kept continuously in warm water will experience more metabolic enhancement than one which only experiences that same temperature for one or two hours per day. Thus, constant test results cannot be directly applied as a daily maximum temperature in a fluctuating stream environment. The literature examined for this paper strongly suggests that constant temperature test results can be used to represent daily mean temperatures ( Hokanson et al., 1977; Clarke, 1978; Grabowski, 1973; Thomas et al., 1986; Hahn, 1977; and Dickerson, Vinyard, and Weber, 1999, and unpublished data, as cited in Dunham, 1999); at least in systems with moderate temperature fluctuations. Growth studies may be conducted for substantially varying periods of time ( 14 to 90 days) but generally encompass time frames that would match reasonably well with periods of maximum summer temperatures ( 20 60 days).

For illustrative purposes we can examine the findings of Hokanson et al. ( 1977). This study compared specific growth and mortality rates of juvenile rainbow trout for 50 days at seven constant temperatures between 8 ° C and 22 ° C and six diel temperature fluctuations ( sine curve of amplitude +/ 3.8 ° C about mean temperatures from 12 ° C to 22 ° C Figure 3.1. Relationship between growth rates and mean temperature exposures. Based on Hokanson et al.( 1977).

R 2 = 0 .9251 0 1 2 3 4 5 6 0 5 10 15 20 25 Page 12 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards Plotting the growth rates against the mean temperatures for both the constant and fluctuating tests produced a characteristic normal distribution for growth rate and temperature ( Figure 3.1 above). Thus a strong relationship appears between the daily mean temperatures in fluctuating tests and those in the constant tests. A pattern was demonstrated, however, where daily mean temperatures in the fluctuating tests at means of 12.5 and 15.5 ° C produced greater growth rates than comparable constant temperatures at 11.8 and 14.8 ° C. At the constant optimal temperature of 17.2 ° C and above, however, this pattern was reversed. This pattern led Hokanson et al. to suggest that the growth of rainbow trout appears to be accelerated at fluctuating treatments when the mean temperature is below the constant temperature optimum for growth and retarded by mean fluctuating temperatures above the constant temperature optimum. Hokanson et al. suggested that water quality standards ( based on weekly mean values) should be set such that the average weekly temperature is below the constant test temperature producing maximum growth.

Like Hokanson et al. ( 1977), other researchers ( Thomas et al., 1986; and Everson, 1973) have found that fluctuating temperature regimes actually enhance growth over what is found at constant temperature exposures; at least where the mean of the fluctuating regime is at or below that of the constant exposure test temperature producing optimal growth. The works by these authors also suggest that high peak temperatures may create stress which will harm growth even though the daily average temperature appears optimal. For example, Thomas et al. ( 1986) noted stress conditions occurring in cycles with daily peak temperatures of 20 ° C.

Variable Feeding Regimes:

Growth rates are related to both temperature and food rates. As temperature goes up, more food is necessary to supply basic physiological needs but also the efficiency goes up for utilizing excess foods. This relationship results in a situation where at maximum feeding rates fish will grow larger in warmer water, but at reduced feeding rates in the same warm water growth rates will suffer. In cooler waters, maximum growth rates are achieved at feeding rates well below those that produced maximum growth in the warmer waters. This relationship between feeding rates and temperature means that laboratory test results would need to be modified to account for the feeding regimes present in natural stream environments to be able to confidently set a very precise maximal growth temperature.

Numerous authors have demonstrated that food availability in the natural environment is well below that used in laboratory growth studies ( Brett et al., 1982; Saski, 1966; Nedham and Jones, 1959; Wurtsbaugh and Davis, 1977; Ensign et al., 1990; Bisson and Davis, 1976; as cited in ODFW, 1992; Elliott 1975, McCullough 1975, 1979, Murphy and Hall 1981, Edwards et al. 1979, Vannote et al. 1980, Bisson and Bilby 1998, and James et al. 1998; as cited in USEPA, 2001, and others). As an example of the influence of feeding rates, McMahon, Zale, and Selong ( 1999) tested bull trout growth and found that at satiation ( maximum) and 66% satiation ration levels growth was highest at 16 ° C, whereas at a 33% satiation ration growth rate was maximized at 12 ° C. Thus in waters of lower productivity, Evaluating Standards for Protecting Aquatic Life in Page 13 Washington's Surface Water quality Standards maximum growth may occur at temperatures well below those that produce optimal growth at high rations.

While the basic relationship between feeding rates and growth at various temperatures is well established, there is a problem with trying to apply an adjustment factor to laboratory test results. In the laboratory tests reviewed for this paper, feeding rates and regimes varied significantly. In addition, the nutritional value can be different between feeds, the size and type of food along with its method of presentation can influence the ability of fish to feed and consequently grow, and the specific starting size of the test fish will greatly influence growth rates. Given that the feeding regimes and test conditions were so highly variable, trying to make a standard adjustment to laboratory test results to try and match natural feeding regimes is problematic. Nevertheless, it is important that this factor be recognized when setting water quality criteria recommendations for juvenile rearing.

There are at least a couple of ways that this factor can be accounted for without having to develop complex growth models to test various temperature regime scenarios. The first is to make a standard 2 4 ° C adjustment downward to the temperature value determined optimal for growth at satiation feeding. The second is to apply the criteria to a relatively brief window of time ( e. g., 2 3 weeks), even though the growth tests often lasted 4 weeks or more, and recognize that temperatures will need to be below this value most of the time in even the warmest years to result in compliance, thus virtually ensuring that temperatures will produce excellent growth overall. In assessing the risks associated with making such simplifying assumptions it is important to recognize that growth rates diminish on either side of the optimal temperature range. It is not substantially different to err slightly on the warmer side of optimal than it is to err on the cooler side of optimal, barring any other detrimental biologic responses. By extending just beyond the warmer side of optimum during the warmest period of the warmest years the fish will actually be experiencing a greater number of days in the optimum range over most years. In the recommendations of this paper, except where noted for testing that examined reduced feeding rates, temperatures that consistently resulted in maximum growth at satiation feeding were used to set the threshold value.

Incubation Studies:

Specific studies were not found that compared the effects of constant and fluctuating temperatures on incubating fish. However, it is assumed in this paper that that incubating fish generally respond to the daily mean temperature. This seems warranted given the strong basis provided through the use of the standardized " temperature unit" calculations in hatchery operations and in fisheries science in general. It is fortunate that many of the incubation studies were conducted with fluctuating water temperatures ( highlighted in the discussions of individual species). This provided a good opportunity to generally check the effect of applying the results as average temperatures and to assess the risks of allowing higher daily maximum temperatures. Additionally, a natural safety factor often exists to protect egg incubation. Since salmonids bury their eggs in the gravel of the stream bed, they are buffered slightly from both daily maximum and daily minimum stream temperatures. The buffering of the stream bed gravel can effectively reduce the daily maximum Page 14 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards temperature by at least 1 1.5 ° C ( Crisp, 1990). While this natural safety factor is not accounted for in laboratory tests it is also not dependable. Therefore, in the recommendations of this paper no adjustment is made to account for this often occurring buffering effect. It is useful, however, when reviewing the potential risks of the recommendations in this paper to recognize that sudden and unseasonable rises in stream temperature during incubation will often not cause similar temperature exchanges in the egg pockets situated in the gravel.

Few studies examined the risk of short term lethality to eggs from unusually high temperatures for individual species, so the few that were conducted are used broadly to suggest limits on daily maximum temperatures during the incubation period for all related species. Limits for daily maximum temperatures are also based on the results from controlled laboratory tests where the temperature regime experienced by the fish was started at varying high daily maximum temperatures and then allowed to fluctuate and fall in concert with the seasonal changes in the natural waters used to supply water for the tests. From these experiments it can be observed what temperatures at the start of the incubation tests are generally associated with reduced incubation performance, and what temperatures appear not to hinder incubation.

Lethality and Acute Effects:

The water quality standards must be applicable to a broad range of human activities. The standards must protect against both gradual basin wide increases in temperature as well as localized shifts in daily maximum temperatures. Rapid or site specific changes in temperature can be caused by unique human activities ( such as industrial cooling waters, process wastewaters, and water releases from reservoirs). While localized extreme changes in water temperature are not as common as the gradual basin wide changes, they do exist, and their regulation through discharge permits and water quality certification programs require careful application of biologically based temperature standards. These localized point sources of temperature change are also those most capable of creating short term lethality to aquatic life as they may discharge water significantly hotter or colder than the ambient water to which organisms are acclimated.

The incipient lethal level ( ILL) is typically determined by exposing juvenile fish to constant temperatures and determining the test temperature that causes 50% mortality of test fish within typically a 7 day exposure period. It would not be appropriate to establish criteria that would allow 50% mortality, however, so the ILL value needs to be adjusted to a level that would not be expected to cause any mortality. The National Academy of Sciences ( 1972) and Coutant ( 1973) recommend subtracting 2 ° C from the LT50 value to determine a safe ( no more than 1% mortality   an LT1) short term temperature limit. Some reasons for extra caution in interpreting lethality studies include that:

1. The time above lethal levels appears cumulative ( DeHart, 1974, 1975, and Golden, 1978); Evaluating Standards for Protecting Aquatic Life in Page 15 Washington's Surface Water quality Standards 2. Adults appear more sensitive than the juveniles which are most commonly tested ( Coutant, 1970; Becker, 1973; Bouck and Chapman, 1975); 3. Individual stocks possess slightly different tolerance levels ( Beacham and Withler, 1991); 4. Indirect acute effects are often cited to occur just below lethal levels ( e. g., increased predation, feeding cessation, migration blockage); and 5. The range between no mortality and high mortality rates is often described by as little as 0.5 ° C ( Charlon, Barbier, and Bonnet, 1970).

The selection of laboratory results for use in developing recommendations focuses on test fish that had previously been acclimated to reasonably cool water temperatures. This recognizes that fish migrating from cooler upstream tributaries or from marine waters may not be fully acclimated to warmer main stem summer river temperatures. It also helps to bridge the gap in protection that occurs when protecting fish from hot thermal discharges occurring in the late fall through early spring period when the ambient river temperatures are often very cold.

Although test results that determine lethal threshold temperatures are used as one line of evidence in this paper for recommending water temperature thresholds that will prevent acute ( short term) effects, the final recommendations are not based on just avoiding lethality. Temperatures that would result in any detrimental acute effect such as causing a barrier to adult fish spawning or migration take precedence in the recommendations. Thus, while a species may be able to survive in a laboratory environment at a given temperature, research may show that the temperature maximum would be unacceptable in natural waters.

ii) Minimum Temperature Thresholds One issue not directly included in the technical recommendations at this time are recommendations for how cold a water body can be allowed to be due to human actions. It is well documented that unseasonably cold waters can be as detrimental to aquatic organisms as unseasonably warm waters. Sudden releases of very cold water can cause rapid lethality to unacclimated organisms, and waters substantially colder than what is optimal can decrease survival of eggs and embryos and detrimentally depress juvenile growth rates. Human activities, such as the removal of overhead vegetative canopies will increase long wave radiative cooling causing potentially harmful drops in the natural winter low temperatures. This may encourage anchor ice, a result of streams freezing, that may cause additional damage to fish and their habitat as it causes super cooling of the water and scours the channel during spring break up ( Jakober et al., 1998; Needham and Slater, 1944; Needham et al., 1945 Maciolek and Needham, 1952). It may be that thresholds for low temperature limits should be considered at some point in the future, and information is included in this paper to assist in setting site specific limits for individual activities. However, to keep the focus of this paper on the area of greatest concern, that of high water temperatures, the issue of cold water limits is not being addressed at this time. Page 16 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards iii) Protection of Untested Species The technical recommendations made in this paper are primarily based upon data obtained on the temperature requirements of our two native char, the five Pacific salmon, rainbow and cutthroat trout, smelt, mountain whitefish, several stream breeding amphibians, and numerous insect species. Rigorous scientific testing generally has not been done on most of the other aquatic species indigenous to Washington's waters. What references have been found for these other species tends to be of a more anecdotal nature; noting what the temperature was when spawning was observed, or indicating the temperature of a waterbody where a species was found. For some of these less well known indigenous species, however, direct testing of their temperature optima and lethal limits has occurred. Based on what temperature information has been found, both direct and indirect, these other species do not appear to possess more sensitive temperature requirements than the species that have been used to make temperature threshold recommendations in this document.

Many of the less well known aquatic species, which often occur together as a community, appear to thrive in waters which are at the upper margin of what is optimal for salmonids, and represent warm water fish communities indigenous to Washington. Recognition of these species has resulted in the recommendation that the state establish a unique level of usesupport that can be assigned to our naturally warmer waters.

The warm waters that occur in the margins and slack water areas of many rivers serve as important habitat to many species that prefer summer water temperatures somewhat warmer than what is healthy for the state's indigenous salmonids. These other species also commonly serve as food fish for salmonids and are important to the overall health of the system. Thus, these warmer stream margins should not be viewed as lost or unhealthy habitat, but as a necessary and natural adjunct to a healthy aquatic system. It is important to note that young salmonid fry also often initially rear in the shallow margins of rivers until reaching a size that allows them to habitat the more active channel, and that these young fry have been commonly shown to have slightly higher temperature preferences than older fry or juvenile fish. Evaluating Standards for Protecting Aquatic Life in Page 17 Washington's Surface Water quality Standards 4. Temperature Requirements of Char, Salmon, and Trout Species In this chapter, the temperature requirements of the char, salmon, and trout species indigenous to the state of Washington are examined. Whenever the data allowed doing so, two temperature values are provided to define the upper end of the temperature range that is fully protective of each species' key life stages. This was generally done for the primary metric recommended which is a 7 day average of daily maximum temperatures. The approach taken recognizes that the upper fully protective endpoint is often more accurately described by defining a narrow range of temperature rather than a single value. The final selection of a single recommended value comes only after the needs of all of the species, their life stages, and stressors are considered together [ see Summary Section 4 g)].

a) Native Char Temperature Requirements i) General Life History Information:

Bull trout ( Salvelinus confluentus) and Dolly Varden ( Salvelinus malma) are the only two species of char native to Washington ( Hass and McPhail, 1991). Perhaps more than any other species, cold waters are critical to maintaining healthy populations of these native char. These two closely related species are difficult to taxonomically identify from one another in the field ( Hass and McPhail, 1991). Cavender ( 1978) may have first recognized that what had previously been considered an interior form of Dolly Varden was in fact a distinct species, now referred to as the bull trout. Goetz ( 1989) suggests that bull trout may be more directly related to the Arctic char ( Salvelinus alpinus), and in fact a sister to the Arctic char Dolly Varden group. Spalding ( 1997) found that for Washington's Olympic Peninsula many of the anadromous char previously assumed to be Dolly Varden keyed out to be bull trout. While important to advancing scientific understanding, the historic problems with discriminating between these char appear to pose little practical problems in terms of setting water quality criteria. This is because Dolly Varden and bull trout are generally considered to have very similar biological requirements, and the management measures needed to protect both Dolly Varden and bull trout may be identical ( WSDFW, 1994).

The Washington State Department of Fish and Wildlife considers the majority of native char stocks in the state as being " Vulnerable Populations" requiring special protection. Bull trout in particular have received considerable publicity in recent years because of their status as a threatened species under the federal Endangered Species Act. The results of a 12 month study evaluating stock status by U. S. Fish and Wildlife Service noted serious declines of bull trout populations statewide ( USFWS, 1997). Rieman et al. ( 1997) examined the distribution and status of bull trout across 4,462 sub watersheds of the interior Columbia River basin and the Klamath River basin and found that bull trout are more likely to occur and the populations are more likely to be strong in colder, higher elevation, low to mid order watersheds with lower road densities. They noted that while bull trout were widely Page 18 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards distributed across their potential range, strong populations may exist in only 6% of this potential range.

Upon hatch, char fry will either remain in the localized area or move downstream to larger streams or lakes to rear ( Goetz, 1989; Williams and Mullen, 1992; Reiser et al., 1997). Movements to more suitable upstream waters has also been observed ( Fraley and Shepard, 1989; Armstrong and Morrow, 1980, as cited in Goetz, 1989). Unless information clearly demonstrates that a stretch of water would not be used for summer rearing even under natural conditions, temperature criteria assigned to these migration paths should also be set to protect the rearing of char fry.

Some research suggests that age 0 1 juvenile char have cooler temperature preferences than age 1+ juveniles; however, there is little consistency in the values identified. The preference values for age 0 1 bull trout range from an average of 4.5 ° C ( Ratliff, 1992), to maximum stream temperatures of 10 ° C and 13 ° C ( Ratliff, 1987; and Martin et al., 1991). Resident forms of bull trout remain in or near their natal streams for their entire life. Fluvial and adfluvial forms may remain in the area of their natal stream for 1 to 3 years and then migrate significant distances to more productive waters for greater juvenile growth opportunities ( Pratt, 1992; Ratliff, 1992; Riehle et al., 1997; Fraley and Shepard, 1989; Goetz, 1989); although, some stocks have also been observed to migrate to lakes or reservoirs immediately after hatching ( Reiser et al., 1997). Sea run ( anadromous) forms will migrate hundreds of miles to take advantage of productive near shore marine habitat ( Goetz, 1989). Temperature standards would ideally be set in consideration of these various life strategies.

The needs of resident forms may be slightly different from the various migratory forms. Juvenile bull trout and Dolly Varden have difficulty competing with several common salmonid species in warmer waters ( Haas, 2001; McMahon et al., 1999). This may partially explain why researchers have observed young juvenile fish remaining in their natal stream for the first several years before moving downstream to warmer and more productive waters. It is plausible that the lack of significant competitors in their cold natal streams may compensate for the reduced productivity of these pristine environments. Since nonmigratory resident bull trout must remain in and defend their natal habitat for their entire life, temperatures here should clearly favor bull trout over competing species such as chinook salmon and rainbow trout ( Martin et al., 1991; Mullan et al., 1992; Ziller, 1992; Adams and Bjornn, 1997; WSDFW, 1994; Haas, 2001). Evaluating Standards for Protecting Aquatic Life in Page 19 Washington's Surface Water quality Standards ii) Spawning Requirements Field Observations of Spawning Initiation Maximum temperatures should generally be below 12 ° C and on a fall season cooling trend at the time char enter their spawning streams ( Fraley and Shepard, 1989). In a study on the Rapid River in Idaho, pairing behavior was noted to begin after average water temperatures dropped from 10 to 6.5 ° C ( generally equivalent to a change in single daily maximum temperatures from 11 7.5 ° C) ( Schill, Thurow, and Kline, 1994). In the same river, Elle and Thurow ( 1994) found that daily maximum water temperatures below 10 ° C influenced the movements of spawners both in and out of the Rapid River. While daily maximum temperatures may need to fall below 9 to 11 ° C ( WSDFW, 1994) for redd construction to begin, no authors have been found to suggest spawning will begin at daily maximum temperatures above 10 ° C. Most place the temperature that triggers spawning below 9 ° C ( Goetz, 1989; Pratt, 1992; Kramer, 1991; Fraley and Shepard, 1989), with the peak of spawning activity not occurring until stream temperatures falls below 7 ° C ( James and Sexauer, 1997; Wydoski and Whitney, 1979). Reiser et al. ( 1997) suggested that a daily average temperature between about 6.8 to 8.1 ° C ( generally equivalent to a single daily maximum range of 7.8 9.1 ° C) was necessary to initiate spawning activity. Temperatures above 8 ° C were noted by Kramer ( 1994) as appearing to cause spawning activity to temporarily cease in char in northwest Washington streams. The Washington Water Power Company ( 1995) studied the distribution of fish in the lower Clark Fork River in Idaho and found that bull trout spawning was confined to an artificial spawning channel created to mitigate the effects of the Cabinet Gorge Dam. Water temperatures in theses spawning areas were consistently cooler ( 5 7 ° C) than other areas of the channel, and during the period of redd construction bull trout used the area of the channel where the temperature was 11 ° C due to ground water seeps.

Bull trout are noted to begin spawning as soon as conditions are suitable and redds are constructed. Temperature may be the primary cue used by the fish to determine when to begin migratory movements ( Elle and Thurow, 1994; Swanberg, 1997) as well as to initiate spawning ( Kramer, 1994). It is important that temperatures at the initiation of spawning be within a range that would not hinder ovulation and would not cause obvious harm to offspring of any early spawning individuals.

The field observations and citations noted above are in strong concurrence that spawning behavior ( pairing and redd construction) will not begin 7DADMax temperatures fall below 8.45 9.45 ° C, and that spawning itself will only be initiated once the daily maximum temperature falls below 7.45 8.45 ° C. Page 20 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards Laboratory Studies of Spawning Initiation Only a single study was found that addressed the question of what temperatures are required to initiate spawning. In a study by Gillet ( 1991) ovulation in char was found to be completely inhibited at constant temperatures above 11 ° C and slowed down above 8 ° C as compared to fish held at 5 ° C. This would be correlated with 7DADMax values of 11.62 11.93 ° C and 8.62 8.93 ° C, depending upon the constant test exposures being treated as if they represent on day average and seven day daily average stream exposures. Transfers from 8 ° C to 5 ° C were found to stimulate ovulations. Gillet also found that exposure to temperatures of 8 ° C prior to ovulation were favorable to fecundity rates, and assumed based on their work that very cold water was only necessary during the last weeks before spawning. The work of Gillet suggests that for the closely related Arctic char, temperatures should be falling below 8 ° C to stimulate healthy spawning, and falling towards 5 ° C to ensure full survival of fertilized eggs ( only 11, 8, an 5 ° C were tested, so specific incubation thresholds were not determined). Based on this one laboratory study it would appear that a 7DADMax of less than 8.62 8.93 ° C is necessary to allow healthy ovulation to occur in bull trout.

Summary on Spawning Initiation Requirements There is strong agreement among both field and laboratory research and observations on the spawning requirements of bull trout. The weight of the evidence supports the position that initial spawning behavior ( pairing and redd construction) is hindered by daily maximum stream temperatures above 9 11 ° C and that the act of spawning may be impaired by daily maximum water temperatures greater than 8 9 ° C.

Laboratory Studies on Incubation Success Only a few studies were found that tested the incubation requirements of bull trout in the laboratory. Fredenberg ( 1992) reported that eggs from wild bull trout incubated at an average temperature of 3.1 ° C had egg survival averaging 97.4% from unfertilized egg to eyeup and 97.1% from unfertilized egg to hatch. Eggs were subsequently collected from the hatchery raised broodstock and incubated at an average temperature of 5.8 ° C ( 5.0 ° C minimum and 6.6 ° C maximum), and while no growth or survival data was collected the author suggested that it appeared normal. Fredenberg, Dwyer, and Barrows ( 1995) collected gametes from wild spawning bull trout from the Swan River drainage of northwest Montana during September of 1993 and 1994. Fertilized eggs were produced by paired matings and incubated in 1993 at approximately 3.1 ° C with a resultant 97.1% survival from green eggs to hatching. Eggs in 1994 were incubated at approximately 6.5 ° C with a resultant 95.5% survival.

McPhail and Murry ( 1979) tested incubation of bull trout at constant laboratory temperatures of 2, 4, 6, 8, and 10 ° C in a series of three replicate tests. In the one test lot that escaped high transit related mortality during movement to the laboratory after fertilization, McPhail and Evaluating Standards for Protecting Aquatic Life in Page 21 Washington's Surface Water quality Standards Murry ( 1979) found that survival was excellent ( 90 95%) at 2, 4, and 6 ° C, good ( 85%) at 8 ° C, and poor ( 20%) at 10 ° C. In the two other test lots, which experienced significant transit related stress ( 40% egg mortality during transit), survival rates were noted to steadily decline from 2 to 4, to 6 ° C and drop to zero at 8 and 10 ° C. Similarly, constant test temperatures in the range of 7 11 ° C were reported to result in " poor" survival in hatchery culture by Brown ( 1985). McPhail and Murry ( 1979) noted that mortalities at low temperatures (< 6.0C) typically occurred at blastopore closure, while at high temperatures (> 8.0) mortality is associated with hatching. In studies on the related species of Arctic char, Humpesch ( 1985) reported optimal incubation to occur at 5 ° C.

The above studies generally found that constant temperatures in the range of 3.1 6.5 ° C capable of producing excellent ( 90 97.4%) survival of char eggs, with survivals equally high throughout the range. At temperatures 8 to 10 ° C survival rates may drop precipitously from 85% to 0%. The research suggests that a constant temperature of 6.5 ° C may most confidently define the upper limit for fully protecting incubation. This would be equivalent to a 7DADMax temperature of 7.43 ° C when correlated as if it were a one week average daily exposure, and equivalent to a 7DADMax temperature of 8.5 ° C when correlated as if it were an incubation season long average exposure ( assuming a stable stream temperature with 0 2 ° C diel variation). Based on the above, the laboratory studies suggest full incubation protection will occur if the highest 7DADMax temperature during the incubation period does not exceed 7.43 8.5 ° C. It is important to note that this process is not trying to determine an acute threshold for eggs or embryos. It only identifies temperatures that can occur at the initiation of incubation that will fully protect native char incubation under a normal temperature regime ( i. e., fall cooling trends).

It is important to note that even though 2 ° C has been shown to be suboptimal at a constant incubation temperature, natural seasonal declines in temperature down to 2 ° C in the incubation period are unlikely to reduce survival rates. Salmonids have been shown to undergo conditioning in the early stage of incubation that allows excellent survival at very low temperatures occurring later. Where the conditioning does not occur, and the eggs are incubated at an early stage at very low temperatures, significant reductions in survival have been noted ( Murry and Beacham, 1986; Seymour, 1956). This assertion is also supported by work showing that newly hatched bull trout alevins are tolerant of temperatures near 0 ° C ( Baroudy and Elliott, 1985) and that the lower limit for hatching in the related Arctic char is less than 1 ° C. Such conditioning, however, may not only protect embryos from later exposure to colder waters but may help increase tolerance for warm water fluctuations as well. Bebak, Hankins, and Summerfelt ( 2000) examined the hatching success and posthatch survival of three stocks of Arctic char and found that if incubation had been well initiated at a favorable ( 6 ° C) temperature then later transfers to waters as warm as 10 12 ° C still allowed for excellent hatch rates ( 90 98%). It is noteworthy, however, that they also found that survival rates post hatch declined over time at both 10 ° C and 12 ° C.

Field Evidence on Incubation Requirements Page 22 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards Little evidence was found from field studies on the incubation requirements of bull trout or Dolly Varden. In one study that was reviewed, however, it was noted that bull trout redds in the upper Flathead River basin in Montana had mean temperatures that ranged from 2.1 5.4 ° C ( Weaver and White, 1985). This season long estimate of average field temperatures would correlate with a 7DADMax temperature range of 4.1 7.4 ° C. It is important to point out that just noting the average temperature of redds does not indicate whether it was healthy, and is not very useful for describing of the upper boundary for successful incubation. For this reason, only the upper half of the range will be used to represent this line of evidence, the next preferred option would be to not use this range at all to estimate incubation requirements. Based on the above discussion, field temperatures of bull trout redds should be considered to have an upper range of 5.75 7.4 ° C.

Conclusion on Spawning and Incubation While spawning and incubation were discussed separately above, it is important to recognize they actually occur concurrently in the natural stream environment. Once spawning has occurred the eggs begin to incubate. The multiple lines of evidence created from the wide variety of field and laboratory studies can be brought together in support of selecting a temperature standard for application at the beginning of the spawning and incubation period. The focus on the temperature at the initiation of incubation is viewed as appropriate since temperatures will be at their highest at this time. They should also be on a trend of fall cooling that will soon reach temperatures that are naturally determined by the elevation and geographic location of the site. The interim conclusions from each line of evidence are summarized below:

Table 4.1. Spawning and Incubation requirements of native char.

Line of Evidence 7DADM  Range ( ° C) Median ( ° C) Field observations on spawning initiation 7.45 8.45 7.95 Laboratory studies on spawning initiation 8.62 8.93 8.77 Laboratory studies on incubation success 7.43 8.5 7.97 Field study on typical average redd temperatures in Montana 5.75 7.4 6.57 Best Estimate of Threshold 7.31 8.32 mid. pt. 7.82 The range of these independent lines of evidence is 5.75 8.93 ° C with a mean range of 7.31 8.32 ° C and an overall midpoint of 7.82 ° C. This strongly suggests that a 7 day average daily maximum temperature of 7.82 ° C will fully protect the spawning and incubation of char. In recognition that temperatures of 8.0 ° C have been noted as hindering spawning in char, it may not be advisable in this situation to select a spawning threshold value from the upper end of Evaluating Standards for Protecting Aquatic Life in Page 23 Washington's Surface Water quality Standards the range presented above. It is concluded that a 7 day average of the daily maximum temperatures of 7.5 8.0 ° C best represents the highest temperature that can occur at the initiation of spawning without causing detrimental effects to either spawning or subsequent incubation.

iii) Juvenile Rearing Field Distribution Work Examining Fish Presence Dunham et al. ( 2001) surveyed the distribution of juvenile/ small bull trout ( Note: small resident stock fish cannot be distinguished apart from juveniles of migratory stocks) in 6 basins ( 109 sites) in Washington state and found that summer maximum temperatures best defined their presence in streams. In their study, 95% of the bull trout were found in streams with temperatures above 12 ° C with an interquartile range of 13.3 14.7 ° C ( with the median and mode both at 14 ° C). This is similar to a study by Rieman and Chandler ( 1999) who examined 581 sites throughout the Western United States and found that the majority of sites with juvenile/ small bull trout had summer maximum temperatures of 11 14 ° C ( 95% were from waters with summer maximums less than 18 ° C). Goetz ( 1997b) surveyed 13 drainages in Washington and Oregon and was unable to find juvenile bull trout in streams with temperatures above 14 ° C. In a study in British Columbia, Hass ( 2001) found that the warmest study streams containing bull trout ( resident juveniles or adults) had summer maximum temperatures of 16 ° C, which is similar to the findings of numerous other researchers that 15 16 ° C formed the upper temperature limit to bull trout ( juveniles or adults) summer distributions ( Fraley and Shepard 1989, Shepard 1985, Goetz, 1989, Pratt, 1992, Martin et al. 1991) and that a temperature of 15 ° C can trigger the out migration of char from otherwise suitable habitat ( Goetz, 1997). The general findings for bull trout discussed above are also supported by the work of Jensen ( 1981) who found that 14 ° C ( as a 10 day mean) appeared to form a barrier to the distribution of the closely related Arctic char.

The above studies demonstrate that daily maximum temperatures in the range of 14 15 ° C ( 7DADMax 13.45 14.45 ° C) set the upper boundary for commonly finding juvenile/ small bull trout. It is important to note that some researchers have both wider and narrow margins of distribution. Some authors have found that colder summer maximum temperatures ( 10 11.5 ° C) formed the general limits to bull trout distributions in specific watersheds ( Ratliff, 1987). While other authors have reported finding juvenile bull trout at much warmer ( 17 20.5 ° C) temperatures ( Brown, 1992; Goetz, 1989, Adams and Bjornn, 1997; Reiman and Chandler, 1999). It was noted by Adams ( 1999) that bull trout found at 20.5 ° C held in the coolest water available in the area (< 17.2 ° C) and looked physically unhealthy. This point is made to remind the reader that the mere presence of a fish does not indicate that it is healthy or that the stream is capable of supporting healthy populations. Page 24 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards Field Work that Considered Dominance, Density, and Competitive Advantage While studies that describe the stream temperatures associated with the presence of a species are a useful line of evidence, they cannot be used to say whether or not the population is in good health at the observed temperature regimes. Researchers have tried to answer the question of what is healthy for bull tout in field studies by identifying sites with high densities of bull trout, and by identifying temperatures beyond which bull trout begin to loose dominance over other competing species. Health has also been assessed more directly by evaluating the condition of the fish using standard bio metrics.

Haas ( 2001) found that a 7 day average of the daily maximums of 11.6 ° C ( correlating with a single daily maximum of 12.15 ° C) consistently determined the dominant presence and better condition of bull trout in 26 sites in the Columbia River drainage in British Columbia. Haas reasoned that bull trout populations would be supported by maintaining summer maximum temperatures below 13 ° C, and noted that rainbow trout were found to be dominant over bull trout and in better condition as summer maximum temperatures approached 14 15 ° C. This corresponds well to the Dunham et al. ( 2001) finding that 90% of the sites that did not have bull trout had summer maximum temperatures greater than 13.5 ° C ( non char sites had an interquartile range of 14.6 19.8 ° C and a median of 17 ° C). It also corresponds well with Williams and Mullen ( 1992) finding that rainbow trout excluded the first two age classes of bull trout at weekly average temperatures above approximately 11 12 ° C ( correlating with single day maximums of 12.49 13.49 ° C). Williams and Mullan ( 1992) found that bull trout growth in the Early Winters Creek basin of northern Washington steadily increased with increasing temperatures at three synchronous test sites having annual maximum weekly average temperatures of 8.7, 10.3, and 11.7 ° C, respectively. The maximum weekly average of 11.7 ° C correlates to a 7DADMax of 12.63 ° C. Growth was not tested at any warmer sites, thus the 7DADMax temperature that would allow for optimal growth in this stream system was not identified, but would likely be greater than 12.6 ° C. Similarly, Martin et al. ( 1991) and Goetz ( 1989, 1997) concluded that bull trout are dominant in streams with summer maximum temperatures less than 13 ° C. Saffel and Scarnecchia ( 1999) examined 18 reaches of six streams and found that the density of bull trout increased with increasing maximum temperature below 14 ° C ( range 7.8 13.9 ° C) and decreased with increasing temperature above 18 ° C ( range 18.3 23.3 ° C). The highest densities were found in reaches with maximum summer temperatures between 10 13.9 ° C. In this work there were no study streams having summer maximum temperatures within the range of 14 18 ° C, so it cannot be said whether or not densities would have begun to decline just above 14 ° C. Kitano et al. ( 1994) found that brook trout and cutthroat trout coexisted with bull trout in the Flathead River basin in Montana in waters with a temperature range of 5.3 8.9 ° C in early September, but they provided no information on the relative health of these populations or on when competition would be impaired.

Based on the above works, it is reasonable to expect that streams with summer maximum temperatures of 12 14 ° C ( 7DADMax 11.45 13.45 ° C) will be capable of producing and maintaining strong populations of bull trout. Not all of the research examined, however, fully supports this assertion. Sexauer and James ( 1997) studied four bull trout streams in the Yakima and Wenatchee River watershed in central Washington that were selected because Evaluating Standards for Protecting Aquatic Life in Page 25 Washington's Surface Water quality Standards they were considered " healthy" and found summer maximum temperatures in the year the study was conducted ranged from 9 12.5 ° C. Further, Ratliff ( 1992) and Ziller ( 1992), reported that bull trout began to lose dominance as summer average temperatures rose above 7.9 ° C ( correlating with single day maximums of 10.45 ° C).

The wealth of studies across the Northwest when considered in combination demonstrate some strong patterns of occurrence. Any study of a single basin or stream needs to be carefully considered prior to accepting its conclusions. For example, in the cold groundwater dominated Metolius River system in Oregon, Ratliff ( 1987) reported that bull trout were rarely found at temperatures above 10 ° C. While true, it is important to recognize that warmer waters are largely unavailable in this tributary system. Thus care should be exercised before concluding that 10 ° C has been shown to create a barrier to bull trout populations. Similarly, many of the studies were conducted over a single year, and thus the long term relationship between the presence healthy populations and maximum ambient temperatures at the site is often not documented. So while Sexauer and James ( 1997) studied streams with healthy populations, they only reported temperatures from a single year. The actual temperature regime for these sites, which hold healthy char populations, may include years with warmer temperatures than those observed during the study year.

Summary of Evidence from Field Studies on Juvenile Rearing A preponderance of juvenile/ small bull trout in Washington may be found in streams with summer maximum temperatures between 13.3 14.7 ° C ( 7DADMax 12.75 14.15 ° C). This is reasonably consistent with surveys extending throughout the Western states that found most juvenile use to occur in stream segments with maximum temperatures not exceeding 14 ° C. It is also well supported by studies of in stream growth, density, and competitive dominance which suggest healthy bull trout streams have summer temperatures that do not exceed 12 14 ° C. While field studies are a very useful line of evidence for developing temperature criteria, they can be strengthened by cross checking the conclusions with laboratory findings.

Laboratory Studies Supporting Juvenile Rearing In a controlled hatchery environment, Fredenberg et al. ( 1995) found that constant exposure to 8.3 ° C produced greater growth of bull trout at maximum rations than at lower test temperatures. This would be equivalent to a single day maximum of 9.79 ° C ( 7DADMax 9.24 ° C) if the constant hatchery temperature is treated as it represented the warmest oneweek average stream temperature; and a single day maximum of 10.85 ° C ( 7DADMax 10.3 ° C) if it were equivalent to a summer season long average stream temperature.

In a laboratory study, McMahon et al. ( 1998) found that growth was highest at a constant 12 ° C, but not significantly less at 14 and 16 ° C at maximum rations. Growth declined sharply at temperatures greater than 18 ° C and less than 10 ° C. In follow up tests, the authors ( McMahon et al., 1999) found that growth at maximum and at 66% of maximum rations Page 26 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards were highest at 16 ° C, but that at 33% of maximum ration growth was maximized at 12 ° C. In modeling the available calories in low productivity streams ( the ration used and the basis for its selection was not provided) against the growth observed in their tests, the authors suggested the optimum growth range of 12 16 ° C would shift to 8 12 ° C. McMahon et al. ( 2000) examined the growth of bull trout over a 60 day period in both constant and fluctuating temperature regimes. Peak growth at a moderately restricted ration ( 0.66) occurred at 12.4 ° C at a constant temperature and at a mean of 12.2 ° C in fluctuating treatments (+/ 3 ° C around the mean  giving a 60 day average daily maximum of 15.2 ° C). Peak growth at an unrestricted ration occurred at 13.2 ° C and at a severely restricted ration ( 0.11) occurred at 12.3 ° C. In this work the authors found that growth was higher in constant exposure tests overall, and opined this was due to the fluctuating temperatures increasing metabolism without increasing food intake. Similar findings were produced using the related Arctic char ( Swift, 1975; as cited in Jensen, 1995; and Jobling, 1983) where maximum growth occurred at about 12 14 ° C ( at satiation rations). These growth studies may help explain why Shepard et al. ( 1984) found that bull trout growth was slower in the middle fork of the Flathead River, Montana, even though it was warmer and more productive. The work of McMahon et al. ( 2000) suggest that an average temperature of 12 13 ° C can produce maximal growth under both severely restricted and satiation diets, respectively. A constant laboratory test temperature exposure of 12 13 ° C can be correlated with 7DADMax summer stream temperature maximums of 12.93 13.93 ° C based on correlations with the warmest one week average stream temperature; and 7DADMax summer maximums of 14 15 ° C based on correlations with the summer season long average stream temperature. There is reason to also believe that in some cases growth could be maximized, or not statistically different, at even higher constant temperatures. Their work also suggests that daily maximum temperatures of 15 16 ° C ( 7DADMax 14.45 15.45 ° C) may be producing thermal stress or excess metabolic demands that may hinder growth in juvenile char that are at otherwise healthy daily mean temperatures. This is supported by the findings of Bonneau and Scarnecchia ( 1996) who noted that temperatures above 15 16 ° C are associated with increased metabolic stress and swimming impairment in bull trout. The line of evidence produced using the above laboratory studies suggests that streams with 7DADMax temperatures not exceeding 12.93 15 ° C are likely to fully support the growth of juvenile char.

Laboratory Studies Examining Competition for Food Brook trout are a species of char that have been widely introduced in the northwest that have often been cited as eliminating bull trout from their native habitat. McMahon et al. ( 1999), found that the presence of brook trout in sympatry ( together) with bull trout resulted in significantly greater growth of brook trout and significantly lower growth for bull trout than occurred with either species in allopatry ( alone), especially at constant water temperatures equal to or greater than 12 ° C. McMahon et al. ( 2000) examined bull trout and brook trout competition under two constant ( 11 and 17 ° C) temperatures. At a constant 11 ° C there were not significant differences in the growth of bull trout and brook trout in allopatry and sympatry. However, at the higher temperature ( 17 ° C) brook trout grew significantly more ( a Evaluating Standards for Protecting Aquatic Life in Page 27 Washington's Surface Water quality Standards 2.5 times greater growth rate) than bull trout in both allopatry and sympatry. observations were also made at temperatures of 8 and 16 ° C. When in the presence of brook trout, bull trout feeding rates declined 50% at 8 ° C and 64% at 16 ° C, whereas feeding by brook trout showed no change. The work of McMahon et al. ( 1999, 2000) suggests that as average water temperatures rise above 12 ° C bull trout may begin to loose their competitive ability against brook trout. It also points out the difficulty of trying to protect bull trout from displacement by brook trout since the brook trout are capable of significantly out competing the bull trout even at very low temperatures ( 8 ° C).

In trying to correlate the laboratory studies on competition to stream temperatures, it is important to recognize that competition may be related as much to the absolute temperature at any point in time as much as a weekly or seasonal average temperature regime. However, since the effect of competition on the health of a species will not be determined by a portion of a single day allowing for detrimental competition, it is still considered reasonable to correlate average stream temperatures with the constant laboratory test temperature at which competition was not favored by water temperature ( 12 ° C). A single daily average and a weekly average are used below to represent the effects found with constant laboratory exposures and make conversions to a 7DADMax temperature metric. The above cited work suggests that a 7DADMax summer temperature of 12.62 12.93 ° C may best describe a stream which does not provide any thermal advantage in competition between bull trout and brook trout. It is important to remind the reader that the laboratory tests did not include constant temperatures within the range of 12 16 ° C making it difficult to determine if a threshold exists within this range above which most of the change in competitive ability occurs.

Summary of Laboratory Studies The work of McMahon et al. ( 1999, 2000) suggest that a constant or average temperature of 12 ° C can produce maximal growth under even severely restricted diets. Their work also suggests that as water temperatures rise above 12 ° C bull trout begin to loose their ability to compete with brook trout. As noted above, the research on competition seems best viewed by comparison with a single week's average temperature, rather than as a single day of detrimental competition. So, while the range produced for the laboratory growth tests is compared as either weekly average temperatures or season long average temperatures, the laboratory study on brook trout competition is only compared here as a weekly average temperature. After appropriately converting the constant laboratory test results to 7DADMax temperature metrics, the studies on growth and competition overlap each other. Growth should be maximized at a 7DADmax of 13.5 15.5 ° C and competition with brook trout should not be materially worsened at temperatures below 13.5 ° C. Page 28 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards Conclusion on Rearing The multiple lines of evidence created from the wide variety of field and laboratory studies can be brought together in support of selecting a summer rearing temperature standard. The interim conclusions from each line of evidence is summarized below:

Table 4.2. Juvenile rearing of native char:

Line of Evidence 7DADM  Range ( ° C) Median ( ° C) Field studies on limit to where most commonly found 13.45 14.45 13.95 Filed studies on density, and dominance 11.45 13.45 12.45 Laboratory Growth Studies 12.93 15 13.96 Laboratory Competition Studies 12.62 12.93 12.75 Best Estimate of Threshold ( averages) 12.61 13.96 mid. pt. 13.29 The range of these independent lines of evidence is 11.45 15 ° C with a mean range of 12.61 13.96 ° C and an overall midpoint of 13.29 ° C. This strongly suggests that streams having 7 day average daily maximum summer temperatures not exceeding 13.29 ° C are fully protective of juvenile/ small bull trout rearing. After cross checking this conclusion against each independent line of evidence, no overriding factors of disagreement appear to exist. The slight conflict with the field studies on density and dominance, and the laboratory competition studies do, however, suggest that rounding the estimate down to the nearest 0.5 ° C increment, rather than up, may be more appropriate. It is therefore concluded that 13 ° C as a 7 day average of the daily maximum temperatures will fully support the life stage of juvenile/ small char rearing.

iv) Migratory Adult and Sub Adult Char Populations As noted previously, fluvial and adfluvial forms of char may remain in the area of their natal stream for 1 to 3 years and then migrate significant distances to more productive waters for greater juvenile growth opportunities ( Pratt, 1992; Ratliff, 1992; Riehle et al., 1997; Fraley and Shepard, 1989; Goetz, 1989). The larger size of these migrants is generally believed to allow them to better compete for resources, and to make use of a larger prey base that includes the juvenile fish of other species. This is similar to the way the ocean is used by Pacific salmon to enable them to grow to significantly greater sizes than would be possible if they were to remain in freshwater tributaries. This may be a very important survival trait of these migratory populations, and serve to free up food resources in the tributary system for juvenile char. These adult and non spawning sub adult fish, may also move out of tributary systems to hold in lower main stem areas during the winter to avoid unsuitable winter conditions of ice and storm flows. In Washington, bull trout may migrate all the way from Evaluating Standards for Protecting Aquatic Life in Page 29 Washington's Surface Water quality Standards headwater streams to the Puget Sound to feed and rear. Relatively little is known about the temperature preferences and requirements of these migratory fish which makes setting temperature criteria for them problematic.

Heimer ( 1965) examined the use by Dolly Varden of an artificial spawning channel on the lower Clark Fork River in Idaho below the Cabinet Gorge Dam. The channel was constructed in an area where cool spring water would make the artificial channel cooler than the main stem river during part of the year. Temperatures in the majority of the spawning channel were between 8 11 ° C. The author noted that fish observed in the spawning area were consistently in the areas of cooler water. As river temperatures declined in the fall a portion of the fish in the spawning area left without spawning. These fish were presumably present because of the cooler waters, as the main stem temperatures in the Clark Fork River did not decline to below 13.9 ° C until after September 26th. The Washington Water Power Company ( 1995) also studied the distribution of fish in the lower Clark Fork River in Idaho and found that while main stem river temperatures were 18 ° C on September 28th temperatures in the adjacent channel used by bull trout for spawning was 11 ° C. These two studies when considered together suggest that bull trout will actively avoid rivers having fall water temperatures above 18 ° C. The strong contrasting temperatures between the river and the channel, the combination of spawning and non spawning fish, competition with other salmonids also using the channel for refuge, and the lack of specific temperature metrics in association with char movements all combine to prevent using these studies to estimate a threshold response.

Swanberg ( 1997) found that bull trout residing in the lower Blackfoot River in Montana migrated out when daily maximum temperatures reached 18 20 ° C, and non spawning subadult fish began returning once maximum temperatures declined to 12 ° C. The few fish that did not migrate were found in association with the confluence of a small cold tributary with a daily maximum temperature of 12 ° C. Elle and Thurow ( 1994) found that adfluvial bull trout in the Rapid River in Idaho began leaving the lower system in peak numbers seven out of nine years as the daily maximum temperatures began to exceed 10 ° C and returned as the temperature of the lower river declined to 10 ° C. These fish moved to lower main stem rivers to hold for the winter. Movements to avoid unhealthy winter conditions are common in salmonids, and Jakober et al. ( 1998) found that bull trout and westslope cutthroat trout in two drainages in Montana made extensive downstream movements as temperatures dropped precipitously in the Fall. These movements were most extensive in mid elevation streams where frequent freezing and thawing led to anchor ice formation and super cooling (< 0 ° C) of the water.

Several very import issues and questions need to be addressed prior to setting criteria to protect these adult and sub adult fish. These include:

  Is it ecologically appropriate to base temperatures in salmon and steelhead strongholds on the temperature requirements of char?   How, and should, populations that are in main stems to rear be separated from those that may be leaving inhospitable winter conditions in the tributaries? Page 30 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards   Is rearing protected only by maintaining favorable temperatures in these lower rivers year round, or can migration out of the lower reaches during maximum summer temperatures be considered a normal and thus acceptable natural pattern?   Should temperatures considered protective of these adult and sub adult fish be based on assumptions of relative food abundance and lack of competition?

Until these questions are reasonably answered, there does not seem to be sufficient foundation in the research to confidently support recommending a temperature threshold value in lower main stem rivers that is colder than that appropriate for the protection of salmon and steelhead.

v) Lethality to Adults and Juveniles As shown above in the discussion of juvenile rearing, waters that fully protect the health of native char will have temperatures well below those posing a threat of acute lethality. Thus, the conclusions that follow are intended for application in the evaluation of special projects. They can also be used as an aid in assessing the relative safety for char moving through main stem rivers predominantly protected for salmon and steelhead.

The only research found directly testing one of Washington's native char species ( bull trout) was the works of McMahon et al. ( 1998, 1999) as published in Selong et al. ( 2001). McMahon et al. ( 1998, 1999) conducted 60 day lethality studies of juvenile bull trout. In their 1998 study, 98% survival occurred at temperatures between 7.5 18 ° C. Mortality was 21% at 20 ° C over the 60 day test period, but was 100% within 24 hours at 26 ° C, within10 days at 24 ° C, and within 38 days at 22 ° C. In the 1999 study, survival was 46% at 21 ° C and 53% at 20 ° C, with the time to 50% mortality varying from 10 days at 23 ° C to 24 days at 22 ° C. Using the data from both the 1998 and 1999 studies, the authors determined a 60 day UUILT ( Ultimate Upper Incipient Lethal Temperature) of 20.8 ° C for juvenile bull trout and estimated that a 7 day UILT ( Upper Incipient Lethal Temperature) would be 23.5 ° C ( Selong et al., 2001).

The work of McMahon et al. ( 1998, 1999) and Selong et al. ( 2001) strongly suggest that lethality will be prevented at constant temperature exposures of 18 19 ° C or less. This assertion comes from two sources of information. The first is that in tests at a constant 18 ° C there was at least 98% survival over a 60 day exposure. The second is derived by using the 60 day UUILT of 20.9 ° C. After applying the adjustment factor recommended by the USEPA ( Brungs and Jones, 1977) to change from a temperature that kills 50% of the exposed fish to a temperature that is unlikely to kill any fish. The non lethal temperature estimate would change to a constant 18.9 ° C ( 20.9 ° C minus 2 ° C). Constant temperatures of 18 19 ° C would be correlated to 7DADMax temperatures of 21.18 22.18 ° C and 1 day maximums ( 1DMax) of 22.13 23.13 ° C when treated as if they were based on weekly temperature exposure. When treated as if they were based on a season long exposure ( which may be justified in this case since the laboratory tests were 60 days long) these values change to 22.64 23.64 ° C ( 7DADMax) and 23.60 24.60 ° C ( 1DMax). This line of evidence suggests Evaluating Standards for Protecting Aquatic Life in Page 31 Washington's Surface Water quality Standards that acute mortality will be prevented in acclimated fish by maintaining 7DADMax temperatures below 21.18 23.64 ° C or 1 day maximum temperatures below 22.13 24.6 ° C.

While a constant temperature exposure would generally be similar to an average temperature in a natural stream, daily maximum temperatures above the lowest determine lethal concentration ( 20.9 ° C with a 60 day exposure) will begin to accumulate lethal stress. To avoid exposure to temperatures that create lethal stress altogether ( would eventually cause lethality if exposure period is sufficient) daily maximum temperatures should not exceed 20.9 ° C ( 7DADMax 19.95 ° C). Since this is not an estimate of a threshold beyond which acute mortality would be expected, it should only be viewed as a line of evidence for establishing a lower bound estimate of temperatures that would avoid lethality and severe stress.

Using the data of Selong et al. ( 2001) we can also estimate the general risk of mortality from multiple days of exposure in the potentially lethal range. By assuming that temperature exposure in the lethal range is additive ( DeHart, 1974, 1975; Golden, 1978), and by examining the potential lethal dose that occurs with each hour spent over the lowest lethal level ( 20.9 ° C), the risk of mortality can be reasonably described. The equation in Selong et al. ( 2001) giving the relationship between exposure temperature and time to mortality ( LC50) can be used to estimate the number of hours that would need to be spent at each daily temperature increment ( one hour intervals used herein) above the an ultimately lethal temperature ( 20.9 ° C) to cause mortality ( LC50). Using this approach, the number of daily cycles of temperature that would occur before causing mortality can be predicted. Based on this technique, bull trout in a stream with a daily average temperature of 20.9 ° C ( 21 ° C) and a diel range above the daily mean of 4.13 ° C would be expected to experience high mortality ( LC50) in approximately 10 days or less. In streams with mean temperatures 19 and 18 ° C, high mortality ( LC50) would occur after 54 and 163 days of repeat exposure, respectively. This approach to evaluating the risk of mortality is only useful in assessing relative risk. Nevertheless, it provides a good support for the position that weekly average temperatures of 18 19 ° C and summer peak daily maximum temperatures of 22 23 ° C ( 7DADMax 21.05 22.05 ° C) pose little risk of creating acutely lethal conditions in char populations.

While having relatively sensitive optimal temperature limits, adult and juvenile char do not appear unusually sensitive to acute temperature limits. With acclimation, juvenile and adult char are very tolerant of temperature extremes in a laboratory environment   capable of withstanding temperatures of   1.2 ° C ( below zero) for up to 5 continuous days and having upper lethal temperature limits similar to, but towards the lower end, of that for juvenile Pacific salmon ( Selong et al. 2001). Page 32 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards Table 4.3. Temperature induced lethality of in native char.

Line of Evidence 7DADMax ( ° C) Midpoint ( ° C) Direct laboratory observation of no mortality, and conversion of LC50 to no effects temperature using Brungs and Jones ( 1977). 21.18 23.64 22.41 Laboratory estimate of temperature exerting lethal stress 19.95 19.95 Modeling risk associated multiple day exposures to fluctuating temperatures 21.05 22.05 21.55 Best Estimate of Threshold 20.73 21.88 mid. pt. 21.31 The range of the independent lines of evidence discussed above is 19.95 23.64 ° C with a mean range of 20.73 21.88 ° C and an overall midpoint of 21.31 ° C. This strongly suggests that not allowing single daily maximum temperatures to exceed 21.31 ° C ( 7DADMax of 21.35 ° C) will prevent acute lethality in char populations. Based on the above it is concluded that an annual highest single day maximum temperature not exceeding 21 ° C will prevent direct lethality to Washington's juvenile native char.

It is important to point out, however, that only juveniles of one stock of bull trout were tested. Juvenile Dolly Varden, other stocks of juvenile bull trout ( Beacham and Withler, 1991), and adults of either species could be somewhat more ( or less) sensitive ( Coutant, 1970; Becker, 1973; Bouck and Chapman, 1975). It would be unwise to assume that temperatures at the upper end of the range identified above are of equal merit for consideration as an acute criteria until more stocks have been tested. The data cited below by Ugedal et al. ( 1994) lend further support for being cautious about assuming the upper end of the predicted range would be fully protective.

Support for the above findings can be found in research on related species of char ( Arctic char and Arctic grayling). The estimated LT50 ( lethal to 50% of test population within 7 days) values for a variety of char species at acclimations of 5 20 ° C generally group between 21.5 24 ° C. Lohr et al ( 1996) determine a 7 day LC50 of 23 25 ° C for juvenile Arctic Grayling; Lyytikainen et al. ( 1997) determined a 14 day LC50 of 23 24 ° C for juvenile Arctic Char; and Baroudy and Elliott ( 1994) determine a 7 day LC50 of 21.5 21.6 ° C for Arctic char fry and parr. These ranges were determine primarily by varying the acclimation temperatures. In a modified CTM test, the authors also found that fry and parr experienced 10 minute LT50 values of 24.79 26.57 ° C at acclimation temperatures from 10 to 20 ° C. Ugedal et al. ( 1994), in conducting a 104 day growth test using Arctic char, found that when water temperature rose from an initial 12 13 ° C ( daily mean) to a brief 20 ° C ( average temperature for approximately 10 days) before falling again a slight increase in mortality ( approx 5%) occurred during the period that water temperatures reached 20 ° C. Evaluating Standards for Protecting Aquatic Life in Page 33 Washington's Surface Water quality Standards Some additional information from studies with these related species are worth noting here. At full acclimation to temperatures of 15 18 ° C, sudden exposure to 29 ° C water produce LC50 values within 2 4 minutes in Arctic char ( Lyytikainen et al., 1997). At an acclimation of 15 ° C a test temperature of 26 ° C produced LC50 results in just 44 minutes. Baroudy and Elliott ( 1994) found that the Arctic char alevins had 7 day UILTs of 18.67, 19.67, 20.83, and 20.79 ° C at acclimation temperatures of 5, 10, 15, and 20 ° C. Alevins experience 50% mortality within ten minutes at 23.33, 25.09 ° C, and 25.39 ° C at acclimation temperatures of 5, 10, and 15 ° C.

Research useful for estimating daily maximum temperatures that will protect developing embryos and alevins was only found for Arctic char ( Baroudy and Elliott, 1994). Since the work of Baroudy and Elliott was based on a non indigenous species of char, and tested only the short term effects to the alevin life stage it is insufficient for setting an acute lethality threshold for char incubation. It can be used, however, to demonstrate that incubation of char is more sensitive then juvenile rearing, and to suggest that daily maximum temperatures would likely need to remain below 16.7 ° C to prevent acute lethality to char alevins. This estimate was made by subtracting 2 ° C from the LC50 value determined at an acclimation temperature appropriate for incubation ( 5 ° C) to convert to a temperature that should not produce any short term mortality ( USEPA, 1977).

b) Salmon and Trout i) General Life History Information Chinook Salmon Chinook salmon ( Oncorhynchus tshawytscha) are found in most of the larger streams of the Columbia River drainage, and the coastal and Puget Sound drainages. Juvenile chinook salmon spend about a year in fresh water before smolting and migrating to the Pacific, where they generally remain from three four years before returning to their natal streams to spawn. Adults begin the ascent of coastal streams in late May and early June and principally spawn through September. Chinook salmon are primarily divided into two stock types, based on the season they initially return to fresh waters. These are spring run and fall run stocks, but in some areas a third, summer run, stock may be identified. Spring run fish begin entering freshwaters from May through June, and typically hold in deep pools and at the mouths of cool tributaries until the fall rains begin and stream levels go up sufficiently to allow them to reach their upriver spawning sites. These spring run fish tend to spawn higher in the watersheds than the fall run stocks. Fall chinook migrate up the streams in August and September and spawn as soon as the spawning grounds are reached when water temperatures are between 5.6 14.4 ° C. Eggs hatch in about two months and the young remain in the gravel for two three weeks prior to emerging. Juveniles remain in freshwater from a few days to three years. Usually, juvenile fall chinook feed for a short time and then migrate to the ocean, whereas most juvenile spring chinook remain in the stream for one year before migrating ( Wydoski and Whitney, 1979). In Washington, 96 of the 98 chinook stocks Page 34 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards assessed began spawning after August 1, and 96 of 98 had midpoints in their spawning periods that were after August 23. After emerging from the gravel, chinook fry may remain in freshwater from just a few days to up to 3 years. Usually, fall chinook feed for a short time and then migrate to the ocean, whereas most juvenile spring chinook remain in the stream for one year before migrating to the ocean ( Wydoski and Whitney, 1979).

Coho Salmon Coho salmon occur all along the Pacific coast. While fourth in abundance of the Pacific salmon, coho provide the dominant harvest of sport fisherman ( Wydoski and Whitney, 1979). In Washington, spawning adults are found in most streams of the upper and lower Columbia River drainage, and in the coastal and Puget Sound drainages. Coho spend their first ( one to two) years in freshwater before becoming smolts and migrating to the ocean. Spawning generally occurs from September through December; although, a late run of large fish is known to spawn in January in the Satsop River. Like all Pacific salmon, adult coho die after spawning. Young hatch in 6 8 weeks depending on water temperature and emerge in about two three weeks. Fry congregate in schools in the pools of the stream. Ruggels ( 1966; as cited by Chapman and Bjornn, 1969) found that coho did not use substrate as cover in the winter, and Hartman ( 1965) found that coho tended to lie near or on pool bottoms in aggregations.

Chum Salmon Chum salmon are found in streams of the Puget Sound and coastal drainages, and up the Columbia to the Wind River ( upstream from the Bonneville Dam). Spawning often occurs just at the head of tidewater. Upon emergence from the stream gravel, chum salmon fry begin to migrate to the ocean. Juveniles migrate to the ocean between March and June where they spend six months to four years. In Washington, chum salmon spawn primarily from October to December. Redds occur in medium or fine gravel in the stream riffles. Most of the high mortality from the fertilized egg to early fry state ( 70 to over 90%) is reported to occur during the embryonic stage due to suffocation from silt. Eggs hatch in two weeks to four and one half months depending upon the temperature. Newly hatched fry ( alevins) absorb their yolk sac in 30 50 days, again depending on temperature. Fry are usually in fresh water for only a few days after emerging from the gravel. They migrate downstream at night from April through June ( Wydoski and Whitney, 1979). Little information was found on which to base a recommendation for juvenile rearing temperature limits for chum salmon; however, this is not a major concern. Considering that juvenile chum may only spend a few days in freshwaters, the temperature threshold established for the pre emergent stages of development should result in cool waters remaining during the out migration period. Thus even without a specific juvenile rearing criterion the freshwater portion of the juvenile lifestage will be fully protected. If unique situations appear to demand that a separate rearing standard be applied, the temperature threshold established to protect other Pacific salmon smolts during sea water adaptation should be applied. Evaluating Standards for Protecting Aquatic Life in Page 35 Washington's Surface Water quality Standards Pink Salmon Pink salmon are the most abundant of the Pacific Salmon. Pink salmon ascend rivers along the Pacific coast; and in Washington, the Stillaguamish, Skagit, Snohomish, Puyallup, and Nooksack are the top producing watersheds. Pink salmon are similar to chum salmon in spending only a brief time in fresh water as juveniles and adults. Spawning in Washington occurs chiefly during August and September, usually near the mouths of streams, but sometimes spawning occurs far up into large rivers, such as the Skagit. Females usually dig redds in a riffle area with small to medium size gravel, but they occasionally spawn in the tail section of pools. In Alaska, a large percentage of pink salmon spawn in the intertidal areas. Eggs usually hatch in thee five months, depending upon water temperature. The alevins and fry remain in the gravel for as long as several months at low temperatures in northern waters before emerging ( Wydoski and Whitney, 1979). Washington state appears to be at the southern end of the range for streams that support consistently exploitable spawning runs of pink salmon. Pink salmon have a two year life cycle which is so invariable that fish running in odd numbered calendar years are effectively genetically isolated from those that run in even years ( Bonar et al., 1989).

Sockeye Salmon In Washington, populations of sockeye travel up the Columbia River to the headwaters of the Salmon River in Central Idaho. Populations also use Quinalt Lake on the Olympic Peninsula, Baker Lake, lakes Washington and Sammamish in the Puget Sound drainage, and Osoyoos Lake and Lake Wenatchee east of the Cascade Mountains. Sockeye differ from the other species of salmon because they require a lake environment for part of their life cycle. Although spawning typically occurs in the gravel of streams some may spawn along lake shores in areas where ground water percolates through the gravel. Eggs hatch in six nine weeks. The young remain in the gravel for another two three weeks. Newly emerged fry move from the spawning stream into the lake associated with the stream. Young sockeye live in the pelagic zone of the lake for one to two years years before migrating to the sea where they will remain for two years before returning to freshwaters to spawn ( Wydoski and Whitney, 1979).

Steelhead Steelhead is the popular name given to the anadromous form of O. mykiss. The anadromous form is found in coastal rainbow and interior redband trout groups and occurs from southern California to Alaska ( Behnke, 1992). Steelhead populations can be broadly divided into spring, summer, fall and winter run stocks, depending upon the time the fish re enters freshwater. Spring and summer run fish enter fresh waters typically from May through August and move upstream to hold over until the following spring to spawn. Fall runs typically enter from September through November and spawn in the spring. Winter run ( December March) steelhead may spawn soon after entering fresh waters. In general, summer run steelhead spawn further upstream in the watershed than the fall or winter run fish. With a spring spawning stock, protection is achieved by not encouraging spring water temperatures to warm above fully protective levels during the spawning and incubation Page 36 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards periods. Juvenile steelhead may remain in freshwaters for one to seven years before emigrating to sea, depending upon the stream temperature and the latitude, although, most stay in fresh water for two years ( Wydoski and Whitney, 1979; Mullan et al., 1992). Mullan et al. ( 1992) note that summer run stocks tend to remain longer in freshwater than winter run steelhead, presumably because the colder temperatures of the headwaters streams preferred by summer run steelhead retards their growth rate.

Rainbow Trout The name rainbow trout is commonly applied to represent any or all of the members of Oncorhynchus mykiss. However, O. mykiss in Washington can be further divided into resident coastal rainbow trout; resident interior redband trout; and steelhead, the anadromous form of the coastal rainbow and redband trout. Coastal rainbow trout populations extend from Alaska to Mexico, and non anadromous, or resident, populations occur throughout the entire range ( Behnke, 1992). Redband trout are found east of the Cascades and in the Columbia River basin, and Behnke suggests that that the native redband trout of each basin has its own peculiarities and could probably be separated into several new subspecies. Behnke also notes that in the desert basins of the western states, the redband trout has evolved adaptations to live in extremely harsh environments characterized by great extremes in water temperature and flow.

Cutthroat Trout In Washington, native cutthroat trout can be separated into coastal cutthroat ( Oncorhynchus clarki clarki) and west slope cutthroat trout ( Oncorhynchus clarki lewisi). Coastal cutthroat exhibit anadromous, potamodromous stream dwelling, potamodromous lake dwelling, and headwater stream resident life history forms; while west slope cutthroat exclude anadromous populations ( Trotter, 1998). Behnke ( 1992) suggests that cutthroat trout enjoy a selective advantage over non native trout in many high altitude headwaters; presumably because they function better in colder waters. He notes that native cutthroat are quickly eliminated from waters where non native trout become established. Cutthroat are displaced from preferred habitat in the presence of rainbow trout and coho salmon. The aggressive interaction of these other species may be heightened by warmer water temperatures and thus the displacement of cutthroat is lessened by cooler water temperatures ( Pauley et al., 1989; Trotter, 1989; and Mullan et al., 1992).

Coastal cutthroat trout ( Oncorhynchus clarki clarki) occur all along the Pacific coast from southern California to Alaska. Though rarely found more than 16 km inland, it is considered the most abundant of the cutthroat subspecies ( Trotter, 1998). Sea run cutthroat live to a maximum age of about ten years, as compared to resident forms which may live for only 4 to 5 years ( Behnke, 1992).

In Washington, sea run cutthroat may re enter fresh water for spawning anytime from July through March ( Pauley et al., 1989). Early entering stocks in Puget Sound and Hood Canal typically occur from July through November with the peak in September and October. Lateentering migration peaks in December and January but continues through March ( Trotter, Evaluating Standards for Protecting Aquatic Life in Page 37 Washington's Surface Water quality Standards 1989; Pauley et al., 1989). In southeast Alaska, Jones ( 1977; as cited in Pauley et al., 1989) found that migration began at 10 12 ° C and peaked at 9 10 ° C.

Pauley et al. ( 1989) suggests that prior to smolting and entering saltwater, sea run cutthroat juveniles may migrate up and downstream several times. They further suggest that in Washington and Oregon, downstream movement is reported to take place from March to June, but peaks in mid May. They note that in southeast Alaska, juveniles have been reported to experience a peak of out migration when water temperatures are between 4 6 ° C. Cutthroat parr may migrate to sea from ages one to six, but age two to four may be most common ( Trotter, 1989; Pauley et al., 1989).

Stream resident forms of coastal cutthroat spend most or all of their life in or very near their natal streams ( Trotter, 1989). In spring when water temperatures reach 5 6 ° C, mature resident cutthroat move onto the spawning gravel. Trotter ( 1989) suggests that potamodromous forms of coastal cutthroat do not move into spawning tributaries until very late winter or spring rather than in autumn to early winter as for anadromous fish. Similar to stream resident forms, they are reported to begin spawning as the water temperature increases to 5 6 ° C, which may occur from February through June. Lake dwelling potamadromous coastal cutthroat first spawn at age 3 or 4, and then spawn almost every year thereafter for the remainder of their lives in the inlet and outlet streams of the lake ( Trotter, 1989). Few sea run cutthroat trout sexually mature before age 4, and not all returning fish spawn their first year back in freshwater ( Trotter, 1989). Fish that do spawn, may return ( 39 41%) to spawn a second time, and some ( 12%) may return for a third spawning ( Trotter, 1989; Pauley et al., 1989).

West slope cutthroat trout, the interior form, have been found to spawn in April and early May with a peak around mid April in Montana ( Fraley et al., 1981). Trotter ( 1999) found an introduced population of west slope cutthroat initiating spawning around June 1 at a temperature of 7 ° C in the Tolt River in Washington, and a natural population initiating spawning on June 29 at a temperature of 11 ° C in a stream in the upper Yakima River basin in Washington. Newly emerged fry move to low velocity stream margins, backwaters, and side channels adjacent to the main channel pools and riffles ( Pauley et al., 1989; Trotter, 1989). Trotter ( 1989) suggests that these young fish may move downstream to the main stem as early as the winter of their first year, but more generally later in the spring. With the onset of winter freshets, the fish may again move back into the tributaries. Older fish may migrate to sea where they will remain for two to five months concentrating in bays, and estuaries along the coast gaining weight before returning to fresh waters. It is considered unusual for cutthroat to over winter in salt waters ( Pauley et al., 1989). Fry of potamadromous forms may spend the first 1 3 years in the tributaries before commencing a lake ward migration. These potamadromous fish may over winter in the lower main stem of the river while anadromous fish are in the marine waters ( Trotter, 1989). Pauley et al. ( 1989) cite research showing that while in freshwaters, cutthroat adults are associated with the deeper pools and slower velocity waters, while the fry are found in shallower, faster areas. Page 38 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards ii) Spawning Requirements Field and General Observations on Spawning Temperatures:

The authors that have provided the following general observations of spawning temperatures rarely provided the associated temperature metric. Thus it is not clear most of the time whether or not they were referring to a range of daily average temperatures or a range of daily maximum temperatures. Other confounding factors include that the authors do not always make it clear that they are separating pairing and redd construction activity with actual spawning, and generally do not provide a copy of their methodology to use in determining if the temperatures were recorded at the site of spawning at the time spawning was taking place. For these reasons, the following information on temperatures at which spawning commonly occurs should be used cautiously.

Chinook Salmon The technical literature reviewed for this paper notes a wide range of temperatures associated with the spawning of chinook salmon ( 5.6 17.7 ° C) ( Seymour, 1956). The majority of these temperature observations, however, cite maximum temperatures below 14.5 ° C [ Bell, 1986 ( literature Summary); Piper et al., 1982; Wydoski and Whitney, 1979]. In the Hanford reach and in the Snake River in Washington, redd construction began as weekly mean temperatures dropped to 15.9 ° C and averaged 13.6 ° C during the weeks of spawning initiation from 1993 1995 ( Groves and Chandler, 1999).

Coho Salmon Coho salmon ( Oncorhynchus kisutch) tend to spawn later and at lower water temperatures than the other Pacific salmon. In Washington, 79 of the 82 stocks of coho salmon assessed begin spawning after September 22, and 80 of 82 have midpoints in their spawning periods that occur after November 1. Spawning activity in coho may typically occur in the range of 4.4 13.3 ° C [ Bell, 1986 ( literature summary); Piper et al., 1982; Chambers, 1956, as cited in Andrew and Green, 1960; Gribanov, 1948, and Briggs, 1953, as cited in Sandercock, 1991].

Chum Salmon Chum salmon are reported to spawn between 1 12.8 ° C, with a range of 7 10.5 ° C being most consistently identified [ Beacham and Murray, 1986; Bell, 1986 ( literature summary)]. In Washington, 65 of the 68 stocks of chum salmon ( Oncorhynchus keta) assessed begin spawning after September 1, and 65 of the 68 stocks have midpoints in their spawning ranges that occur after October 8. Evaluating Standards for Protecting Aquatic Life in Page 39 Washington's Surface Water quality Standards Pink Salmon In Washington, 10 of the 12 pink salmon ( Oncorhynchus gorbuscha) stocks assessed begin spawning after September 1, and 10 of 12 have midpoints in their spawning periods which occur after September 22. Spawning typically occurs between 7.2 14 ° C ( Bonar et al., 1989), and may be optimally supported at temperatures from 7 12.8 ° C [ Sheridan, 1962; Bell, 1986 ( literature summary)]. This potential optimum range coincides well with an identified peak in spawning activity at 10 ° C identified by Sheridan ( 1962).

Sockeye Salmon In Washington, 8 of the 8 stocks of sockeye salmon ( Oncorhynchus nerka) assessed begin spawning after September 7, and 8 of 8 have midpoints in their spawning ranges that occur after October 3. Temperatures to support spawning activity in sockeye salmon have been identified as ranging from 7.2 12.2 ° C ( Piper et al, 1982), with a preferred range between 10.6 12.2 ° C ( Bell, 1986, literature summary). Chambers ( 1956; as cited in Andrew and Geen, 1960) reported that sockeye spawn on the falling portion of the cycle at 12.8 to 8.3 ° C. Andrew and Geen ( 1960) reported that spawning temperatures of sockeye in the Fraser River range from 7.2 to 12.8 ° C with a peak at about 10 ° C.

Steelhead Trout In Washington, 101 of the 105 spring spawning steelhead stocks assessed ended spawning before July 1 ( 91 of the 105 ended prior to June 15), and 101 of 105 have midpoints in their spawning periods that occur before May 7. Spawning occurs primarily in the spring as water temperatures are rising. Bell ( 1986, literature summary) noted that spawning has been observed at temperatures ranging from 3.9 21.1 ° C. Hunter ( 1973; as cited in Swift, 1976) noted the preferred temperatures for spawning range from 4.4 12.8 ° C.

Rainbow Trout Both the coastal rainbow and the redband trout spawn in the spring, stimulated by rising water temperatures. Behnke ( 1992) suggests that along the Pacific coast a water temperature of about 3 6 ° C may initiate spawning activity, but that actual spawning does not occur until the temperatures reach 6 9 ° C. While this spawning activity would typically occur from late December through April, in some very cold headwater streams local temperatures may delay spawning until July or August for some stocks. Bell ( 1986, literature summary) set the range for spawning at 2.2 18.9 ° C; and Piper et al. ( 1982) concluded that rainbow trout spawning should occur between 10 12.8 ° C.

Cutthroat Trout Bell ( 1986, literature review) has suggested that the spawning range is 6.1 17.2 ° C. Fraely et al. ( 1981) evaluated the spawning habitat of west slope cutthroat trout in Montana. They found that the better spawning streams had maximum temperatures of 11 13 ° C and mean Page 40 Evaluating Standards for Protecting Aquatic Life in Washington's Surface Water quality Standards monthly maximum temperatures that exceeded 10 ° C only during July and August. The poorer quality spawning streams had higher maximum summer temperatures, with two having 18 ° C and 19 ° C as the average maximum temperatures during July.

Cutthroat trout spawn in the spring, stimulated by a rising water temperature. While temperatures of 3 6 ° C may initiate spawning activity by coastal cutthroat from late December through April, actual spawning may not occur until temperatures reach 6 9 ° C. Spawning may extend from December through May in Washington, but peaks in February ( Trotter, 1989; Wydoski and Whitney, 1979; Pauley et al., 1989; Behnke, 1992). Sea run cutthroat tend to spawn close to deep pools ( Pauley et al., 1989) in low gradient areas of small tributaries ( Wydoski and Whitney, 1979; Trotter, 1989) where they may avoid competition for rearing area with steelhead and coho salmon. Pauley et al. ( 1989) suggest that searun cutthroat travel farther upstream to spawn than either steelhead or coho salmon where they rear sympatric with resident cutthroat populations. While cutthroat home very precisely to their natal streams to spawn, immature fish may migrate from marine waters to non natal areas to feed ( Pauley et al., 1989).