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Cetacean Assessment and Ecology Program

Big GOALS Accomplished: Surveying for Cetaceans in the Gulf of Alaska (pg 2, 1)

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Eleven scientists from four organizations (National Marine Mammal Laboratory, Cascadia Research Collective, Bio-Waves, and HDR, Inc.) participated in the GOALS II survey conducted from 23 June to 18 July 2013. Four survey strata were designed to account for the four distinct habitats within the GOA TMAA (Fig. 1). Tracklines were designed to provide uniform sampling coverage within each stratum using an equal-spaced zigzag sampler configuration (Strindberg et al. 2004; Fig. 1). Utilization of both visual and passive acoustic methods allowed for 24-hour operations and increased the likelihood of detecting elusive beaked whales. Additionally, photographs were collected for comparison to existing catalogs and satellite tags were deployed on an opportunistic basis.

During GOALS II, the visual team completed 4,155 km of transect, with an additional 349 km of transit (Figs. 2, 3). There were 646 sightings (1,705 individuals) of 11 confirmed cetacean species (Figs. 2, 3). The acoustic team conducted round-the-clock monitoring with a towed-hydrophone array for 6,304 km of transect effort. There were 379 acoustic detections of six confirmed cetacean species: Baird’s, Cuvier’s, and Stejneger’s beaked whales; killer whales (Orcinus orca); sperm whales; and Dall’s porpoise (Phocoenoides dalli) (Fig. 4). Additionally, 186 sonobuoys were deployed and analyzed for presence/absence of calls. Calls were detected from seven confirmed species on 140 sonobuoys: blue whales, fin whales, humpback whales, killer whales, sei whales (B. borealis), North Pacific right whales, and sperm whales (Fig. 5). Photographs of five cetacean species were collected for photo-identification purposes: fin whales, humpback whales, blue whales, killer whales, and Baird’s beaked whales. One blue whale, one killer whale, and eight humpback whales were matched to historical catalogs.

Two satellite-transmitter tags were attached to monitor movements of cetaceans. One was deployed on a blue whale and transmitted for 9 days, and the other was deployed on a Baird’s beaked whale and transmitted for 15 days. Both whales were tagged near the Surveyor Seamount (Fig. 6) within 6 km of each other. The blue whale traveled about 250 km south of the survey area, headed west near the Patton Seamount chain, and then began moving north; its final transmission was about 100 km southwest of the survey area on 9 July. Maximum distance from the deployment location was 317 km on 5 July. Based on photo-identification matches, this blue whale had been previously identified off Baja California, Mexico, in 2005. The Baird’s beaked whale stayed within the seamount stratum for 9 days, spending 6 days in the vicinity of the Surveyor Seamount before heading northeast to the Pratt Seamount and then southeast to the Durgin Seamount. The animal then headed southeast until its last transmission on 15 July, at its maximum distance of 482 km from the deployment location (300 km from the survey area).

Density (Table 1) and abundance (Table 2) (uncorrected for the proportion of animals missed on the transect line) were estimated from line-transect data for six cetacean species. The abundance of large whales not identified to species for visual detections was computed and allocated to blue whales, fin whales, and humpback whales proportionally within each stratum. Pooled density (D) and abundance (N) estimates for the survey area were calculated for blue whales (N = 78; D = 0.001; CV = 1.22), fin whales (N = 3,581; D = 0.022; CV = 0.28), humpback whales (N = 3,054; D = 0.019; CV = 0.71), killer whales (N = 950; D = 0.0058; CV = 0.73), sperm whales (N = 296; D = 0.0018; CV(N) = 0.57), and Dall’s porpoise (N = 11,924; D = 0.072; CV = 0.28). A second density and abundance estimate was obtained for sperm whales using acoustic localizations from the towed-hydrophone array (N = 215; D = 0.0013; CV = 0.18).

Results from this survey provide one of the most comprehensive data sets on cetacean occurrence and distribution within the central GOA. Visual and acoustic detections were sufficient to calculate density and abundance estimates for six cetacean species. New information on movements and habitat use within the GOA were documented through the first satellite-tag deployments on blue and Baird’s beaked whales within this region. Photographic data contributed to knowledge on seasonal presence of identified individuals. Overall, GOALS II was overwhelmingly successful and provided valuable new data on cetaceans within an area of the GOA that is rarely surveyed.

By Brenda K. Rone


