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Ocean Carrying Capacity Program

Age-0 Pollock Distribution in the Eastern Bering Sea

The Ocean Carrying Capacity (OCC) program conducted its annual Bering Aleutian Salmon International Survey (BASIS) from 14 August to 30 September 2004. The objectives of BASIS are to identify the physical and biological mechanisms that affect the migration, distribution, and early life history of Pacific salmon and other commercially important species in the Bering Sea.

Of these species, walleye pollock is one of the most abundant pelagic fish in the Bering Sea. Besides being one of the largest fisheries resources in the world, pollock are important prey to marine mammals, seabirds, and piscivorous fishes. Because of walleye pollock’s commercial importance, OCC scientists have assessed the distribution and abundance of age-0 pollock in the eastern Bering Sea during BASIS cruises.

Age-0 pollock distribution and CPUE during the 2004 (Fig. 1) and 2003 (Fig. 2) BASIS research cruises in the eastern Bering Sea.
     Legend for figures 1 and 2
Figure 1, see caption
Figure 1.  14 August–30 September 2004.
  Figure 1, see caption
Figure 2.  21 August–8 October 2003.

During the 2004 cruise, a total of 2.6 million individual age-0 pollock were caught at 143 stations. Age-0 pollock were distributed throughout the eastern Bering Sea from lat. 55°30'N to lat. 64°N. The greatest catch per unit effort (CPUE) of pollock occurred at stations along the 50-m contour line within Bristol Bay and north to lat. 59°N (Fig. 1 above). Total catch in 2004 increased by 50% from 2003, when 1.3 million age-0 pollock were caught at 151 stations. Pollock distribution differed between 2003 and 2004, with the greatest CPUE of pollock in 2003 occurring in the middle domain (between 50 and 100 m) on the longitude 162°W transect (Fig. 2 above).

A variety of factors influence pollock distribution and abundance. Wind and current patterns, competition, prey availability, and predation all play a critical role in pollock distribution and biomass. Future OCC studies will look for relationships between prey availability, oceanographic conditions, and age-0 pollock diet and energy density.

By Angela Middleton

ABL Weather Station

The year 2004 in southeastern Alaska began with an exceptionally mild winter quarter (January– March) with above average air temperatures and below average snowfall. The spring quarter (April– June) continued this trend with record high air temperatures in May and June and record low rainfall in June. These unusual conditions may influence future salmon harvests in southeastern Alaska. The high temperatures resulted in record high stream and lake temperatures approaching and (in some cases) exceeding 20°C, stressing juvenile fishes rearing in low-elevation streams. Additionally, the low spring snowpack and low rainfall resulted in some small streams with water flows too low for early returning salmon to enter the streams. July frequently has cooler weather and more rainfall than June, and the continuing warming trend was not beneficial to salmon returning to spawning streams in July and August. Sufficient rain to raise stream flows was not seen until mid-September, much too late for most of the pink salmon and early chum salmon runs.

The abnormally high sea surface temperatures reported from Auke Bay were also evident in the oceanic areas of the Gulf of Alaska. Through most of the summer, the sea surface temperatures were 1°–2° C above the climatic mean. This not only reflects unusually warm air temperatures over the Gulf of Alaska, but also the transport of warmer than average waters from the south by the Alaskan Gyre. Possibly associated with these warm water conditions was the finding of a Pacific Ridley turtle (Lepidochelys olivacea) carcass near Yakutat, Alaska, and the sightings of white sharks (Carcharodon carcharias) off Noyes Island in August and Yakutat in September. Also, two thresher sharks (Alopias vulpinus) were caught by salmon fishermen in southeastern Alaska this season. In September, a longliner caught two jumbo squid (Dosidicus gigas) off the Fairweather Grounds between Sitka and Yakutat. Jumbo squid are rarely seen as far north as San Diego, California, but in 2004 the species was reported also off the Washington coast.

By Bruce Wing


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