During 1988 to 1991, sampling efforts were conducted to determine prevalences of Bitter Crab Syndrome (BCS) in Tanner crabs from the Gulf of Alaska, the Benng Sea and the boundary area of the Chukchi Sea and Arctic Ocean Stained hemolymph smears i n d~c a t e d that prevalences of BCS In Chionoecetes balrdi from the Gulf of Alaska were zero to 7 2",, in Pnnce William Sound, zero in Cook Inlet and reached 3 6 % in the coastal waters of Kodlak Island Fiom there, prevalences declined southwesterly to 1 3 % and zero along the Alaska Peninsula and the eastern Aleutian Islands In the Bering Sea, the trend consisted of fluctuating low prevalences of BCS that increased by northerly latitudes in C opllio reaching the highest levels of 14 6 to 29 1 % in Norton Sound and 13 3 to 15 5 % In the C h u k c h~ Sea/Arctic Ocean boundary area The prevalences In C bard1 from the eastern/northeastern Benng Sea were between zero and 2 4 % Prevalences of BCS from Russian waters in the western Bering Sea ranged from 0 9 and 1 1 % in C b a i r d~ and C opllio respectively Sample stations where equally large numbers of both Tanner crab species were examined suggested little difference in para-s~t e prevalences
Seasonal variations in the diets of Pacific cod Gadus macrocephalus and walleye pollock Theragra chalcogramma were examined from fish collected during 5 sampling periods from August 1998 to June 1999 in the Kodiak Island area in the Gulf of Alaska. Both species were shown to be generalist predators, eating a wide variety of fish and invertebrates. Pollock, which are limited to pelagic prey, can be considered more specialized than cod. Cod consumed 78 prey items, and pollock consumed 45 prey items, with 28 items shared by both species. Individual pollock, however, typically concentrated on a single prey item, while individual cod stomachs contained a wider variety of prey. The principal prey of Pacific cod was Tanner crab Chionoecetes bairdi, comprising > 28% of the cod diet by weight. The most common prey item for walleye pollock was the euphausiid Thysanoessa. Over the 5 sampling periods, the prey evenness and niche width occupied by the 2 species were similar, but seasonal differences were evident.
We used a 112-year time series of Alaskan fishery catches to test competing hypotheses concerning trends in mean catch trophic level, a widely used indicator of fisheries sustainability. We found that mean trophic level has generally remained steady or increased in recent decades on Alaska-wide and regional scales, indicating stable catches of high trophic level taxa. During historical periods of declining mean trophic level, catches of upper trophic level taxa either increased or remained steady, contrary to the predictions of the “fishing down the food web” hypothesis. Further, a climate index was highly correlated (r = 0.69–0.97) with mean trophic level and (or) the related fisheries in balance (FIB) index across climate regime shifts in the 1940s and 1970s, indicating that climate effects, particularly on high trophic level taxa, can act as the major driver of variability in these parameters. These results provide a contrast to the view of ubiquitous declines in mean trophic level of fishery catches, driven by overexploitation and serial stock replacement.
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