Nancy D. Davis

Interannual variability in stock abundance and body size of Pacific salmon in the central Bering Sea

Abstract Variability in catch-per-unit-effort (CPUE) and mean body size was examined for pink, chum and sockeye salmon collected with research gillnets in the central Bering Sea in July from 1972 to 2000. The CPUEs for all three species showed significant increasing trends, but with large interannual variability. The CPUE of pink salmon was higher in odd years than in even years, and abruptly increased in the odd years post-1989. Chum salmon also showed odd/even year fluctuations, which were out-of-phase with those of pink salmon. Sockeye salmon showed no biennial such fluctuations. The CPUEs of chum and sockeye salmon were higher during 1979–1984 and 1992–1998, but lower during 1985–1991, especially for younger age group such as ocean age 2 and 3. Data for sea surface temperature (SST) and abundances of chum and sockeye salmon during four periods (1972–1976, 1977–1984, 1985–1990, and 1991–2000) indicated a portion of chum and sockeye salmon were distributed in the northern Gulf of Alaska in 1985–1990, when SST in the Gulf of Alaska was low. However, the fish were more abundant in the Bering Sea in 1977–1984 and 1991–2000 when SST was relatively high in the Gulf of Alaska. Body size of pink salmon showed a significant decreasing trend. Chum and sockeye salmon also showed significant decreasing trends in body size at ocean age 3 and older ages, but not at ocean age 2. Significant negative relationships between CPUE and body size were found within species. No significant correlations were found between an Aleutian low pressure index (ALPI) with CPUE and body size, but the increases in CPUE around the late 1970s and early 1990s may be partly be the result of shifts in the distributions of chum and sockeye salmon caused by SST changes related to the regime shift in 1977 and 1989 identified by the ALPI.

Interannual and Spatial Feeding Patterns of Hatchery and Wild Juvenile Pink Salmon in the Gulf of Alaska in Years of Low and High Survival

Abstract To improve understanding of the mechanisms affecting growth and survival, we evaluated the summer diets and feeding patterns (prey composition, energy density, and stomach fullness) of hatchery and wild juvenile pink salmon Oncorhynchus gorbuscha in Prince William Sound (PWS) and the northern coastal Gulf of Alaska (CGOA). Our study (1999-2004) included 2 years of low (∼3%), mid (∼5%), and high (∼8-9%) survival of PWS hatchery pink salmon. Because variations in diet should affect growth and ultimately survival, we expected that the variations in diet, growth, and survival would be correlated. During August in the CGOA, pteropod-dominated diets and higher gut fullness corresponded to high survival (5-9%), and copepod-dominated diets and lower gut fullness corresponded to low survival (3%). Within years, no significant differences were found in diet composition or gut fullness between hatchery and wild fish or among the four PWS hatchery stocks. Diets varied by water mass (habitat) as juveniles mov...

Activity of the pituitary–gonadal axis is increased prior to the onset of spawning migration of chum salmon

SUMMARY The activity of the pituitary–gonadal axis (PG axis) in pre-migratory and homing chum salmon was examined because endocrine mechanisms underlying the onset of spawning migration remain unknown. Pre-migratory fish were caught in the central Bering Sea in June, July and September 2001, 2002 and 2003, and in the Gulf of Alaska in February 2006. They were classified into immature and maturing adults on the basis of gonadal development. The maturing adults commenced spawning migration to coastal areas by the end of summer, because almost all fish in the Bering Sea were immature in September. In the pituitaries of maturing adults, the copy numbers of FSHβ mRNA and the FSH content were 2.5- to 100-fold those of the immature fish. Similarly, the amounts of LHβ mRNA and LH content in the maturing adults were 100- to 1000-fold those of immature fish. The plasma levels of testosterone, 11-ketotestosterone and estradiol were higher than 10 nmol l–1 in maturing adults, but lower than 1.0 nmol l–1 in immature fish. The increase in the activity of the PG-axis components had already initiated in the maturing adults while they were still in the Gulf of Alaska in winter. In the homing adults, the pituitary contents and the plasma levels of gonadotropins and plasma sex steroid hormones peaked during upstream migration from the coast to the natal hatchery. The present results thus indicate that the seasonal increase in the activity of the PG axis is an important endocrine event that is inseparable from initiation of spawning migration of chum salmon.

Stock Origins of Chinook Salmon in the Area of the Japanese Mothership Salmon Fishery

Abstract The record catch of 704,000 chinook salmon Oncorhynchus tshawytscha by the Japanese mothership salmon fishery in 1980 intensified concern about the effect of high seas interceptions of salmon reared in North America. The goal of this study was to update and refine estimates of the relative proportions of Asian and North American chinook salmon stocks in the mothership fishery area in the Bering Sea and north Pacific Ocean. Linear discriminant analysis of scale pattern data was used to classify samples of immature chinook salmon aged 1.2 (one winter in fresh water, two winters at sea) from the area 46-62°N, 160°E-175°W in June and July 1975-1981 to four regions: Asia, western Alaska, central Alaska, and southeastern Alaska-British Columbia. Western Alaska, which included Canadian Yukon stocks, was further subdivided into three subregions: Yukon River, Kuskokwim district, and Bristol Bay. Overall classification accuracies averaged 74, 79, and 86%, respectively, in four-, three-, and two-category re...