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.