Marine Ecology of Western Alaska Juvenile Salmon
Edward V. Farley, Jr., James Murphy, Jamal Moss, Angela Feldmann, and Lisa Eisner
Abstract.—During the past five years (2002–2006), the Auke Bay Laboratory’s Ocean Carrying Capacity program conducted surveys of western Alaska juvenile salmon Oncorhynchus spp. along the eastern Bering Sea shelf. The goal of our juvenile salmon research is to understand mechanisms underlying the effects of the environment on the distribution, migration, and growth of juvenile salmon in the eastern Bering Sea. The primary findings indicated that there were spatial variations in distribution among species; juvenile coho O. kisutch and Chinook O. tshawytscha salmon tended to be distributed nearshore and juvenile sockeye O. nerka, chum O. keta, and pink O. gorbuscha salmon tended to be distributed further offshore. In general, juvenile salmon were largest during 2002 and 2003 and smallest during 2006, particularly in the northeastern Bering Sea (NEBS) region. Fish, including age-0 pollock Theragra chalcogramma and Pacific sand lance Ammodytes hexapterus were important components of the diets for all species of juvenile salmon in some years. However, annual comparisons of juvenile salmon diet indicated a shift in primary prey for many of the salmon species during 2006 in both the NEBS and southeastern Bering Sea (SEBS) regions. In addition, the average CPUE of juvenile salmon fell sharply during 2006 in the SEBS region. It is speculated that spring sea surface temperatures (SST’s) on the eastern Bering Sea shelf impact the growth and marine survival rates of juvenile western Alaska salmon through bottom-up control in the ecosystem. Cold spring SST’s lead to lower growth and marine survival rates for juvenile western Alaska salmon; warm spring SST’s have the opposite effect.