CHANGE IN CHUM SALMON (ONCORHYNCHUS-KETA) STOMACH CONTENTS ASSOCIATEDWITH FLUCTUATION OF PINK SALMON (ONCORHYNCHUS-GORBUSCHA) ABUNDANCE INTHE CENTRAL SUB-ARCTIC PACIFIC AND BERING SEA

The abundance and stomach contents of salmonids (Oncorhynchus spp.) an d the biomass of prey organisms were examined in the central subarctic Pacific and Bering Sea in the summer of 1991 and 1992. Salmonids were caught by surface longline using the same level of fishing effort. Ch um (O. keta) and pink (O. gorbuscha) salmon were the predominant speci es, representing 44% and 36% of the total catch (n = 1275) in 1991. In 1992, chum salmon composed 85% of the total catch (n = 603), but the catch of pink salmon decreased to 1% of the total catch due to the odd /even year fluctuation of Asian pink salmon abundance in the study are a. It was found that chum salmon changed their dominant diet from gela tinous zooplankton (pteropods, appendicularians, jellyfishes, chaetogn aths, polychaetes and unidentified materials) in 1991, when pink salmo n were abundant, to a diet of crustaceans (euphausiids, copepods, amph ipods, ostracods, mysids and decapods) in 1992, when pink salmon were less abundant. Local crustacean biomass (wet weight; mg m(-3)) had sig nificant negative correlation with the CPUE (catch number per 30 hachi ) of pink salmon in 1991 (r = -0.586; P = 0.026) and that of chum salm on in 1999 (r = -0.616; P = 0.014). There may be a limitation in the a vailable prey resource for production of salmonids.