Latitudinal variations in abundance of phytoplankton, macrozooplankton, salmonids, and other epipelagic fishes in the northern Pacific ocean and Bering sea in summer

• Published in: Bulletin - National Research Institute of Far Seas Fisheries (Japan) no. 36
• Main Authors: Nagasawa, K. (National Research Inst. of Far Seas Fisheries, Shimizu, Shizuoka (Japan)), Shiomoto, A, Tadokoro, K, Ishida, Y
• Format: Journal Article
• Language: English
• Published: 01.03.1999
• Subjects: BERING SEA; BIOMASA; BIOMASS; BIOMASSE; BONY FISHES; COPEPODA; ETE; MAR DE BERING; MER DE BERING; NORTHWEST PACIFIC; ONCORHYNCHUS; PACIFICO NOROESTE; PACIFIQUE NORD OUEST; PECES OSEOS; PLANCTON; PLANKTON; POISSON OSSEUX; PREDATOR PREY RELATIONS; RELACIONES PREDATOR PRESA; RELATION PREDATEUR PROIE; SUMMER; VERANO
• ISSN: 0386-7285

Latitudinal changes in abundance of phytoplankton, macrozooplankton, salmonids (Oncorhynchus spp.) and other epipelagic fishes were surveyed from mid-June to early July in 1992 and 1993 along a transect at 179:30W from 38:30N-58:30N. In the Bering Sea (52:00N-58:30N) where salmonids were abundant, macrozooplankton biomass was low whereas phytoplankton abundance was high. In the Transition Domain (42:00/43:00N-46:00N) with low salmonid abundance, macrozooplankton biomass was high but phytoplankton stock was at a low level. Salmonid abundance annually varied in the subarctic North Pacific, and when salmonids were abundant there, macrozooplankton biomass was low but phytoplankton stock was high, and vice versa. These results imply that salmonid predation may have resulted in the low abundance of macrozooplankton, which may have enhanced the phytoplankton stock. In the regions with low salmonid abundance, the proportion of large-sized phytoplankton (10 mum) was low but that of copepods was high, possibly because reduced predation pressure of salmonids may have enhanced the copepod grazing on large-sized phytoplankton. The catch of pink salmon (O. gorbuscha)was high in 1993 and this species seems to play an important role in reducing the macrozooplankton biomass in central North Pacific in summer. Since the macrozooplankton biomass in the Transition domain is controlled by the feeding of planktivorous fishes (e.g., Pacific saury Cololabis saira) migrating from the more southerly subtropical North Pacific (38:30N-42:00/43:00N), these fishes appear to give stronger negative effects, than salmonids, on the abundance of macrozooplankton in the Transition Domain where salmonid abundance is low