More on the Factors that Limit the Abundance of Pacific Salmon (Oncorhynchus spp., Family Salmonidae) during the Ocean Phase of Their Life History

Abstract

Two different viewpoints on the factors that limit the abundance of Pacific salmon in the sea and ocean phases of their life history are compared. According to traditional notions, food resources in sea and ocean epipelagic biotopes are limited and there is a severe competition for food between different species of the genus Oncorhynchus, which is particularly exhibited by the pink salmon O. gorbuscha. This results in a reduced abundance and worsening of some biological parameters of both pink and other salmon species. Negative anomalies of sea surface temperature, which decrease the food supply for these fish, are also traditionally considered as a factor that seriously restricts the salmon distribution in the marine life-history phase. A different point of view was expressed in the 1980s by the authors at TINRO-Center, based on comprehensive ecosystem studies of the Far Eastern seas and the North Pacific. According to this view, the food resources in the extensive salmon feeding range are not strictly limited and salmon play a secondary role in trophic webs within the subarctic epipelagic layer. The conclusion that salmon is a stenothermic fish was not confirmed, particularly for the cold-water conditions (salmon are found in the northern Bering Sea and the Sea of Okhotsk, with its harsh Arctic conditions, even in winter). New data obtained in 2018 support the latter viewpoint: in that year, the biomass of Russian salmon reached the historical maximum, primarily due to pink salmon, and the Russian catch of Pacific salmon was absolutely record-breaking, 677 900 t.