Vol 45, No 7 (2019)

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.

The chum salmon in the Amur River basin is represented by two races, that is, summer-run and fall-run races. In the summer-run race, one population is known to use a specific type of spawning grounds. The fall-run race includes three populations with different types of spawning grounds. These four populations correspond to four eco-geographical groups separated reproductively by geographical boundaries of the geomorphological zones, as well as temporally and ecologically. In China, chum salmon has not been recorded from the spawning grounds of the Amur basin for already more than 50 years. In the Russian Federation, 100% of summer-run chum salmon spawn completely at parafluvial springs in late July and August; 77.1% of fall-run chum spawn at orthofluvial springs in September–November; 20.4% of fall-run chum spawn in the downstream part of the spawning range at parafluvial springs in September; and 2.5% of fall-run chum spawn in lakes near the Amur River mouth at orthofluvial springs in October and November.

The characteristics of the farming of hatchery-reared juvenile Yesso scallop, Mizuhopecten yessoensis, in suspended net cages off the eastern coast of Primorsky Krai are studied. The work was conducted at a farm located northeast of Moryak-Rybolov Bay during the first 10 days of November 2018. The values of survival and growth rates of scallops on collectors and grow-out cages were determined. The survival rate of the Yesso scallop spat after being transported from Shandong Province, China and seeded in suspended cages was 85%, which is consistent with the regional standard. A high mortality rate of juvenile scallops (56–90%) was recorded in September–November. The mean size (shell height) of hatchery-reared spat in the cages in November did not differ from that of spat on collectors in southern Primorsky Krai. In the waters near Moryak-Rybolov Bay, the growth rate of scallops was somewhat lower than in southern Primorsky Krai but, nevertheless, higher than in Vladimir Bay and Aniva Bay. The mean body weight of scallop spat in November was 1.5 ± 0.1 g. The possible causes of the increased mortality rate of the bivalves and the solutions of the problem are discussed.