Survival of pacific salmons in the North Pacific in winter-spring season

Influence of several factors (water temperature, food supply, predatory, size of juveniles) on pacific salmons survival during wintering is considered on the data collected from the upper pelagic layer in surveys conducted by Pacific Fisheries Research Center (TINRO) in the North-West Pacific. There is highly unlikely that the temperature influences on fish mortality directly. There is no obvious proof of negative influence of the low temperature on food base of salmons, as well. The lowering of forage zooplankton biomass in the Subarctic Front zone in February-March is insufficient for the salmons starvation taking into account that the total abundance of planktivorous nekton is also lowered in this area and generally in the Subarctic waters in winter-spring, so the food supply cannot be considered as a crucial factor of the salmons survival. Seasonal changes with lowering of feeding intensity, lipid accumulation, and somatic growth in winter known for pacific salmons aren’t forced by poor food base but are a feature of their species-specific life strategy with cyclic changes of metabolism. Predators are not abundant in the Subarctic zone in winter, so the predatory also cannot cause the high mortality of salmons. Relationship between the size of juveniles and their mortality in winter is considered in detail for the Okhotsk Sea stocks of pink salmon and there is concluded that the size of juveniles cannot be a predictor of their year-classes return for spawning. Thus, any single factor doesn’t determine winter mortality of pacific salmons but their survival is likely determined by a complex interaction of abiotic and biotic factors

On steadyness of stereotypes in conceptions on marine ecology of pacific salmons (Oncorhynchus spp.)

Some conceptions on marine ecology of pacific salmons (Oncorhynchus spp.), established in the second half of the last century, are discussed from critical position, as overemphasizing of the sea surface temperature influence on distribution of salmons and formation of their year-classes strength, deficiency of food (particularly in winter time) and fierce competition for food, pink salmon «suppression» over other salmon species and own adjacent generations, limited carrying capacity of the Subarctic zone for salmons, distortion of the epipelagic communities structure in the North Pacific by mass artificial reproduction of chum salmon, etc. Most of these ideas have not been confirmed by the data of long-term monitoring in complex marine expeditions conducted by Pacific Fish. Res. Center (TINRO) in the Far-Eastern Seas and adjacent North Pacific waters since the 1980s till nowadays. The data show that pacific salmons are very ecologically plastic species with wide temperature range of habitat. Salmons are able to considerable vertical migrations crossing easily the temperature gradient zones and different water masses. They have wide feeding spectra. Migrating dispersed, they successfully get their ration, even in vast areas with relatively low concentration of prey (macroplankton and small nekton). Total biomass of all species of pacific salmons in the North Pacific does not exceed 4-5 million tons (1.5-2.0 million tons in the Russian waters), whereas the stocks of other mass species of nekton are hundreds of millions of tons. The salmons consume 1.0-5.0 % of the total consumption by nekton in the epipelagic layer in the western Bering Sea, 0.5-1.0 % in the Okhotsk Sea, 5.0-15.0 % at East Kamchatka, and less than 1 % in the Pacific waters at Kuril Islands, So, the role of pacific salmons in trophic nets of the Subarctic waters is rather moderate. Therefore, neither pink salmon, nor chum salmon can be seriously considered as the species responsible for reorganization of large ecosystems and fluctuating of other mass nekton species