The pink salmon invasion: a Norwegian perspective

Abstract

In the period 1956–1979, more than 220 million of pink salmon Oncorhynchus gorbuscha (Walbaum 1792) eggs from the southern part of Sakhalin Island in the Pacific Ocean were transported to the northwestern part of Russia (Gordeeva et al., 2015). The hatched fry were stocked to several rivers draining to the White Sea and Barents Sea,which is part of the Arctic Ocean, bordering on the North Atlantic Ocean. These introductions resulted in large catches of adult O. gorbuscha during the 1970s, especially in the White Sea (Niemelä et al., 2016). However, self-reproducing populations appeared not to become established, perhaps because the O. gorbuscha were not adapted to the local climatic conditions and timing of spawning. Low water temperatures during the autumn may have caused mortality of the developing embryos (Gordeeva et al., 2015). The more northerly located River Ola (59_ 350 N; 151_ 160 E; close to Magadan) in eastern Russia was chosen as the donor population for all subsequent ova introductions. Introductions during the 1980s resulted in selfreproducing populations of the odd-year brood line; which indicated that the River Ola population was better adapted to the hydrothermal regimes in the recipient rivers (Gordeeva et al., 2015). During the 1990s, stocked fry in Russian rivers were mostly based on eggs from local catches of odd-year spawners in the White Sea area (Niemelä et al., 2016). According to Niemelä et al. (2016), the translocation of O. gorbuscha eggs from the Pacific Ocean ended in 1998, while releases of fry from local catches ended in 2000. Consequently, catches later than 2001 in the White Sea, Barents Sea and North Atlantic Ocean and rivers draining to these areas originate from selfreproducing populations, mainly in rivers draining to the White Sea (Niemelä et al., 2016). This successful translocation of O. gorbuscha to create a self-sustaining population represented a distance of over 5,600 km as the crow flies. By far, odd-year spawners dominate the established populations (Gordeeva & Salmenkova, 2011). Several introductions of an even-year brood line from Ola River did not provide perceptible results, but still, low numbers of O. gorbuscha enter the rivers in even-years (Gordeeva et al., 2015).