Comparative genetic variability of pink salmon from different parts of their range: native Pacific, artificially introduced White Sea and naturally invasive Atlantic Scottish rivers.

Trans-oceanic movement, stocking and subsequent establishment of Pacific pink salmon (Oncorhynchus gorbuscha) into the Atlantic White Sea area have resulted in their spreading further across the northern Atlantic, with spawning being reported in a number of regions within this area. Such expansions of non-native species bring potential risks to the ecosystems in question. It has not yet been established if the spawning events of pink salmon observed are the result of self-sustaining populations in these areas, or are because of repeated invasions of strayers from the White Sea stocks. In 2017 pink salmon were observed in a number of Scottish rivers in historically large numbers. This study set out to examine genetic variation in these fish and compare this to fish in Pacific founder regions and the White Sea translocated populations. A total of 286 samples from Scotland, the Atlantic White Sea, the Pacific Okhotsk region and Northern Pacific Bering Sea were screened using a 1018 bp sequenced region of the Cytochrome b mtDNA gene and 205 of these samples for 13 microsatellites. Significant bottleneck and founder effects were observed in the White Sea stocks in both mitochondrial and nuclear DNA, including loss of diversity and changes in haplotype and allele proportions. Scottish fish were indistinguishable from White Sea populations and as such it was not possible to determine if the fish were strayers from this region or returning fish from previous spawning events in Scotland. Therefore, although the fish caught in Scotland have their origins in the White Sea population, it may not be easy to determine whether self-sustaining populations have, or are becoming, established in the UK using genetic analysis and other techniques may need to be used.