Geographic distribution, abundance, diet, and body size of invasive pink salmon (Oncorhynchus gorbuscha) in the Norwegian and Barents Seas, and in Norwegian rivers

Abstract

We report for the first time the geographic distribution, abundance, diet, and body size of invasive pink salmon (Oncorhynchus gorbuscha) in the Norwegian and Barents Seas and Norwegian coast and rivers. We found that pink salmon have spread throughout the Norwegian Sea and along the Norwegian coast, and abundance increased by several orders of magnitude in 2017, with no signs that it has peaked. Marine pink salmon diet comprised mainly fish larvae, amphipods, and krill, but their relative importance varied with geographic distribution. North of 67.5°N, Amphipoda, herring, and saithe were more important, while south of 67.5°N, Euphausiidae and mesopelagic fish abounded. Pink salmon body size was larger in the northern rivers, and to the north of the Norwegian Sea and the Barents Sea, relative to the southern rivers and sea areas. Pink salmon were feeding in the ocean during the winter and spring, and in coastal areas immediately before return to the rivers, but not after they had entered the rivers. There was no geographical pattern in the seasonal timing of river ascent. The geographic pattern in abundance and diet of pink salmon, as reported here, offer a measure of the ecological effect of the invasion.

Prospects for the future of pink salmon in three oceans: From the native Pacific to the novel Arctic and Atlantic

“…In every waterbody except for the Laurentian Great Lakes (Kennedy et al, 2005), pink salmon return to coasts after about 12-14 months in the ocean to migrate into rivers and spawn. Like entering rivers as late as September (Anon, 2022a(Anon, , 2022bDiaz Pauli et al, 2023;Vistnes, 2017Sørvik, 2022. Once pink salmon enter a river, they may still return to the estuary before making a final spawning migration (Morita, 2022).…”

“…Concerns further strengthened when the largest pink salmon run ever to the region occurred in 2021, with catches exceeding those of native Atlantic salmon (Salmo salar Salmonidae) in Norwegian rivers (https://www. ssb.no/jord-skog-jakt-og-fiske ri/fiske -og-fangs t/stati stikk/ sjofi ske-etter -laks-og-sjoaure, Diaz Pauli et al, 2023).…”

Rapid genetic adaptation to a novel ecosystem despite a massive bottleneck

“…Of those genes, we show simulated and observed data indicative of a strong response to selection in per2 (period circadian protein homolog 2-like) on chromosome 22, which research in other organisms suggests plays a significant role in an individual's daily clock and matches considerable changes in day length between the progenitor and introduced populations. Finally, the combined result of genetic adaptation despite a significant bottleneck has important implications not only for how and when introduced species might colonize new habitat, especially invasive European pink salmon (Diaz Pauli et al, 2022;Sandlund et al, 2018), but also for populations or species at conservation risk that might experience similar demographic declines.…”

Evidence of potential establishment of pink salmon Oncorhynchus gorbuscha in Scotland

“…A similar decline was also seen in many other southern intrusions (Ireland, Sweden, Denmark and Germany). Nonetheless, the total number of reported fish increased in Norway from 11,483 to 15,721 (river catches) with most catches concentrated in the rivers of Finnmark and Troms (Berntsen et al ., 2020; Diaz Pauli et al ., 2022). A notable increase in O. gorbuscha records was also reported for Greenland and Iceland (Nielsen et al ., 2020; G. Guðbergsson, pers.…”

“…In 2021, the total number of O. gorbuscha entering North Atlantic tributaries was the highest recorded, especially in Norway where more than 112,000 fish were caught in fresh water (Diaz Pauli et al ., 2022). The increase was also noted in the Great Britain and Ireland: 171 O. gorbuscha were reported in Scotland (FMS; 2022: Figure 1) with records as far south as the River Tamar (Devon/Cornwall border) in England.…”