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

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 degrees N, Amphipoda, herring, and saithe were more important, while south of 67.5 degrees 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.