Pink salmon. Photo Eva B. Thorstad
Invasive pink salmon, which has its native distribution in the Pacific Ocean, has spread from deliberate releases in north-eastern Russia, and is now widely distributed throughout the Norwegian Sea and along the Norwegian coast. Numbers increased by several orders of magnitude from 2015 to 2017, and thereafter increased further with no indication that the number of pink salmon has peaked yet.
The geographic distribution, abundance, diet, and body size of invasive pink salmon in the Norwegian and Barents Seas and Norwegian coast and rivers have for the first time been analysed and reported. The results suggest that pink salmon may have a marine migration pattern like Atlantic salmon, with some individuals staying in the eastern part of the Barents Sea, while others migrate westward and into the northern part of the Norwegian Sea.
The marine diet of introduced pink salmon in the north Atlantic Ocean and Barents Sea area 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 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 for spawning.
The dominance of Euphausiids, fish, and amphipods in the diet of pink salmon in the Norwegian Sea is very similar to previously reported stomach content of Atlantic salmon sampled in the same area during the summer and early winter.
In the North Pacific Ocean, pink salmon are known to impact the marine ecosystem through competition for prey with other fish and birds.
In the Norwegian and Barents Seas, pink salmon, based on the diet found in this new study, can potentially compete with other abundant pelagic fish species such as herring, capelin, polar cod, blue whiting, and Atlantic salmon. In numbers, these other species, except Atlantic salmon, are at present several orders of magnitude more numerous than pink salmon returning to Norwegian and Barents Seas rivers. Pink salmon in the Atlantic Ocean are, therefore, not expected to have a large-scale effect on the ecosystem, due to their relatively low numbers in the sea until now. However, pink salmon may still have local effects from grazing on fish larvae and other prey in estuaries, fjords, and other coastal areas.
Read the new publication here:
Pauli, B.D., Berntsen, H.H., Thorstad, E.B., Homrum, E., Lusseau, S.M., Wennevik, V. & Utne, K.R. 2023. Rapidly increasing abundance of pink salmon (Oncorhynchus gorbuscha) in the Northeast Atlantic Ocean and in Norwegian rivers. ICES Journal of Marine Science 80: 76-90. https://academic.oup.com/icesjms/article/80/1/76/6916929?login=true