Ecological effects of Pacific pink salmon in a river system in Finnmark

By: Kathy Dunlop // Institute of Marine Research. Antti Eloranta[1] // University of Jyväskylä. Guttorm Christensen and Jenny Jensen // Akvaplan-niva. Rune Muladal // Naturtjenester i Nord. Mark Wipfli and Erik Schoen // University of Alaska, Fairbanks. Yajie Lui and Ekaterina Aasmaa // UiT The Arctic University of Norway [1] Also affiliated with the Norwegian Institute for Nature Research

A large influx of pink salmon to Norwegian watercourses in 2017, 2019, and 2021 sparked concern over their impact on aquatic ecosystems, and in particular the ecosystem services provided by native salmonids.

This sudden increase in pink salmon numbers in Norway, thought to be linked to favourable climate conditions for pink salmon reproduction and survival, is expected to continue as water temperatures rise with climate change and large numbers of fish continue to arrive from Russia.

Despite mounting concern, media coverage, and a public demand for management practices, little research has been conducted in either freshwater or marine ecosystems to understand the potential ecological effects associated with this species. However, a lot can be learned from research on the ecological roles and effects of pink salmon in their native range in the northeast Pacific. This knowledge can be used to guide research and management here in Norway.

Collaboration

In August and September 2019, two visiting scientists came from the Pacific coast to northern Norway. Mark Wipfli and Erik Schoen travelled from the University of Alaska, Fairbanks, to join colleagues in Vesterelva, eastern Finnmark, to study potential effects of marine-derived energy and nutrients from pink salmon eggs and carcasses on the ecosystems of rivers and riverbanks.

Anadromous fishes, such as Pacific and Atlantic salmon, that migrate between the highly productive marine and less productive freshwater environments, transport energy and nutrients that subsidise freshwater and terrestrial food webs, thereby altering freshwater ecosystem processes. Through their research in Alaska, Mark and Erik have demonstrated the significant effect of these marine-derived subsidies on the structure and function of riverine ecosystems. For example, the nutrients that adult spawning salmon delivered to ecosystems around rivers increase the productivity and biomass of biofilm, aquatic invertebrates, and freshwater fishes.

In addition, the removal of carcasses by terrestrial animals (such as foxes and birds) to adjacent habitats along the waterways allows marine-derived energy to enter surrounding terrestrial ecosystems. However, the role of marine-derived resources from pink salmon in Norway’s terrestrial and freshwater ecosystems remains unstudied.

Fieldwork in Vesterelva

As part of the Terrestrial Fram Flagship project “Pacific salmon effects on terrestrial ecosystem structure and services”, several summer field expeditions to Vesterelva were made before, during, and after pink salmon spawning in August 2019.

The presence of marine-derived resources from pink salmon was examined in aquatic and terrestrial vegetation and invertebrates by measuring stable isotopes. Juvenile Atlantic salmon and brown trout were sampled in a river stretch where pink salmon were spawning and in an area inaccessible to pink salmon spawners. Pink salmon eggs were found in the stomachs of both juvenile Atlantic salmon and brown trout in the pink salmon spawning reaches.