The population of pink salmon, or humpback salmon, in Norway dramatically increased in past years so much that there may be 10 times as many fish in two years, threatening the existence of the local Atlantic salmon.
Pink salmon is considered an invasive species in Norway. The country tries to limit its population to the lowest possible. Yet in other regions the fish is valuable.
Pacific salmon, Russian salmon, Pink salmon, Humpback salmon, the species has many names.
They originate from the Pacific Ocean but were introduced from 1956 to 1998 in the Kola Peninsula in Russia. Then they began to appear in the northern Norwegian waters in the 1960s.
Pink salmon are not very good at finding their way home to spawn but only a few hundreds humpback salmons were recorded in Norwegian fresh waters until 2015. Then, the population started to dramatically increase.
An invasive alien species threatening Atlantic salmon
According to Norway's official statistics, 111,700 humpback salmon, accounting for 191 tonnes, were caught and killed in Norwegian rivers in 2021. Only 13,900 salmon were reported in 2019 when they started to officially record catch of the species.
The capture of 100,000 was mostly the result of volunteers spread across several dozens of river in Finnmark, the northernmost Norwegian region which shares borders with Finland and Russia, during summer 2021 to avoid the fish to procreate.
The Norwegian Directorate of Fisheries received NOK 1 million (US$112,000) as part of an urgent measure to combat humpback salmon but volunteers don't think the government investment would be enough when they will come back in 2023.
Humpback salmon have a two-year life cycle. They are present in even- or odd-year cohorts and fish sharing the same watershed spawning grounds are reproductively isolated and genetically distinct.
Norway sees a large population of fish coming back to spawn during odd years.
And according to the biologist Rune Muladal from Naturtjenester, there could be as many as 1 million pink salmons in 2023, NRK reported. Exact predictions seem difficult, but if true, there would be 10 times as many pink salmons as in 2021.
Humpback salmon decay in Norwegian rivers
Pacific salmon grow fast. Faster than farmed salmon.
They look similar to Atlantic salmon at sea except that their tail is spotted. But when they come back to spawn in fresh water, the physical appearance of males are completely transformed and they start to grow a hump on the front part of their backs.
After having spawned, the fish don't come back to sea. They instead die and eventually decay in freshwater.
Locals feel invaded by the humpback salmon.
While fish rot in Norwegian rivers, some biologists like Rune Muladal wonder the impact on the environment. Consequences are unsure.
On one side, the fish can prove to be very nutritious for other animals, scavengers and birds. But as fish rot, bacteria could grow and diseases may spread among other species, including in fish farms, an important business activity for Norway.
Humpback salmon is in fact resistant to a parasite which the Atlantic salmon isn't. Norwegian farmed salmon is even blamed for being contaminated by insecticides to kill the parasite.
The pink salmon is an alien species and Norway wants to limit its population because it can become a threat to the Norwegian Atlantic wild salmon. Atlantic salmon may flee Norway or be in competition with the Pacific salmon, if it is not killed by diseases carried by the Russian salmon.
While the pink salmon population increases in Norway, 40% less Atlantic salmon was captured in rivers in 2021 than in 2020.
A threat or a resource?
Globally, population of salmon tend to decrease and climate change is said to be a cause along with water pollution. But pink salmon seem to be resistant in warm temperatures, giving them a competitive advantage.
With a dominant humpback salmon species, not only do Norwegians see a threat to biodiversity, they also worry about tourism.
Recreational fishing brings 12,500 tourists in Finnmark, mainly from Finland, to fish salmon or sea trouts.
But humpback salmon don't have as a good reputation as Atlantic salmon in Norway. A retailer sells smoked salmon as Pacific salmon instead of the negatively connoted humpback salmon.
Yet, in Russia, Canada or Alaska, pink salmon is a food fish if captured before their transformation. And in the Pacific, where the species comes from like in Alaska, organizations advocate for the conversation of humpback salmons.
Norway's Minister of Fisheries Odd Emil Ingebrigtsen believes that humpback salmon is a resource. And so does a company like Lyder Fisk AS, a successful business helping to eradicate the King crab, another invasive species in Norway which is yet very tasty.
But commercialization of pink salmon is not yet much developed in the country.