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Pink salmon: problem or resource?
The pink salmon is blacklisted in Norway, but new studies show that many animals benefit from the invasion of Russian salmons in Norwegian rivers.
In recent years, pink salmon have invaded Norway.
It began in the 1950s when pink salmon were released in Russian rivers on the Kola Peninsula. In the former Soviet Union, the introduction of new species was seen as a positive initiative. Another example is the king crab.
Pink salmon is the most numerous of the Pacific salmon species and a crucial resource for the fisheries. This was why it was released several times, until the late 1990s.
But like the king crab, the pink salmon don't respect national borders, which has resulted in an invasion into Norwegian rivers in recent years.
Winners and losers
A group of scientists have studied the effects of pink salmon on ecosystems. The project is called Climate Effects on Terrestrial Ecosystems, Landscapes, Communities and Indigenous Peoples, and is funded by the Fram Centre’s research programme.
In two different studies, researchers found that when pink salmon swim up rivers, it means more food for scavengers, fish and birds.
“Both studies provide information about the ecological impact in Northern Norway of the nutrients and energy from pink salmon and their eggs. We expect the presence of pink salmon in Norway will have both winners and losers, both in terrestrial and freshwater ecosystems,” says Katherine Dunlop, researcher at the Institute of Marine Research.
Unwanted guest
In 2017, pink salmon were caught in more than half of the salmon-bearing rivers in Norway, and many were reported in 2019 as well.
According to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), the proliferation of such invasive species is one of the main causes of declining natural diversity globally, the Norwegian Environment Agency states.
The Scientific Committee for Food and the Environment maintains that large pink salmon stocks will increase the likelihood of disease in wild salmon and farmed fish.
Naturtjenester i Nord is a nature conservation service in Northern Norway which participates in the research and has been monitoring Norwegian rivers for more than twenty years. They have registered an increase of pink salmons.
“In recent years we’ve observed increasingly more pink salmon, which appear to have established populations in several waterways,” says Rune Muladal, Managing Director, Naturtjenester i Nord.
A report prepared by the Norwegian Institute for Nature Research (NINA), confirms the increase in pink salmon stocks. A total of 20,029 catches of pink salmon were recorded in Norway during 2019, significantly more than the 6,594 catches of pink salmon recorded in 2017.
Field studies in Finnmark
Field studies were done along Vesterelva in Finnmark County. This is a small river that flows into the Varanger Fjord. There have been large stocks of pink salmon in this river in some years. The fact that Vesterelva has a waterfall is beneficial from a data-collection perspective because pink salmon do not seem to migrate upstream in heavy currents or rivers with powerful waterfalls.
This made it possible for scientists to use the upper part of the river as a control ecosystem that is not affected by pink salmon.
These are the first pink salmon studies ever conducted in Northern Europe, and they provide information about the various mechanisms at play and they quantify the transfer of energy and nutrients from saltwater to fresh water. The findings are comparable to research done in the United States.
“Not surprisingly, we had similiar results in the Northern Norway research as in our studies in Alaska. Many animals, including aquatic invertebrates, seem to benefit ecologically from the fact that pink salmon swim up the rivers,” says professor Mark S. Wipfli, University of Alaska Fairbanks (UAF).
Both positive and negative impacts
From the original natural habitats of pink salmon, it is known that the marine nutrients brought upriver by salmon can have a positive effect on both terrestrial and freshwater ecosystems.
Bears, foxes, and birds eat the spawning and dying fish. The increased access to nutrition promotes the growth of microalgae and bottom fauna in rivers, and fish fry help themselves to the highly nutritious pink salmon eggs.
This last point is particularly interesting for the Norwegian salmon species, because winter in the far north often means that they often starve due to short days, low production and scarce prey. To build up good reserves of fat in autumn would greatly benefit the native salmon species, and a higher supply of nutrients from pink salmon eggs can be a good source of nutrition.
“Our results showed that the high-energy eggs of the pink salmon have yet to become an important dietary element for most salmon juveniles, but pink salmon are probably here to stay, which means they will continue to be a source of high-energy food for mature salmon,” Kathy Dunlop says.
“Although we mostly saw positive effects of pink salmon in our studies in Norway, concerns about disease transmission, competition, oxygen depletion from dead and rotting pink salmon and other issues need to be investigated in more detail to understand the entire scope and long-term impact of pink salmon in Norwegian rivers,” Mark Wipfli says.
Swim far in calm rivers
The Vesterelva river has a waterfall that pink salmon do not appear to climb.
But the scientists are aware of the fact that pink salmon can migrate hundreds of kilometres up some of Norway’s long, calm rivers.
“Pink salmon have an enormous proliferation potential, but one should not disregard some of the potentially positive effects this could have in a few waterways, as the study shows."
"But even if pink salmon are a source of energy for other organisms, this could increase the number of scavengers and vermin. For example, mink and otter will be increasingly attracted to waterways with large stocks of pink salmon. We might see that the formation of pink salmon stocks changes ecosystems,” Rune Muladal says.
References:
The studies were conducted by researchers from: Akvaplan-niva, Institute of Marine Research, NINA – Norwegian Institute of Water Research, University of Alaska Fairbanks, USA, University of Jyväskylä, Jyväskylä, Finland
Kathy Dunlop et al: Evidence of energy and nutrient transfer from invasive pink salmon (Oncorhynchus gorbuscha) spawners to juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in northern Norway. Ecology of freshwater fish, 2020. Doi.org/10.1111/eff.12582
Kathy M. Dunlop et al: Terrestrial and semi-aquatic scavengers on invasive Pacific pink salmon (Oncorhynchus gorbuscha) carcasses in a riparian ecosystem in northern Norway. Biological Invasions, 2020. Doi.org/10.1007/s10530-020-02419-x
NINA report: Pink salmon in Norway, 2019. (In Norwegian)
