The Norwegian Broadcasting Corporation webpage

While Alaskans welcome back a swarm of pink salmon forecast to push the summer’s total salmon harvest near the 200 million mark once considered an unobtainable fishermen’s fantasy, 4,000 miles away on the opposite side of the planet the Norwegians are in a tizzy about their exploding returns of the smallest and fastest-growing of the Pacific salmon.

The government-owned Norwegian Broadcasting Corporation (NRK), earlier this month labeled the fish “the biggest environmental disaster facing Norwegian rivers.”

The story was packaged online with a video of Norwegians hauling a beach seine stuffed with hundreds if not thousands of squirming fish from a river in Finnmark, the country’s northernmost and easternmost county.

Volunteers in many places are now making an effort to clear Norwegian rivers of the fish, Norwegian Minister of Climate and Environment Sveinung Rotevatn told NRK.

Pink salmon – or humpies as Alaska often call them in recognition of the large, humped backs that develop on males as they approach the spawning grounds – are not native to the Atlantic ocean lapping at Norway’s coast.

Creeping south

But hatchery pinks released by Russian fish culturists have been steadily colonizing streams and rivers in Norway moving as far south of Ireland in search of new spawning habitat. Ireland issued a pink salmon alert after one of the fish was caught in the River Moy on June 27.

The Moy is reputed to be “the most prolific salmon river in Ireland,’‘ the salmon in question being Atlantic. There are concerns that if humpies show up in the numbers for which they are famous, they could push native Atlantic salmon off the spawning grounds.

What has been happening in the Atlantic in recent years is what has long been feared but has yet to materialize in the North Pacific ocean, where fish culturists began trying to establish populations of Atlantic salmon in 1874, a practice that continued for more than 50 years without success.

In recent years, salmon farmers began raising Atlantic salmon in net pens in Washington and British Columbia, Canada and there arose a fright that Atlantics escaping the farms could accomplish what the fans of hatcheries failed to accomplish a generation earlier.

“….About a million (Atlantic salmon were) released each year from 1923 to 1928,”  Tony Farrell, a professor in the Faculty of Land and Food Systems at the University of B.C., told the Vancouver Sun in 2017.

The effort turned out to be a big waste of money.

“There appear to be only three authentic records of Atlantic Salmon being taken by anglers, all small fish, and none since 1926,” according to the Electronic Atlas of the Wildlife of British Columbia. “The introductions have obviously been failures.”

The atlas was developed by the Lab for Advanced Spatial Analysis at the University of British Columbia.

Atlantic salmon have not shown themselves very good at adapting to and colonizing new habitats. Pinks are another matter.

Invaders

The Norwegian pinks trace back to 1959 Russian introductions to rivers draining into the White Sea, according to a peer-reviewed paper published by Norwegian, Finnish and Russian scientists in 2019.

“Since the first observations in Norway in 1960, pink salmon has been an irregular element in Norwegian fauna,” they wrote. “In some rivers in the northernmost part of the country (around 70 degrees N), pink salmon have been observed in most years, although in widely varying numbers.

“Further south, numbers have in most years been low. However, in 2017, pink salmon were observed in rivers along the entire coastline, and in high numbers in many rivers. In 2017, pink salmon was also caught in rivers in the UK and Ireland, in countries in mainland western Europe, as well as in Iceland and on the east coast of Canada.”

The scientists concluded that naturally reproducing populations of the fish are now established in at least a dozen rivers in Finnmark. The scientists admitted it’s still difficult to determine the reasons for the expansion, but a warmer ocean looks to play a role.

“In the North Pacific, the increasing pink salmon abundance observed over the recent decades is mainly due to the increasing number of odd-year fish, which has been associated with increasing sea temperatures,” they noted. “Climate warming may therefore favor establishment of pink salmon in rivers in the northern part of Norway. We have, however, no information that allows an assessment of how this will influence possible establishment further south along the Norwegian coast, where river temperatures are substantially higher.”

“The sudden increase of pink salmon in Tana as well as in rivers all over Norway and elsewhere in western Europe in 2017 is not easily explained,” they added. “Without any stocking neither in Russia nor in Norway, it must all be due to natural production. It appears obvious that this cohort must have experienced favourable conditions during all life stages. The reports of pink salmon in northwestern Europe also illustrates the broadcast spreading of adult pink salmon. This may bode for a dramatic expansion….”

In the Pacific, Alaska has been the big beneficiary of environmental changes that appear to favor the short-lived pinks over longer-lived Chinook, coho and sockeye salmon.

The 2021 Alaska forecast predicts about two-thirds of the statewide catch will be pinks. The forecast harvest of 124.2 million of the fish, if achievied, will exceed the all-species, statewide catch of 118.3 million salmon last year.

Pink dominance

The 2020 harvest was comparatively low becuase, in general, even-year pink salmon from Alaska are less productive and genetically distinct from odd-year pink salmon. A similar phenomenon is now being witnessed in the Atlantic where 2017, 2019 and now 2021 saw the big numbers of pinks.

Though the Norwegians are worried about negative pink salmon influences on native Atlantic salmon, the scientists aren’t so sure of what is going to happen.

“The impact of invasive pink salmon in Norwegian rivers cannot be properly assessed based on present data,” they wrote. “The general characteristics of pink salmon ecology in freshwater may indicate limited impact, but the changes observed in other cases of transplanted pink salmon renders limited value to such general assessments.”

Pinks could force Atlantics onto less productive spawning grounds, they observed, or not. The carcasses of spawned out pinks in European rivers could cause “local oxygen deficiencies” or feed the river ecosystems, thus creating more food for young Atlantics rearing in-river.

Consequences in the marine environment are even harder to predict, but they observed “that pink salmon and Atlantic salmon likely have similar diets during marine feeding.”

Ocean competition for food between pinks and Chinook, sockeye and coho has been hypothesized as a reason Gulf of Alaska stocks of the latter three species have been generally been declining in size and number for years.

As with so many things in nature, the Norwegian, Finnish and Russian scientists specultated, the consequences might well be dose related.

“The impact on the native anadromous salmonids is likely related to the abundance of pink salmon,” they wrote. “A high number of aggressive pink salmon on the spawning grounds of native salmonids may cause disrupted or failed spawning by the natives.

“Furthermore, a high abundance of pink salmon fry feeding in the rivers for a few weeks will most probably depress the availability of space and suitable zoobenthos for other salmonids.

‘In the North Pacific Ocean, it is shown that in years with unusually abundant pink salmon, the food resources are depressed, with a negative impact on other Pacific salmon species, other pelagic fishes and sea birds.”

Or  so some studies  have suggested. The Alaska Department of Fish and Game holds to the view that there is not enough evidence to support the hypothesis that record numbers of pinks in the Pacific could be the reasons other species are in decline.