The “Ick” that infects many walleye pollock; the inset box provides a closeup of a filet/NOAA

Hints of a new risk for Yukon Chinook

A news analysis

Scientists with the National Oceanic and Atmospheric Administration (NOAA) have come up with a new possibility as to why Bering Sea pollock fisheries might be harming Yukon River king salmon.

But it has nothing to do with the salmon bycatch that has had Alaska Rep. Mary Peltola pandering to Western Alaska subsistence fishermen and others who want to believe salmon bycatch in the state’s largest volume fishery is decimating Yukon returns

When it comes to bycatch, the scientists are in agreement it doesn’t account for the number of missing Yukon Chinook, as the largest of the Pacific salmon are called by most of those outside of Alaska.

Remember when there was a national chant to “listen to the scientists?”

Well, it could be that the time has come to listen again and maybe put a little more public money into funding further research into Ichthyophonus hoferi (Ick for short), a common fungal parasite that infects walleye pollock.

The parasite causes marketing problems for the pollock fishery in that it leaves unsightly specks in pollock filets. So NOAA researchers went looking to find out how common the parasite.

“Our study revealed that Ichthyophonus hoferi infects walleye pollock ages 1 to 18 throughout the Eastern Bering Sea. Prevalence in adult walleye pollock (age 4 plus) was nearly 30 percent, much higher than that in juveniles,” they have reported.

“It is currently unknown what effect Ichthyophonus may have on walleye pollock at the population level or on individual fish, but in other fish hosts, infections have been associated with increased energetic costs and reduced swimming stamina.”

Chinook a victim?

It is in those “other fish,” such as Yukon Chinook, that things get interesting.

The researchers noted that Ick “could impact host fitness, population abundance or recruitment to the fishery if energetic reserves are compromised due to other stressors such as unfavorable ocean conditions or reduced prey availability.

“(And) this parasite can be transmitted through the diet; walleye pollock is a central prey item for many fish in the region. Therefore, walleye pollock might act as a reservoir of infections for other species either through direct feeding on small pollock as prey or feeding on processing waste from commercial fishing practices.”

Larger pollock, those ages four and up, are the prime target of the Bering Sea pollock fisheries, which processes some of its catch at sea and dumps the waste from processing back into the sea.

The volume of this waste is large, on the order of millions to hundreds of millions of pounds.

After pollock are fileted board ship, the filets head for the ship’s freezers, and the 66 percent of the fish that remains intact after fileting heads back to the sea as waste, according to one study. 

Normally, this would be thought of as a good thing. In ecological terms, this waste is just more food for the ecosystem. Fish and birds that would normally expend calories pursuing live pollock or other fish can more easily dine on the waste products of dead pollock.

And it has been documented that among the fish dining on the spew of offal pouring out of Bering Sea catcher-processors are Chinook salmon.

Scientists studying the stomach contents of bycatch Chinook in 2009 reported that “of the 15 offal samples, nine yielded usable sequences, all of which were positively identified as walleye pollock.

“These results suggest that walleye pollock offal supplements the diet of Chinook salmon during winter.”

This could be a symbiotic relationship that is good for Chinook by providing them an easy food source to help them survive the winter, or it could be a bad thing if it leads to large numbers of the fish being infected by a potentially debilitating and sometimes deadly parasite.

Sick fish increasing

A peer-reviewed study in the Journal of Aquatic Animal Health in 2004 reported that “before 1985, Ichthyophonus was unreported among Pacific salmon from the Yukon River; (but) now it infects more than 40 percent of returning adult Chinook salmon.

“…Clinical signs (of the parasite) increased each year from 7 percent in 1999 to 27 percent  in 2003 at the mouth of the river.”

There were also hints that the infections were killing salmon as they tried to make their way upstream to spawning grounds hundreds of miles from the ocean.

“As fish approached the upper reaches of the Yukon River (in Canada) and the spawning areas of the Chena and Salcha rivers (in Alaska), infection prevalence dropped significantly to less than 15 percent in females on the Yukon River and less than 10 percent for both sexes in the Chena and Salcha rivers, presumably because of mortality among infected prespawn fish,” wrote the University of Washington’s Richard Kocan, the lead author on the study.

Kocan and his co-authors at the time were unable to identify a source for the infections.

“Ichthyophonus was not found in 400 Pacific herring from the Bering Sea or in 120 out-migrating juvenile Chinook salmon from two drainages in Alaska and Canada,” they reported. “Freshwater burbot from the middle Yukon River were subclinically infected with Ichthyophonus, but the origin and relationship of this agent to the Chinook salmon isolate is unknown.”

The fact the out-migrating juveniles weren’t infected would appear to indicate they weren’t picking up the parasite from river-resident burbot, but the sample size for those salmon was small and anything is possible.

Still, the new findings of how common Ick is in Bering Sea pollock, and thus how common it is likely to be in waste from those fish, raises some serious questions given that the Alaska Department of Fish and Game was in 2021 reporting that the number of Ick-infected fish in the Yukon was up to 44 percent.

State researchers are of the opinion a disastrous decline in Chinook returns to the Yukon is tied to poor survival of out-migrating young salmon, but there are big, unanswered questions about how the survival of young salmon might be affected by the condition of Ick-infected parents.

A peer-reviewed study of Ick-infected salmon in the Chena and Salcha rivers concluded “that while Ichthyophonus infection slightly reduces spawning success of infected females, its impact on the spawning population as a whole appears minimal.”

But the sample size for that study was small, 1,281 carcasses; conducted on streams only part way up the vast Yukon drainage; and not designed to look at the survival of alevins in the gravel, emerging fry or smolt migrating to sea.

Little is known about the effects of Ick on what is known as a salmon’s “lifetime reproductive success.”

A 2021 study pointed out the need for far more research into “studies that investigate the effects of aquatic stressors, such as anthropogenic effects, pathogens, environmental factors in both freshwater and marine environments, and assessing overall body condition.”

A warming connection?

Meanwhile, there are questions as to how this might be linked to a warmer Bering Sea, which has caused a huge boom in returns of sockeye salmon to Bristol Bay and pink salmon to Russia but could be producing the opposite consequences for Yukon Chinook.

Kocan, the UW researcher, in 2008 told a Los Angeles Times reporter that a warming Bering Sea and warmer-in-summer Yukon River could also be working to the benefit of the more than 500-million-year-old, global pathogen. 

“Everything is getting warmer, and that’s how climate change is going to redistribute all kinds of disease,” Kocan said. “Parasites have their optimum conditions – upper and lower limits. We’ll notice where they show up but not necessarily where they disappear.”

There is now no doubt that Ick has shown up in ever greater abundance in Yukon Chinook. The data is clear on that.

What is unclear is whether these infections are in any way tied to the pollock fishery and – in turn – whether the dramatic decline in the number of Chinook returning to the Yukon is Ick related although a 2011 study of herring did find that “infected (juvenile Pacific) herring incurred significant energetic costs, the magnitude of which depended on fish condition at the time of infection, fat versus lean.”

That study also found that “the greatest impacts of infection occurred in colder temperatures, suggesting Ichthyophonus-induced reductions in body condition may have greater consequences in the northern extent of herring’s range, where juveniles use most of their energy reserves to survive their first winter.”

There are many unknowns here, not to mention other possible explanations for Yukon salmon declines.

Man-altered environment

Some scientists have theorized that a large number of the big salmon could now be disappearing into the stomachs of killer whales, harbor seals, Steller sea lions in the Northeast Pacific.

So-called “charismatic megafauna,” those animals have been managed primarily for abundance by the U.S. government since the 1970s. The Marine Mammal Protection Act of 1972 put them off limits to all but Alaska Native hunters of whom there are few. 

A large team of scientists reporting in a peer-reviewed study published in 2017 said they found that “from 1975 to 2015, biomass of Chinook salmon consumed by pinnipeds and killer whales increased from 6,100 to 15,200 metric tons (or from 5 million to 31.5 million individual salmon).

This is orders of magnitude above the trawl bycatch of less than 35,000 Chinook per year from 1991 to 2019 as reported by NOAA.

“Though there is variation across the regions in our model, overall, killer whales consume the largest biomass of Chinook salmon, but harbor seals consume the largest number of individuals,” the authors of the marine-mammal study wrote. The decrease in adult Chinook salmon harvest from 1975 to 2015 was 16,400 to 9,600 metric tons. Thus, (overall) Chinook salmon removals (harvest + consumption) increased in the past 40 years despite catch reductions in fisheries due to consumption by recovering pinnipeds and endangered killer whales.”

They suggested that “long-term management strategies for Chinook salmon will need to consider potential conflicts between rebounding predators or endangered predators and prey,” but there have been no attempts to open hunting seasons for seals or sea lions in the years since the study was published.

And where predator control operations have been directed at marine mammals, such as the mouth of the Columbia River or in Seattle’s Shillshole Bay, they have been controversial.

“Nearly 22,000 comments received during public review of the (Columbia River) program were opposed and fewer than 200 were for it,” the Seattle Times reported in 2020. “But a task force in May overwhelmingly recommended approval of a kill program.”

Friends of Animals has now incorporated the Columbia River kill into its efforts to stop people from eating fish altogether because of “the horrors of the fishing industry.”

 “Sea lions were hunted nearly to extinction for their pelts, but after the 1972 Marine Mammal Protection Act the species has rebounded, from a low of 30,000 to more than 250,000. Now, state wildlife agencies, with help from the federal government, are allowing the killing of hundreds of sea lions that they blame for catching salmon and steelhead trout below dams on the Columbia River,” according to the organization.

But marine mammals aren’t the only predators of Yukon Chinook. How many of the fish die in commercial fisheries on the western (Russian) side of the Bering Sea is wholly unknown, but it’s possible some or many could be caught there given the wide-ranging habits of salmon.

Recent genetic testing of chum salmon catches off the Alaska Peninsula found that a fishery once accused of heavily exploiting Yukon and Kuskokwim River chum stocks is preying largely on Asian salmon.

“The Asia group was the largest contributor (42.5 percent) to the total South Alaska Peninsula commercial chum salmon fishery, followed by east of Kodiak (16.9 percent), South Peninsula (13.2 percent), Coastal Western Alaska (12.8 percent), and Chignik/Kodiak (8.9 percent),” according to the 2022 state study. 

Early data from this year indicated the percentage had climbed above 50 percent Asian chums, apparently reflecting the large runs of chum salmon that were forecast in Russia and Japan for this year.

Up-to-the-minute data on catches for those two countries is hard to find, but the bounty of chums on the western side of the Bering Sea was cited by Trident Seafoods – Alaska’s largest salmon processor – when it last week announced a decision to slash the Alaska chum prices paid fishermen to 20 cents per pound, less than half of the average statewide payment to fishermen for chums last year.

Another unknown for Yukon and Kuskokwim Chinook is how the now huge abundance of sockeye, chum and pink salmon in the Bering Sea affects the bigger fish in terms of competition for food.

There are significant overlaps in the diets of all of these salmon and past research has suggested the Bering boom, especially in smallish pink salmon that appear to have a competitive advantage in warm waters, could be creating problems for Chinook.

Inspired by Alaska’s success in farming pinks, Russia hatcheries boosted their production of hatchery pinks and chums by 40 percent in the 2000s, according to the Wild Salmon Center, which was by the mid-2010s claiming some success in convincing the Russians to back off plans for even more hatchery production.

“Russian hatchery releases appear to have plateaued, while the United States and Japan continue to release more hatchery fish into the ocean than Russia does,” the organization reported in 2016. “Good hatchery practices are only one piece of the puzzle, but they are vital to ensuring sustainable fisheries. With better practices in place, we’re hopeful (wild) Sakhalin (River) runs and commercial fisheries have started the long path to recovery.”

The Center has since been declared “undesirable” and banned from Russia.

In a statement announcing that declaration, the Moscow Times reported last month that “the Prosecutor General’s Office alleged that the WSC used its work as ‘a cover for the implementation of projects aimed at restraining Russia’s economic development.’

“It also accused the NGO (non-governmental organization) of promoting ‘seemingly beneficial initiatives to create specially protected natural areas in the Russian Far East with the aim of excluding these territories from use, restricting fishing activities for Russian industrial companies, and blocking gas and oil extraction industries in the Sakhalin region in the interests of foreign non-governmental companies and individuals.'”

Russia, like the Prince William Sound region of Alaska, has embraced hatcheries, and hatchery operators in Russia have one-upped those in Alaska by cutting out the middlemen. The Russian hatcheries both produce and harvest the fish.

There are no commercial fishing harvests, and harvests at the hatcheries help hold down processing costs.

“There are currently five hatcheries in Sakhalin, and a dozen in mainland Russia focused on breeding salmon broodstock,” Hatchery International reported in 2021. “Some forecasts envisaged that Russia could boost (the) salmon catch to 1 million tons per year in the case that the salmon reproduction campaign is further expanded.”

The hatchery business appears to have only expanded since then. A Russian business website reported the latest hatchery to be constructed in the Russian Far East was to have come online last year, and it reportws significantly more than 13 hatcheries in operation in the Russian Far East.

 Ivan Radchenko, head of the Sakhalin Oblast Fisheries Agency on the western side of the Bering Sea, told the publication, Alekseev that “aquaculture today is handled by 68 salmon fish farms. Every year these plants raise and release about 1 billion young Pacific salmon into the region’s spawning rivers.”

Russie would appear to be in the process of trying to top Japan and Alaska in the production of free-ranged salmon.

The implications for wild Pacific salmon everywhere are unclear although the North Pacific Anadromous Fish Commission, a treaty organization of the North Pacific fishing nations, has already raised the question of whether Japanese, Russian and Alaska hatcheries are pumping too many fish into the ocean to the detriment of wild fish.

When hatchery operators in all these countries now talk about what they’re doing to “increase the survival” of their fish, such as raising them in ocean pens like farmed salmon to grow them bigger before sending them out to sea, what they are really talking about is how to increase the odds their salmon can out-compete other salmon, most notably the wild ones.

And the long-term implications of such policies are as unknown as the consequences of Yukon Chinook dining on pollock offal.