Shrinking salmon

big king

Late Kenai River angler Les Anderson’s world record king salmon of 97 pounds, 4 ounces might stand forever if the work of Jan Ohlberger and other researchers at the University of Washington is to be believed.

What they have discovered in looking at decades of data on kings is a population of  steadily shrinking salmon.

“While changes in age proportions showed some region-specific trends,” they wrote in a paper published last month in the journal Fish and Fisheries, the size of the biggest fish – the ones that spend four- to five-years in the ocean – has been going down, down down since 2000.

Ohlberger said he can’t say whether this demographic shift will continue forever, but the trend line is clear.

Strangely, too, “the size-at-age of ocean-1 and ocean-2 has increased over time,” the paper adds.

Young fish appear to be growing fast, a sign of generally good ocean conditions, but then either their growth slows or the biggest among them disappear.

“Declining sizes of older ocean fish were found for both wild and hatchery Chinook (king) salmon along the coast,” the researchers wrote. “Our spatial analysis of changes in size-at-age revealed that the dominant trends are remarkably consistent across the entire Northeast Pacific Ocean.”

The research team, which included Bert Lewis of the Alaska Department of Fish and Game, could arrive at no definitive cause for the decline in size, but suggested further study of killer whale predation might be warranted.

“Resident killer whales….selectively prey upon Chinook salmon, particularly the oldest and largest individuals,” they wrote. “About 90 percent of Chinook salmon eaten by residents are 4–6 years old, and the abundance of resident killer whales has continuously increased since the 1970s.

“Currently, the total number of resident killer whales in the Northeast Pacific Ocean is estimated to be at least 2,300 individuals with many populations increasing two to three times over the last 40 years….

“Bioenergetics calculations suggest that the residents currently inhabiting the coastal waters between northern California and southern Alaska (not including those along the Aleutian Islands and in the Bering Sea) consumed roughly 10,000 metric tons of Chinook salmon in 2015.”

Big, bad wolf

Predation, as Alaskans well know from the state’s long-running debate over wolf control, is a very touchy subject. The old “balance of nature” theory that held that predators killed only the old and the weak – except in island ecosystems where the introduction of cats, rats, pigs or foxes can spell extinctions – has given way to the recognition nature is neither simple nor perfect.

“The famous ‘balance of nature’ is perhaps better understood as the ‘multiple possible balances of nature’,” as Emma Marris writes in Nature – The International Weekly Journal of Science.

Predators in most cases don’t eliminate prey in large ecosystems, but they can certainly alter population numbers. In this scenario, it’s not like the whales could wipe out the giant kings of legend; but maybe they could reset the balance so that very few of the big fish exist.

Then, of course, another question arises: Could their killing of larger numbers of big kings, if that is happening, eventually alter the genetics of the population as a whole as it was once feared anglers were doing on the Kenai?

“Previous work has suggested that size declines in Chinook salmon may be caused by sufficiently strong and selective fishing and the resulting evolutionary trait changes,” Ohlberger writes. That could – the emphasis being could – “produce an evolutionary response towards smaller average sizes and ages of Chinook salmon within a few decades,” he said.

Big fish, little fish

The kings that spend four and five years at sea are, of course, the ones that draw anglers to the Kenai. These are the trophy fish that spend enough time feeding in the ocean to grow to 60 pounds or more.

Anderson’s catch was something of a misfit – a rare, 6-ocean fish that came back in the first of the Kenai’s two, king salmon runs. The early fish are generally thought to be smaller, and in recent years they have been a lot smaller, but then all the kings have been shrinking.

The records of the International Game Fish Association largely tell the tale. From the 12-pound-line-class record category through the stronger line-classes and into the Junior division, every record is held by a king caught before 2001 with most of the fish being caught in the 1980s.

The ’80s were the years of big fish on the Kenai.

In 1990, longtime and now retired Kenai fishing guide Bix Bonney told Deseret News outdoor writer Ron Grass that “last year there were between 15 and 20 fish over 80 pounds that were caught.

Bonney might have been exaggerating, but if he was it wasn’t by much. Through the ’80s, there were a lot of 80-pound kings caught in the Kenai and many expected to see a 100-pound Chinook to crush Andersen’s record.

The standards for the state’s  “Trophy Fish Program” date back to those days. Anglers who catch a fish above a specified weight qualify for a state certificate noting they landed a true Alaska trophy,

“King salmon minimum weight for the Kenai River is 75 lb. For the rest of the state, it is 50 lb.,” the rules say. The rule was set at a time when there were so many fish over 50 pounds caught on the Kenai, state officials grew tired of handing out certificates.

The rule seems badly antiquated now. There’s no telling how many years could pass before an angler again qualifies a state-certified, trophy Kenai king.

Smaller, smaller, smaller

The big fish started disappearing in the ’90s, and by the start of the new millennium, a lot of people were getting worried.

Fears grew that Kenai anglers were messing up the genetics of the river’s Chinook by high-grading the biggest fish. The thought was the genes for older age and bigger fish might be eliminated and the monster kings would disappear forever.

“Size and age of king salmon can be inherited from the parent spawners. Because of this, in fisheries with relatively high overall exploitation, selective harvest of the largest king salmon over time could cause a decrease in the percentage of older fish returning in future years,” biologist Tim McKinley wrote in a paper prepared for the Alaska Board Fisheries at the time.

“Two conditions must be met if the fishery is the reason for fewer, larger early-run king salmon: 1) larger, older fish have had a higher harvest rate in the fishery than smaller, younger fish; and 2) age, and thus size, must be passed on as a characteristic.”

McKinley went on to write that there appeared little evidence for a genetic shift in the Kenai, but that, theoretically, it could happen. That was enough for the Board.

In 2003, the state instituted a “slot limit” on the Kenai designed to protect big kings. It originally required anglers to release unharmed any king between 40- and 55-inches long but eventually the bottom size was pumped up to 46 inches.

A king salmon pushing up against the lower limit will weigh in the neighborhood of 35 to 40 pounds. A fish over 55 inches will likely start near 65 pounds.

Kings over 65 pounds were once common in the Kenai. To keep track of how common, the state in 2003 began requiring all kings over 55 inches be brought to a Fish and Game office to be measured, examined and sealed.

Over the course of the next 14 years, the biggest fish sealed by the state weighed 80 pounds. It was caught more than a decade ago. Over the last nine years, only one king salmon over 55 inches has been caught and sealed.

One. It was a barely legal male at 55.5 inches in length. It weighed 71.1 pounds. It would not even have qualified as a state-certified, “trophy” Kenai catch.


It is pretty clear that the once giant four-, five- and rare six-ocean fish aren’t all that big anymore.

“Another fact about king salmon from the Kenai River is that it isn’t how old Kenai River king salmon are that make them unique,” McKinley wrote in that report back in the early 2000s, “but it is how fast they grow while in the ocean or their ‘size at age.’ For instance, a seven-year-old king salmon (a five-ocean fish) on the Kenai River might be 55 inches long and weigh 85 pounds, while the same age fish in other rivers in Southcentral Alaska might only be 40-45 inches long and weigh 50 pounds.”

Some of this was at the time thought to be tied to the prime habitat of the Kenai. Studies of the Kenai and Deep Creek, a nearby Kenai Peninsula salmon stream, done in the 1990s showed that king salmon smolt leaving the Kenai were bigger.

Bigger smolt could have held a competitive advantage that just kept getting bigger as the fish matured at sea. And there was always the belief, though it was never documented, that Kenai salmon were somehow genetically programmed to be mutant giants. That  idea looks somewhat more suspect now.

The whims of nature

As it turns out, the complicated interactions at play might be even more complicated than anyone ever imagined. Twenty-years ago, nobody even saw killer whales as a potential on the horizon.

And the marine ecosystem was complicated before the whales finned their way into the picture.

The problem with the ocean is a lot of the predators are prey when little and a lot of the prey become predators when big. It remains a given that big fish eat little fish, but some of the little fish that survive grow up to become big fish that eat the little fish spawned by fish once trying to eat them.

“The causes of the declining size and age trends are likely complex and involve multiple factors that may interact,” Ohlberger writes. “Changes in predation rates on the oldest and largest fish by expanding populations of resident killer whales is a hypothesis that appears largely consistent with the observed changes, but it remains untested. In the light of the presented findings, this and other hypotheses should be evaluated in more detail in future studies before firm conclusions about the underlying causes can be drawn.”

The group does rather boldly push back against “climate change,” the go-to answer for so-many environmental studies these days, with the observation that temperatures in the coastal waters of the Northeast Pacific have been “highly variable with only weak increasing trends over the past few decades.”

They also question the likelihood of food competition, an issue that keeps popping up again and again as Alaska manages its wild salmon for ever greater returns and the hatchery dumping off salmon into the North Pacific by Alaska and Pacific Rim nations steadily ratchets upward.

The paper does not, however, totally reject this possibility.

While it does not appear the billions of immature pink and chum salmon now being dumped in the ocean every year compete directly with Chinook, the authors write, the “indirect effect of increasing abundances of other salmonids on the prey base of older Chinook salmon in the ocean, for instance through impacts on other life-stages of the prey that are not targeted by Chinook salmon or through more complex food web linkages, cannot be ruled out as a potential driver of changes in age-size structure.”

Welcome to the puzzle.

4 replies »

  1. Come on, put the blame where it belongs…….. Having a trophy fishery on the spawning grounds where smaller kings are released and the big hogs are killed. Genetics are being selected by the sport fishery. Just like down south where 4 point or better restrictions on mule deer have produced huge 3x3s and fork horns because those are the genetics that allow a buck to live and breed. You want big fish, you have to let a good number of them survive to spawn instead of taking most of them out and allowing the smaller fish to do most of the breeding. The same thing seems to be going on the last few years at the main Bay hatchery with the reds. The smaller reds slip through the nets and are being used for spawners and now the reds there have shrunk in size.

  2. Craig,
    I would say, it is not just that “The once giant 4, 5 and 6 ocean fish aren’t all that big anymore”…
    I would say those species are no longer with us.
    The new kings are smaller, fewer in numbers, spend less time feeding in the ocean and may have been genetically “diluted” by breeding with hatchery stocks.
    It is a brave new world regarding our manipulated salmon stock from “fish ranching” procedures that have allowed for huge commercial harvests of hatchery pinks and reds.

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