Scientists studying pink salmon in Alaska’s Prince William Sound have come to a startling conclusion: Female hatchery fish gone feral reproduce at only about half the rate of their wild cousins.
The finding, if confirmed by further studies, could have broad implications for the management of mixed stocks of wild and hatchery salmon.
Why hatchery fish perform so poorly in their natural environment is unknown, Alaska Department of Fish and Game biologist Chris Habicht said Friday.
The agency researcher cautioned, as well, that the latest finding is based on data from only one reproductive cycle. The dismal spawning success of hatchery fish during 2014-2016 could be a statistical anomaly. Future studies could find higher returns and even out the results when averaged over the years.
But at this time, the suspicion is that due to some mechanism or mechanisms unclear, wild fish out produce their domesticated cousins about two to one. Similar spawning differences, albeit smaller in scale, have been seen with Chinook and coho salmon and steelhead trout in the Pacific Northwest.
Many salmon stocks in the Northwest are depressed. As a result, efforts have been made to raise fish in hatcheries and release them into streams and rivers in hopes they will go wild and boost wild salmon numbers.
Scientists who spent six years studying reintroduced Chinook (king) salmon on the Cedar River in Washington state found the results of one such experiment complicated.
“Permitting hatchery females to bypass the dam and spawn seems to have been beneficial as they greatly increased the number of second-generation recruits,” the team led by Joseph Anderson of the University of Washington reported in “Evolutionary Applications” in 2012. “On the contrary, the demographic benefit of allowing hatchery males to enter was negligible because males were surplus to the needs of the females, and the return per spawner data indicated a fitness cost of 10 to 30 percent one generation after hatchery propagation. The long-term population consequences of
permitting the hatchery males to breed are more difficult to assess because our study design confounded the genetic and environmental effects of captive breeding.
“It is possible that the hatchery males simply were less successful at
acquiring mates, but did not transmit a fitness cost to their offspring relative to naturally spawned males. However, a similar study attributed the lower return per spawner induced by hatchery ancestry to genetic effects and these fitness costs carried over to the next generation of wild-born offspring.”
So-called “fitness costs” have never before been found to significantly affect the reproduction of pink salmon gone wild.
All look alike
Salmon are hard for the inexperienced to distinguish from each other in the ocean where they are all silvery torpedoes varying in size from a few pounds to almost 100 pounds.
Returning to freshwater as adults, however, some undergo significant physical changes. Male pinks develop a large, dorsal outgrowth that has given them the common name – humpback salmon or humpies. Male chum salmon grow large teeth that led to them be called dog salmon.
Salmon life cycles are as varied as their physical configurations as they move onto spawning grounds.
Kings, so named for being the biggest of the five species of salmon common to North America, spend a year in freshwater before going to sea for one to five years. Coho (silver salmon) and steelhead have similarly long life cycles.
Pinks, on the other hand, spend almost no time as juvenile fish in freshwater.
Now the most populous salmon in the North Pacific Ocean, pink salmon head for the ocean as soon as they emerge from the gravel into which they were spawned six to eight months earlier. They then spend 18 months at sea before returning.
Because pinks and chums need spend so little time in hatcheries before release compared to their longer-lived cousins, many fisheries biologists had thought the risks of domestication and loss of fitness for the wild were smaller for those fish, said scientist Ray Beamesderfer at Fish Science Solutions in Oregon. Beamesderfer has worked extensively in the Pacific Northwest and Alaska for more than three decades.
Habicht admitted to being a little surprised by what state scientists found in the Sound.
“There are two types of things that could be going on here,” he said.
One involves timing. It could be the hatchery fish are not genetically programmed to arrive at the best time for spawning or don’t spawn at the optimum time.
The other could be altered mating behavior or fitness that compromises the reproductive success of the hatchery fish.
The Alaska numbers on reproductive success are based on the number of hatchery and wild salmon spawning in five streams in the western Sound and the returns of offspring from those fish. Scientists can now genetically fingerprint the salmon to distinguish hatchery fish from wild fish.
Problem, no problem?
Both Habicht and Beamesderfer agreed there is still a lot to be learned about what this all means, most notably whether this was a one-time occurrence, a short-term issue related solely to hatchery strays, or a longer term problem that gets passed on to the young of salmon of hatchery origin and hybrids.
“Looking at the patterns among hatchery-hatchery, hatchery-wild and wild-wild crosses may go a long way to answering this question,” Beamesderfer said.
Habitch said the state is still in the early stages of years of study. The first goal of the study was to look and see if there were hatchery-related changes in the in-stream spawning success of pinks. That now appears to be the case.
The next question is to determine whether the changes truly means anything. Salmon in hatcheries have exhibited an amazing ability to quickly evolve to adapt to the hatchery environment. It is possible hatchery fish could do the same in reverse in the wild in just a few generations.
But even if that best-case scenario turns out to be what finally happenes, there is the existential question of why. Why do hatchery fish returning to their natural environment perform so badly?
“What kind of things may be causing that?” Habicht said. “We really want to know why.”
Meanwhile, there are practical implications the state agency must begin to consider.
Most of the salmon fisheries in the Sound are what are called “mixed stock fisheries.” Commercial fisheries prosecuted on mixed stocks harvest salmon bound for many different streams and rivers at the same time.
Fishery managers are left to juggle commercial openings so that enough salmon escape nets to meet what are called escapement goals for all streams. Those goals might need to be revised upwards in waters where fishery managers now have reason to believe the fish face an in-stream loss in productivity due to the poor performance of spawning hatchery strays.
Sorting out the mix could be complicated. A 2012 study of the Sound found that hatchery fish have wandered into three-quarters of the region’s streams, and in more than half the streams, the hatchery strays make up 10 percent or more of the total return.
The study published in Environmental Biology of Fishes at that time warned that “hatchery techniques can shift the timing of spawning such that progeny from hatchery-wild mating do not spawn at an optimal time for reproduction” – one of the reasons now cited as a possible explanation for the low returns for wild-spawning hatchery pinks.
The 2012 study also cautioned that escapement goals might need to be adjusted to account for hatchery fish spawning in the wild. The latest research adds some weight to these earlier hypotheses.
The timing could not be much worse for Sound hatcheries, a powerful economic engine in the region. In December, they had to fight off a petition to the state Board of Fisheries from the Kenai River Sportfishing Association and other outdoor groups that called for a cap on releases of hatchery salmon.
The sportfishing groups are worried about the straying of Sound pinks into Cook Inlet and the possibility that shrunken king and sockeye salmon returns are tied to their losing out to about 1.5 billion young hatchery fish in the competition to survive at sea.
Alaska, which banned the farming of salmon, is a world leader in the hatchery production and oceanranching of the fish. The Anadromous Fish Commission, a Pacific-wide salmon monitor, last year reported Alaska now releases more than five times as many fish as the states of Washington, Oregon, Idaho and California combined, and about two and a half times as many as the combined total of those states and the Canadian province of British Columbia.
Unfortunately, the fish renowned for faithfully returning to their place of birth to spawn, aren’t always such good navigators. Huge numbers of Sound pinks showed up in Cook Inlet, almost 150 miles from home in the Sound, in 2017. Hatchery pinks overwhelmed some streams in the Homer area. State geneticists found five streams in that area where the number of Sound pinks outnumbered native wild fish.
That alarmed some Kenai Peninsula residents, but the real worry is a fear that pink salmon could be displacing and reducing returns of Chinook, sockeye and coho in Cook Inlet.
Prized by anglers and dipnetters from throughout Alaska’s urban core and the mainstay of a commercial fishery bigger than the resource can support, those have become the most fought-over salmon in the state.
From 1985 to 1994 – as the Sound hatchery program was growing to near the size it is today – the commercial catch of sockeye (red) salmon in the Inlet averaged about 5.3 million fish per year, according to state fisheries data.
For the past 10 years, it has averaged under 2.9 million reds. Some of the reduction is attributable to increases in escapement goals for the Kenai River, the Inlet’s biggest sockeye producer. But even if that is accounted for, there is still a difference of nearly 2 million sockeye between the two 10-year averages.
The Fish Board’s hatchery committee is slated to meet in Anchorage on March 8 to dig into the hatchery issue again. Sound strays are one of the topics on the agenda.