What risk do hatchery fish pose to Prince William Sound’s pinks?

By August 30, 2018 September 4th, 2018 Fisheries, Southcentral

Pete Rand pulls otoliths from a pink salmon on Hartney Creek near Cordova. (Photo by Aaron Bolton/KBBI)

Recently, an argument over whether hatcheries are causing more harm than good has been heating up. The debate is nothing new, but an Alaska Department of Fish and Game study is about to take a step toward answering a question central to the debate: do hatchery fish that spawn with wild populations pose a threat to those stocks?

Pete Rand, a research ecologist with the Prince William Sound Science Center, is explaining to a group of new field staff how to sample pink salmon carcasses on the banks of Hartney Creek just outside of Cordova.

Rand picks up one of several pinks lined up on the rocks in front of him and cuts just behind its gills before using a pair of tweezers to tear off a tiny piece of its heart. Then, he cuts into the skull or “brain case” as he calls it and extracts two white otoliths, or ear bones. They’re smaller than the head of a pin.

An otolith after its pulled from a pink salmon carcass. It’s smaller than the head of a pin. (Photo by Aaron Bolton/KBBI)

“I put my fingers in the eye socket and you basically want to take the top of the head off,” Rand said as his knife crunched into the decomposing skull of a pink salmon.

Under a microscope, Fish and Game will be able tell from the ear bones if each fish was raised in a hatchery.

In just a few days, three field crews will travel to five remote streams on the western side of the sound where they will repeat this ritual thousands of times.

“We sample from the very beginning of the spawning season all the way to the end, and we sample daily,” Rand said. “The objective there is to sample as many of the spawning pink salmon as we can.”

This study and previous work has shown that the closer a wild stream is to a hatchery, the more likely hatchery fish will stray into that system. Rand says some streams near Prince William Sound’s four major pink salmon hatcheries can see high stray rates, varying from 70 to 90 percent each season.

The big concern is that when those strays spawn with wild fish, they’re passing on genes that could reduce future generations’ genetic fitness. In other words, does having a hatchery originated parent influence a wild salmon’s ability to survive in nature?

“That’s the ultimate question we’re trying to get at with this field project,” Rand said.

To answer that question, the samples are shipped to Fish and Game’s genetics lab in Anchorage. Any heart tissues belonging to hatchery fish are discarded, but the ones from wild pinks are processed.

“We take a small piece of that heart and then put it in a tube, add a bunch of chemicals, go through a bunch of different reactions and pull out the DNA,” said Chris Habicht, who manages the lab.

He explains that after about a week of processing, his team can identify lineages of wilds pinks and fish with varying degrees of genes passed down from hatchery stocks.

A pink salmon otolith under the microscope. The dark bands represent unique marks made by increasing the water temperature for timed intervals before hatchery fish are released into the wild. (Image courtesy of Alaska Department of Fish and Game)

The number of returning offspring each family tree produces will indicate whether hatchery fish reduce the productivity of the wild stocks they spawn with. But that’s about as far as the answers will go.

“If we do find a difference between these natural-origin, hatchery-origin fish in terms of how many progeny they produce, we won’t know what the mechanism for that difference is,” Habicht noted.

While that may be a step forward in Fish and Game’s eyes, the study has its critics, who argue the project, which received a large chunk of funding from hatchery operators and processors, is biased. Critics’ main issue with the project is that it doesn’t include a control stream with little or no hatchery influence to compare results to.

Bill Templin is Fish and Game’s chief fisheries scientist. In his Anchorage office, he acknowledges some of the study’s shortcomings.

“It’s very difficult to find a control,” he said. “What we did though is controlled for high stray-rate streams and low stray-rate streams. So, you get some idea of a contrast.”

Templin says what the study does provide shouldn’t be overlooked. He says the results will be valuable to the department and the Board of Fisheries when hatcheries request production increases or other permit changes.

But he cautions against any notion that this study will spark a major shift in hatchery management. He said it’s just a first step and that the results alone might not be the best way to answer the question at the heart of the hatchery debate.

“Questions of how much is too much or whether there’s harm or not are very difficult to answer,” Templin noted, “because they also require human valuation, human judgement. That has to be worked out in a different venue than in a scientific study. “

Those decisions may play out on the Board of Fisheries, which is scheduled to hold its first work session on hatcheries in October. However, it may do so without any results from Fish and Game’s hatchery-wild study. The first report is due in December.

For the curious and informed.

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