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Managing Snake River Steelhead With A-Run, B-Run Dichotomy: Is There A Better Way?
Posted on Friday, August 11, 2017 (PST)

As they set harvest limits on steelhead fisheries in the Columbia and Snake rivers, managers have long used timing, the number of the fish crossing dams and the length of the fish as their yardsticks. According to a recent study, this technique for fisheries managers may be an oversimplification and even out of date.

 

Typically A-run steelhead arrive in the river earlier and are shorter (less than 78 centimeters: about 31 inches) than the later arriving B-run steelhead (longer than 78 cm) that are thought to be heading to the Snake River.

 

Although that dichotomy has been useful in the past to make quick decisions about fisheries, the study says it is not useful for conservation.

 

“The boilerplate descriptions of A and B steelhead groups are not 100 percent right, which hinders the achievement of fisheries management goals based on those characterizations,” said researcher Timothy Copeland, fisheries program coordinator for the Wild Salmon & Steelhead Monitoring Program with the Idaho Department of Fish and Game. “Further, those categories gloss over the diversity that exists among some very different populations. For conservation considerations, which include assessment of diversity, simple categories are not useful at best and counter-productive at worst.”

 

Now, he continued, “genetic techniques have been developed that can provide timely information to fisheries managers and address conservation needs; managers in the Columbia Basin should consider how to incorporate this information into the management structure. This would address one of the classic fisheries management problems: how to manage weak stocks in mixed-stock fisheries.”

 

“Life History Diversity of Snake River Steelhead Populations between and within Management Categories” was published online in the North American Journal of Fisheries Management (http://www.tandfonline.com/doi/abs/10.1080/02755947.2016.1264506?journalCode=ujfm20).

 

Copeland’s co-authors are Michael Ackerman, fisheries biologist, Kristin Wright, fisheries biologist, and Alan Byrne, staff biologist, all with IDFG.

 

Although steelhead management has long been based on the number of fish passing mainstem dams along with a fish’s length, Copeland said there has more recently been a quest by fisheries management agencies to be more specific about wild steelhead in the Snake River basin.

 

“Our goal was to pull together some of that information to compare and contrast the life history diversity of Snake River steelhead populations in the wild,” he said. “We looked at length, run timing, age, and sex ratio. There were differences that roughly accord with the A/B categories but there was a lot of overlap. Interesting trends were present in all of those characteristics but we found a gradient of life history features rather than a sharp break.”

 

The study says there is “a continuum of life history diversity in wild Snake River steelhead populations, which makes simple categorization fraught with error. Although the run-type dichotomy was the best means available for the management of Columbia River fisheries in the past, it is not useful for monitoring population status, assessing ESA recovery plans, and tracking progress toward delisting from the ESA.”

 

It pointed to new tools and methods such as parentage-based tagging and genetic stock identification, all offering a finer resolution of population abundance and diversity.

 

The researchers found that both A and B populations of steelhead produce fish under 78 cm in length and fish that return later, after August 25, according to the study, but few A-run steelhead were larger than 78 cm. The mean percentage of steelhead that stayed for two years in the ocean for the A-run population was 52.1 percent, while the percentage for the larger B-run fish was 82 percent, and some stayed three years.

 

Copeland said that it was not clear how the current management structure for steelhead in Columbia River fisheries was created and how it came to be applied to conservation assessments in the Snake basin.

 

“I found that surprising, considering the importance of some of the decisions based on it,” he said. “Apparently, in the 1990s, several potential ways to distinguish steelhead stocks were on the table but only the length category scheme could be applied in a manner timely enough for fishery management. When Snake River steelhead were listed under the ESA, there were few useful datasets, so dam counts by length were then used for very different purposes. That has created a lot of confusion about the meaning of A and B when you are talking about steelhead.”

 

The abundance of wild and hatchery steelhead is important when managers determine allowable harvest, which for sport and nontribal commercial fishing is up to 2 percent of the impact on wild A- and wild B-group fish, while it’s 13 to 20 percent for tribal fisheries, the study says.

 

The allowable tribal harvest rate for non-ESA listed fall chinook is 21.5 percent to 45 percent – fish that are harvested while steelhead are present – so it is important that the assessment of the steelhead groups be “accurate to achieve salmon harvest objectives and to protect vulnerable wild steelhead populations,” the study says. “In actuality, these two objectives compete.”

 

The “dismal” return of both A- and B-run steelhead this year is “likely caused in large part by the poor ocean conditions we’ve had off the Pacific Coast over the last few years,” Copeland said. “The implications of this study bear on how steelhead populations should respond to a bad year. Populations with a younger age structure tend to respond more quickly when conditions get better because it doesn’t take as long for them to reproduce. But there is a risk of loss of genetic diversity or even extinction when things are bad.

 

“Older populations have a more diverse age structure, which spreads risk, but they tend to respond more slowly when conditions are good,” he said, referring to B-run fish. “Steelhead are pretty resilient but hopefully there won’t be two or more bad years in a row to give that a definitive test.”

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