Caspian terns feeding on young fish have a significant impact on runs of steelhead in the Columbia River, research by Oregon State University suggests.
Through detailed analysis of steelhead survival and Caspian tern predation rates, the researchers found that the birds are not only preying on fish that would perish for some other reason, but are adding to the annual death toll by eating steelhead smolts that would have survived without tern pressure.
In scientific terms, the findings indicate that the terns are having an “additive” effect on prey mortality rather than a “compensatory” one.
The study was published recnelty in Ecological Applications.
In the Columbia Basin, 13 of 20 populations of anadromous salmon and steelhead are listed as threatened or endangered under the Endangered Species Act.
Caspian terns, a protected migratory bird species native to the region, have been the object of predator management in the Columbia Basin in an effort to protect smolts, especially steelhead smolts, from being eaten before they can swim downstream to the ocean.
The largest breeding colony of Caspian terns in the world was formerly on a small island in the lower Columbia River estuary between Oregon and Washington. It hosted more than 10,000 breeding pairs in 2008, just prior to implementation of nonlethal management to reduce colony size to between 3,125 and 4,375 breeding pairs.
“There has been little research, however, into whether reduced predation actually results in greater overall salmonid survival, either at the smolt stage, where the predation is taking place, or across the lifetime of the fish,” said Oregon State’s Dan Roby, professor emeritus in the Department of Fisheries and Wildlife of the College of Agricultural Sciences.
“Without clear evidence that reduced predation means greater survival to adulthood, management to reduce predator impacts would be a waste of time and resources.”
To tackle the question, Roby and collaborators at Real Time Research, Inc., of Bend and the University of Washington looked at 11 years’ worth of mark-recapture-recovery data for almost 80,000 steelhead trout smolts from the Upper Columbia population that were tagged and released to continue their out-migration to the ocean.
After release, the tagged fish were exposed to predation throughout multiple stretches of river on their journey toward the Pacific.
The tag-recovery data made possible estimates of the weekly probability of steelhead survival, mortality from being eaten by birds and death from other causes.
“This approach allowed us to directly measure the connection between smolt survival and tern predation,” Roby said.
Estimates of tern predation on steelhead were substantial for most of the years studied, he said. And increases in tern predation probabilities were connected with statistically significant decreases in steelhead survival for all of the years evaluated and both of the fish life stages studied: smolt out-migration and smolt-to-adult returns.
“Our results provide the first evidence that predation by Caspian terns may have been a super additive source of mortality during the smolt stage and a partially additive source in the smolt-to-adult life stage,” Roby said.
“A persistent pattern was clear: For each additional 10 steelhead smolts successfully consumed by Caspian terns, about 14 fewer smolts from each cohort survived out-migration.”
Another pattern: On average, for every 10 steelhead smolts eaten by terns, one fewer individual from each cohort returned to the Columbia Basin as an adult.
“Our model shows that mortality from tern predation was primarily additive and therefore has a credible, significant impact on prey survival,” Roby said.
“Predator-prey models need to consider additive effects of predation across life stages to avoid exaggerating potential benefits from management actions aimed at reducing predator populations to enhance prey populations. The primary value of the study is by analyzing the true effects of natural predators on populations of their prey, and thereby assessing the conservation value to prey of managing predators.”
Roby notes that the study by OSU, Real Time Research, and the University of Washington contradicts recently published research by scientists with the U.S. Fish and Wildlife Service and the Fish Passage Center, who found that steelhead mortality due to tern predation is compensatory.
That paper, in the Journal of Wildlife Management, suggests that “management efforts to reduce the abundance of the [tern] colonies are unlikely to improve the survival or conservation status of steelhead.”
Collaborating with Roby were corresponding author Quinn Payton, who has a doctoral degree from OSU, and others from Real Time Research, and Nathan Hostetter of the University of Washington.
The Public Utility District No. 2 of Grant County, Washington, the Bonneville Power Administration and the U.S. Army Corps of Engineers funded the research.
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General season archery elk hunters who were unable to hunt because they were displaced or personally impacted by wildfires may exchange their tag for a general season any legal weapon elk tag, the Oregon Department of Fish and Wildlife has announced.
The exchange option is available only to general season archery hunters who never had a chance to hunt during the 2020 season.
“Personally impacted” means living in an area that was evacuated due to wildfires or being a first responder, law enforcement, firefighter or utility worker who was unable to hunt. Having family and friends that were impacted or not being able to hunt a specific area does not qualify for a tag exchange.
To exchange an unused tag, fill out the following form: https://odfw.wufoo.com/forms/archery-elk-tag-exchange-form/ Hunters will be required to attest that they did not hunt during the archery season.
Archery elk hunters exchanging their tag will need to choose a tag for one of the following seasons instead (see the Big Game Regulations for more details about these seasons).
Rocky Mountain elk second season, Nov. 7-15 in some NE Oregon units (Bag limit: One spike elk)
Coast elk first season, Nov. 14-17 (Bag limit: One bull elk)
Coast elk second season, Nov. 21-27 (Bag limit: Bull or spike, see regulations)
Hunters are advised to begin this process as soon as possible and no later than Wednesday at 5 p.m. the week before the season begins. The form has deadlines for each of the tag exchange choices because the process will take at least a day and hunters need to pick up their new tag before the hunt begins. E-taggers will simply need to sync their app once the process is completed. Paper taggers can print the new tag from their online account or visit a license sale agent.
Other hunters personally impacted by the wildfires who were unable to hunt the 2020 season due to personal circumstances from the wildfires may be eligible for a refund of their tag. More information on when ODFW refunds for tag and preference points is available at https://myodfw.com/articles/2020-wildfires-impact-hunting-fishing-wildlife.
“It was a very tough September for Oregonians, and the direct human impacts have been dramatic,” said Linda Lytle, ODFW License Services Manager. “We wanted to offer this option to general season archery hunters who had their plans upended due to wildfires.”
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ODFW is asking successful forest grouse and mountain quail hunters to return a wing and a tail from each bird they harvest.
To find specific barrel locations see this map https://arcg.is/18uj5f or call the ODFW office closest to your hunt.
Biologists use the wings and tails to collect information on species, age, hatch date, recruitment and sex ratios of the birds. They’ll use this information to get a clearer picture of grouse and quail populations that will help determine hunting seasons. Since wing collections started in 1980, hunters have submitted more than 30,000 grouse wings!
Wing analysis is one of several surveys ODFW uses to monitor forest grouse and mountain quail populations in Oregon.