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18,000 spring Chinook cross Bonneville in single day; sea lion numbers, predation spike upward

18,000 Spring Chinook Cross Bonneville In Single Day; Sea Lion Numbers, Predation Spike Upward

Posted on Friday, May 02, 2014 (PST)

A host of spawning spring Chinook salmon arriving at the lower Columbia River’s Bonneville Dam has coincided with a rush of sea lions eager for a feast.

Chinook passage substantially increased the past two weeks to a total 79,874 Chinook and 3,867 steelhead this year through April 30. That is now higher than the past three years, but about average for the past 10 years to date, according to a bi-weekly report prepared by U.S. Army Corps of Engineers researchers at the dam.

The study, ongoing since 2002, aims to evaluate marine mammal feeding habits below the dam and potential impacts on salmon and steelhead stocks that are listed under the Endangered Species Act.

A single day high of 17,972 salmonids passing on April 30 is the third highest one day total seen since 2002. That passage total included 17,409 adult Chinook salmon as well as 519 Chinook jacks and 43 steelhead.

Total sea lion salmonid catch by sea lions through April 30 (2,456 expanded by interpolating for weekends) has doubled in the last two weeks.

The actual sea lion catch observed by researchers so far this year includes 947 taken by California sea lions and 756 taken by Steller sea lions. Also observed taken have been 53 steelhead, 73 white sturgeon (all but one by Steller sea lions) and 163 fish whose species could not be identified.

“It is now slightly above average for all the years we have observed,” the report says of this year’s salmonid consumption by predators.

The sea lions, mostly males, forage up and down the coast in winter and spring with some swimming up the Columbia to take advantage of returning smelt (eulachon) and salmon and steelhead runs. Most leave the river by late May as their mating season approaches.

“Predation and abundance really increased over the past 2 weeks, but it may be slowing down some now as a few individuals appear to have moved back down to Astoria,” according to Robert Stansell, who heads the sea lion research at the dam.

The total number of Chinook taken below the dam by sea lions has tripled from the number reported two weeks earlier.

According to the report, the states of Oregon and Washington trapped six California sea lions this week that were eligible for removal as part of a federally approved effort to reduce predation on salmon below the dam. The removal program has been in place for much of the past six years as part of authority granted by the states under Section 120 of the Marine Mammal protection Act.

This year’s removals now total 15. The animals were euthanized. Only California sea lions that have been identified as preying on salmon and made numerous visits to the dam are eligible for removal. The authorization does not allow removal of Steller sea lions

Through 2013, wildlife managers removed a total of 58 California sea lions – 13 of which were sent to zoos and aquaria – that met the federal criteria.

Things really picked up the past couple of weeks, “as the spring Chinook run began to increase rapidly,” the report says. About 60 California sea lions (Zalophus californianus – CSL) have been seen at Bonneville so far this year, and 24 of those are returning individuals.

“This is similar to 2010, when more ‘new’ CSL were seen at the dam than returning individuals. So far, we have been able to identify a maximum of 27 CSL present on any one day.

“Steller sea lion (Eumetopias jubatus - SSL) numbers have also picked up these past two weeks but are still averaging much less than the past three years. The maximum number of SSL seen any day so far this year was 41. We have documented approximately 53 different SSL’s visiting the dam so far. All but 20 of the SSL have been confirmed as seen in past years, although there are likely more new individuals.”

The Corps research reports

Columbia Basin Bulletin The Columbia Basin Bulletin e-mail newsletter is produced by Intermountain Communications of Bend, Oregon and supported with Bonneville Power Administration fish and wildlife funds through the Northwest Power and Conservation Council's Columbia Basin Fish and Wildlife Program. Articles republished by The Dalles Chronicle with permission.


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