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Proposed Salmon-Tagging Study Seeks Better Info On Lower River Sea Lion Predation
Columbia Basin Bulletin January 23, 2009
NOAA Fisheries' Northwest Fisheries Science Center is seeking funding, and regional approval, for a pilot study that could lead to a better understanding of the impact predatory seals and sea lions have on spawning spring chinook salmon in the lower Columbia River.
The research would involve netting salmon as they turn into the river at Buoy 10, outfitting them with PIT tags if they are not already so equipped, releasing the fish back into the river and then counting how many make it to Bonneville Dam, about 146 river miles upstream.
"It's a critical uncertainty that we need to know," said John Ferguson, head of the NWFSC's Fish Ecology Division. The agency's May 2008 biological opinion for the Federal Columbia River Power System includes a long list of actions for implementation that are intended to assure the Columbia/Snake river dams won't jeopardize the survival of 13 basin salmon and steelhead stocks that are listed under the Endangered Species Act.
The BiOp's "reasonable and prudent alternative" includes research aimed at learning what is limiting fish survival and what actions might work best to improve survival. RPA 69 directs the action agencies to "monitor the spatial and temporal distribution of sea lion predation attempts and estimate predation rates."
The BiOp says that "downstream of Bonneville Dam, the presence of the dam, in combination with increasing numbers of predacious marine mammals (especially California sea lions) in the tailrace of this project, has resulted in a substantial impact to adult spring-run Chinook and winter-run steelhead populations."
That phenomenon has been studied for the past seven years. The research was triggered because of a jump in pinniped numbers since the turn of the century. But little is known about level of predation from below the tailrace to the mouth of the river.
"… the proportion of adult migrants lost in addition to harvest between the river's mouth and Bonneville Dam (rkm 234) has never been measured in a scientifically rigorous manner," according to a "pre-proposal" narrative for the pilot study. "Until all sources of freshwater mortality have been estimated, total in-river survival cannot be precisely calculated and the information incorporated into fishery management decisions."
The proposed pilot study would employ lower river commercial fishermen using so-called tangle nets. The smaller mesh nets have been used in recent years in mainstem spring chinook fisheries because post-release mortality is lesser than with large mesh gill-nets.
The captured fish would be scanned for the presence of a PIT tag. If a tag is present, it would be recorded and the fish would be included in the study. If a PIT tag is not present one would be injected into the fish. A small dorsal fin tissue sample would be collected from each fish for genetic identification.
The passive integrated transponder tags, typically inserted in juveniles so their movement can be monitored for a variety of research purposes, hold information about the fish such as the tagging location, organization responsible for the tagging, species, run, weight, length, wild or hatchery type, marks and general health.
Fish would be held for a time in flow-through recovery tanks developed for the mainstem fisheries. Those fisheries require that fish without a clipped fin be released back to the river. The unclipped fish are, potentially, wild, listed salmon.
Since the fishing operations seem to attract pinnipeds in search of easy prey, the study fish would be ferried away from their original capture point before release.
The pilot study fish could be identified by an PIT-tag detection array in place in Bonneville's fish ladders.
"The objective of this initial investigation will be to provide a preliminary mortality estimate and estimate sample sizes required for a future, full-scale study," according to the narrative.
"We're trying to walk before we run," Ferguson said. "We'd use this first year to work out the techniques" that could be used in the future in more full scale studies.
NOAA has been fine-tuning and discussing the proposal internally and recently has sought input and support from other fish management and hydro entities.
Most have been "supportive of it in concept," Ferguson said.
"It's not going to be easy," the Washington Department of Fish and Wildlife's Bill Tweit said of the prospect of quantifying marine mammal impacts on salmon in the lower Columbia. "But getting a handle on it is a good idea."
As an example, last year state managers were encouraged when early fisheries produced relatively high catch rates, which is normally a sign that a strong run is in progress. But the actual return ended up well below the preseason forecast. Harvest cutbacks were forced to reduce impacts after managers realized the return was not as big as forecast.
Were sea lions a factor? Likely yes, but no one knows how much of a factor.
Tweit said a pilot project is the right approach, given the complicated technical issues involved.
"I think that's very sound. I do think it's possible to get a pilot out there" this spring, he said.
Ferguson said the pilot remains in the talking stages. Needed is buy-in from state and tribal fish managers and the action agencies -- the U.S. Army Corps of Engineers and Bureau of Reclamation, which operate the dams, and the Bonneville Power Administration, which markets power generated in the system and uses revenues collected from ratepayers to pay for fish and wildlife mitigation projects.
The preliminary cost estimate for the pilot study is $225,000. A funding source, or sources, had yet to be nailed down this week though the Corps has offered to furnish the needed PIT tags. It was initially hoped NOAA's BiOp implementation funding could be used but that appropriated source faces a 50 percent reduction.
Bonneville "is open to discussing it" but first wants its technical concerns about the pilot addressed, Ferguson said. The pilot project was discussed briefly at last week's system System Configuration Team meeting. The SCT is a multi-agency forum created to prioritize the spending of money appropriated for the Corps' Columbia River Fish Mitigation program. CRFM projects include research and capital projects at the dams intended to improve fish survival.
Three lower river fishermen have already volunteered to do the netting, Ferguson said.
Preliminary analyses indicates that between 80 and 380 adult PIT-tag detections will be required to provide the desired 5 percent margin of error in a survival estimate to Bonneville Dam, according to the project narrative. The goal would be to PIT tag between 500 and 1,000 adults at the mouth of the river. Sampling and tagging would occur one to three times per week from early March through late May.
"Mortality rates of salmon during this life stage could be substantial, particularly during years when adult returns, river flow, and turbidity are all low," the pilot study's narrative says. "This mortality is currently assigned by default to ocean residence during life cycle modeling activities because PIT-tagged adults are not detected until they begin ascending dams."
The end calculations would involve the subtraction of fish known to be lost in lower river harvests and those fish destined to enter tributaries or hatcheries below Bonneville Dam based on the genetic analysis. Handling effects on the fish, post-release mortality caused by the netting, natural mortality, straying and other factors must also be taken into account. The post-release mortality caused by the tangle nets has been estimated at 14.7 percent for chinook and 18 percent for steelhead.
The pilot study narrative notes that it "is estimated that more than 1,000 sea lions (mostly California sea lions) inhabit this reach at times during the spring migration period. These animals migrate as far upstream as Bonneville Dam where they hunt and kill large numbers of adult salmon in the dam's tailrace as the fish congregate before ascending the fish ladders."
The growing presence of California and Steller sea lions below the dam and documented salmon consumption there prompted the states of Idaho, Oregon and Washington to seek authorization under the Marine Mammal Protection Act to remove some of the pinnipeds in order to reduce predation. That authority was granted by NOAA Fisheries last spring but was never fully implemented, in large part because of a legal challenge brought by the Humane Society of the United States.
NOAA's FCRPS BiOp says the removal of California sea lions from below the dam is expected to increase the absolute survival of migrating adult spring-run chinook by 5.5 percent and of winter-run steelhead by 14.2 percent.
The ongoing research at the dam only charts observed predation on salmonids and other fish in the area within 0.5 mile below the dam.
Page Updated: Thursday May 07, 2009 09:15 AM Pacific
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