Invasive Species are Greatest Threat
by Matthew Preusch
Most discussions about the causes of declining salmon runs focus on the four H's: habitat, hatcheries, harvest and hydropower. But the most important factor may be an I, as in invasive species.
That's the conclusion of a new report from the National Oceanic and Atmospheric Administration's Northwest Fisheries Science Center in Seattle.
You can see a PDF of the report here.
The study, which was published in the journal Bioscience, is sure to be controversial because much of the Northwest's multi-billion dollar salmon recovery work is centered on improving habitat, mitigating the damage of power-producing dams and curtailing commercial or recreational fishing.
This report argues the greatest threat to fish are non-native species like crappie or bass that can eat up juvenile salmon as the make their way downstream from their birthplace to the ocean.
"On a per-run basis, the mortality attributed to (invasive species) predation may be similar to that associated with juvenile passage through each of the eight dams on the Columbia and Snake rivers, estimated at approximately 5% to 15% per dam," the study says.
"These non-natives are here -- we're not going to get rid of them," said the report's lead author, Beth Sanderson. "But they are managing the native predators, and in my opinion, that means we could manage non-native predators."
Another interesting tidbit from the study: The spawning population of non-native American shad in the Columbia River is about 5,000,000, five times more than the annual salmon run on the river, but "no studies have quantified the impacts of shad on salmon ecosystems."
Sanderson said a greater amount of the money dedicated to the 13 salmon stocks in the Northwest listed as threatened or endangered should go to battling invasive species.
And at least one longtime salmon advocate agrees.
"There's no question that invasives are a major threat, right along with hydropower and a loss of habitat," said Jim Martin, former chief of fisheries for the Oregon Department of Fish and Wildlife.
Martin cautions that working on invasives shouldn't come at the expense of addressing the effects of dams and habitat loss, as well as the growing threat of climate change.
COMMENT Posted by JBarleycorn on 03/05/09
Interesting article. The authors' findings aren't terribly surprising, but I'm glad they took the time to look at the impact of non-native fish on native salmonids. I've been studying the Columbia River salmon problem for years and always wondered why no one had bothered to take a serious look at the impact of bass, catfish, shad, and other non-native fish on native salmonids. Surprise, surprise, surprise, it ain't good. Of course you won't see anti-bass stickers next to the anti-sea-lion stickers on the bumpers of jacked up 4x4 trucks. Hypocrisy runs deep in the so-called "sportsman" subculture.
That said, the headline is misleading. Turning the Columbia River into a system of reservoirs has encouraged the proliferation of non-native predators. It's hardly "either or." It's both. Take out the dams, take out the predators.
Hopefully some day we'll start taking an honest look at the irrational, unsustainable mixed-stock ocean fishery. Not as sexy as shooting sea lions, though, and it doesn't make a very good bumper sticker....
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