Invasive Species Threaten Salmon in Pacific Northwest

Posted Mar 2, 2009 by Bob Ewing
A study published in the March 2009 issue of BioScience concludes that nonindigenous species pose a threat to native salmonids.
Salmon and other native fish of the Pacific Northwest, most notably salmonids, are considered threatened or endangered. Hundreds of millions of dollars are spent annually on researching their populations and on amelioration efforts.
To date, the majority of the funding has been directed toward studying the impacts of habitat alteration, hatcheries, harvest, and the hydrosystem--the "all-H's." However, a study published in the March 2009 issue of BioScience concludes that nonindigenous species may pose at least as much of a threat to native salmonids, principally through predation, as the all-H's do.
Beth L. Sanderson, of the Northwest Fisheries Science Center in Seattle, and two colleagues drew these conclusions after assembling all known occurrence and distribution records for nonindigenous species found in roughly 1800 square kilometers of hydrologically connected areas throughout Washington, Oregon, and Idaho.
The spatially explicit database they compiled from these records indicates that nonindigenous species--the majority of which are plants and fish--are present in all of those connected areas, and number as many as 486 in some watersheds.
The status of freshwater aquatic fauna is especially dire, in particular, nonindigenous fishes compete with or prey on native fishes, posing a serious threat to the persistence of the natives.
The researchers assembled reports of predation by 6 of the 60 nonindigenous fish species found in the region: catfish, black and white crappie, largemouth bass, smallmouth bass, walleye, and yellow perch. These aggressive, introduced predators consumed hundreds of thousands to millions of juvenile Pacific salmonids at just a handful of sites, and, for some of the species, salmonids constituted a large fraction of their diet.
Despite the clear evidence that invasive fishes have a substantial impact on economically important salmonids, only a very small percentage of research funding is devoted to examining the threat that nonindigenous species pose to native communities.