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Researchers Think Salmon Recovery Must Weigh “Native” Invader Impacts, As Well As Invasive Species’
Posted on Friday, October 12, 2012 (PST)

So-called “invasive” or “nonnative” species – plants and animals that cause disruptions in the natural way of things when introduced to a new environment - have policy makers and scientists struggling for answers.

And so do “native invaders,” a term that includes such creatures as northern pikeminnow, Caspian tern and even species of trout that have always called the Columbia River basin home. Those native species’ environmental role can change, because of a variety of factors, and can cause problems for their longtime neighbors, such as Pacific salmon.

“Human alteration of ecosystems may drive native species to invader status, causing ecological and economic damage rivaling that of non-native invasive species,” according to an article published last month.

“Native invaders - challenges for science, management, policy, and society” was published in the September edition of the scientific journal Frontiers in Ecology and the Environment. The article was initially published online June 15.

Lead author is Michael P. Carey of NOAA Fisheries’ Northwest Fisheries Science Center in Seattle and, until recently, the U.S. Geological Survey’s Alaska Science Center in Anchorage. Other authors include Beth L. Sanderson and Katie A. Barnas, also of the NWFSC, Julian D Olden of the University of Washington, School of Aquatic and Fishery Sciences, Seattle.

The article can be found at:

http://www.esajournals.org/toc/fron/10/7

Species that have made the transition from native to native invader – such as the terns, pikeminnow, marine mammals and rainbow trout - cause complications for “the development and implementation of countermeasures in science, management, society, and policy as a result of conflicting goals from diverse human interests,” the article says.

“These species are in the spotlight because each poses a substantial predatory threat to imperiled Pacific salmon (Oncorhynchus spp) listed under the ESA,” the article says. The researchers examined native invaders in the Pacific Northwest in an attempt to illustrate the scientific, management, societal, and policy challenges that arise when native species become invaders.

“By identifying the process by which native species become invasive, resource managers may garner support from policy makers and the public for mitigation and control activities to alleviate ecological impacts.

“Recovery strategies need to explicitly address the invasive effects of a native species because the nuances of spatial and temporal impacts differ from those of non-native species,” the article says.

Native invaders tilt their home environment by spreading within their historical range, attaining extreme abundances, and exerting severe per-capita effects as a result of predation or competition.

“Historically, Caspian terns lived in small colonies scattered throughout inland portions of the PNW (Suryan et al. 2004) but more recently, substantial numbers relocated to artificial habitat – created by dam construction and waterway dredging – in the Columbia River Basin,” the paper says. Such artificial islands provide excellent nesting habitat, thanks to the stable water levels that result from flood control measures, and the absence of native predators. Hatchery produced salmon smolts, as well as wild listed fish, provide a convenient food base.

As a result, the Columbia estuary tern colony has become what is believed to be the world’s largest. And each spring the birds eat millions of young salmon and steelhead that are migrating toward the ocean.

With rainbow trout – one of the region’s favored angling targets – good intentions can go awry.

“The economic value of recreational fisheries only serves to place further pressure on resource managers to increase the distribution and abundance of game species regardless of harmful effects,” the article says.

“When stocked into new systems within their natural range, which includes the U.S. Pacific Coast (from Alaska to Mexico) and the eastern coast of Asia, rainbow trout inflict invasive ecological impacts, including the extirpation of native amphibians,” according to the article’s authors. “For example, from 1918 until 1973, the U.S. National Park Service stocked rainbow trout in fishless lakes in Mt. Rainier National Park in Washington State. These stocked trout devastated native food webs by causing a trophic cascade, and primary producers (diatoms) have yet to recover in these lakes, even decades after fish removal.

“In addition, management agencies regularly supplement existing rainbow populations with larger individuals to artificially enhance density and/or size structure, resulting in elevated competition with and predation on other native species.

“Stocking rainbow trout also creates genetic concerns for wild trout; introgression (gene flow from one species into another species or subspecies by hybridization and backcrossing) of hatchery origin rainbow trout with wild populations may reduce the fitness of the wild populations.”

The construction of dams and resulting creation of reservoir habitat on the mainstem Columbia has led to high abundances of pikeminnow, which in turn has resulted in higher predation on salmon. Likewise the construction of dams, Bonneville Dam in particular, has resulted in higher concentrations of fish in certain areas, and higher capture efficiency for sea lions, the paper says.

To date, “there has been no systematic examination of the importance of native invader impacts.” That needs to be done, the researchers say.

“The next step for determining a quantitative threshold for native invaders would be to improve researchers’ ability to identify native invaders and develop mitigation strategies. Overall, a more comprehensive view of native invaders, one that considers multiple processes and ecosystems, is necessary to improve conservation and management efforts for native species.

“Science can provide valuable information to guide policy decisions; however, policy makers need to communicate with scientists in order to make decisions under these conflicting goals. Clearly, policy conflicts will be the most contentious when they present mutually exclusive choices, pitting the scientifically supported need for control against the economic and recreational benefit of the human activity responsible for creating the native invaders,” the paper says.

“Frontiers in Ecology and the Environment,” issued 10 times per year, consists of peer-reviewed, synthetic review articles on all aspects of ecology, the environment, and related disciplines, as well as short, high-impact research

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