Researchers create tool to help protect native fish from hybridizing with non-natives

Oregon State University researchers have created a tool to assess the risk of hybridization between native and non-native fish, a development that could help natural resource managers trying to protect endangered freshwater fish species or endangered.

The introduction of non-native species poses challenges to native species, including competition for resources and habitat, exposure to diseases carried by introduced species, and the risk of hybridization, which occurs naturally in populations. wild as part of the evolutionary process.

The Oregon State research, just published in the journal Frontiers in Environmental Science, focusing on two species: bull trout, a fish native to western North America that is protected under the Endangered Species Act; and brook trout, native to eastern North America, introduced to the West more than 100 years ago for recreational fishing.

Bull trout were once abundant in Oregon, Washington, California, Nevada, Idaho, and Montana, but today are found in less than half of their historic range and no longer exists in California. They are threatened by the degradation and fragmentation of habitats, the blocking of migratory corridors, poor water quality, the effects of climate change and fisheries management practices, including the introduction of brook trout.

Although some studies have documented hybridization between bull trout and brook trout, there has not been enough research to allow natural resource managers to quantify the risk of hybridization, said Oregon State researchers.

“The goal was to provide a tool that would allow managers to consider potential long-term impacts when planning restoration or conservation projects,” said Michael Manning, lead author of the paper which has worked on the research as a researcher from Oregon. State graduate student.

The researchers developed a hybridization risk model, which could also be applied to other species that hybridize in freshwater, such as cutthroat or rainbow trout and coho and chinook salmon.

Guillermo Giannico, freshwater fish ecologist and co-author of the paper, compared the model to programs people use to decide where to live.

“In this case, there’s this algorithm that combines information about the distance to the nearest supermarket, the cost of living, where the schools are,” he said. “This risk model we created is pretty much the same. It tells you if it’s a good neighborhood for fish based on the slope of the stream, from the substrate to the bottom of the stream. of water, water temperature, water flow changes throughout the year.”

In Oregon, 55% of bull trout habitat is in the northeastern part of the state, in the John Day and Powder/Burnt River basins. Additional Bull Trout habitats are located in the Malheur/Owyhee, Klamath, Deschutes, Willamette Valley, and Columbia River watersheds.

The researchers studied 47 sub-basins, a US Geological Survey term for a subsection of a river drainage area. The sub-basins encompass an average area of ​​approximately 1,125 square miles. Of the sub-catchments they studied, 11 had only bull trout, 16 had only brook trout, and 20 had both species.

In Oregon, brook trout occur in 9.8% (120 miles) of bull trout spawning habitat. The model showed that an additional 57 miles of bull trout spawning habitat would be at extreme risk of hybridization if brook trout were introduced to these areas.

The model also identified 13% (177 miles) of all bull trout spawning habitat as being in the moderate to extreme hybridization risk category. Of those 177 miles, 90% is in northeastern Oregon.

The researchers note that the model is valuable because of its ability to identify hybridization risks in small stream sections (at the 100-meter scale), that brook trout already exist in the Bull Trout spawning habitat or lack thereof.

This level of detail allows natural resource managers to identify individual stretches of watercourses that may be candidates for brook trout removal, to model the potential risk of hybridization if brook trout flat is reintroduced or incorporate brook trout introduction or expansion scenarios, they said.

The other co-authors of the paper are Ivan Arismendi and J. Andres Olivos, both of the Department of Fisheries, Wildlife and Conservation Sciences at the Oregon State College of Agricultural Sciences.

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