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Study Shows Successful Reintroduction Of Oregon Chub Also A Genetic Success
Posted on Thursday, January 19, 2017 (PST)

Biologists have found that the reintroduction efforts of a little known fish – the Oregon chub –resulted in a genetically diverse population of the fish in the Willamette Valley, according to a recent study.


The Oregon chub plays an important role in the floodplain ecosystem in the Willamette River Basin as an important food source for predators, including both birds and mammals, according to corresponding researcher, Pat DeHaan, fish biologist with the U.S. Fish and Wildlife Service at the Abernathy Fish Technology Center in Longview, WA.


Once listed as endangered, the Oregon chub became the first fish species to be removed from the federal Endangered Species list after all of its recovery goals had been met. It was downlisted to threatened in 2010 and removed from the list altogether in 2015, all due to the efforts of a number of Willamette River basin partners.


“Introductions of new populations, such as the ones we included in our study, were a big part of this conservation success,” DeHaan said, adding that there were some important findings in the study.


“Overall, we found that the introduction program for Oregon chub was successful at creating populations with levels of genetic diversity similar to those observed in natural populations (this isn't always the case with introduced populations),” he said. “We also found that introduced populations with multiple sources had greater genetic diversity than populations introduced from a single source.”


Finally, he said, the study found that there were a number of genetic and demographic factors leading to the increased genetic diversity in the introduced populations, including genetic variation in the source population, the number of source populations and the number of founding individuals.


“Influence of Introduction History on Genetic Variation in Introduced Populations: A Case Study of Oregon Chub,” was published online October 7, 2016, in the North American Journal of Fisheries Management (


DeHaan’s co-authors are Brice Adams, fish biologist with the Service at the Abernathy Fish Technology Center; and Paul Scheerer and Brian Bangs, both fish biologists with the Oregon Department of Fish and Wildlife’ Native Fish Investigations Program in Corvallis.


Most naturally occurring populations of Oregon chub are found from the floor of the Willamette Valley up to 445 meters (1,460 feet) in the Coast and Cascade ranges in ponds, sloughs, oxbow lakes and low velocity creeks, according to the study. Their population declined in the 1970s and 1980s, mostly due to flood control operations, habitat losses and the introduction of non-native species. The fish was listed as endangered in 1993.


Population introduction was one of the measures taken for the chub’s recovery. The introductions, a closely monitored process according to the study, used hundreds of founding individuals and multiple source populations. Some 26 introductions have been established since 1988 and 21 are still viable populations.


Populations introduced from multiple sources had greater levels of genetic diversity than those populations introduced from single source, according to the study.


“If increasing genetic diversity for a threatened species is a goal of population introduction programs, these data suggest using multiple source populations will provide a means to achieve this goal,” the study says. There is a danger to combining multiple sources, however, and that is the “loss of co-adapting gene complexes through outbreeding depression.”


For future introduction programs, the authors suggest using multiple introduction strategies.


“We found that it’s important to consider a number of different factors such as genetic diversity in potential source populations, the number of donor individuals, and the number of source populations, when planning successful introductions,” DeHaan said. “We also demonstrated the usefulness of collecting genetic data before initiating population introduction efforts.”


Although some introduction programs avoid combining source populations because of genetic or logistical reasons, it could be a way to increase genetic diversity, the study concludes.


“This study provides a good example of how some of our lesser known fish species like Oregon chub can teach us conservation lessons that are pertinent to a number of threatened and endangered fishes and other species,” DeHaan said. “Introductions and re-introductions of threatened and endangered species are becoming more and more commonplace and this study helps provide information for biologists and managers planning future introduction efforts.”


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