JWM: Fisher reintroduction going well in Olympic Peninsula

In the mid-1900s, fishers were extirpated from Washington state, despite being found historically in various parts of the U.S. Pacific Northwest. But high demand and prices for their pelts in the late 1800s and early 1900s led to overharvesting of the medium-sized weasels. That, in addition to heavy logging in old growth forests and loss of habitat connectivity due to human development, put an end to the species in the state as well as many populations in the region.

“That was the perfect recipe for extirpation from a region or a state,” said Jeff Lewis, mesocarnivore conservation biologist at the Washington Department of Fish and Wildlife.

The animals persisted north of the border in British Columbia, and a couple of remnant populations held on in Oregon, Idaho and Montana. Starting in 2008, the Washington Department of Fish and Wildlife, the National Park Service, Conservation Northwest and other partner organizations began translocating healthy fishers trapped in central British Columbia to Washington state. The state department worked with the British Columbia Ministry of Environment & Climate Change Strategy, paying private trappers above market value for fishers. Veterinarians checked the fishers (Pekania pennanti) before transporting them to the Olympic Peninsula where they were released.

Ninety individuals were ultimately moved from 2008-2010 with the intent of creating a founding fisher population. Nearly all of them were released with VHF location transmitters, while a handful of animals had surgically implanted transmitters and five males had satellite collars.

Wildlife biologist Patti Happe from Olympic National Park releases a translocated fisher. Wildlife Biologist, Olympic National Park. Credit: Coke Smith

In a study published recently in the Journal of Wildlife Management, Lewis and his colleagues analyzed the fishers’ survival in the Olympic Peninsula. The transmitters typically have a lifespan of two years, giving researchers information on fishers from 2008 to the end of 2011.

The information told researchers that the fishers traveled a lot after initial release. Lewis said that to the animals, it was as if “you just dumped them on Mars—they probably don’t know how to think of this area yet.” He added that moving around in unfamiliar territory can result in more danger to fishers. “They have to do some basic reconnaissance.”

However, the juvenile fishers moved farther after the reintroductions than adults. This was surprising, the researchers said, as studies of native established populations tend to show the opposite with fishers in the wild that have not been reintroduced—adult females had the lowest survival rates compared to juveniles. Usually in the wild, juveniles have lower survival than adults in established populations as they move more while searching for their new home territory. They are also caught in traps and harvested more often as they move about where trapping occurs.

The researchers believe that juveniles have higher survival in this reintroduced population may be because young fishers that haven’t had the chance to get used to their previous environment in British Columbia adapt better to their new environment. “That may give them a leg up,” he said.

Adults, on the other hand, are used to a different area and spend more time trying to apply what they learned about habitat selection and prey in their original territories. The temperate rainforests of the Olympic Peninsula are quite different from the sub-boreal forests of central British Columbia.

“All the things they learned there might not apply to the new place,” Lewis said, adding that in some ways they have to start all over again.

It’s important to take this into account when conducting reintroductions, Lewis said. Where possible, it might be worth translocating more juveniles than adults. Though since the younger fishers don’t reproduce right away, it’s still worth including some adults. So far, the trapping efforts have naturally produced more juveniles than adults anyway.

Overall, fisher survival was highest during the first year after the reintroduction and lowest in the second. The third year showed intermediate survival. The researchers don’t know why, and Lewis said these results could just be due to a relatively low sample size. But wildlife managers are still detecting fishers from the first reintroductions, and their descendants, a decade later. Wildlife managers first detected reproduction in 2009, as they reported in 2019.

“Those survival rates were sufficient to start a self-sustaining population,” Lewis said. “This population has persisted—it’s not done growing.”

A fisher peeks out of its enclosure before reintroduction. Credit: Coke Smith

Lewis and his team determined the cause of death for 24 of the fishers they recovered. Of those, predation accounted for 40% of the deaths, while 20% died from vehicle strikes

Lewis said information gleaned from the Olympic Peninsula reintroduction has already been taken into consideration in other translocation projects into the North and South Cascades.

For example, in the Olympic Peninsula, Lewis said the animals they reintroduced were spread too thinly between nine areas they believed had optimal habitat for fishers. That meant the fishers may have struggled to find each other in the beginning. Lewis said it would have been better to release them closer together “so it’s hard for them to avoid each other,” then let them spread out naturally to other areas.

“We were worried more about keeping them out of fights than them finding each other during the mating season. It was a rookie mistake and I wish I would have done it differently,” he said, adding that they later released fishers in the Cascades closer together.

“We think it’s paying off too,” he said of the Cascades reintroductions. “There’s no way that these animals missed each other.”

This article features research that was published in a TWS peer-reviewed journal. Individual online access to all TWS journal articles is a benefit of membership. Join TWS now to read the latest in wildlife research.

Header Image: A fisher jumps through the snow. Credit: Ken and Mary Campbell