Post-release survival of translocated fisher: implications for success

Post-release survival of translocated fisher: implications for success

Conservation Northwest / Feb 10, 2022 / Fishers

Bucking the norm, juveniles are beating survival odds, and the reintroduction of fisher to Washington is looking strong.


Research article originally published January 24th, 2022 – The Journal of Wildlife Management – The Wildlife Society

Jeffrey C. Lewis | Kurt J. Jenkins | Patricia J. Happe | David J. Manson | Paul C. Griffin

Fisher face in snow in West Virginia. Photo: Forest Wander

It is one of those Sunday mornings where the mountain air is brisk and effervescent. With their boots crinkling against the soft ground, researchers hike along the beaten path on a field study. They leave behind roads and signs of human activity, checking their radio tracker frequently. They start to slow. Just a bit further, they say. From a distance, there! They spot a long, dark, weasel-like figure scurrying along with their recent offspring through the forest understory. The researchers jot down some notes of the surrounding den conditions and mark their location. For a short while, they admire these elusive carnivorous mammals before watching them dart away.

By now, you might already be familiar with the fisher (Pelania pennanti). Contrary to the name, they rarely eat fish. The fisher population once roamed the coniferous forests of Washington and North America. But the high price and desire for fisher pelts in the late 1800s led to their imminent decline, essentially eradicating them throughout the Washington landscape.

Since 2002, we have partnered with the Washington Department of Fish and Wildlife (WDFW), the National Park Service (NPS), and other government, Tribal, and non-profit allies to restore fishers to Washington state. Although rare to witness conservation translocations successfully re-establish a self-sustaining population, the persistence and widespread distribution of fisher over the last two decades have proven to be very promising.

All rights reserved to the Journal of Wildlife Management and the Wildlife Society. Lewis et Al.

Recent findings determined that both reproduction and survival rates of post-release fisher match those of established resident populations in other parts of the species’ range. Essentially, they are doing great in their new home!

Of the cohort of 90 fishers that were reintroduced to the Olympic Peninsula from 2008 to 2010, only 35 mortalities were reported. The primary cause of death was due to natural predation. The other 40 percent of individuals lost were split between roadkill and other indeterminable factors. Future management strategies can use this data on mortality sources to identify safer, more optimal areas for recovery.

Counter to previous reports of resident fisher populations, survival rates were greatest among juveniles and males instead of adults and females, respectively. This outcome can be due to the lack of competing males in the reintroduced population area, relative to the resident populations where territorial defense is more present. Additionally, post-release adults may have already developed habitat preferences less favorable in new conditions, whereas juveniles were more likely to adapt to their new environments right out of the box.

That said, neither the translocation process itself nor the duration in captivity had a statistical impact on a fisher’s chance of survival. Looking ahead, translocation design may now consider prioritizing the release of female fisher near established areas where juvenile males are present to recalibrate the reintroduced population with more natural breeding opportunities.

The fisher reintroduction program in the Olympic Peninsula is most exciting for researchers to follow in real-time. It provides opportunities to further study the factors that influence species’ survival and optimize wildlife conservationists’ translocation efforts.

These recent findings indicate that the scientific parameters and management set throughout our fisher reintroduction have made important contributions towards their viability in the region. As we continue to track their growth, maybe all fisher in the Olympic Peninsula will soon be recognized as just another resident fisher.

Read more on the Fisher Reintroduction Program in Washington:

Fisher up close. Photo: USFS