TWS2022: Fishers in northeast exposed to rodenticides

When researchers were studying fisher survival and reproduction in New York state using radio collars, they noticed individuals that were otherwise healthy had died from relatively minor injuries or failed to recover following routine handling. When they tested their livers, the scientists found high levels of rodenticide.

“It’s pretty well known that fishers are exposed to rodenticide on the West Coast,” said Georgianna Silveira, a master’s student at the SUNY College of Environmental Science and Forestry. “But populations there are different than the Northeast. In the Northeast, fisher populations are larger and more stable.”

Silveira presented research at the recent Annual TWS Conference in Spokane, Washington looking at rodenticide exposure and population trends among fishers throughout the Northeast. That wide view is important, Silveira said, because the source of rodenticide exposure is unknown. “Looking at a region-wide scale, we can come up with the large-scale, repeatable patterns of exposure sources,” she said.

Silveira also had some personal reasons for wanting to conduct the research. Before starting at SUNY ESF, she worked for a municipal government on plans that often used rodenticides. She became interested in the effects of the chemicals on other wildlife in the ecosystem. “I found out about this project, and it fit perfectly with my previous experience,” she said.

To conduct the research, Silveira tapped into fishers (Pekania pennant) that were legally harvested by fur trappers in several northeastern states and tested a subset of their livers for rodenticide.

One benefit to using trapped fishers rather than collecting carcasses that were found dead naturally is that the latter could have higher rates of mortalities as a result of being exposed to rodenticide, since they’re already dead. The trapped specimens are more representative of the potential rodenticide exposure in the standing or live populations, she said.

So far, Silveira’s preliminary results have suggested that the wildland-urban intermix, where houses dot the otherwise forested landscape, is driving rodenticide exposure in fishers. “This is interesting and useful in future regulations for development when there are concerns about protecting wildlife,” Silveira said. “It looks like proximity to built environments, specifically structures, not agricultural buildings, are driving exposure.” In addition, the issue seems to arise in more isolated areas that are surrounded by wild land.

To see if rodenticide exposure impacts fishers on the population level, Silveira looked at historical harvest data and population trends and compared that with rodenticide exposure. “The initial results from that were kind of concerning,” she said. “We saw a pretty strong relationship between predicted probability of population declines and predicted rodenticide exposure.”

But Silveira noted that the research needs yet to take into consideration additional factors that could affect fisher populations. “Other things are potentially threatening the species, like increasing development and changes in habitat quality,” she said, adding that fishers rely on old-growth forest.

If additional research does show a correlation between fisher death and rodenticide, Silveira said, it would provide a strong impetus for more public campaigns regarding rodenticide use. “It’s challenging when you make changes to regulations to get everyone on board,” she said. “But if we see increasing concern about impacts on wildlife, I think people will be receptive to it.”

Header Image: Fishers in the northeastern U.S. have been exposed to rodenticides. Credit: ForestWander Nature Photography