Op-Ed: Rodenticides have devastating impacts fishers
June 19, 2024 | By Jennifer Lovett 
Fisher. Photo courtesy of Vermont Department of Fish & Wildlife
As a conservation biologist, I am alarmed about recent data concerning the impact of anticoagulant rodenticides on Vermont’s wildlife. These chemicals are commonly used to kill rodents in urban, rural, agricultural, industrial, and suburban locations. These toxins work by preventing blood from clotting and causing fatal internal hemorrhaging. Anticoagulant rodenticides poison wildlife in two ways: when a targeted animal eats the bait and dies several days later, or when a predator or scavenger eats prey that has eaten poisoned bait. Secondary poisoning has been documented in birds of prey like eagles, hawks, and owls, as well as mammals like foxes, fishers, bobcats, and coyotes.
Fishers belong to the weasel family, are native to North America and closely related to the American marten, an endangered species in Vermont. As top predators, fishers eat small to medium-sized mammals, fruits, nuts, berries, reptiles, and amphibians. They are territorial, elusive, solitary, prefer dense forested habitat and nest hidden in the cavities of large trees. Fishers are extremely sensitive to human-caused environmental disturbances and a healthy fisher population is the sign of a mature and well-balanced forest ecosystem. But fisher populations appear to be declining in New England due to habitat loss and fragmentation, recreational trapping, and the use of rodenticides.
Rodenticide poisoning of non-target wildlife is a significant conservation concern. Recently, multiple studies conducted across the country and in Canada have demonstrated that fishers, among other predators, are highly impacted by anticoagulant rodenticides and that these toxins pose a threat to their populations. As a keystone and indicator species, declining fisher populations is a real cause for alarm. The impact of these toxins on other species is equally concerning.
A 2023 study focused on the prevalence of anticoagulant rodenticides exposure in fishers in New England. Biologists from the Vermont Fish & Wildlife Department were among the researchers who found that 98% of the Vermont fishers in the study tested positive for anticoagulant rodenticide compounds. Results demonstrated that fishers “are highly exposed to a wide spectrum of [anticoagulant rodenticides] across Vermont.” The authors stated, “the near universal exposure of the fishers sampled suggest that [anticoagulant rodenticide] exposure is widespread and represents an underestimated health risk to wild fishers.” The data included in Vermont Fish & Wildlife’s 2023 furbearer newsletter indicates that the fisher population is in decline.
In another study, conducted by researchers at SUNY Environmental Science and Forestry, fishers from five northeastern states were tested and Vermont had the highest incidence of anticoagulant rodenticide exposures with 100% of the fishers testing positive. The researchers found that “rodenticide exposure is an important driver of population decline.”
Regulations associated with anticoagulant rodenticides are aimed at protecting children and domestic pets from accessing poisons. Consequently, they are most often placed outside buildings in ready-to-use or refillable bait stations/containers making poisoned prey accessible to wildlife. Despite EPA regulations on the use of commercial rodenticides, they are still available online to anyone. Unlawful use is a serious problem and several states have recently introduced legislation to restrict or ban certain anticoagulant rodenticides.
Fishers are critically important to Vermont's ecosystems and data suggest rodenticides may play a large role in their decline. According to Audubon Vermont, there are more than 175 rat poison products available on the open market, which do not pose the same level of risk to rodent-predators. In addition, many basic non-lethal preventative measures can reduce rodent infestations. A ban on the use of anticoagulant rodenticides would be environmentally beneficial and a moratorium on fisher trapping would add needed protections for this vulnerable and important species.
A former art museum curator and art teacher, Jennifer Lovett is a conservation biologist living in Starksboro.