High prevalence of anticoagulant rodenticide exposure in New England Fishers (Pekania pennanti).

Anticoagulant rodenticides (ARs) are increasingly recognized as a threat to non-target species including native wildlife. Fishers (Pekania pennanti) are generally considered deep forest inhabitants that are not expected to have high exposure to ARs. To evaluate the distribution and levels of ARs in fishers, we analyzed liver samples from fisher carcasses (N = 45) opportunistically trapped across Vermont and New Hampshire between 2018 and 2019. Liquid chromatography-mass spectrometry was used to detect and quantify 11 different ARs in the liver tissue of each fisher at the time of trapping. All but one sample analyzed were positive for exposure to ARs, and 84% were positive for more than one type of AR. The most prevalent ARs detected were diphacinone (96%) and brodifacoum (80%). No samples had detectable levels of coumachlor, coumafuryl, difenacoum, pindone, or warfarin. These results are mostly consistent with findings for fishers in California as well as with a variety of rodent specializing avifauna throughout the Northeast USA but, show a higher prevalence of exposure and a different distribution of AR types than other studies. These results help establish current baseline exposure to ARs in fishers in the Northeast USA and suggest that ARs could pose a threat to wild mesocarnivore species in this region.