Fishers and Rodenticide

Anticoagulant rodenticides are commonly used to control rodent populations. However, other wildlife can be accidentally exposed either by consuming the bait or by eating the poisoned rodents (secondary toxicity).

In 2017, ten fisher livers collected in 2013 and 2014 and stored in the CWHL wildlife tissue bank were tested for the presence of anticoagulant rodenticides. Tissue bank samples are collected from animals submitted for either cause of death determination or training purposes in necropsy workshops or fur school demonstrations. Samples were tested for the most common compounds including chlorophacinone, diphacinone, warfarin, brodifacoum, bromodialone, difenacoum, and difethialone. 

The majority of the samples tested positive for brodifacoum, followed by bromodialone and diphacinone. Of the seven samples that tested positive for rodenticide, three of them were positive for more than one type. Because there is only one rodenticide in any one commercial product, it shows that these animals are being exposed multiple times over a short period to these compounds.

The toxicity of rodenticides is dependent on both the dose and the susceptibility of the species. Unfortunately, such toxicity data is not available for wildlife species. However, levels were high enough in two samples to suggest that rodenticide poisoning could be the primary cause of death.

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