Death by poisoning of the forest-dwelling creatures soars to more than 200 percent.
Pity the poor fisher. First of all this member of the weasel family suffers the unfortunate fate of having fur that we humans apparently like to wear. Fisher pelts have been valued for fashion since the 18th century and over the years trapping these cat-sized animals has taken a fluctuating toll on their numbers. Strike one. But who could have ever predicted the predicament that California’s relatively rare forest-dwelling fishers (Pekania pennant) are in now?
A newly published study in the journal PLOS One reveals that fishers have become victim to increased poisoning deaths to the tune of a 233 percent increase compared to 2012. The toxicants are associated with illegal marijuana farms tucked into public and tribal lands in Northern and Southern California.
As TreeHugger reported in 2012, previous studies have showed that rat poisons were being found in the tissues of fishers when they were nearby illicit pot farms Northern California and the southern Sierra Nevada. This new study looked at the deaths of 167 fishers, which revealed that poisoning accounted for 10 percent of all fisher deaths. In all 85 percent of the fishers were found to have been exposed to rat poison, and generally the exposure was to multiple types of poison. In two cases, never-before seen rodent poisons (cholecalciferol and bromethalin) were to blame.
"We know that a 10 percent change in mortality rate is enough to determine whether fishers in California are able to expand their population size or not," says Dr. Craig Thompson, a wildlife ecologist and one of the authors of the study. "Now we know that rodenticide poisoning alone is enough to keep fisher populations suppressed in the state, even without accounting for the fact that low doses of these poisons also cause the animals to be lethargic and susceptible to disease, which in turn increases the potential for other sources of mortality."
The U.S. Fish and Wildlife Service recently proposed putting fishers on the list in California, Washington and Oregon as threatened under the U.S. Endangered Species Act. Meanwhile, the California Department of Fish and Wildlife has listed fishers in the southern Sierra Nevada as threatened under the California Endangered Species Act.