Although there is no recent evidence to prove that the Pacific fisher still survives within the local Stanislaus Forest, CSERC staff periodically receives credible fisher sightings from people with strong backgrounds in wildlife and biology. The staff continues to search for the fisher in remote river drainages or hard-to-access forest habitat that meets fisher needs. If fishers do persist in scattered areas in the region, the local population is clearly very small and at high risk. Any additional stressor such as rodenticide poisoning could mean the difference between survival or potential recovery. The grow site shown above is typical of many areas where poison baits are discovered on national forest land in California. Scientists working to study fishers in the Sierra and Sequoia National Forests and in the National Parks of the southern Sierra have learned a great deal about the fisher over the past decade. One focus of their studies of radio-collared fishers has been to identify causes of mortality (such as predation by mountain lions and bobcats or deaths caused by vehicle strikes along busy roadways). A few years ago, one researcher found a fisher staggering around as if drunk. The fisher died, and toxicology analysis proved that the fisher had been exposed to highly toxic rodenticides (most likely from a pot plantation grow site).
Since then an expanded study of rodenticide impacts on the fisher has led to alarming discoveries. Some fishers that have died have been proven to be killed solely by rodenticide poisons, but large numbers of fishers killed by predators have been shown to have significant levels of rodenticide in their systems. Did the poison in their system cause them to be disoriented or otherwise incapable of evading a predator? On November 4th, a new study (Gabriel et al., 2015) was published in PLOS One. That paper details how recovered fisher carcasses were subjected to a complete necropsy to determine the cause of death and whether they exhibited indications of infections, disease, or poisoning. Thirteen fishers in the two California fisher populations were determined to have died of toxicosis that was likely associated with marijuana cultivation. The study also showed that rodenticides are posing an increasing threat to fishers in California. Since fishers are omniverous, they not only may suffer from feeding on poisoned prey, they may also be attracted directly to the poison baits. In addition, due to the diversity of poisons being spread across many areas of national forest lands, there is high potential for synergistic or additive effects to magnify the toxicity when fishers are exposed to multiple kinds of poisons.
The bottom line is that needless fisher deaths are being caused by poisoning from illegal rodenticide use on public forest lands. The lack of rodenticide clean-up by agencies at discovered marijuana grow sites poses an significant threat to not just the fisher, but to other wildlife species as well on public lands. It is up to CSERC members and others to raise the issue with key policiticians and the media to attempt to get speedy removal of toxic chemicals from sites on public lands