WWETAC Projects

Project Title:  Prevalence of rodenticide in fishers in the Sierra National Forest: ecological implications of illegal marijuana cultivation on public lands in the western United States.

Principal Investigators
: Kathryn Purcell, Research Wildlife Biologist; Craig M. Thompson, Research Ecologist, USDA Forest Service Pacific Southwest Research Station, Fresno, CA


Collaborators: James Baldwin, Statistician, USDA Forest Service Pacific Southwest Research Station; Mourad Gabriel, Doctoral student and veterinary pathologist, University of California at Davis; Richard Sweitzer, Research Professor, University of California at Berkeley

Key Issues/Problem Addressed:      

Currently, Sierra National Forest law enforcement estimates that thousands of pounds of toxins, including rodenticides, pesticides, herbicides, and fertilizers, are being used and/or abandoned on the Sierra National Forest each year in conjunction with illegal marijuana cultivation. Hundreds of cultivation sites have been found and reclaimed on the Sierra National Forest over the past ten years, and law enforcement estimates hundreds more remain undetected. Similar rates of contamination are seen in other national forests and national parks throughout the western United States. The toxins used at these sites, many of which are banned within the United States, represent a significant threat to wildlife due to the lethality, potential for bioaccumulation, and the fact that they are being used without regard to regulations governing quantity applied, proximity to streams or other water sources, and combining multiple compounds.

Setting and Approach:         

The spatial and temporal overlap between the Kings River Fisher Project and the Sierra National Forest / High Sierra Trail Association marijuana cultivation site reclamation efforts provides a unique opportunity to begin evaluating the impact of toxins on wildlife in Sierra National Forest.  Fisher (Martes pennanti) are a species of great regional conservation concern, and they are exposed to these toxins both directly (eating flavored bait) and indirectly (eating poisoned rodents). Furthermore, as mesocarnivores they are subject to predation by larger animals such as bobcats and mountain lions. Exposure to toxins could easily make a fisher more susceptible to other causes of mortality such as predation or disease, thereby masking the presence of the toxin and their influence. 

Specifically, we propose to overlap data on individual fisher home range and exposure rates with the locations of marijuana gardens and the primary toxic compounds found at each site in a spatially-explicit analytical framework. We will examine whether the presence of marijuana cultivation sites impacts an animal’s probability of survival and whether animals encountering cultivation sites are more likely to be exposed to toxins.

Progress to Date:

To date, we have completed necropsies on 47 fishers, testing for the presence of anticoagulant rodenticides (ARs). Forty of the samples (85%) tested positive. Home range and movement information is available for 37 of these animals. Analyses indicate that survival is lower for animals whose home ranges overlap cultivation sites.  A peer-reviewed manuscript summarizing these findings and outlining potential implications is in preparation.

This work will help raise awareness of the threat posed by illegal marijuana cultivation on public lands. While focusing on fishers, the work has broad applications to a number of management issues including endangered species conservation, water quality, and public safety.