Prevalence of toxins in fishers on the Sierra National Forest resulting from illegal marijuana cultivation

Project Description

Sierra National Forest law enforcement estimates that thousands of pounds of toxins, including rodenticides, pesticides, herbicides, and fertilizers, are being used or abandoned on the Sierra National Forest (NF) each year in conjunction with illegal marijuana cultivation. Hundreds of cultivation sites have been found and reclaimed on the Sierra NF over the past 10 years, and law enforcement estimates that 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 owing to their lethality and 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 in combination.

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 on the Sierra NF. Fishers (Martes pennant) are a species of great regional conservation concern. 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 toxins 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 affects an animal’s probability of survival and whether animals encountering cultivation sites are more likely to be exposed to toxins.

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.

Purpose and Scope

To test for the presence of toxins related to marijuana cultivation in the mesocarnivore Martes pennant (fisher) on the Sierra National Forest. We will then examine whether the presence of marijuana cultivation sites affects an animal’s probability of survival and whether animals encountering cultivation sites are more likely to be exposed to toxins.

Methods

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 affects an animal’s probability of survival and whether animals encountering cultivation sites are more likely to be exposed to toxins.

Key Findings

To date (2011), 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.

Project Deliverables

Peer reviewed manuscript