There is a new predator in the forest these days. It has arisen quietly over the years. Any wildlife feeling hungry when they come upon it in the Sierra is vulnerable. This predator is amazingly small for the scope of its damage; it can’t run fast or climb high.

This new predator is rodenticide in pellet form, used in violation of all safe-use regulations in our national forests by large-scale marijuana growers. Rodenticides are being used to protect young and tasty marijuana seedlings from wildlife roaming through the forest looking for a meal. Chemicals never meant to be used more than 50 feet from homes are now scattered across forest hillsides. Piles of poisons are left around hundreds of plants even though only a few pellets can be lethal. Miles of water pipe are lined with these pellets to protect the stolen water source. Camps are circled with pellets to protect human food sources and sleeping areas.

University of California scientists originally became aware of this problem when Rick Sweitzer, associate professor in the Department of Environmental Science, Policy and Management at UC Berkeley, and his wildlife research team retrieved a radio-collared fisher whose cause of death was unclear. Sweitzer and his team are researching are studying the fate Pacific fishers as part of the Sierra Nevada Adaptive Management Project (SNAMP).

Necropsy (an autopsy for animals) of the fisher carcass by Mourad Gabriel of UC Davis and the Integral Ecology Research Center found rodenticide poisoning to be the cause. With these new findings, the livers from previous fisher mortalities in the SNAMP study were reexamined for evidence of rodenticide exposure. They discovered that more than 80 percent of dead fishers examined had been exposed to rodenticide. These toxicants can persist in animal tissues or the environment for potentially hundreds of days. At least five dead fishers found by researchers in SNAMP and a second fisher study in northern California have been confirmed to have died of rodenticide poisoning, the scientists reported in the science journal PlusOne.

Considering the hundreds of marijuana grow sites found every year on public lands, the scale of the damage to California’s natural resources may be unprecedented. Grow sites are also found containing massive amounts of fertilizers, herbicides and pesticides, all of which are being used without concern for run off or aquatic species nearby. Marijuana plants are removed from these plots when found, but these chemicals are often left behind.

Although this problem might seem overwhelming, there are efforts to address it. The non-profit Environmental Reclamation Team has cleaned up hundreds of grow sites since 2005. They remove and document all of the poisons found along with the miles of plastic irrigation line and piles of trash. More efforts like this are needed if we are to maintain rare animals like the Pacific fisher as well as all the other species who have the potential of coming in contact with these poisons.