Rat poison being used by those growing marijuana illegally is killing wild animals and threatening rare populations of fishers in Sierra Nevada, according to a study published in the journal PLOS ONE.
Researchers from the University of California, Davis, studying threats to two populations of fishers in California discovered commercial rodenticides in dead fishers near Redwood National Park and in the southern Sierra Nevada in and around Yosemite National Park, leaving them to conclude that fishers were picking up the poison at marijuana growing operations in the area.
“Our findings were very surprising since non-target poisoning from these chemicals is typically seen in wildlife in urban or agricultural settings,” said lead author Mourad Gabriel, a UC Davis Veterinary Genetics Laboratory researcher and president of the Integral Ecology Research Center. “In California, fishers inhabit mature forests within the national forest, national parks, private industrial and tribal community lands – nowhere near urban or agricultural areas.”
Fishers, relatives of minks, martens, otters and wolverines, are considered a “sensitive species” and have been named as candidates for the endangered species list in California, Oregon and Washington. Their populations have dropped dramatically in past decades thanks to trapping, predator control programs and development, but the current threat of being poisoned out in the wilderness hadn’t really been a consideration before.
For the study, researchers trapped, collared and released fishers and then compared their movements with known marijuana growing sites. Of the 58 fisher carcasses tested 79 percent were exposed to one or more anticoagulant rodenticide.
These poisons are commonly used for pest control and in growing operations, but their effects aren’t always immediate. Second-generation poisons can kill with one dose, but may take up to a week before signs start showing and animals die of internal bleeding. Before then, they’re more vulnerable to dying of other injuries that may have been minor, or predation.
It’s unclear in this case if the fishers are eating poisoned prey, or if they’re going after the poisons directly, but researchers noted that the deaths they documented in different areas fell between mid-April to mid-May – prime planting season – and also pointed out how this could effect fisher kits who are born at that time and are more vulnerable to losing their mothers who they are dependent upon for survival.
Concerns were also raised about how these poisons would affect other carnivores, including the Sierra Nevada red fox, American martens, wolverines, gray wolves or raptors, such as northern spotted owls, California spotted owls and great gray owls.
“If fishers are at risk, these other species are most likely at risk because they share the same prey and the same habitat,” said Gabriel. “Our next steps are to examine whether toxicants used at illegal marijuana grow sites on public lands are also indirectly impacting fisher populations and other forest carnivores through prey depletion.”
Unfortunately, these rodenticides aren’t just a threat to fishers and their prey, but continue pose risks to wildlife, pets and people wherever they’re used.
Please sign and share the petition urging major retailers to pull d-CON, one of these deadly poisons, from their shelves.
Photo credit: National Park Service