Illegal marijuana farms threaten Californian fishers according to a new study published in the PLOS ONE journal on Wednesday. The research was trying to uncover reasons behind the high mortality of the species in California and discovered an unnerving cause.
Surprisingly, a very common cause of death turned out to be ordinary rat poison which the species is being exposed to. The fact that the animals were constantly being exposed to large quantities of rat poison in the middle of a remote forest habitat raised a few warning flags for scientists investigating the species.
The researchers performed necropsies on over 150 fishers between 2007 and 2014, at three different locations in California, in order to determine their causes of death.
While they found that predators such as bobcats and coyotes were responsible for 70 percent of the mortalities and that natural diseases were the second most common reason after that, accounting for an additional 20 percent of the mortality, they were left with a puzzling ten percent of deaths caused by poisoning due to exposure to common rat poison.
Although the poison isn’t a leading cause of death, up to 85 percent of the animals are exposed to it and traces of the chemicals can be found in their bodies eventually, even if the weasels end up dying due to a different cause. It is a troubling discovery as the fisher population is just recovering in California after a serious decline and is not stable yet.
Fishers are omnivorous weasels of medium stature that live only in forest habitats and the species has suffered major declines in the past as the animals used to be hunted for their fur during the 1800s and the 1900s. Although their numbers have risen in recent years, the species is still considered threatened in parts of the U.S. where the population is low.
In California, one of the existing two segments of fishers is listed as threatened under the California Endangered Species Act as it only contains 300 animals altogether. This is what prompted the research into the mortality of the weasels in the first place.
Scientists are now concerned about the deadly effects of the poison exposure, as data collected during the study shows this exposure might increase in following years. After a presentation on the findings, the team was approached by local police officials that helped them solve the mystery of the poison’s presence in the middle of the forest.
The authorities explained that illegal marijuana farms use rat poison in order to protect the crops. Lead author of the study Mourad Gabriel later accompanied police on raids to such locations and verified the use of rat poison in such places.
The weasels either eat the poison directly or eat a smaller animal that consumed it, thus suffering from its ill effects.
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