Furry fishers, don’t blame the Gold Rush

The boom in logging and fur trapping triggered by Gold Rush settlement of the Sierra Nevada has long been blamed for the steep decline in California’s population of fishers.

But a new study concludes that the small forest animal was in trouble long before hordes of settlers started trapping them and chopping down the old growth trees they nest in.

Comparing genetic material collected from contemporary wild fishers with DNA extracted from bone and pelt samples dating from the 1880s to 1920s, researchers from the U.S. Forest Service and the University of Montana didn’t find any significant difference in diversity. “This suggests that a population reduction, and its concurrent reduction in genetic diversity, occurred prior to the dates of the historical samples,” they wrote in a study recently published in the online journal PLoS One.

In California, the cat-sized animal exists in two isolated populations, one in the state’s northwest and the other in the Southern Sierra. Though the steep, sparsely populated Southern Sierra may have acted as a fisher refuge from Gold Rush activities in northern and central parts of the range, the authors concluded the state’s fisher population took a sharp dive more than 1,000 years ago.

That period coincides with the Medieval Warm Period, a time of severe, prolonged drought that the researchers speculate may have caused the population to drop.

The findings could have implications for recovery efforts for the fisher, a member of the weasel family that is a candidate for listing under the federal Endangered Species Act.

Noting ongoing debates about whether biologists should introduce fishers to new areas to spur more genetic diversity in the small Southern Sierra population, the authors cautioned that “the results of this study show that both populations have persisted in isolation far prior to the European settlement of California. Therefore, attempting to restore connectivity between them would be inconsistent with the historical record and run the risk of losing local adaptations that evolved in each population.”