Study finds intersex bass near wildlife refuges in Northeast U.S.

Intersex small- and largemouth bass were found in waters near national wildlife refuges throughout the Northeast United States, according to a study from the U.S. Geological Survey (USGS) and the U.S. Fish and Wildlife Service (FWS). Of the fish tested, 85 percent of male smallmouth bass and 27 percent of male largemouth bass were intersex.

Intersex conditions—the presence of both male and female characteristics in an animal that should exhibit the characteristics of just one sex in its lifetime—occur when pesticides, pharmaceuticals or other chemicals disrupt the hormonal systems of an animal.

“It is not clear what the specific cause of intersex is in these fish,” said Luke Iwanowicz, a USGS research biologist and lead author of the paper, in a release. “Chemical analyses of fish or water samples at collection sites were not conducted, so we cannot attribute the observation of intersex to specific, known estrogenic endocrine-disrupting chemicals.”

Among the sites sampled were several locations in the Chesapeake Bay region, including near the Patuxent Research Refuge, Susquehanna National Wildlife Refuge and Rappahannock River Valley National Wildlife Refuge.

This study comes just after the release of a separate report from the Pennsylvania Department of Environmental Protection (DEP) and Pennsylvania Fish and Boat Commission identifying endocrine-disruptors, pathogens and parasites as the most likely causes for a decline of smallmouth bass in the Susquehanna River.

The USGS and FWS report, “Evidence of estrogenic endocrine disruption in smallmouth and largemouth bass inhabiting Northeast U.S. national wildlife refuge waters: A reconnaissance study,” is available online.