Transgender bass fishing

"Intersex" male bass found throughout protected Northeast US waters

By Brian Bienkowski for the Environmental Health News

Eighty-five percent of male smallmouth bass tested in or nearby 19 National Wildlife Refuges in the U.S. Northeast had signs of female reproductive parts, according to a new federal study.

The study, led by the U.S. Geological Survey and U.S. Fish and Wildlife Service, also reported that 27 percent of male largemouth bass in the testing sites were intersex.

The study is the first of its kind in National Wildlife Refuges and adds to growing evidence that endocrine disrupting chemicals are getting into U.S. lakes, rivers, streams and reservoirs—no matter how protected the waters seem. And such contamination seems to affect the reproductive development of some fish species, which can lead to threatened populations.

For the bass in this study, those considered “intersex” either had a protein that is used to make egg yolk typically found in females, or immature egg cells in their testes, said co author Fred Pinkney, a biologist with the U.S. Fisheries and Wildlife.

“The eggs were in the very, very early stages,” he added.

But any change to fish reproductive systems could possibly threaten overall fish populations and ability to properly reproduce.

During the fall seasons of 2008 to 2010, the researchers tested a total of 118 male smallmouth bass from 12 locations and 85 percent were intersex. They tested an additional 173 male largemouth bass from 27 sampling sites and 27 percent were intersex.

It’s not entirely clear why the bass were intersex as the researchers did not test the waters for specific chemicals, said lead author Luke Iwanowicz, a research biologist with the U.S. Geological Survey.

However, the suspected culprits of the sex changes are endocrine disrupting compounds.

This includes hormones, industrial chemicals and pesticides that are or mimic estrogen hormones. These compounds enter rivers and streams via permitted effluents, stormwater and agricultural runoff, and wastewater treatment plants, where excreted birth control and natural estrogens pass through relatively un-altered.

The study is just the latest to find intersex fish in U.S. waterways and builds on a U.S. Geological Survey study in 2009 that showed intersex male fish in nine U.S. river basins, though that study didn't include Northeast basins. The bass tested in the Northeast waterways had a higher prevalence of intersex than the fish in the 2009 study. 

It seems that certain fish species may be more sensitive to estrogenic compounds than others, as evidenced by the disparity between largemouth and smallmouth bass in this study. Previous studies also have reported that smallmouth bass seem more susceptible to intersex changes.

However it’s not clear if this is actual physical sensitivity to the chemicals or if it’s due to some species spending more time in more contaminated habitats.

National Wildlife Refuges are areas protected by the U.S. Fish and Wildlife Service. There are more than 560 such refuges nationally.

The national refuges tested spanned from eastern Ohio up to Maine and included: the Patuxent Research, Susquehanna, Montezuma, Great Swamp, Wallkill River, Great Meadows, Assabet River, Rappahannock River Valley, Mason Neck, Back Bay, John Heinz, Erie, Cherry Valley, Great Bay, Lake Umbagog, Sunkhaze Meadows, Missisquoi, Moosehorn and Ohio River Islands refuges.

Pinkney said the bass indicate that many aquatic species in Northeast U.S. refuges may be exposed to estrogenic chemicals.

“The U.S. Fish and Wildlife Service encourages management actions that reduce runoff into streams, ponds and lakes—both on and off of refuge lands,” he said.
 

For questions or feedback about this piece, contact Brian Bienkowski at bbienkowski@ehn.org.