Study Finds Causes for Mutant Bass in Susquehanna River

Pittsburgh Post-Gazette - 15 December 2015
By Don Hopey

The Susquehanna River’s decade-long mutant bass mystery moved a cast closer to a solution with the release of study findings that for the first time identified herbicides and endocrine-disrupting compounds from agricultural sources as likely causes.

The multi-year study released Monday by the state Department of Environmental Protection and the Pennsylvania Fish and Boat Commission also found that pathogens and parasites are probable contributors to the mutations and population decline afflicting what was once one of the best bass fisheries in the eastern U.S.

“This study does not identify a single smoking gun. But it does point the way toward likely causes, which we will continue to pursue,” said DEP Secretary John Quigley, who said the complexity of the lengthy river system has challenged researchers.

The Susquehanna River flows from upstate New York, south through Pennsylvania’s agricultural middle, and Maryland, and is the largest source of fresh water entering the Chesapeake Bay. It’s also a major source of agricultural runoff containing phosphorous, nitrogen and sediment pollutants, and natural animal hormones in manure, which could disrupt bass reproduction. 

“The study is important because it admits that the river is sick and that the bass are sick,” said Fish and Boat Commission executive director John Arway, who has worked on the issue since 2001, when fingerling bass populations in the river declined precipitously.

The small bass population crashed again in 2005, and the DEP and the commission began to identify older bass with tumors, round sores and lesions.

“We could have said in 2005 that parasites and pathogens were likely causes,” Mr. Arway said, “but now to say that herbiicides and endocrine disrupting compounds are also scientifically likely causes is the new thing and a big step.”

The next step is to identify the sources of those endocrine disruptors and herbicides, and follow up with a long-term, mandatory plan to reduce them in the river, Mr. Arway said.

“We know where the herbicides are being applied most heavily and we know that exposure to them is depressing the immune systems of the bass,” Mr. Arway said. “We’re inching closer, but the DEP is still not willing to say its the [farm] nutrients reaching the river.”

Researchers also must determine how the herbicides from farms, roadside weed spraying and lawn application interact with naturally occurring, normally benign bacteria and pathogens, said Neil Shader, a DEP spokesman. He said the DEP is seeking to widen streamside buffers next to farm fields to reduce runoff of herbicides.

“Somehow those parasites and pathogens have been turbocharged,” Mr. Shader said, “and are proving to be lethal to those bass.”

Don Hopey:, 412-263-1983 or on Twitter @donhopey