Don Cosden, assistant fisheries director with the Maryland Department of Natural Resources, said the finding of intersex largemouth bass on the Shore was "a little surprising," since the condition had seemed limited mainly to smallmouth bass in the Potomac and Susquehanna watersheds.
Cosden said largemouth and smallmouth bass populations declined in Shore rivers several years ago after drought made the water saltier, forcing the fresh-water fish farther upstream. There'd been no reports of die-offs or illness — until lately, when officials discovered a virus particular to largemouth bass in rivers on the Shore and in the Potomac.
The UM researchers did check some Shore streams, Yonkos said, but didn't find many intersex fish. Then again, he said, they didn't find that many male largemouth bass.
Roger Tragesar, president of the Maryland Bass Federation, said his group's members are concerned about reports of intersex bass, but still unclear what if anything they may mean to the health or abundance of the fish. "I don't think we're flip-flopping or losing a lot of sleep over it just yet," Tragesar said, "but we certainly want people to stay focused on it and do everything they can to determine why this is happening."
Intersex smallmouth bass were first detected by accident in the Potomac River seven years ago as scientists were investigating fish kills and lesions there. The same intersex condition turned up subsequently in fish in the South Branch of the Potomac, the Shenandoah and the Monacacy.
Vicki S. Blazer, a U.S. Geological Survey scientist who found those intersex fish, this year found the trait in smallmouth bass caught in the Susquehanna River and in the Juniata River. Biologists had noted a drop in young smallmouth bass in that watershed in recent years.
Intersex fish appear to be fairly widespread, though. A U.S. Geological Survey study published last year found male fish with eggs in their testes in nine rivers nationwide. The trait was most common in the Southeast, and particularly in bass.
"The largemouth and smallmouth bass do seem to be more prone to the condition," said Jo Ellen Hinck, lead author of that study. "But we're not sure why. We do not know what is causing it."
Scientists suspect that the intersex fish may be linked to contaminants found in rivers, streams and lakes. Researchers have been able to induce the condition in fish by exposing them to a wide variety of chemicals or mixtures that act like hormones and can disrupt an animal's development, reproduction or immune system.
Among the suspected contaminants are pesticides, pharmaceuticals, personal care products and animal waste. They have all been widely found in water ways, though researchers have yet to prove any connection with the intersex condition, reproductive problems or illness in fish.