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.
A virus that can cause disease and death in largemouth bass has been found in otherwise healthy northern snakeheads taken from two Virginia waterways. According to the U.S. Geological Survey (USGS), the finding raises the possibility that northern snakeheads could be carriers of the pathogen, capable of transmitting it to other fish in the Chesapeake Bay.
The pathogen, known as the largemouth bass virus, has been found in bass, sunfish and other members of the freshwater sunfish family, but largemouth bass are the only fish known to develop disease from it.
The largemouth bass virus appears to attack the swim bladder, causing fish to lose their balance and float near the surface of the water. According to the Virginia Department of Game and Inland Fisheries, the virus has been found in waters across the state, but its impacts are often short-lived and largemouth bass can build up resistance to the disease.
While the pathogen doesn’t seem to affect the health of northern snakeheads, the habitat of this invasive fish often overlaps with that of largemouth bass, which may favor transmission of the virus.
On a quiet cove in Southern Maryland, a series of orange and white markers declares a stretch of water off limits to fishing. Under the surface sits spawning habitat for largemouth bass, a fish that contributes millions of dollars to the region’s economy each year and for whom two such sanctuaries have been established in the state. Here, the fish are protected from recreational anglers each spring and studied by scientists hoping to learn more about them and their habitat needs.
The largemouth bass can be found across the watershed and is considered one of the most popular sport fishes in the United States. While regional populations are strong, a changing Chesapeake Bay—think rising water temperatures, disappearing grasses and the continued arrival of invasive species—is changing bass habitat and could have an effect on future fish.
For decades, scientists with the Maryland Department of Natural Resources (DNR) have collected data on the distribution of largemouth bass, tracking the species and monitoring the state’s two sanctuaries in order to gather the knowledge needed to keep the fishery sustainable. Established in 2010 on the Chicamuxen and Nanjemoy creeks, both of which flow into the Potomac River, these sanctuaries have been fortified with plastic pipes meant to serve as spawning structures. And, it seems, these sanctuaries are in high demand during spawning season.
On an overcast day in April, three members of the DNR Tidal Bass Survey team—Joseph Love, Tim Groves and Branson Williams—are surveying the sanctuary in Chicamuxen Creek. Groves flips a switch and the vessel starts to send electrical currents into the water, stunning fish for capture by the scientists on board. The previous day, the team caught, tagged and released 20 bass; this morning, the men catch 19, none of which were tagged the day before.
“This [lack of recaptures] indicates that we have quite a few bass out here,” said Love, Tidal Bass Manager.
Indeed, the state’s largemouth bass fishery “is pretty doggone good,” Love continued. “That said, we recognize that the ecosystem is changing. And I don’t think anybody wants to rest on the laurels of a great fishery.”
As Love and his team learn how largemouth bass are using the state’s sanctuaries, they can work to improve the sanctuaries’ function and move to protect them and similar habitats from further development or disturbance.
“We can speculate where the best coves are, but this is the ground truthing that we need to do,” Love said.
In the fall, the team will return to the cove to count juvenile bass and report on juvenile-to-adult population ratios. While the assessment of the state’s sanctuaries is a small-scale project, it is one “aimed at the bigger picture,” Love said.
Love’s team is “doing what we can to improve the use of these coves by bass.” And protecting bass habitat and improving water quality will have a positive effect on the coves overall, creating healthier systems for neighboring plants and animals.
“By protecting these important areas, we are also protecting the larger ecosystem,” Love said.
Photos by Jenna Valente. To view more, visit our Flickr set.