Yellow perch are popular sport fish, prized for their flavor. Their spawning runs up streams during the late winter are heralded as an early sign of spring in the Chesapeake Bay region.
But the ability of yellow perch to reproduce has fallen off sharply in recent decades, with many egg yolks abnormally formed. Water pollution from suburban sprawl may be the cause, according to a new report by the U.S. Geological Survey, Maryland Department of Natural Resources, and U.S. Fish and Wildlife Service.
“The abnormalities were most frequent and severe in perch from the South and Severn Rivers, the two tributaries with the most highly suburbanized watersheds,” says the report, which was written by Dr. Vicki Blazer of the U.S. Geological Survey and six colleagues. These abnormalities “may result from exposure to environmental contaminants,” although more studies are needed to determine exactly which pollutants.
In the Chesapeake Bay region, the problems with yellow perch appear to be most severe in the highly suburbanized triangle formed by Washington, Baltimore, and Annapolis, according to the report.
When biologists examined the eggs closely, they found deformed yolks and abnormal sacs around the yolks.
The researchers compared rates of these abnormalities in areas of the state with different amounts of suburban development, as expressed by the percentage of the land that was covered with blacktop or buildings. The scientists examined the South River south of Annapolis, where 25 percent of the land is developed; the Severn River north of Annapolis, where 21 percent of the land is developed; as well as the Mattawoman Creek area in southern Maryland (10 percent developed); Allen’s Fresh, also in southern Maryland (5 percent developed), and the Choptank River (2 percent developed).
The study looked at fish eggs in 2007, 2008, and 2009, and found that the abnormal yolks and egg envelopes were found much more often in the more suburbanized landscapes (surrounding the Severn and South rivers). In the Severn River area, for example, none of the eggs was fully developed, according to the report.
The implication is that pollution running off of the suburban landscape may be responsible for disrupting the reproduction of the fish. Now, the next step for the researchers is to pinpoint which contaminant.
If it turns out that, in fact, polluted runoff from developed neighborhoods is the problem, then solutions might include tighter regulation of suburban sprawl. Also helpful might be parking lots and driveways that are permeable to water, so less runoff flushes into streams; and stormwater control ponds and ditches full of wetlands plants to slow the flow of runoff and absorb pollutants.
To learn more about the problem, click here.
By Tom Pelton
Chesapeake Bay Foundation