The Link Between Smallmouth Bass Mortality and Disease and the Need to Reduce Water Pollution in Chesapeake Bay Tributaries
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Summary
Over the last decade, one of the most prized freshwater sport-fish species—smallmouth bass—has suffered fish kills and perplexing illnesses in several Bay tributaries. These tributary rivers include the South Branch of the Potomac River in West Virginia, the Shenandoah and Cowpasture Rivers in Virginia, the Monocacy River in Maryland, and the Susquehanna River in Pennsylvania. In the Susquehanna River, smallmouth bass populations have plummeted, with catch rates of adults falling 80 percent between 2001 and 2005 in some areas. According to the Pennsylvania Fish and Boat Commission, the population has not recovered.
Smallmouth bass do not tolerate pollution well. Thus, they are an indicator of water quality. While the specific causes of the deaths and illnesses among smallmouth bass remain unclear, leading fisheries biologists studying the problem believe that a "perfect storm" of contributing factors has overwhelmed a sensitive species.
The Chesapeake Bay Foundation (CBF) compiledthis report by interviewing five leading smallmouth bass experts and examining peer-reviewed journal articles, as well as reports from federal and state agencies. Some conclusions include:
- Fishing for the species is responsible for $630 million annually in sales in Pennsylvania, Maryland, Virginia, and West Virginia, the four Bay states where fish kills and diseases have occurred. Sales of boats, fishing rods, and more contribute to that figure. Additionally, smallmouth bass are responsible for $193 million annually in salaries and wages for about 5,700 people employed in fishing-related jobs and $41 million in state and local tax revenues.
- Phosphorus and nitrogen pollution levels are high in many of the river segments where fish have died or become sick.In the Susquehanna River and tributaries, average phosphorus pollution levels in 12 of 24 sites monitored by the U.S. Geological Survey between 2007 and 2011 were among the worst in the Chesapeake Bay watershed. And 11 of these 24 sites had total nitrogen pollution levels that were among the worst in the region. ("Worst" is defined as ranking in the top third for levels of these pollutants among 65 sites studied in the Bay watershed). Some monitoring sites along the Monocacy River and the Potomac River and its tributaries also registered high levels of these pollutants.
- Scientists believe that nitrogen and phosphorus pollution may be contributing to fish deaths and diseases in two ways. The first is by spurring the growth of parasites (myxozoans and trematoads) and their hosts (worms and snails). The second is by feeding algal blooms that raise pH levels and lower oxygen concentrations, stressing young smallmouth bass.
- A type of parasite (Myxobolus inornatus) has been found in juvenile smallmouth bass that have been dying in the Susquehanna River.This parasite is similar to one that causes a deadly disease in trout. The parasite’s possible host (a bottom-dwelling worm) may be encouraged by nitrogen and phosphorus pollution.
The problems of smallmouth bass should matter to everyone. Not only are "smallies" a financially valuable sport fish, but they are also an indicator species that is sensitive to pollution. Other fish and animals could also be suffering similar die-offs and illnesses, but we would not necessarily be aware, because an outdoors culture and industry has not been built up around them. So we should listen to what bass are telling us about our ecosystem.
The Chesapeake Clean Water Blueprint lays out the steps that need to be taken to reduce pollution and improve water quality in local rivers, streams, and the Chesapeake Bay. Make a difference for smallmouth bass.Sign our pledge to protect the Bay and the Blueprint.
