“perfect storm” of pollution, parasites,
warming water temperatures, and endocrine
(hormone)-disrupting chemicals is threatening
one of the Chesapeake Bay region’s most popular sport fish, smallmouth bass.
CBF’s recent report, Angling for Healthier
Rivers, details how smallmouth bass have
suffered disease, die-offs, and sexual abnor-malities over the last decade in five Bay
tributaries: the Susquehanna River in
Pennsylvania; the Monocacy River in
Maryland; the South Branch of the Potomac
River in West Virginia; and the Shenandoah
and Cowpasture Rivers in Virginia.
Smallmouth are beloved by freshwater anglers
because they are a spectacular gamefish.
“Smallmouth bass are one of the great
sport fisheries,” said CBF President Will
Baker. “But in the Susquehanna and other
rivers in the region, smallmouth bass are in
Fishing for smallmouth bass is important for
the region’s economy, responsible for about
5,700 jobs and $630 million annually in
sales of boats, fishing gear, and other goods
in Pennsylvania, Maryland, Virginia, and
West Virginia, according to the report.
John Arway, Executive Director of the
Pennsylvania Fish and Boat Commission, said
in Angling for Healthier Rivers, “I am truly concerned that I’ll be Director when the last bass
is caught out of the [Susquehanna] River.”
Smallmouth less than a year old are dying at
high rates. Catch rates of smallmouth bass in
the middle Susquehanna River fell by 80 percent between 2001 and 2005 and have not
Although the problems afflicting smallmouth
bass are complex and still only partially
understood, one factor is clear and can be
controlled. Reducing phosphorus and nitrogen pollution to meet the Clean Water
Blueprint will help reduce stress on smallmouth bass and other fish, even as it
improves water quality for everyone who
enjoys the Bay’s rivers and streams.
Research Fisheries Biologist, Dr. Vicki
Blazer, who contributed to the report, concluded that phosphorus and nitrogen pollution, rising water temperatures, and a
variety of endocrine-disrupting chemicals
appear to be playing roles in weakening the
immune systems of the fish, making them
more vulnerable to naturally occurring bacteria, viruses, and parasites.
“It’s almost like you reach the perfect storm
situation,” said Dr. Blazer in the CBF report.
“There have been stressors and smallmouth
bass have been able to overcome them or deal
with them. But eventually, they get to a point
where they cannot deal with them anymore.”
Scientists believe that phosphorus and
nitrogen pollution may be contributing
to fish deaths and diseases in two ways.
The first is by spurring the growth of parasites
(myxozoans and trematodes) and their hosts
(worms and snails). The second is by feeding
algal blooms that raise pH levels and lower
oxygen concentrations, stressing smallmouth
bass and other species of fish.
Fortunately, state and local governments can
reduce these pollutants by investing in
stormwater-control projects, upgrades to
wastewater treatment plants, and efforts to
fence cattle out of streams. Cleaner rivers
will give these valuable sportfish a sporting
chance to live.
u To read the report, visit cbf.org/smallmouthbass.
AAngling for Healthier Rivers The Link Between Smallmouth Bass Mortality and Disease and the Need to Reduce Water Pollution in Chesapeake Bay Tributaries
Nitrogen and phosphorus pollution
contribute to a “perfect storm” of prob-
lems that are killing smallmouth bass.
This smallmouth bass, caught in
Pennsylvania, suffered from gill erosion.
The Link Between Smallmouth Bass Mortality and Disease
and the Need to Reduce Water Pollution in Chesapeake Bay Tributaries
This is a summary of CBF’s April 2013 report, Angling for Healthier Rivers.
The full report can be found online at cbf.org/smallmouthbass.