Smallmouth Bass are Making a Comeback

Rivers Grove with smallmouth bass - cr Rivers Grove - 1171x593

Fishing guide Rivers Grove shows off a healthy Pennsylvania smallmouth bass.

Rivers Grove

After years of struggling with pollution and disease, some populations of smallmouth bass are making a slow recovery.

Much like how the fish strike spinnerbaits high in the water, recovery for portions of smallmouth bass populations is on the rise in Chesapeake Bay tributaries. 

But human and environmental factors have contributed to disease and deaths of young and old “bronzebacks” for more than a decade. And other age groups of smallmouths in Pennsylvania, Maryland, Virginia, and West Virginia waters still struggle to survive.

Disease-related mortality of young smallmouth bass was first documented in the Susquehanna River in 2005. In the years that followed throughout the Bay watershed, adult smallmouths that were caught had lesions, blotchy skin, open sores, and wart-like growths. Smallmouth bass surveyed in the Potomac, Shenandoah, and Susquehanna rivers had sexual abnormalities that included eggs growing in their testes, a condition called “intersex.”

Populations decreased dramatically.

Smallmouth bass are sensitive to environmental conditions, much like the “canary in the coal mine,” warning scientists of pollution problems before they afflict other fish and mammals.

In the 2013 CBF report “Angling for Healthier Rivers,” Dr. Vicki Blazer, research fisheries biologist with the U.S. Geological Survey (USGS), and colleagues theorized that smallmouth bass were under siege by a “perfect storm” of pollution, chemicals, and climate.

In 2020, it is still believed that rising water temperatures caused in part by climate change, nitrogen and phosphorus pollution, and endocrine-disrupting chemicals like herbicides, cosmetics, detergents, and hormones from animal and human waste are stressing the smallmouths and weakening their immune systems.

“I feel strongly that we do have immunosuppression going on,” Dr. Blazer said this week. “It might not be all the time. Maybe it is when temperatures are high, or you have runoff exposing the fish to multiple different chemicals.” 

Referring to a paper to be published in the American Fisheries Society magazine, Dr. Blazer says, “We all agree that in the end, to make it very clear that while there seems to be some recovery, that could change and that it is important to keep looking at fish health as well as the various environmental stressors.”

Dr. Blazer says that extreme weather events and high water flows have significant impact on smallmouth populations. “I think a lot of the fisheries management people think that high flows in the spring are primarily washing away the nests and the young if they are there,” she says. 

Spawning occurs in the spring when water temperatures get to about 60 degrees Fahrenheit. Males build nests in gravel near the shore and stand guard over newly hatched fry. 

Dr. Blazer also wonders about the effect of chemicals that end up in the water with runoff. “One of my questions is, how much that affects populations, particularly when we have runoff at a time when the most vulnerable life-stage is there—the fish that have just hatched or young,” Dr. Blazer says. 

“We’ve found some really high levels of herbicides right after runoff events in the spring, because that is when they are there,” Dr. Blazer adds. “Again, it depends on when that storm event happens and what has been occurring on the local land prior to it.” 

High water and turbidity can be added stressors on adult fish that are already stressed and cause their mortality.

A muddy river rushes over partially submerged trees and islands and flows under a railroad bridge.

In Pennsylvania, a muddy Susquehanna River seems to boil after days of relentless July rains in 2018 cause major flooding.

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“The other thing we are looking at, particularly, are agricultural best management practices and how those over time may be affecting populations,” Dr. Blazer adds.

Dr. Blazer sees multiple reasons to reduce the runoff of nitrogen and phosphorus.

“There are things that can co-occur with the nitrogen and phosphorus, but the nutrients are also going to contribute to increased parasite load. Some of the bacteria help proliferation of potential pathogens that the fish are exposed to,” she says. “Then if they are immunosuppressed on top of it, then again you have that perfect storm.”

Another risk for immunosuppression are per- and poly-fluoroalkyl substances (PFAS) the USGS discovered in blood plasma of smallmouth bass in Maryland, Pennsylvania, and West Virginia tributaries of the Bay.

“We found some pretty high levels at some of the sites and higher than a lot of other fish species that I can find in the literature,” Dr. Blazer says. “But I don’t think the water levels are very high, so there’s a case where the fish are bioaccumulating another kind of chemical like PCBs or mercury and you may not find high levels in the water at a given time.”

PFAS are a group of chemicals used for decades in water-repellant fabrics, firefighting foam, and other products. They have been found in ground and surface water, fish, and even human bodies.

Also, a study by Susquehanna University’s Freshwater Institute in 2019 found tiny plastic particles, also called microplastics, in 100 percent of smallmouth bass digestive systems surveyed.

In the Keystone State, it is thought that early smallmouth mortality was due to a virus that also claims largemouth bass. The Pennsylvania Fish and Boat Commission and Michigan State University partnered on a study that indicated the virus could cause mortality.

Here are snapshots of how smallmouth populations appear to be doing in Bay states.


The Susquehanna River was listed as one of five best bass fishing rivers in America in 2005. That year, young smallmouth bass started dying off in the Susquehanna and the Juniata rivers.

Catch rates of adults had fallen 80 percent between 2001 and 2005.

In 2012, the Pennsylvania Fish and Boat Commission prohibited fishing for smallmouths from May 1 to June 15 in much of the Susquehanna, in order to create less stress and protect spawning fish. When survey results showed the bass met recovery benchmarks, the seasonal restrictions were lifted in 2018 for smallmouth and largemouth bass in the middle and lower Susquehanna and lower Juniata rivers. Catch and release restrictions continue to be applied to those portions of the Susquehanna and Juniata.

Geoff Smith, Susquehanna River biologist with the PFBC, thinks an extreme weather event last year may have claimed many of the adult smallmouths “There was a high-water event at the end of June last year,” Smith says. “They are going into the spawning period, which is stressful, and this is above the stress they already had. I was out there in the spring of 2019, pre-spawn, and we had fish everywhere.” 

Still, he says the class of young fish from 2019 appears to be huge. “We have a good population of small fish coming into the population in 2019 as well as a good class in 2020,” he says. “We are going to have what appears to be two strong classes recruiting to the population and will fill in those gaps relatively quickly.”

Smith says the 2019 class of bass are being caught now. “They are going to be 8 to 10 inches roughly by this fall,” he says. “By roughly two to three years by our estimation, those fish will be a foot long.”

Rivers Grove, who owns Rivers Guide Service in Adams County has been catching those fish.

“There is definitely a decline in the bigger class of smallmouths 16- to 20-inches in both the Susquehanna and Juniata rivers,” Grove says. 

But from his seat on the water, he sees things turning around. “This year to me has shown definite improvements with lots of small fish and a lot of fry that are doing well,” Grove says. “I truly believe that if we have a few more spring seasons like 2020, things will be back were they need to be.”

The threat from the “perfect storm” of pollution continues to be in play in the Commonwealth.

The Pennsylvania Department of Environmental Protection’s (DEP) latest biennial report identified 25,468 miles of Commonwealth waters as being harmed by polluted runoff and other elements. That is 5,500 more miles than in its 2016 report.

Two years ago, the DEP determined that the Juniata River in Huntingdon County down-river to a section of the Susquehanna at Lancaster County, should be impaired as unsuitable for aquatic life due to high pH.

Smith said high pH causes an imbalance in the fish. “Everything about the fish is controlled by the water around it,” he says. “As the pH around it changes, it changes its ability to regulate itself.”


The smallmouth bass fishery in Virginia had its share of death and disease 15 years ago, especially in the Shenandoah River.

Deaths and fish with lesions were reported on the North Fork of the Shenandoah, a tributary of the Potomac, in 2004. In 2005, the bass died along 100 miles of the South Fork.

Smallmouth mortality occurred in the Cowpasture River, a tributary to the James River, in 2007, 2008, and 2009.

The fishery rebounded in Virginia, until high water that plagues the other Bay states struck the Commonwealth. “The smallmouth fishery in the Shenandoah watershed was in very good condition prior to the high flows we experienced in 2018 – 2019,” says Brad Fink, fisheries biologist with the Virginia Department of Game and Inland Fisheries. “It also seemed to impact many other species in the Shenandoah, but we typically only collect data on gamefish species.”

Now, the pattern of low numbers of smallmouths in some locations and stable populations in others seems to go with the high flows. “The upper and lower stretches of the North Fork Shenandoah River seem to have been impacted by the flows, but the middle reach around Woodstock seems to still be holding fish,” Fink adds.

He says numbers of smallmouths in the lower section of the South Fork Shenandoah seem to have been impacted by high flows. In the upper reach, upstream of Luray, fishing seems to be fine, minus a few big fish from poor recruitment in the years right after 2010.

While recruitment in 2018 was also low due to high flows that June, Fink says prospects are good for the smallmouth population on the South Fork. “Based on our annual fall sampling in 2019, the South Fork Shenandoah River had the third best spawning success over the last 23 years,” he says. “This will certainly aid in the recovery of the smallmouth bass fishery in the coming years.”    


A fish-kill in 2009 eliminated 65 percent of the smallmouths in the Monocacy River.

Elsewhere in Maryland, the number of young smallmouth bass got low enough in the Northern Potomac River, because of high river flows in May, that the state raised and stocked fish.

“When you have a high flow during or immediately after smallmouth bass spawning activity, you are going to see a big impact on subsequent juvenile numbers,” says Michael Kashiwagi, regional fisheries manager with the Maryland Department of Natural Resources. “The flows scour away spawning nests or, if they have spawned, wash away the juveniles downstream. High turbidity can also interfere with feeding.” 

Kashiwagi pointed to 2018, when major flooding in early June wiped out the new class of young smallmouths for that year.

Maryland’s effort to raise smallmouths was unsuccessful in 2019, but the 30 adult fish collected this year produced 30,000 one-inch fingerlings that were stocked in July. West Virginia contributed 10,000 from its hatcheries.

Kashiwagi says there was still some good reproduction in the rivers in 2019 and people are catching more of those 6 to 8-inch fish this summer. “We’ve got the larger ones,” he says, “but the catch rate has decreased.” 

The smallmouth population on the Monocacy River is in similar condition to that of the Northern Potomac. “We surveyed there this summer and recruitment looked very, very good,” Kashiwagi says. “That system is a little smaller than the Northern Potomac, so is perhaps slightly more stable. Fish numbers have been more consistent within that system.”

Kashiwagi says disease and lesions are not as common for Maryland smallmouths as they have been for the fish in Pennsylvania. 

West Virginia 

A string of smallmouth bass health problems was first observed in 2002 in South Branch of the Potomac River in West Virginia, when some fish died, and others had lesions. Toxic blooms of blue-green algae were blamed.

“This year I don’t think they saw as much in terms of lesions and mortality as they have in other years,” Dr. Blazer says. “They would tell you it’s kind of holding steady right now.”

B.J. Small 90x110

B.J. Small

Pennsylvania Communications & Media Relations Manager, CBF

[email protected]

Issues in this Post

Fishing   Runoff Pollution   The Susquehanna River  


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