The number of young bass that survive to become adults has plummeted in about 100 miles of the Lower Susquehanna, as well as parts of the Juniata, over the last decade. (Karl Blankenship)
Karl Blankenship is editor of the Bay Journal and Executive Director of Chesapeake Media Service. He has served as editor of the Bay Journal since its inception in 1991.
According to the Chesapeake Bay Journal, a recent study indicates the smallmouth bass population in the Susquehanna River are suffering a population collapse possibly connected to hormone-altering compounds and herbicides, weakening their immune systems.
The multi-year study, which involved dozens of scientists from multiple state and federal agencies as well as universities, said that exposure to endocrine-disrupting compounds and herbicides, along with infections from parasites and pathogens, were the “most likely” reasons that few young smallmouth bass in the river have survived to become adults since 2005.
Several studies have found evidence of endocrine disrupters, which interfere with the hormone system in animals and fish, around the Bay watershed. Sometimes those findings were associated with isolated fish kills, but the Susquehanna report is the first time those compounds have been identified as the likely culprit in causing a widespread population collapse in the region.
Smallmouth bass once attracted anglers from around the world to the Bay’s largest tributary, but during the last decade the number of young fish that survive to become adults has plummeted in the middle section of the river from Sunbury, where the river’s West and North branches merge, to York Haven, a few miles north of the Maryland line. The collapse has also been observed on the lower portion of the Juniata, one of the Susquehanna’s largest tributaries. Altogether, about 100 miles of river are impacted.
The Pennsylvania Fish and Boat Commission has banned recreational harvest of the fish, but the population has not recovered and remains at less than a third of what it was a decade ago.
In addition, adult smallmouth bass have turned up with a variety of maladies, such as lesions, sores and dark blotches. A recent study found a surprisingly high rate of intersex — a condition in which adult males contain types of cells usually found only in females.
The poor health of smallmouth bass in much of the river has alarmed anglers, environmentalists and the Fish and Boat Commission, all of whom have called on the state Department of Environmental Protection to list the river as “impaired” — a designation that would ultimately require the development of a cleanup plan.
The DEP has resisted the designation because it could not identify what, if any, pollutants were causing the problem, though in recent years it has supported increased monitoring. It also helped coordinate the scientific review that was aimed at narrowing down the likely factors from a long list of suspects.
“This study does not identify a single smoking gun but it does point the way toward likely causes, which we will continue to pursue,” DEP Secretary John Quigley said in releasing the findings Dec. 14.
The scientists started with a list of 14 potential contributing factors, but ruled out eight, such as changes in river flow, changes in food quality and several others considered unlikely to cause fish mortality based on available information.
Several others were considered “uncertain” causes because of a lack of data, but scientists thought they could be contributing to the problem by stressing fish. Those included things such as increased water temperatures in some years, low dissolved oxygen, increases in harmful algae and habitat degradation.
But available information, the scientists said, pointed to two factors as the most likely causes:
- Endocrine-disrupting chemicals and herbicides: Both have been shown to suppress the fish’s immune system and were found at higher levels within the study areas than in other areas around the state. Endocrine disrupters stem from several different sources including wastewater treatment plants, pharmaceuticals and a variety of chemical products. Many herbicides also act as endocrine disrupters, and the study said two common herbicides — atrazine and metolachlor — were at higher concentrations in the problem area than in other areas.
- Pathogens and parasites: Several types were found in infected fish. Most of those found in the river typically do not kill fish — and, in fact, are found in other Pennsylvania rivers — but the study suggested that the weakened immune systems of the Susquehanna fish made them more vulnerable to the infections.
While the study identified the chemicals as a “most likely” contributor to the problem, it stopped short of proving the link. The study said it is hard to test small fish for exposure to those chemicals, but noted that the presence of intersex in adult fish, which has been linked to endocrine disrupters and certain herbicides, suggests those chemicals are present at levels that would affect smaller fish.
The next steps in the study will focus on determining the sources of chemicals, and whether the factors listed as uncertain causes are also contributing to the problem.
Read the rest of the story here.