Based on a multi-agency, multi-year study of one of the most complex river systems in Pennsylvania, the two most likely causes for the population decline of smallmouth bass in the Susquehanna River are endocrine-disrupting compounds and herbicides; and pathogens and parasites, the state Department of Environmental Protection said Monday.
The DEP, the Pennsylvania Fish and Boat Commission, and nearly 50 participants and six partner agencies released the findings Monday. The results narrowed the initial field of 14 possible causes to two.
The DEP said the study came after a smallmouth bass population crash in 2005 that was followed by such bass maladies as tumors and lesions. The team collected more than 30,000 water quality records annually, along with a review of existing research to isolate the possible causes that keep young-of-the-year smallmouth bass from growing into adulthood, the DEP said in a news release.
Give the results of the study, the Chesapeake Bay Foundation urged impairment listing for the lower Susquehanna.
“The time to start to remedy the sick Susquehanna River and save a world-class smallmouth bass fishery is now,” foundation executive director Harry Campbell said in a news release. “As causes of diseased and dying smallmouth bass continue to be studied, it provides even more evidence that the 98 miles of the Lower Susquehanna River should be recommended for impairment when the DEP’s Integrated Water Quality Report comes out in February.
“An impairment declaration will start the healing process, so that the waterway that millions of Pennsylvanians depend upon, and provides half of the freshwater to the Chesapeake Bay, can benefit from an unwavering level of restoration, resource investment, and pollution study,” he added.
Scientists began the study in 2014. A challenge in the study was how tributaries at times don’t mix in the Susquehanna River for more than 40 miles.
“What looks like just one body of water acts like five unique rivers, all with different characteristics,” DEP Secretary John Quigley said in a news release.
Of the 14 initial candidate causes identified by the workgroup, only two were determined to be likely causes: endocrine disrupting compounds/herbicides, and pathogens and parasites.
“We appreciate the assistance of the U.S. EPA, DEP and our other partners in the evaluation of many possible stressors to the smallmouth bass population using the CADDIS process,’” said John Arway, executive director of the Pennsylvania Fish and Boat Commission. “The health of the smallmouth bass in the Susquehanna River continues to be compromised and this analysis rules out certain causes, prioritizes other uncertain causes for further study and most importantly identifies likely causes which can be targeted for action.”
The original potential causes included high flows, pH and dissolved oxygen (deemed unlikely as a result of this study), as well as invasive species, habitat and algal blooms (deemed uncertain).
DEP said the next step is to focus on identifying the sources of the compounds and herbicides and what is causing the increased prevalence and lethality of pathogens and parasites.
“This study does not identify a single smoking gun,” Quigley said. “But it does point the way toward likely causes, which we will continue to pursue. On top of that, through this study, DEP staff developed new approaches to monitoring this complex system, dramatically increasing our water quality monitoring capacity in the Susquehanna River, and providing tools that we can use to ensure fishable, drinkable water statewide.”
“The Susquehanna River’s smallmouth bass fishery once attracted anglers from all over the world,” Arway said. “I am confident that the results from the CADDIS study along with the continued commitment by DEP to identify the causes and reduce the sources will provide for the recovery and return of that once world class recreational fishery.”
For more on the study, go to www.dep.pa.gov.