Smallmouth bass still haven't recovered from a precipitous population drop in the Susquehanna River 10 years ago, according to a report released Monday by the Pennsylvania Department of Environmental Protection.
Research conducted by multiple state agencies attributes herbicides, pathogens and parasites as the main causes for the reduction.
“Young smallmouth bass are not growing up to be adult bass in sufficient numbers,” said John Quigley, secretary of the state DEP.
Quigley said the study, which began in 2014, is as distinct as the Susquehanna itself.
“The river is very complex," he said. "What looks like one body of water acts like five unique rivers, all with different chemical characteristics.”
Water program specialist Dustin Shull reported endocrine disrupting compounds like hormones and herbicides appeared at higher concentrations within the subject area than in comparison sites, but researchers still don't know the source.
Rod Kime, DEP water pollution biologist, said although the river has many key tributaries, it is not impossible to track the decline. Scientists have already ruled out food quality, temperature and river flow volume.
“We would observe any pathogens or parasites that are infecting the fish, and we would be able to identify those pathogens,” Kime said. "From that, we can trace back to their potential pathways of how they may have gotten into the river and how they are infecting the fish.”
Quigley said the study will likely move into the tributaries next, a process that could last into 2017.