Putting Together Pieces of the Puzzle: Contaminants, Pathogens, and Smallmouth Bass Population Dynamics in the Susquehanna River Basin

*/ The Susquehanna River is an important resource for communities within the Chesapeake Bay Watershed. Recent discussions about the river’s health have often focused around concerns about the status of smallmouth bass fish populations – which are viewed as an indicator of overall river health. In the mid-2000s, fisheries managers in Pennsylvania began documenting young of the year (YOY) mortality events and clinical signs of disease. Shortly thereafter, managers began observing declines in abundance of adult fish. During this same time period, there was evidence of endocrine disruption (intersex or testicular oocytes and plasma vitellogenin) in male fish, and it was discovered that multiple parasites and pathogens were infecting YOY. It was hypothesized that exposure of YOY to chemical contaminants was resulting in immunosuppression and thereby contributing to high infection rates by a variety of pathogens. By 2005, fish abundance was low and estimates of YOY natural mortality peaked. In recent years (2015-2017), however, abundance of smallmouth bass in the Susquehanna River is approaching or exceeding levels observed prior to the decline. A vast array of environmental variables has been identified as possible contributing factors to mortality and population level declines. This talk will focus on trying to understand the combined effect of those factors on smallmouth bass population dynamics in an effort to provide insight into the overall health of the Susquehanna River.