Potential threats to smallmouth bass (Micropterus dolomieu) in the Juniata River Basin, Pennsylvania, USA

Abstract

The Susquehanna River basin is one of the largest and most diverse watersheds in the northeastern United States, however, its historically renowned Micropterus dolomieu (smallmouth bass–SMB) fishery has been in decline since the mid-2000s. Agricultural herbicide runoff has been identified as a major risk for Susquehanna basin SMB populations given their effects as endocrine disrupting compounds (EDCs). During the summers of 2016 and 2017, we assessed potential threats to SMB populations in 11 tributaries to the Juniata River, the second largest tributary to the Susquehanna River. Passive water samplers were installed for 38–39 days in ecologically important tributaries to quantify six common herbicides, and SMB were collected from nine sites in 2016 and 2017 to assess their health and morphology. Our passive water samplers showed markedly higher EDC concentrations than has previously been documented in the Juniata basin, with atrazine occurring at all sites and in the highest concentrations (11.09–91.02 ng/L). SMB blood samples revealed complete prevalence (100%) of vitellogenin, an egg protein precursor, in male fishes further confirming previous rates male vitellogenisis. Additionally, SMB hepatosomatic index (HSI) was statistically higher in female SMB than in male SMB (P < 0.001), and higher than many previous regional SMB studies further highlighting a contaminant-based stressor. Finally, a geometric morphometric analysis of SMB body shape indicated morphologies to be significantly site-based. Morphological differences were in line with the ram-suction feeding continuum, further revealing potential vulnerability in SMB sub-populations where EDCs may alter food web dynamics and prey availability. Overall, our study of the Juniata River Basin highlights high EDC concentrations alongside high rates of male vitellogenisis and elevated HSI, and proposes novel theory for morphological vulnerability in SMB sub-populations.

Keywords

• endocrine disrupting compounds
• smallmouth bass
• atrazine
• agrochemicals
• intersex
• tributaries