Temporal and spatial variation in endocrine disrupting compounds and young-of-theyear smallmouth bass health in the upper Juniata River system

Over a 2-year time frame in summer 2016 and 2017, we quantified the dynamics of endocrine disrupting compounds (EDCs) in the upper Juniata River system. EDCs have been implicated as a likely cause of declines in recruitment and thus adult smallmouth bass (SMB) populations in the lower Juniata and Susquehanna Rivers since 2005. We studied the mainstem of the upper Juniata River (near Mapleton), and 5 other major tributaries in the drainage system. Specifically, we quantified EDC levels (estradiol equivalents, EEQ in ng/L) across a range of flow types at 9 different sites and subsequently looked at how these hydrologic conditions (e.g., peak storm flows vs. ascending flow, vs. base flows, etc.) and landscape characteristics among sites may explain the variation in EDCs. In addition, we measured EDC levels along a continuum of the Juniata River downstream of a waste water treatment plant to quantify decay patterns once entering water. Finally, at each site we collected information on young-of-the-year (YOY) SMB condition and diet. We used non-lethal gastric lavage techniques to extract diet contents and sacrificed a subset of individuals to estimate efficiency. EDC concentrations varied widely within sites at the same time, within sites at different times, among sites, and between years, but levels thus far in our surveys have not surpassed 1 ng/L, a threshold considered to be a concern for fish health. Initial analyses indicate that river discharge and flow characteristics related to storm runoff cannot explain variation in EDCs, nor have we identified landscape characteristics at 2 spatial scales that can explain variation. Thus far, we could not detect a trend in EDC concentrations downstream of the waste water treatment plant. In 2016, YOY SMB were numerous and were in excellent health, but were nearly absence during the same time in 2017. Most individuals contained at least some prey items, which on average consisted of about half aquatic prey and half terrestrial or neustonic prey. Rusty crayfish diet lacked resemblance to diet in YOY SMB. After gastric lavage, only a few fish were found to have some stomach contents remaining when dissected in the lab. Furthermore, nearly all YOY SMB fully recovered from field lavage experiences. Our study has identified levels of EDCs in the upper Juniata River systems that should be considered important for addressing ecological health in the broader Susquehanna River basin. Advancing our understanding of the dynamics of these emerging contaminants and their potential effects on smallmouth bass will require tracking and measuring specific compounds. We found gastric lavage to be a safe and effective technique to study YOY SMB feeding ecology without having to kill numerous individuals of this popular gamefish