Diet of Young-Of-The-Year Smallmouth Bass in the Upper Juniata River System

The decline of young-of-the-year (YOY) smallmouth bass (SMB, Micropterus dolomieu) recruitment and adult densities in the Susquehanna River basin since 2005 raises concern for the health and well being of the fishery. Our study focused on understanding the feeding ecology of YOY SMB in the upper Juniata River watershed, a major tributary to the Susquehanna River. We studied the mainstem of the upper Juniata River, and the major tributaries forming and joining the river. We sampled the YOY smallmouth bass for a two-year period during the summer of 2016 and 2017. Our specific objectives were to 1) characterize the diet of SMB and a potential invasive competitor, the rusty crayfish (Orconectes rusticus), 2) document the physical condition and external health of individuals, and 3) evaluate the effectiveness of gastric lavage to extract diet contents at an early life history stage. A subset of individuals was sacrificed to check lavage efficiency and these individuals were also sent to be examined for histopathological anomalies that may result from pharmaceutical contamination (i.e., endocrine disrupting compounds) that is considered to be a likely cause of SMB decline. We also quantified habitat conditions using rapid visual techniques and ecological health of each site following the protocols for the Pennsylvania Index of Biotic Integrity for wadeable freestone streams. PA IBI scores (range 34 – 67) and habitat conditions (range 46 – 70%) were rather poor in both years. In summer (July and August) 2016, YOY SMB were numerous and were in excellent health, but were nearly absence during the same time in 2017. Few external anomalies consisted of parasites only. Most individuals were full of prey items, which on average consisted of about half aquatic prey and half terrestrial or neustonic prey. Rusty crayfish diet contents lacked any resemblance to diet contents in YOY SMB. Gastric lavage techniques were effective at removing gut contents and only a few individuals were found to have stomach contents remaining when dissected in the lab. Furthermore, nearly all YOY SMB fully recovered from field lavage experiences. Only 2 individuals died, and this was likely due to extreme river surface water temperatures (89 F) at the time of sampling. Thus, gastric lavage is a safe and effective technique to study YOY SMB feeding ecology and important links between recruitment, diet, and food quality without having to kill numerous fish