Degree Name

Master of Science (MS)

Semester of Degree Completion

Fall 2019

Thesis Director

Robert E. Colombo

Thesis Committee Member

Scott J. Meiners

Thesis Committee Member

Anabela Maia

Abstract

Large rivers are highly important systems; being exploited both commercially and recreationally. Because of this usage by humans, close monitoring of the ecology of theses rivers is of the utmost importance. The Long-Term Electrofishing project (LTEF) monitors the fish communities of the Illinois, Mississippi, Wabash, and Ohio rivers using day time, pulsed-DC electrofishing during the late Spring through the early Fall each year. Given that previous studies have noted diel and seasonal changes in catch and composition of fish communities, the addition of night time electrofishing may be beneficial to the overarching goals of the LTEF. This study sought to determine whether significant diel and seasonal changes are occurring in the Wabash and whether these changes are significant enough to warrant additional sampling the LTEF protocol. To investigate this question, I used night time, pulsed-DC electrofishing at fixed sites corresponding to LTEF sites in the Lower Wabash River from October 2016 to November 2017. I compared catch per unit of effort (CPUE), length distributions, and family composition between my night time electrofishing data and LTEF day time electrofishing data from 2017. Additionally, I compared these three parameters between seasons using my night time data. Diel comparisons showed some variation in catch rates between night and day but were proportionate in composition. Similarly, seasonal comparisons showed variation in catch rates but generally lower catches of all families during the Winter. Night time electrofishing had a significantly higher mean CPUE than day time sampling (p < 0.05), the three most prevalent families being Catostomidae, Cyprinidae, and Sciaenidae. Of the three families, only Sciaenidae had a significantly different length distribution; showing a shift towards smaller fish during the night (p < ii 0.025). Seasonally, average CPUE did not differ significantly between seasons (p > 0.05). However, the individual families compared had significantly lower CPUEs in the Winter and Sciaenidae had significantly higher CPUEs in the Fall compared to other seasons (p < 0.008). Seasonal length distributions of Sciaenidae did not differ significantly, however. Other fish families did have significant seasonal differences in length distributions, generally showing a shift towards mid-sized fish in the Summer (p < 0.008). These results indicate that diel and seasonal variations do occur in the Wabash. However, Given the proportionality of families captured between night and day as well as the relatively low catch rates in the winter, I would not recommend the addition of night time electrofishing or extended seasonal sampling to the LTEF as it would not benefit the overarching goals of the project.

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