Degree Name

Master of Science (MS)

Semester of Degree Completion

2014

Thesis Director

Eric K. Bollinger

Abstract

Larval and juvenile life stages of fish are numerically the dominant component of fish populations. These early life stages experience high levels of mortality due, in part, to anthropogenic disturbances, but little is known about which habitats they utilize in large-rivers, as they are often difficult to sample and identify. My study examined the larval and juvenile fish assemblages in different habitats within the lower 322 km of the Wabash River. Fish were sampled with a conical-cylindrical ichthyoplankton net (larvae) and a DC-electrified mini-Missouri trawl (juveniles) between May and October 2013. Larval fish were collected every two weeks from mid-May through late July and then monthly from August through October; juvenile fish were sampled monthly May - October. Both gears were used to sample fish from three bend habitats (inside bend, outside bend, and main channel). Additionally, larval fish were collected from tributary mouths. Eggs collected in the samples were used to model passive drift in the system and compared egg CPUE between habitats to larval densities. I found that density patterns between habitats varied between these eggs and larval fish, suggesting that larvae were not passively drifting in the system. My results indicate that larval fish within certain family groups are able to utilize habitats differently than if they were only passively drifting with the flow of water, and are instead selecting for channel margin habitats. I also found that juvenile fish assemblages within inside bend were more similar than assemblages within outside bend and main channel habitats; however, these patterns were less distinct for larval and juvenile fish during fall when the habitats became more homogenized, suggesting that some environmental characteristic, most likely flow, was influencing assemblage composition. The electrified trawl was effective at sampling small-bodied fish as almost 88% of the total catch was less than 120 mm and 33 species were sampled at total lengths less than 200 mm. Because this distribution is noticeably different than electrofishing and hoop netting surveys, I recommend combining trawling with these gears to supplement surveys in large rivers to better survey the early life history stages of fishes.

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