Estimation of Small Bodied Fish Community Assemblages in a Large Unimpounded River Using a Novel Gear

Studies of larval and juvenile fish assemblages are uncommon on large rivers due to habitat variability and the difficult and time consuming nature associated with small bodied fish collection and identification. We sampled small-bodied fish in the Wabash River using a DC-electrified mini-Missouri trawl to assess the spatio-temporal variation in young of year and small-bodied fish species. Trawling was accomplished monthly from May to September along 8 bends from three habitats: inside bend, outside bend, and main channel. We collected a total of 1857 fish from nine different families, and 40 species.  The size of fish captured ranged from 10 to 1120mm (mean=69.5mm, SE=3.07), with 89% of the catch being under 120mm in length. NMDS was utilized to assess the sampling differences between habitat types. We found the inside bends were significantly different in species composition than the main channel or outside bend habitats (p<0.05). Additionally, the inside bend assemblage was significantly different upstream compared to downstream of the White River confluence (p=0.03). One factor driving this difference is an effect of water depth. Larger bodied fish were also sampled, suggesting that an electrified trawl is capable of sampling adults, though it is more effective at sampling juvenile fish.