Assessing fish collections from random and fixed site sampling methods on the illinois river

Abstract

The fish assemblage of the Illinois River is monitored annually through a long-term electrofishing (LTEF) program. Through the LTEF program, fish species composition and abundances are examined in six navigation reaches using a fixed site sampling design. We added a series of random sites to the LTEF sampling program in 2005 and 2007 to supplement current monitoring efforts. We used random and fixed site samples to assess fish species richness, relative abundance, and species-specific contributions to catches. We collected 17,537 fish from both sampling designs. Total fish and mean catch per hour was greater for fixed sampling (10,221 and 379.1, respectively) compared to random sampling (7316 and 259.6, respectively). Total fish species richness was 70, with 63 and 62 species collected through fixed and random samplings, respectively. Fish species diversity and evenness was greater for fixed site sampling. Eight fish species were unique to the fixed site design with seven fish species unique to random sampling. Fish assemblage analyses showed that catches for each sampling design contained a similar base set of species. Our results suggest that the goals of specific long-term monitoring programs may dictate the sampling method to be used. Whereas fixed site sampling may be biased toward potentially more and a greater diversity of fishes, random site selection will be unbiased and may provide greater spatial coverage. © 2012, Copyright Taylor & Francis Group, LLC.