Few studies have addressed within-year temporal variation of IBI scores. We compared index of biotic integrity (IBI) scores for two summer sampling events from a large river during 25 annual periods. The results indicated that IBI scores calculated from June samples were not significantly different from July samples. Spatial autocorrelation was present, such that sites that were closer together produced similar IBI scores and could not be considered independent. Temporal autocorrelation was present, but was not strong. Lower quality sites (low IBI score) did not have higher variation than higher quality sites. Our results show that a single sample of fishes by boat electrofisher during the summer in a large river such as the Wabash River can produce a repeatable estimate of IBI score. Thus, repeated or additional sampling within the summer season to improve the quality of the evaluation is not warranted.
Habitat use of 20 tagged walleye (Sander vibeus) was monitored using ultrasonic biotelemetry under varying flow conditions in the Wabash River from June through September 2003. The study area was a free-flowing 20-km reach of the upper Wabash River from Lagro (rkm 633) to Rich Valley Indiana (rkm 612). Boat electrofishing was used to estimate the population and to collect individuals for biotelemetry. Summer walleye movements were short in distance and use of cover type, lateral river position, and substrata varied with river discharge. Eiectrofishing surveys indicated low walleye abundance in the upper Wabash River. Three walleye-sauger hybrids were captured, suggesting natural reproduction. Tagged individuals showed versatility in habitat use.
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