DEMOGRAPHICS AND THE ECOLOGICAL ROLE OF THE CHANNEL CATFISH (ICTALURUS PUNCTATUS) IN COMMERCIALLY EXPLOITED AND UNEXPLOITED REACHES OF THE WABASH RIVER WITH IMPLICATIONS FOR THE FLATHEAD CATFISH (PYLODICTIS OLIVARIS)

Catfish are a major component of the Wabash River fish assemblage and are commercially fished below river kilometer (Rkm) 500. From Rkm 322 through 499 the commercial fishery is subjected only to Indiana fishing regulations. In this reach of river, there is a 254-mm minimum total length limit on both sport and commercially harvested catfish. Below RM 322, the Wabash River forms the state boundary of Indiana and Illinois. In this region of river there are two different length limits on commercially harvested catfish with Indiana having a 254-mm length limit and Illinois having a 381-mm length limit. There is no length limit on sport harvest of catfish by Illinois anglers; however, there is a 254-mm length limit on the Indiana sport fishers. The primary objective of this study was to assess the general population dynamics of the channel catfish (Ictalurus punctatus) under various sport and commercial fishing regulations and to determine the sources of energy for this species. To accomplish this, I sampled both fished (IN, IN & IL) and unfished (NON) treatment reaches of the Wabash River during fall 2001 through 2004 using three-phase alternating current (AC) electrofishing and cheese baited, 25-mm and 32-mm bar-mesh hoop nets. Of the 2,807 catfish collected, 91% were channel, 8% were flathead (Pylodictis olivaris) and 1% were blue catfish (I.furcatus). Length frequency distributions and mean age of fish differed across the three different gear types (P \u3c 0.02), with electrofishing sampling larger, older channel catfish. Densities estimated from catch per unit effort (CPUE) did not differ among treatment reaches (NON, IN, IN & IL) using hoop nets (25-mm: P \u3c 0.1, 32-mm: P = 0.4); however, electrofishing CPUE was greater in the unfished reach compared to the two commercially exploited reaches (P \u3c 0.001). Additionally, length frequency distributions and stock indices differed among treatment reaches (P = 0.017). As suggested by the high relative stock density of preferred length fish (RSD-P) values, more large catfish resided in the unfished reach than the fished reaches. Age structure also varied among reaches. More old fish were in the commercially unexploited treatment reach, leading to greater mean age (P \u3c 0.005). Ages derived from the articulating process of the pectoral spine agreed well with those determined from the sagittal otolith. Mortality estimated from the slope of the regression of age on Log10 frequency (catch curve) was greater for both gear types in the commercially exploited reaches than in the non exploited reach. Mean length at age 5 and condition of channel catfish was greater in the commercially exploited reaches than the unexploited reach. There was a positive relationship between channel catfish electrofishing CPUE and habitat quality as measured by the qualitative habitat assessment index (QHEI). Yield-per-recruit modeling of the commercially exploited river reaches predicted that at the current level of harvest the channel catfish fishery is sustainable; however, if both states adopted a 254-mm length limit and fishing mortality increased both growth and recruitment overfishing would likely occur even at fairly low levels of harvest (30% fishing mortality). Yield-per-recruit modeling of the flathead catfish population suggested this population was not sustainable at any of the length limits modeled. Based on stable isotope analysis of δ13C and δ15N, channel catfish did not differ in their trophic status among the treatment reaches, and the structures of the food webs among reaches were similar. These results provide additional support to the hypothesis that growth and condition are functions of density. The results of this study suggest that a harvest reserve in a large river acts similarly to marine reserves, in that density increases on the reserve lead to decreased growth and condition of individuals on the reserve