Food habits and dietary overlap of nongame insectivorous fishes in Flint Creek, Oklahoma, a western Ozark foothills stream

— Insectivorous fishes were sampled from March, 1983 to February 1984, in Flint Creek, Delaware Co., Oklahoma. There was insignificant habitat segregation between Etheostoma spectahile and E. punctulatum and seasonal habitat partitioning between Cottiis carolinae and both darters. Mature £. spectahile ate primarily chironomids and mayflies, whereas juveniles fed primarily on microcrustaceans. Mature £. punctulatum consumed fewer Ephemerella and Leptophlebia than E. spectahile , feeding on Stenonema and other crustaceans. Juvenile E. punctulatum fed mainly on amphipods and mayflies, and juvenile E. spectahile ate primarily microcrustaceans. Cottus carolinae elected primarily mayflies in spring-summer and chironomids in January-February. Coefficients of dietary overlap were highest between larger E. spectahile and juvenile E. punctulatum and lowest between immature E. spectahile and mature E. punctulatum . Overlap between the two darters was significantly correlated with differences in mean prey size (p<0.0005). Overlap between sizes of £. spectahile was also significantly correlated to differences in mean prey sizes. Etheostoma spectahile generally preferred smaller prey than £. punctulatum . All three species avoided Stenelmis . Cottus carolinae avoided microcrustaceans. The study showed that resource partitioning among these three insectivorous fishes is affected by complex interactions of habitat and prey electivity, and prey size selectivity. Darters and other nongame insectivorous fishes, such as sculpins and madtoms, are often found coexisting in the same stream (Diaber 1956, Braasch and Smith 1967, Page and Smith 1970, 1971, Novak and Estes 1974, Page 1974, Flynn and Hoyt 1979, Matthews etal. 1982, Wynes and Wissing 1982). In such systems, resource partitioning by coexisting species is expected (Cause 1934, Zaret and Rand 1971). Smart and Cee (1979), Matthews et al (1982) and Wynes and Wissing (1982) have shown varying degrees of segregation of food and habitat use in coexisting darter species. Northcote (1954) studied the ecology of two sculpin species, and Daiber (1956) compared the feeding habits of the mottled sculpin and the fantail darter. Ecological segregation has also been shown among several other groups of sympatric freshwater fishes (Zaret and Rand 1971, Moyle 1973, Mendelson 1975, Werner and Hall 1976, Sural et al. 1980, Baker and Ross 1981). Several factors may influence competition for food between cohabiting fishes. These include primarily: (1) the utilization of different habitats, (2) prey size selectivity, and (3) the selection of specific prey species. Spatial segregation by stream fishes is difficult to assess, and studies based on seine hauls may be deceptive, since the method of capture potentially disturbs them to the point where their distribution may no longer represent natural activities, or the sampling area is so large that important differences in microhabitat usage are obscured. The food habits of some darters and sculpins change as they mature (Koster 1937, Bailey 1952, Daiber 1956, Braasch and Smith 1967, Page and Smith 1970, 1971, Scalet 1972, Page 1974, Flynn and Robert 1977, Schenec and Whiteside 1977, Layzer and Reed 1978). This suggests an age-related change in the strategies of food partitioning. Different size classes of a species are often found in different habitats. This potentially reduces both interspecific and intraspecific competition. The selection ofdifferent prey or diflferent prey sizes may be influenced by many factors such as morphological, physiological, and behavioral characteristics of both the predator and prey. Preliminary studies of darter food habits in Flint Creek, Oklahoma, suggested a difference in the magnitude of dietary overlap, depending on the size classes of fishes compared. Although Smart and Cee (1979) separated fish into age groups, most studies have reported indices of overlap without sub'Study supported in part by National Science Foundation Grants #DEB 78-12.56. 5 and #BSR 8308422 and the Faculty Research Fund of NTSU. "Department of Biological Sciences, North Texas State University, Denton, Texas, 76203.