The Response of Fishes to Periodic Spring Floods in a Southeastern Stream

Movement of fishes onto a fringing floodplain was studied by seining and trapping during five spring floods. We collected 26 species from the inundated floodplain; the known channel fauna is 42 species. Species numerically dominant on the floodplain were Fundulus olivaceus, F. notti, Gambusia affinis, Notropis welaka, N. texanus, N. roseipinnis, Lepomis macrochirus, L. cyanellus and L. marginatus. Catch-per-effort in traps was generally greatest on the upper floodplain during the day and greatest nearer the channel at night. Night activity of fishes on the floodplain was apparently low. Several species, which we term flood-quiescent forms, were common in the channel (e.g., Lepomis megalotis and Percina nigrofasciata) but did not exploit the floodplain. Activity (as catch per trap-hour) of P. nigrofasciata was negatively correlated with floodinduced turbidity. A flood-exploitative species, Notropis texanus, had higher population abundance during 3 high-flow years than in 3 low-flow years, suggesting that spring flooding may exert significant control over fish community structure. INTRODUCTION Periodic flooding is characteristic of most lotic systems. Based on channel morphology and gradient, floods may be erosive and thus potentially destructive to the stream habitat, or depositional, exhibiting creeping and being generally nondestructive to channel morphology (Welcomme, 1979). Most studies of the effects of flooding on aquatic organisms have treated erosive floods (e.g., Paloumpis, 1958; John, 1963, 1964; Greenfield et al., 1970; Seegrist and Gard, 1972; Hanson and Waters, 1974; Hoopes, 1975; Harrell, 1978), in which severe faunal disruption often occurs. Adaptations of organisms to erosive floods are either for surviving high flow rates through behavioral or morphological modifications, or for life history characteristics allowing rapid recolonization. Few studies have addressed the effects of nondestructive flooding on North American streams. Such floods occur in low gradient systems in which floods are primarily characterized by lateral expansion rather than increases in depth (Welcomme, 1979). While lateral expansion of rivers onto floodplains is best developed in tropical areas (Welcomme, 1979), many North American streams, especially in the southeastern United States, also show (or showed prior to levee construction and channelization) well-developed fringing floodplains (Viosca, 1927; Gunter, 1957; Bennett, 1958; Guillory, 1979). Such natural floodplains may be seasonally inundated. Forbes (1925) pointed out the importance of inundated floodplains as breeding grounds and foraging areas for fishes and aquatic invertebrates. Wickliff (1945) recorded movement of fishes onto an inundated floodplain. Starrett (1951) determined that certain minnows spawn in backwater areas and suggested that flooding was an important factor controlling minnow populations. Bennett (1958) believed that periodic flooding of the Mississippi and Illinois rivers was beneficial to largemouth bass populations. Guillory (1979) found that a number of Mississippi River species used inundated floodplains as