Spring flow and habitat-mediated effects on reproductive effort of the Fountain Darter
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Reductions in Edwards Aquifer spring flows are hypothesized to reduce reproductive effort of spring-associated fishes. Purposes of this study were to test relationships among spring flow, associated habitat changes, and reproductive effort of the federally-listed Fountain Darter Etheostoma fonticola, a spring-associated fish inhabiting Comal and San Marcos rivers of central Texas. Study objectives were to quantify annual reproductive effort (i.e., ovarian stages, gonadosomatic index, and batch fecundity) across a gradient of flows (0.01 m3/s to 3.7 m3/s) and aquatic habitats using natural and anthropogenically-altered stream reaches (N = 4) within the Comal and San Marcos rivers to represent in situ flow reductions. Contrary to previous studies reporting constant year-round spawning effort, annual reproductive cycle of the Fountain Darter consisted of an optimal reproductive season (January through April), and tailing reproductive season (May through August), lack of spawning in September, and a leading reproductive season (October through December). Among reproductive seasons, stages of ovarian condition, gonadosomatic indices, and batch fecundity generally were not different along a flow gradient or among habitats, though two exceptions were noted. Gonadosomatic index and batch fecundity were greater (P < 0.05) at the higher flow environment (4.1 m3/s) during optimum reproductive season and greater (P < 0.05) at the lowest flow environment (0.01 m3/s) during the leading reproductive season. Collectively, seasonality of reproductive effort was similar to sister taxa (Cypress Darter E. proeliare, Least Darter E. microperca), though protracted, and reproductive effort was not related consistently to flow environment observed during the study period. However, other measures of reproductive effort (e.g., numbers of larvae hatched, survival of larvae through recruitment age) are necessary to quantify in order to assess the relationship among Fountain Darter population viability and flow environments.