Sex-Specific Movement Response of an Estuarine Sciaenid (Cynoscion nebulosus) to Freshets

Abstract

During a 2.5-year acoustic telemetry study in a Louisiana estuary (Calcasieu Lake), two major freshets occurred (peak river flows >350 m 3 s −1) in separate years and seasons, which provided an opportunity to evaluate the movement response of adult spotted seatrout (Cynoscion nebulosus) to large pulses of freshwater entering the estuary. A total of 172 spotted seatrout (101 females, 49 males, and 22 fish whose sex was unknown) were implanted with acoustic transmitters (battery life ~1 year) and released across four separate tagging events in the spring and fall of both 2007 and 2008; the movements of these fish were monitored by an estuarine-wide array of 60 receivers. Both freshets considerably reduced salinities in the upper bay, from 15–20 to <5. Interestingly, spotted seatrout exhibited a sex-specific response to these freshet-induced low salinities (<5). During both freshets, males continued to utilize and remained in the upper bay, but females left the area and moved (>10 km) to the lower bay where salinities were higher (10–20). This sex-specific movement response to changing salinities has not been explored or demonstrated previously in spotted seatrout. Accordingly, these results provide environmental mangers with unique information on how salinity dynamics affect the accessibility of this economically and ecologically important species to both anglers and scientific surveys. This information also provides insight into how this species may respond to large-scale freshwater diversions that are being planned as part of coastal restoration efforts along the Gulf coast of the USA. More broadly, our results add to a limited but growing body of evidence that environmental preferences of estuarine and coastal fishes often differ between sexes and that the variable abiotic conditions, so characteristic of estuaries, can have important behavioral consequences for mobile organisms living in these systems.