Survival and Growth in Multiple Size‐Classes of Hatchery Red Drum over Three Simulated Seasons

Abstract

The Texas Parks and Wildlife Department's (TPWD) Marine Stock Enhancement Program has introduced an average of 20 million fingerling Red Drum Sciaenops ocellatus into bays across Texas annually since 1983. Red Drum fingerlings are released during seasons outside of wild juvenile Red Drum recruitment, exposing them to conditions that they would not normally encounter as early stage juveniles in the wild. Furthermore, releases encompass a wide range of sizes outside of the target release size of 35 mm (20–60 mm), implying that survival and growth in the wild may vary with body size and body condition upon release. This study determined the impacts of season and initial release size on overall growth rate, body condition, and survival of Red Drum fingerlings by exposing two discrete size‐classes to a laboratory simulation of conditions expected to be encountered in the wild for 1 month after harvest from grow‐out ponds. Fish with an initial size of 35 mm TL or greater had higher overall survival over all three seasons of release than smaller fingerlings; however, final body condition (Fulton's K) was not significant across size‐classes. Growth rates of both size‐classes were highest in summer, indicating that elevated temperatures can benefit fish within the full range of release sizes. Fitted multiple linear regression modeling also determined that water temperature and size‐class were significant indicators of estimated growth rate. In addition, growth rates in wild fish as estimated from TPWD fisheries‐independent samples were consistently lower than those in experimental fish of both size‐classes during all three simulated seasons. This research suggests that releasing larger‐sized (>35‐mm TL) Red Drum may significantly improve survival, especially during seasons with more variable temperature conditions at the beginning and end of the TPWD hatchery release season.