Habitat characterization, habitat use and associated growth of juvenile spotted seatrout (Cynoscion nebulosus) in a Mississippi bay system: Implications for stock enhancement practices.

摘要

The spotted seatrout (Cynoscion nebulosus) is the most targeted recreational fishery species in Mississippi coastal waters. Consequently, the Seatrout Population Enhancement Cooperative stock enhancement program was initiated to investigate methods for supplementing this heavily exploited population. Given ecological data needs for both wild and hatchery-reared (HR) juveniles of the species, habitat mapping, directed sampling and a caging study were conducted. Submerged aquatic vegetation (SAV), oyster shell and non-vegetated substrates were mapped at water depths < 2 m in Point aux Chenes Bay, Mississippi, using a sidescan sonar, which provided more accurate estimations of habitat coverage, particularly for SAV, compared to point-based sampling. Applying habitat strata delineated from sidescan mapping, late-juvenile spotted seatrout [125 - 275 mm total length (TL)] were sampled in SAV, marsh-edge and non-vegetated habitats as part of a seasonal gill net survey conducted in 2011 and 2012. Spotted seatrout ranging from 138 to 485 mm TL were collected using a small-mesh gill net, and 65% of collected individuals fell within the targeted late-juvenile size range. Overall mean catch-per-unit-effort of C. nebulosus did not differ for abundance or biomass between years, but both metrics were significantly higher in SAV habitats. Employing cage enclosures that excluded predators and competitors, cumulative survival of HR fish introduced into natural conditions was 69.2% over a 29 d period, and specific growth rate was negative in all cages but significantly higher in SAV and non-vegetated shorelines than in non-vegetated open water. At the time of recovery, prey items occurred in the stomachs of 49% of fish surviving the entire trial period, and major prey taxa consumed by HR fish were consistent with those found in diets of wild fish. This study supports previous findings of the importance of SAV to the early life stages of C. nebulosus and extends that understanding to the late-juvenile stage. However, SAV was limited in spatial coverage, and spotted seatrout utilized all habitats sampled in the study area. Study results also indicate that HR spotted seatrout can survive natural environmental conditions and transition to wild prey after release into a natural ecosystem.