Estuarine recruitment, growth, and first-year survival of juvenile red drum in North Carolina

摘要

For many marine and estuarine fishes, there is growing evidence that processes occurring during the juvenile life stage can contribute to determining the relative success of recruitment of annual cohorts into the fishery. We studied two consecutive annual cohorts of juvenile red drum Sciaenops ocellatus from estuarine arrival through age 1 in two estuarine systems of southeastern North Carolina. For age-0 cohorts, relative abundance generally peaked in mid to late fall, and fish were present in shallow-water habitats through December before presumably moving to deeper waters during winter. Reappearance of red drum in shallow-water habitats during spring occurred between late March and late April depending on spring warming rates. Considerable differences in relative abundance of age-0 red drum were observed between estuaries; such differences may be related to variations in estuarine hydrology and flushing rates, which probably affect larval delivery and distribution. Otolith-derived hatch date distributions indicated that red drum juveniles in North Carolina were produced between July and October; interannual differences (of up to 30 d) in peak spawning times were correlated with variable nearshore water temperatures during summer. Juvenile growth rates during fall ranged from 0.45 to 0.75 mm/d, and mortality rates were between 1.6% and 4.1 % per day; ratios of weight-specific instantaneous growth to instantaneous mortality were greater than 1.0 for all cohorts during their first fall. Both growth and mortality varied between estuaries and years, suggesting local-scale control of these vital rates. Discrete overwinter loss rates ranged from 35% to 67%, indicating that fall cohorts of juvenile red drum could be negatively affected by variable overwinter mortality. First-year vital rates and demographics of red drum cohorts in North Carolina displayed considerable spatial and temporal variability that could potentially affect eventual year-class success, highlighting the need for further understanding of the linkages between juvenile ecology and fishery recruitment.