Spatial and temporal variability in recruitment timing, relative abundance, and mortality of juvenile red drum (Sciaenpos ocellatus) in southeastern North Carolina

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Christopher B. Stewart (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Fred Scharf

Abstract: For many estuarine dependent fishes with protracted spawning periods, there is growing evidence that processes occurring during the juvenile life stage contribute to shaping year-class strength. Juvenile red drum, Sciaenops ocellatus, were collected from the New River and the Cape Fear estuaries continuously from estuarine arrival through age one using 18.3, 30.5, 60.1m seines, as well as multi-panel gillnets over a two year period. The relative abundance of age-0 red drum peaked in mid to late fall each year, and fish were present in shallow habitats into December before presumably moving to deeper waters during winter. Reappearance in shallow water habitats during spring was abrupt and occurred between late March and late April depending on spring warming rates. Red drum were consistently present in shallow areas until the next fall and were captured routinely in seines (through June) and gillnets (into September). Relative abundance of age-0 red drum was markedly higher throughout the entire first year of life in the New River compared to the Cape Fear River during the single year when both systems were sampled. Analysis of previous hydrodynamic research completed in each system suggests that differences in flow dynamics and flushing rates may play a role in the delivery of early juvenile red drum to these systems. Ages estimated from sectioned sagittal otoliths were used to backcalculate hatch date distributions and calculate daily instantaneous mortality rates. Hatch date distributions indicated that red drum typically spawned from July to October in southeastern North Carolina. However, peak spawning in both systems was indicated to occur significantly earlier in August during 2004 compared to early September as observed in 2003, and may have been a result of warmer nearshore water temperatures during summer 2004. Instantaneous mortality coefficients (Z) for age-0 postsettlement red drum during the 2004 fall period were 0.030 (3.0%/d) in the New River and 0.016 (1.6%/d) in the Cape Fear River. Large differences in relative abundance of juvenile red drum during fall combined with significant differences in mortality rates (higher in New River) between estuaries suggests the potential for density-dependent mortality to occur during the juvenile stage. Cohort-specific mortality rates illustrated a trend of lower mortality for earlier hatched red drum in both estuaries, however patterns were highly variable and non-significant. Discrete overwinter loss rates ranged from 35-63% between November and May suggest that year-class strength of red drum may be further regulated by overwinter mortality. The findings of this study suggest that a combination of both abiotic (temperature, salinity, and tidal currents) and biotic processes occurring during the post-settlement stage have the potential to significantly alter initial patterns of recruitment and subsequent year-class strength of red drum in North Carolina estuaries.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Keywords
Channel bass--Mortality--North Carolina, Channel bass--North Carolina--Cape Fear River Basin, Channel bass--North Carolina--New River, Channel bass--Seasonal variations--North Carolina
Subjects
Channel bass -- North Carolina -- New River
Channel bass -- North Carolina -- Cape Fear River Basin
Channel bass -- Mortality -- North Carolina
Channel bass -- Seasonal variations -- North Carolina