Factors Influencing the Mortality and Distribution of Subadult Red Drum in North Carolina
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Date
2008-08-13
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Abstract
Subadult red drum Sciaenops ocellatus are ecologically and economically important in North Carolina, but little is known about factors influencing their mortality and distribution in estuaries. I first assessed the effect of fishing on red drum abundance using 24 years of tagging data. The tag-return model incorporated all first returns from fish caught-and-released and accounted for age-dependent selectivities that varied by fate of the fish. Estimated fishing mortality rates (F) were high and variable before regulation changes in 1991, but decreased in magnitude and variability after 1991. A dome-shaped selectivity pattern was estimated to account for migration of older fish into coastal waters. To quantify the natural mortality rate and seasonal Fs for red drum, I conducted the first field test of a combined telemetry – tag return approach. Estimated Fs were similar in seasonal pattern and magnitude between tagging and telemetry, but joint estimates were influenced primarily by tagging. Natural mortality rate was low and influenced primarily by telemetry. The combined approach provides a new tool to estimate mortality rates for myriad fish species. Next, habitat use of subadult red drum was quantified with a combination of fishery-independent sampling, telemetry, and generalized additive models. At a large scale, red drum were associated with shallow, nearshore waters, sometimes with seagrass. To determine the influence of prey, I examined red drum stomachs and used generalized additive models to relate physicochemical and prey attributes to telemetered red drum at a small scale. Telemetered red drum were negatively related to salinity and positively related to dissolved oxygen and total prey. Last, I used tagging and telemetry to quantify the large- and small-scale movements of subadult red drum. Movement rates and directions were influenced by age of fish and region and season of tagging, and suggest that the spatial scale of management and regulations currently employed in North Carolina are appropriate. Tagging and fishery-independent surveys have provided valuable information to improve red drum management.
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Red drum, mortality, Sciaenops ocellatus, habitat use, movement, telemetry, tagging, survival
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Degree
PhD
Discipline
Zoology
