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Population demographics of southern flounder in the New River, North Carolina gill net fishery

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
William E. Smith (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Ken Pollock

Abstract: The North Carolina (NC) fishery for southern flounder (Paralichthys lethostigma) is currently listed as overfished by the North Carolina Division of Marine Fisheries, and in 2005 management changes were enacted in the fishery in order to achieve a 2005 reduction in fishing mortality. Virtual Population Analysis models are currently used to assess fishing mortality (F) in the NC southern flounder stock, but direct estimates may be more accurate. Direct estimates of F in the New River, NC gill net fishery for southern flounder were obtained for years 2005 and 2006 using tag-returns and accounting for return rate, tag retention, and mortality due to tagging. Annual estimates of F and their probability distributions, F2005 = 1.02 (SE = 0.095) and F2006 = 1.54 (SE = 0.222), indicated a high probability that F attained the targeted fishing mortality of Ftarget = 0.95 in 2005 and a very low probability (p=0.0068) that F attained the target in 2006 in the New River gill net fishery. High interannual variability in F was found, which agrees with recent stock assessments. The results suggest that under the current regulations, F will potentially continue to exceed the target in some NC estuaries, and additional management measures may be necessary in order to reduce F to the target in all systems in which the fishery is executed. Recoveries of previously tagged fish were used in a catch composition analysis of the length frequency, size at age, and maturity of southern flounder harvested in the New River gill net fishery, demonstrating the potential effects of the fishing strategy on longterm yield. Examination of the length frequency distribution indicates that approximately 36% of the catch is composed of sub-legal southern flounder that are discarded, with unknown consequences on mortality. It appears that the fishery is targeting age-1 southern flounder (88% total catch), and all age-0 and age-1 fish exhibited above average growth for southern flounder in NC. 28% of females captured in the months previous to the spawning season were distinguishable as mature, and approximately 19% of the catch may have had the opportunity to spawn in the spawning season previous to their capture, suggesting that much of the catch is immature. Recent evidence suggests that a high removal rate of fast-growing, immature animals can have deleterious effects on long-term yield in the fishery. Yield per recruit analysis and maturity schedules demonstrated that delaying age at entry into the fishery until age-2 may potentially provide higher, more stable yields that are robust to interannual variability in fishing mortality, while also allowing more fish to spawn before becoming subject to the fishery.

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
Southern flounder--North Carolina--New River, Southern flounder--North Carolina--Population, Flatfish fisheries--Environmental aspects--North Carolina--New River
Subjects
Southern flounder -- North Carolina -- New River
Southern flounder -- North Carolina -- Population
Flatfish fisheries -- Environmental aspects -- North Carolina -- New River