Title

Population dynamics, structure and per-recruit analyses of yellowedge grouper, Epinephelus flavolimbatus, from the northern Gulf of Mexico

Author

Melissa Cook

Date of Award

2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Coastal Sciences, Gulf Coast Research Laboratory

First Advisor

Bruce H. Comyns

Advisor Department

Coastal Sciences, Gulf Coast Research Laboratory

Abstract

Age, growth and reproduction research was conducted on yellowedge grouper, Epinephelus flavolimbatus , obtained from the commercial harvest and National Marine Fisheries Service scientific cruises in the Gulf of Mexico (GOM) during 1979-2005. Fish ranged in size from 107-1,170 mm total length (TL). Ages ranged from 0 to 85 years; maximum age greatly exceeded previously reported ages. Bomb-produced 14 C was used to validate ages determined by counting otolith growth increments. A strong linear relationship existed between otolith weight and fish age (R2 = 0.84). The von Bertalanffy growth equation was TL=970.8(1-e -0.063(t+4.84) ). Length and age structure yellowedge grouper harvested today are considerably smaller and younger than those in the past. Yellowedge grouper are monandric protogynous hermaphrodites and have an extended spawning season from March through September. Results indicated a change in the sex ratio over the last 25 years due to a 14% decrease of males. Size at sexual maturity and size at transition have also decreased. Yellowedge grouper were distributed throughout the GOM, but regional differences in population density, size and age structure and sexual maturity suggest at least two or three separate stocks occur in the GOM. Yellowedge grouper in the western GOM were larger, older and more abundant while fish in the eastern GOM were smaller and younger. Yellowedge grouper in the eastern GOM aggregate in denser patches than those in the western GOM. Yield-per-recruit and spawning stock biomass-per-recruit analyses were applied to determine biological reference points and evaluate the status of the fishery. Results indicated stocks cannot sustain high levels of fishing mortality (F <0.10). Yellowedge grouper are currently experiencing growth overfishing but not recruitment overfishing. The importance of male spawning stock biomass-per-recruit was demonstrated and is suggested as an additional tool for use by managers to avoid stock collapse when managing a protogynous hermaphrodite. Significant changes in the age, length and sex structure were found, particularly in the eastern GOM, since the onset of commercial fishing. Continued monitoring of life history parameters is necessary to ensure continued survival of this species in the GOM.