Graduation Year

2010

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Kendra Daly

Co-Major Professor

Richard Cody

Committee Member

Robert Muller

Committee Member

Ernst Peebles

Keywords

age, growth, reproduction, hermaphroditic, overfishing

Abstract

Knowledge of many life history parameters are essential to properly assess and manage fish species. Although the snowy grouper, Epinephelus niveatus, is a commercially valuable fish, which is harvested throughout the Gulf of Mexico, little is known about its age, growth, and reproduction from this region. In this study, snowy grouper from the northern and eastern regions of the Gulf of Mexico were examined primarily using commercially-derived samples that were collected between 1984 and 2004. A total of 1,200 snowy grouper with fork lengths between 242 and 1,190 mm were collected. Sectioned saggital otoliths were used to determine the age of 774 specimens which varied from 1 to 44 years, considerably older than previously recorded. Ninety gonad samples were histologically examined; the sample population consisted of 82 females in various stages of development, 3 males, and 5 transitional fish. Female fish had ages that ranged between 3 to 14 years, with fork lengths from 330 to 880 mm and male fish had ages that were between 17 to 25 years in age, with fork lengths from 955 to 1,080 mm. Transitional fish had ages from 6 to 13 years, with fork lengths from 474 to 930 mm. The results of this study suggest that sexual maturity in females was reached around five or six years, and transition in some fish occurred as early as five years but was observed in older fish. The few males that were collected were older and larger than those fish identified as females. Snowy grouper grow slowly but consistently throughout the first 15 years or up to approximately 1,000 mm in length, at which point growth slows. The von Bertalanffy growth model fitted to all the observed data was L(t) = 1,057 * (1-e-0.0939(t+2.5375)). Snowy grouper recruit into the fishery at around age two, approximately 300 mm fork length. The truncated nature of the age distribution and low number of males collected suggest that snowy grouper in the Gulf of Mexico are likely experiencing overfishing, and more research on the species is necessary to facilitate proper management and conservation.

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