Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

First Advisor

Charles A. Wilson

Abstract

The purpose of this dissertation was to describe the association of red snapper, Lutjanus campechanus, with oil and gas platform habitat in the northern Gulf of Mexico. Ages were estimated using transverse sections of sagittae. Annuli were validated to have formed yearly. Age estimates ranged from less than 1 to 54 years. Von Bertalanffy growth models were significantly different for males and females; females exhibited a faster initial growth rate but achieved a lesser maximum length than did males. The variability in age among individuals of a given length or weight class precluded formulation of age at size keys. Otolith weight provided a more precise estimate of age than did length or weight. Spawning season commenced in May and extended through September. The presence of multiple oocyte maturation stages within ovaries evidenced a heterochronal spawning pattern. Estimated batch fecundities ranged from 455,919 to 2,096,519 ova and correlated moderately well with fork length. Spawning frequencies were estimated variously as 4.5 days, 5.4 days, and 7.6 days. Fifty percent maturity was achieved in both sexes at 290 mm fork length. All individuals greater than 420 mm fork length were mature. Red snapper were caught with hook-and-line, treated (control, gas bladder deflation, tagging, tagging with deflation), and released into a holding net for varying lengths of time (24, 30, 36, 48 hours) to assess post-capture mortality. Results indicated an average mortality rate of 20% at 21 m depth, with no significant difference between treatments, or time-in-net. There was a significant difference in mortality between season, and an interaction between season and treatment, with higher mortalities observed in the summer. Gas bladder deflation did not significantly enhance survival at 21 m. Behavioral observations of red snapper in association with oil and gas platforms were collected with remotely operated underwater video systems. Schools of small juveniles were most often observed in close association with the platform structure, whereas larger adults were most often observed as solitary individuals. Both the adults and juveniles appeared to partition habitat by selecting different depth locations along the vertical gradient of the structure.

Pages

76

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