| dc.description.abstract | Warsaw grouper (Hyporthodus nigritus) and snowy grouper (H. niveatus) are deepwater grouper (F. Epinephelidae) found in the western Atlantic Ocean from the northern eastern seaboard of the United States of America to the central coast of Brazil, including in the Gulf of Mexico and Caribbean Sea. Considered periodic life history strategists, both species are long-lived, with slow growth and late maturation and therefore, are exceptionally vulnerable to overexploitation. Furthermore, both species are likely protogynous hermaphrodites (individuals first mature as females and after an environmentally dictated size or age transition to male) whose populations are sustained through episodic recruitment and infrequent year-class success when environmental conditions promote survival and settlement. However, little is known of their general life history due to the difficulties of common fisheries research methods for deepwater species due to barotrauma caused mortality associated preventing the use of techniques designed to directly estimate population demographics (e.g. abundance, density, age and growth, mortality, etc.), such as in-situ visual surveys or mark and recapture. Here, I attempt to clarify some population demographics using indirect estimation methods to assist in the development of effective fisheries policy. In order two accomplish these ends, the population structure of both species was assessed by analyzing and comparing the geochemical makeup of fish otoliths (“ear stones”) collected from different geographical regions of the Gulf of Mexico (GOM). For both Warsaw grouper and snowy grouper, the chemical composition in otoliths resulted in region-specific signatures leading to the conclusion that individual movement between regions is minimal and therefore mixing limited, thereby suggesting the population is composed of distinct regional components and potential subpopulations. Before evaluating potential differences in population demographics from potentially distinct regions, a bomb radiocarbon age validation was conducted on both species. Typical of deepwater species, bomb radiocarbon age validation revealed an inherent underage bias for older fish in age determination methods, likely due to inability to distinguish annual growth increments in later ages as a result of depressed growth rates. These revelations led to a substantial increase in longevity estimates for both species, with both validated to have a minimum estimate of age-56. Using a newly validated age determination method and insights into population structure, age-length relationships were developed for Warsaw Grouper from multiple regions of the GoM. Growth relationships consistently resulted in a slower growth and lower natural mortality than current estimates, with subtle differences between the eastern GoM and western GoM. These results help to clarify population structure and demographics for two data-limited species subjected to commercial and recreational fishery exploitation that can be directly applied to fishery management and the development of effect conservation policy. | en |
