Master of Science (MS)
Oceanography and Coastal Sciences
Fish otoliths are composed of inorganic calcium carbonate that aid in gravity and auditory reception. Substances permanently accrete to otolith surfaces in distinct temporal patterns of alternating opaque and translucent rings; these rings are direct proxies for a fish’s age. The objective of my research is to demonstrate how otoliths can be used through time and space to estimate both age and growth of fish. I investigated the spatial differences in age distributions and growth models for red snapper, Lutjanus campechanus, at four natural shelf-edge reefs in the northwestern Gulf of Mexico. Red snapper cohorts ranged 1987-2010 cohorts, with the majority (91.69%) of individuals between 4 to 9 years (2001-2009 cohorts) of age. The mean age across all sites was 7.2 years, and the modal age was 6 years. The 2006-year class dominated the distribution (22.98%) and the modal cohort was 2005. Differences in the von Bertalanffy growth parameter k were not detected despite significant differences in mean-size-at age in older age classes. Results suggest that habitat quality may be paramount in investigating red snapper demographics at shelf reefs. In addition, I investigated the temporal differences in freshwater drum Aplodinotus grunniens, age and growth estimates between ancient and modern freshwater drum populations. Ancient otoliths were recovered from shell middens associated with the Tchefuncte culture and the modern otoliths were collected from the commercial fishery in southeastern Louisiana between 1987-1989. Ancient otoliths were radiocarbon dated to 650 BCE, separating the two populations by ~2,600 years. Both populations exhibited a truncated age structure but significantly differed in age frequency distributions and mean age estimates. Mean otolith weight-at-age estimates were similar when plotted against biological age. Estimates of growth rates were difficult to obtain due to low sample sizes in young and older freshwater drum age-classes and the interment of ancient otoliths. Results suggest that mean otolith weight-at-age may be the most appropriate method for modeling growth. Furthermore, fishery exploitation and fisher gear selectivity may have been similar between the Tchefuncte and modern commercial fishers, despite the common assumption that ancient fish populations reached greater sizes-at-age and exhibited faster growth rates.
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Kormanec, Marshall James, "Otoliths Then and Now: A Study of Ancient and Modern Fish Populations in Louisiana's Coastal Waters" (2015). LSU Master's Theses. 627.
Cowan, James H., Jr.