Abstract
Data limited species are a global concern for fisheries science and management. For example, historical fisheries exploitation has led to conservation concerns for Atlantic halibut (Hippoglossus hippoglossus) and coastal sharks off the eastern United States. The 2015 Atlantic halibut stock assessment was rejected, and the 2017 and 2019 data-limited assessments were unable to determine stock status. Large coastal sharks (Carcharhinidae, Sphyrnidae, and Ginglymostomatidae) are managed as a complex, which was most recently assessed in 2006. The 2006 stock assessment was rejected, and the National Marine Fisheries Service lists species-specific stock assessments of coastal sharks as a priority. Previous Atlantic halibut and large coastal shark complex stock assessments were rejected in part, because of uncertainties with indices of abundance. The trawl survey used to monitor Atlantic halibut catches few fish, and the surveys used to monitor coastal sharks are local and short-term. The goal of this dissertation was to improve abundance estimates for these species by standardizing fisheries dependent and independent catch rates for stock assessment. In Chapter 2, Atlantic halibut fishermen in Maine were interviewed to help create a standardized index from their logbook data which indicates a stable or increasing stock over the last decade that is consistent with fishermen perceptions. In Chapter 3, a fisheries independent survey for large coastal sharks was standardized in the Bahamas to account for changes in sampling and environmental variables, and the standardized series indicates relatively stable catch rates for the tiger shark (Galeocerdo cuvier), blacktip shark (Carcharhinus limbatus) and lemon shark (Negaprion brevirostris) but highly variable catch rates of nurse sharks (Ginglymostoma cirratum). In Chapter 4, a Bayesian state-space surplus production model was applied to lemon sharks in the southeastern United States. The model incorporated prior knowledge of lemon shark demography and a combination of eleven indices of abundance and indicates a relatively stable trend is stock abundance since the mid-1990s, with some estimates of prior depletion. Results from Chapter 2 and 3 are expected to provide valuable information, on data-limited species, for management as a relatively empirical indicator or input to analytical stock assessment models. The results from Chapter 4 improve understanding of lemon shark population trends and provide information for fisheries managers that will hopefully provide a solid basis for future management advice. Chapter 5 provides a synthesis of findings and perspectives from each chapter, including overarching lessons and recommendations for future research. Ultimately, developing abundance trends and relatively simple stock assessments for data limited species can help to ensure they are sustainably harvested.