| Abstract: | Species composition and abundance are important metrics to identify when addressing community structure and ecosystem health due to variable environmental factors. Data collected from the Texas Parks and Wildlife Department bottom longline survey was used to examine species composition, relative abundance and environmental effects on demersal fishes caught along the continental shelf of the northwestern Gulf of Mexico. Surveys from 195 locations in the northwestern Gulf of Mexico also included environmental data: salinity, temperature, dissolved oxygen, and depth. Generalized additive models were used to assess trends in richness, diversity, evenness, and relative abundance; and generalized linear models with binomial distributions were used to assess significant effects of collected environmental data on predicted presence probabilities of dominant species from the survey. A total of 2,802 individuals were caught during the survey consisting of 56% elasmobranchs and 44% bony fishes. Species richness, diversity and relative abundance were mainly affected by region, year, and depth. Six species accounted for 93% of the total catch including blacktip sharks Carcharhinus limbatus, Atlantic sharpnose sharks Rhizoprionodon terraenovae, gafftopsail catfish Bagre marinus, red drum Sciaenops ocellatus, spinner sharks Carcharhinus brevipinna, and bull sharks Carcharhinus leucas. Region and the interaction between temperature and dissolved oxygen were the most common significant effects on species presence. Results from this study provide baseline data for demersal fishes in the northwestern Gulf of Mexico, allowing for future evaluations in changes of the species composition and abundance over time. The electronic version of this dissertation is accessible from https://hdl.handle.net/1969.1/198046 |
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