Assessing Northshore Nekton Abundance, Substrate, and Environmental Conditions In the Northern Gulf of Mexico: Are There Differences Among Three Adjacent Coastal Areas and Have There Been Changes Over Three Decades (1986-2015)?

Abstract

Fishery-independent data on fishes and crustaceans collected in spring and fall over three decades (1986–2015) from coastal areas of southeastern Louisiana, Mississippi, and Alabama were analyzed to determine if these areas differed in species composition and environmental conditions over this period. Multivariate community analyses revealed significant differences in species composition among the three areas in trawl collections for both spring (ANOSIM, R = 0.543, p \u3c 0.001) and fall (R = 0.722, p \u3c 0.001), while seine collections were not significantly different among the areas for either season (spring, R \u3c − 0.06, p = 0.61; fall, R \u3c 0.167, p = 0.14). The most important factor contributing to these differences was the presence of more shell substrate at the Louisiana sites (LINKTREE analysis, B% = 86, p \u3c 0.05). Abundance data for common species were used to test for changes over the three decades. Blue crabs (Callinectes sapidus) and least puffers (Sphoeroides parvus) experienced decreases in four of eight area–season–gear scenarios. Four species of flatfishes also experienced multiple declines. Salinity increased at the Louisiana trawl sites over the period in both spring (+ 2.92; ANOVA, p \u3c 0.001) and fall (+ 5.97; ANOVA, p = 0.001–0.002), while spring trawl sites became warmer in Mississippi (+ 2.15 °C; ANOVA, p = 0.001–0.002). Alabama trawl sites became warmer in both spring (+ 3.36 °C; ANOVA, p \u3c 0.001) and fall (+ 1.91 °C; ANOVA, p \u3c 0.001). With declines in species and changes in environmental conditions, this region faces multiple challenges in maintaining its estuarine fisheries