Connectivity and Habitat Use of Two Coastal Pelagic Species, Spanish Mackerel (Scomberomorus maculatus) and Florida Pompano (Trachinotus carolinus)

• Main Author: Schrandt, Meagan N
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2015
• Subjects: Aquatic sciences; Biological oceanography; Ecology
• ISBN: 035535473X; 9780355354737

Spanish Mackerel and Florida Pompano are two schooling coastal migratory pelagic fishes that are commercially and recreationally harvested in the northern Gulf of Mexico and readily cross state management boundaries, which complicates state and regional management plans. I propose that understanding the local ecology of the species, and the degree of connectivity between juveniles and adults within a population as well as among adults across various management areas, can help inform management decisions. Here, I addressed several issues relevant to state and regional level management of species that cross state management boundaries, focusing on the nearshore fisheries of Spanish Mackerel and Florida Pompano, where some of these issues are unknown or not well-understood. Specifically, (1) I evaluated how local abundance patterns of Spanish Mackerel in Alabama’s state waters responded to changes in harvest pressure, evaluated their migration patterns via examining temporal trends in abundance, and determined whether the spatial abundance patterns resembled habitat specialization or generalization. A relatively constant abundance index and year class strength indicated the stock seems to be relatively stable. Seasonal catch rates coincide with the proposed annual migration patterns, and there is evidence for a habitat generalist strategy. (2) I used a field survey to further assess the current abundance and distribution of both species—and their drivers—in the surf zone in the northern Gulf of Mexico. Catches were seasonally greater in the spring, and adult fish presence was better predicted by habitat whereas juvenile Florida Pompano presence was predicted by sampling month and salinity. No measured variables were good predictors of abundance. (3) I then used a mesocosm experiment to examine the potential foraging benefits of schooling in juvenile Florida Pompano since schooling behavior of coastal pelagic fishes can increase vulnerability to harvest. Fish foraging in groups had greater foraging success, suggesting a foraging benefit to schooling, and may also play into why there were predictable relationships with presence, but not abundance of fish in the field survey. (4) I analyzed the cytochrome oxidase subunit I DNA sequences of Spanish Mackerel collected from Texas to North Carolina and Florida Pompano collected from Texas to the Florida panhandle to assess the current distribution of haplotypes (unique DNA sequences), and I found no evidence of genetic population differentiation in either species. Although the genetic analyses indicated a well-mixed population, only tens of individuals are needed to homogenize the genetics; however, this may not be enough individuals to replenish areas of depletion. Therefore, (5) I used otolith microchemistry to assess connectivity of juvenile and adult Florida Pompano in the northern Gulf of Mexico and estimated that exposed beach habitats contributed nearly 75% of individuals to the adult fishery. Lastly, (6) I estimated the number of natal sources contributing to three neighboring states’ Spanish Mackerel fisheries in the northern Gulf of Mexico and found that all three states receive recruits from multiple natal sources, and that all states share the same dominant, common sources. Overall, my results suggest that local (state) Spanish Mackerel and Florida Pompano populations are influenced by the population dynamics of a larger (i.e., beyond Alabama’s neighboring states), mixed population. The geographic extent of the larger population has yet to be fully elucidated.