Ecological and Fisheries Management Implications of Competition Between Red Snapper and Vermilion Snapper

Abstract

Red (Lutjanus campechanus) and vermilion (Rhomboplites aurorubens) snapper are two of the dominant species in the northern Gulf of Mexico (GOM) reef fish complex. These two species share similar habitats and diets, but little is known about the way that they interact. It is widely believed among local fishermen that red snapper feed more aggressively than sympatric predators and competitively exclude them from both prey and baits. Thus, there is public concern that the growing red snapper stocks will negatively affect vermilion snapper as well as other species. In this thesis I (1) examined the extent of spatial and dietary overlap between red and vermilion snapper, (2) experimentally compared the feeding behavior of the two species and examined the effects of their feeding interactions, and (3) compared the catchability of the two species. Red and vermilion snapper frequently cohabited reefs in the northern GOM and their diets overlapped with marginal significance despite a lack of samples from smaller red snapper. The experiment results show that red snapper are the dominant forager of the two species, as red snapper fed at a higher rate and more successfully than vermilion snapper. These findings indicate that red and vermilion snapper do compete for prey resources and that increasing red snapper abundance could affect vermilion snapper. Lastly, comparisons of red and vermilion snapper abundance measured using video surveys and catch data revealed that red snapper are indeed more catchable than red snapper. This difference in catchability has immediate implications for catch-based stock assessments.