An investigation of the trophic role of three pelagic fishes of the Western coast of the Gulf of Mexico, using ECOPATH model

Abstract

The spanish and king mackerels (Scomberomous maculates and S. cavalla) and the blue runner (Caranx fusus) are important pelagic fish resources along the coasts of the Gulf of Mexico. Interdependences between them have been studied through simple multispecies yield models. Simulated changes in fishing effort suggest S. cavalla and C. fusus populations are more stable than S. maculates. The ecosystem model, previously obtained with ECOPATH II, was used to simulate gradual changes in biomass. Ecosystem response tends to maintain the thermodynamic equilibrium by adjusting the biomass/energy flows. The predator/prey and competence interdependences show impacts of different magnitude, depending on how species are using the ecosystem resources. However, the main variations occurred through respiration and flows into detritus. Spanish and king mackerels share some resources like anchovies, herrings and shrimp; however, the Spanish mackerel has a wider trophic spectrum. The blue runner shares some food resources with the above species, but it also uses some others. The specific biomass flows in the prey/predator relationships, the specific foraging index, the niche overlap and the relative population abundance explain the higher variability of the Spanish mackerel population.