The trophic role of lutjanid fish and impacts of their fisheries in two ecosystems in the Gulf of Mexico

The trophic role of snappers was evaluated on the continental shelves of the south-western Gulf of Mexico and the Yucatan in the south-eastern Gulf of Mexico. Mass-balanced, steady-state trophic models of the two ecosystems were constructed with Ecopath and perturbations were simulated in the ecosystems with Ecosim by increasing fishing mortality. Impacts were measured by changes in biomass of snappers and other groups, and in some indices of stability: persistence, recovery time and resilience. The snapper populations differed between ecosystems. The western Gulf of Mexico system appeared more complex and more stable than the Continental Shelf of Yucatan. Although overall stability indices between ecosystem suggested a similar structure and function, there were clear differences at a group level. Correlation of stability attributes between groups suggested differences in the role of snappers between the ecosystems suggesting that each stock should be managed individually

Energy flow and network analysis of Terminos Lagoon, SW Gulf of Mexico

The food web in Terminos Lagoon, south-western Gulf of Mexico was dominated by the detrital pathway, with benthic invertebrates playing a significant role in transferring energy from detritus to higher trophic levels. The fish yield per unit of net primary production was only 0.04%. Fractional trophic levels ranged from 1.0 to 3.31, with fish occupying the highest trophic levels. Using network analysis, the system network was mapped into a linear food chain and five discrete trophic levels were found with a mean trophic transfer efficiency of 7%. Analysis of mixed trophic impacts showed that fish had very little impact on the other compartments, due to their relatively low biomass and consumption, with exception of the Engraulidae. Detritus and lower trophic levels had significant positive impacts on other groups in the system, suggesting 'bottom-up' control of the food web. A high detritivory: herbivory ratio (4.6: 1) indicated that most of the primary production was recycled through the detritus-based food web. A Finn cycling index of 7% and average path length of 10 were obtained

Life history of the gray snapper at the warm edge of its distribution range in the Caribbean

Knowledge of the life history of populations at the warm edge of their distributional range can provide a better understanding of how they will adapt to climate warming, including potential poleward redistribution. The range of Gray Snapper Lutjanus griseus has the potential to expand along its northern temperate fringe, but little is known about this species in the warmest portion of its range. We studied the age, growth, reproduction, and mortality of commercially caught Gray Snapper in the Guatemalan Caribbean, where sea surface temperature consistently exceeds 26°C. Longevity was estimated as 10 years, and von Bertalanffy growth parameters that were consolidated through Bayesian estimation incorporating earlier estimates from the Caribbean region were as follows: asymptotic length (L∞) was 35 cm, the growth coefficient (K) was 0.56 year−1, and the theoretical age at zero length (t0) was −0.7 year. Gray Snapper grew slowest in April, prior to the rainy season, and at the onset of the reproductive season, which lasted to September. Fifty percent of the Gray Snapper matured at 31 cm and at 3.5 years of age. Gray Snapper had a lower maximum size, longevity, and peak reproductive investment, a protracted spawning season and reproductive life span, and elevated natural mortality at the warm edge of their distribution relative to temperate climates. Despite the plasticity in life history of Gray Snapper observed in this study, their potential to further adapt to warming remains unknown