Modeling Discards in Stock Assessments: Red Grouper Epinephelus morio in the U.S. Gulf of Mexico

To be as accurate as possible, stock assessments should account for discard mortality in fisheries if it occurs. Three common approaches to modeling discards in assessments are to lump dead discards with landings, treat dead discards as their own fleet, or link them conversely with landings through use of a retention function. The first approach (lumping) implicitly assumes that the selectivity of landings applies also to discards. In many cases, that assumption is false, for example, if discards comprise smaller fish than do landings. The latter two approaches avoid the assumption by modeling discards explicitly with their own selectivity pattern. Here, we examine these approaches to modeling discards. Using a simulation study, we demonstrate that the two approaches to modeling discards explicitly can provide identical results under both static and time-varying conditions. Then, using a stock assessment case study of red grouper Epinephelus morio in the U.S. Gulf of Mexico, we demonstrate that in practice the approaches to modeling discards can provide different outcomes, with implications for the resultant management advice. We conclude by comparing and contrasting the different approaches, calling for more research to elucidate which approach is most suitable under various sources of error typically encountered in discard data.

Genetic and biophysical modelling evidence of generational connectivity in the intensively exploited, Western North Atlantic red grouper (Epinephelus morio)

Understanding the connectivity of reef organisms is important to assist in the conservation of biological diversity and to facilitate sustainable fisheries in these ecosystems. Common methods to assess reef connectivity include both population genetics and biophysical modelling. Individually, these techniques can offer insight into population structure; however, the information acquired by any singular analysis is often subject to limitations, underscoring the need for a multi-faceted approach. To assess the connectivity dynamics of the red grouper (Epinephelus morio), an economically important reef fish species found throughout the Gulf of Mexico and USA western Atlantic, we utilized two sets of genetic markers (12 microsatellite loci and 632 single nucleotide polymorphisms) to resolve this species’ population genetic structure, along with biophysical modelling to deliver a spatial forecast of potential larval “sources” and “sinks” across these same regions and spatial scale. Our genetic survey indicates little, if any, evidence of population genetic structure and modelling efforts indicate the potential for ecological connectivity between sampled regions over multiple generations. We offer that using a dual empirical and theoretical approach lessens the error associated with the use of any single method and provides an important step towards the validation of either of these methodologies.

Red Grouper (Epinephelus morio) Shape Faunal Communities via Multiple Ecological Pathways

Organisms that modify the availability of abiotic resources for other species can alter the structure and function of ecological communities through multiple pathways. In Florida Bay, red grouper (Epinephelus morio) engineer habitats by excavating sediment and detritus from karst solution holes and are also predators that consume a variety of benthic crustaceans and fish, some of which colonize engineered habitats. The effect of red grouper on these communities is complex as colonizing species interact with red grouper in different ways, including both direct (e.g., predator–prey) and indirect interactions. Here, I present the results of an experiment designed to test the direct effects of red grouper on faunal communities associated with Florida Bay solution holes by excluding red grouper from solution holes for four weeks. Red grouper presence generally had positive effects on the abundance, richness, and diversity of faunal communities associated with engineered habitats. Few strong interactions were observed between red grouper and colonizing species, mainly juvenile coral reef fishes. These results suggest that by acting as both a predator and habitat engineer, red grouper shape unique communities, distinct from those of surrounding areas, and influence the composition of communities associated with manipulated habitats.

Redescription of Philometra margolisi Moravec, Vidal-Martínez et Aguirre-Macedo, 1995 (Nematoda: Philometridae), a gonad-infecting parasite of the red grouper Epinephelus morio (Serranidae) in the Gulf of Mexico

The insufficiently known nematode species