Interspecific Interactions May Influence Reef Fish Management Strategies in the Gulf of Mexico

This study highlights the importance of interspecific interactions among marine organisms and the effect that these trophic interactions have on the development of effective, adaptive management strategies for reef fishes in the Gulf of Mexico. To represent the spatially and temporally constrained, interspecific interactions among reef fishes we employ Atlantis (a spatially explicit, biogeochemical ecosystem model) as our simulation tool. Within Atlantis, we evaluate the performance of a two‐point harvest control rule (HCR) that adaptively increases fishing mortality linearly between upper and lower biomass thresholds based on the available biomass of the stocks. This example demonstrated the use of a “blanket” two‐point HCR that assessed the available biomass of several reef fish species (often co‐caught in fishing gear) both simultaneously and objectively. To estimate the impact of reef fish fishing on species abundance and biodiversity in the ecosystem, we examined four “low” and four “high” fishing mortality (F) scaler scenarios. All model projections are forward looking, representing a 50‐year time horizon (2010 to 2060). We evaluated the performance of the two‐point HCRs under the eight fishing mortality scenarios using ecosystem metrics that were previously found to robustly track changes in ecosystem function caused by fishing. We found that the lower F scenarios produced an ecologically distinct ecosystem state compared with the higher F scenarios, where relatively higher levels of fishing mortality (particularly on predators such as the deep Serranidae group) resulted in an increase in prey availability in later years of the simulation. This led to an increase in the overall productivity of the ecosystem over time and higher catch and biomass of most other reef fish groups at equilibrium (year 50). Our results suggest that a better understanding of interspecific interactions among targeted reef fishes and their prey is critical to developing ecosystem‐based management strategies for the Gulf of Mexico

A Simulation‐Based Evaluation of Commercial Port Sampling Programs for the Gulf and Atlantic Menhaden Fisheries

© 2020 American Fisheries Society. Biological data that are collected in commercial port sampling programs are a critical component of the assessment and management of Gulf Menhaden Brevoortia patronus and Atlantic Menhaden Brevoortia tyrannus. The menhaden port sampling program represents one of the longest continuous commercial sampling efforts in the United States; however, this sampling program has not been evaluated recently to determine whether the program adequately characterizes the size and age structure of the catch despite significant changes in the spatial extent and magnitude of the fisheries in the last three decades. We conducted a simulation study to evaluate current menhaden fishery sampling targets and to examine the relative performance of a suite of alternative targets. To simulate data collection, we conducted a bootstrap analysis of the observed port sampling data. These observations were resampled with replacement across a range of current and alternative combinations of number of trips and fish sampled per trip. At the current target for sampling intensity and allocation, the mean sample weight and proportions at age for ages 2 and 3 are well characterized in both the Gulf and Atlantic menhaden fisheries. The proportions of age‐1 fish in the catch differed by stock and region, with samples from the northern Atlantic regions displaying the greatest uncertainty overall. The proportions of age‐4 and older fish were poorly characterized in both fisheries, which is likely due to their rarity in the population (Gulf) and lack of spatial overlap between the fishery and the stratified distribution of menhaden by age along the coast (Atlantic). Our results indicate that reducing the number of fish that is sampled per trip from the current target of 10 to as few as four would have a minimal effect on estimates of mean size and proportions at age in the catch. Increasing the number of sampled trips will not greatly improve the characterization of catch size or age composition