Research could inform efforts to better monitor bycatch in commercial nets and manage menhaden with their importance to sportfish in mind
Researchers from the National Oceanic and Atmospheric Association, University of Miami, and University of Florida recently completed a study that modeled the ecosystem of the Gulf of Mexico with a focus on Gulf menhaden. The model was developed to assess the ecosystem effects of different menhaden fishing policies, focusing on how menhaden predators would respond to changes in forage availability and bycatch risks.
The researchers also quantified tradeoffs between menhaden harvest and predator biomass to develop ecological reference points—metrics that would help manage the menhaden fishery in the context of the fish’s relevance to the entire ecosystem. ERPs are currently used to manage the Atlantic menhaden fishery, after years of advocacy by anglers.
The TRCP reported on the preliminary results of this study back in 2021. The final published results confirm the findings we shared at that time: Gulf menhaden support about 40 percent of the diets of both king and Spanish mackerel and about 20 percent of the diets of red drum, sea trout, seabirds, and blacktip sharks.
The newly published results also indicate which predators are most sensitive to menhaden harvest and why. King mackerel, Spanish mackerel, blacktip sharks, and red drum are most impacted by the resulting shortage of forage in the water. Tarpon, sea trout, and croakers are most at risk of getting scooped up and killed in the massive purse seine nets deployed by the menhaden reduction fishery.
In the Atlantic, striped bass are the predators that are most sensitive to Atlantic menhaden harvest. This is why stripers were the key species considered in the 2020 development of ERP targets and thresholds, which aim to leave sufficient menhaden in the water as forage for bass and other species, like bluefish, weakfish, and spiny dogfish.
In this Gulf model, the most sensitive predator species to Gulf menhaden harvest was king mackerel, but intermediate relationships were found between menhaden and nine other predator groups. An ERP target could therefore be developed based on the ten most affected predator groups.
The authors suggested that a 20-percent reduction in commercial menhaden landings, compared to 2018-2020 levels, would leave enough menhaden in the water to support these ten predator species at their biomass targets.
Interestingly, the results showed that biomass for many predators was more affected by the commercial harvest of menhaden than by fishing pressure on the predator species itself. This was most notable for red drum and croaker, because of the effects of bycatch. Red drum are a favorite target of anglers in the Gulf, yet the menhaden reduction fishery might catch more redfish as bycatch than the whole recreational sector does.
Unfortunately, the Gulf menhaden fishery has little to no recent bycatch data and no observer coverage during the season. The TRCP has been advocating for updated bycatch analyses in the menhaden fisheries on both the Gulf and Atlantic coasts, and it is our hope that this model will drive that process forward.
This model can be used to inform stakeholders and policymakers of the tradeoffs between different management actions, while considering predator-prey interactions, fishing pressure, and bycatch. It could fuel the development of ERPs for the Gulf menhaden fishery, which mirror that of the Atlantic menhaden fishery.
This updated science is an exciting step forward for the improved management of Gulf menhaden and the predators that rely on them. The TRCP and its partners will be working diligently to gain more information on the role of menhaden in the Gulf of Mexico ecosystem and how mackerel, red drum, and sea trout are affected by the industrial menhaden fishery that currently has no catch limit and very little state and federal oversight.