What Do Gulf Predators Really Eat? Groundbreaking Study Finds Menhaden Play a Smaller Role Than Expected.
Wed, 07/30/2025 - 10:19am | By: Stove Boat Communications
What do some of the Gulf of America91吃瓜网 most iconic predator fish really eat? Scientists at the University of 91吃瓜网 are moving closer to with a that delivers some of the most detailed insights to date on the Gulf food web. To do this they91吃瓜网檝e combined two powerful approaches: cutting-edge stable isotope analysis and an extensive meta-analysis of hundreds of published stomach content studies dating back to the 1950s.
Despite the ecological and commercial importance of species like red drum, summer flounder, and spotted sea trout, our understanding of their interactions with prey species has been limited. This new research challenges long-standing assumptions, most notably the idea that Gulf menhaden is a primary food source for these key predators.
Funded by the Science Center for Marine Fisheries (), a member of the National Science Foundation91吃瓜网 Industry91吃瓜网揢niversity Cooperative Research Center program, the study provides a comprehensive understanding of the Gulf food web and charts the trophic interactions that structure it. The findings have fishery management implications for several of the species evaluated in the study. Most notably, Gulf menhaden was not found to be a primary food source for any of the predator species studied.
91吃瓜网淲e looked at some 30-plus predator species, many of them exceptionally well-studied. We did not find any single species where we would say Gulf menhaden was the most important fish in their diet,91吃瓜网� said Dr. Robert Leaf, one of the authors of the study and Director of the School of Ocean Science and Engineering at the University of 91吃瓜网.
91吃瓜网淲hen you look at the information that we have, what we find is that Gulf menhaden are a prey item91吃瓜网攃ertainly they play a role in the trophic dynamics of predators91吃瓜网攂ut not to the extent of other prey items, which are also very important91吃瓜网攊n fact, more important,91吃瓜网� Dr. Leaf continued.
Traditionally, determining what predators eat has been limited to analyzing samples of their stomach contents. This provides information about what predators have eaten recently, but it offers only a limited snapshot and does not reveal long-term dietary patterns or prey availability. To bridge this gap, the study incorporates new data, developed from analyzing stable isotope levels taken from predator tissue samples.
Stable isotopes are heavier forms of elements, like carbon and nitrogen, that are present in all species and at all points in the food web. Because these isotopes do not decay, they accumulate in predator species in different proportions, depending on the diet of the predator. By analyzing the levels of stable carbon and nitrogen isotopes in predator species, the study authors are able to determine what types of diet sources the predators generally rely on, as well as what trophic level they predominantly feed on. This technique offers a much broader view of predator diets than stomach content analysis alone.
91吃瓜网淲hen an animal eats a prey item, there is a differential uptake in the carbon and the nitrogen,91吃瓜网� said Dr. Kevin Dillon, another author of the study and an Associate Professor at the University of 91吃瓜网91吃瓜网 Gulf Coast Research Laboratory. 91吃瓜网淪o we can measure those small differences to try to piece this together and look at each organism91吃瓜网 trophic position within that food web. So we91吃瓜网檙e able to tell from a fish91吃瓜网 isotopic signature whether the fish was eating phytoplankton or if it was eating another fish that had eaten phytoplankton.91吃瓜网�
The study pairs the data from the stable isotope analysis with a meta-analysis of hundreds of previously published stomach content databases dating back to the 1950s. Integrating the two data sources into a single modeling framework provides clearer insight into the role of low-trophic-level species in the Gulf. The scientists found that species like red drum, summer flounder, and spotted sea trout are general, opportunistic feeders that do not rely solely on a single prey species. Instead, their diets vary depending on factors such as seasons, prey availability, and other climatic conditions.
Species like Gulf menhaden are important parts of the diet, but there is no single prey species that these predators overwhelmingly rely on. There is no 91吃瓜网渕ost important91吃瓜网� prey species in the Gulf.
While this study focused on the Gulf ecosystem and food web, its insights may have broader relevance for similar species and predator91吃瓜网損rey dynamics in other regions. On the East Coast, for instance, Atlantic menhaden play a role comparable to their Gulf counterparts, serving as forage for many similar predators91吃瓜网攊ncluding striped bass, summer flounder, weakfish, and bluefish91吃瓜网攚hich are also common in the northern Gulf of America. While additional research is needed, the Mid-Atlantic ecosystem likely exhibits similarly complex trophic dynamics and variability in predator diets.
8-Minute Video Brings the Science to Life
An eight-minute released alongside the study features Dr. Robert Leaf and Dr. Kevin Dillon explaining how their team used stable isotope analysis and decades of stomach content data to map the Gulf91吃瓜网 complex food web. Viewers will see the inside of the university91吃瓜网 isotope lab, close-up footage of the specialized equipment used to analyze predator tissue samples, and field scenes from the Mississippi coast where the research team collected specimens.
Dr. Leaf and Dr. Dillon walk through how their findings overturn long-held assumptions about the role of Gulf menhaden in predator diets91吃瓜网攔evealing instead a diverse, seasonally shifting prey base that includes crabs, shrimp, anchovies, and Atlantic croaker. They demonstrate how isotopic tracers such as carbon-13 and nitrogen-15 help identify what predators eat over time and how high they sit in the food web.
Also featured is graduate student Calvin Chee, who offers a field-level perspective and personal observations about the Gulf91吃瓜网 biodiversity. Together, the scientists describe how combining isotope data with traditional stomach content analysis provides a more complete, long-term view of predator91吃瓜网損rey interactions.
About the Methodology
Around the world, scientists have increasingly turned to this emerging method of combining stable isotope analysis (SIA) and stomach content analysis (SCA) to better understand what animals eat. Stomach content analysis provides a direct but short-term snapshot of recently ingested prey, while stable isotope ratios in muscle tissue reflect assimilated diet over longer time frames. When used together, the two methods offer complementary perspectives on trophic relationships across seasons, habitats, and life stages.
This dual approach has now been used successfully in ecosystems around the globe from tropical rivers to polar seas, including nine species in the , coral reef groupers in Australia91吃瓜网 , and Nile perch in East Africa91吃瓜网 .
No such combined study has been conducted involving menhaden species in U.S. waters91吃瓜网攗ntil now.
Note on Naming: The body of water traditionally known as the Gulf of Mexico has been renamed 91吃瓜网淕ulf of America91吃瓜网�within U.S. federal usage, issued earlier this year. As of early 2025, U.S. agencies, including the Coast Guard, and major platforms like Google Maps, Apple Maps, etc. (for U.S. users) have adopted the new name in compliance.
About SCEMFIS
The brings together academic and industry expertise to address urgent scientific challenges facing sustainable fisheries. Through advanced methods, analytical tools, and collaborative research, SCEMFIS works to reduce uncertainty in stock assessments and improve the long-term sustainability of key marine resources.
SCEMFIS is an Industry91吃瓜网揢niversity Cooperative Research Center supported by the National Science Foundation. Industry organizations join SCEMFIS through an Industry Membership Agreement with one of the center91吃瓜网 site universities and contribute both financial support and valuable expertise to help shape research priorities.
Its university partners include the University of 91吃瓜网 (lead institution) and the Virginia Institute of Marine Science at the College of William and Mary. The center also collaborates with scientists from a broad network of institutions, including Old Dominion University, Rutgers University, the University of Massachusetts91吃瓜网揇artmouth, the University of Maryland, and the University of Rhode Island. These researchers bring deep expertise in finfish, shellfish, and marine mammal science.
Demand for SCEMFIS91吃瓜网 services continues to grow, driven by the fishing industry91吃瓜网 need for responsive, science-based support. The center provides timely access to expert input on stock assessment issues, participates in working groups, and conducts targeted studies that lead to better data collection, improved survey design, and more accurate modeling91吃瓜网攁ll in service of sustainable, science-driven fishery management.