Quantifying the Trophic Importance of Gulf Menhaden within the Northern Gulf of Mexico Ecosystem

Abstract

The Gulf Menhaden Brevoortia patronus is frequently cited as playing a predominant role in the trophic structure and function of the northern Gulf of Mexico (GOM) marine ecosystem, yet much work remains in quantifying its ecological importance. We performed a meta-analysis of diet studies to quantify the trophic role of Gulf Menhaden within this ecosystem. Of the 568 references consulted, 136 identified predator–prey interactions involving Gulf Menhaden, menhaden Brevoortia spp., or unidentified clupeid prey items. Overall, 79 species were reported to consume menhaden, and no significant difference was detected between the Atlantic Ocean and the GOM in the mean occurrence of Brevoortia spp. in predator stomachs. We employed a probabilistic approach using maximum likelihood estimation to quantify trophic interactions within the northern GOM, with a focus on the trophic role of Gulf Menhaden. The estimated contribution of identifiable menhaden to the diets of all predators generally ranged between 2% and 3%; the largest dietary contribution was identified for Blacktip Sharks Carcharhinus limbatus (8%), and lower estimates (<2%) were obtained for oceanic species, including sharks, billfishes, and tunas. When diet compositions were adjusted for unidentified prey by using the proportion of fish species biomass in the ecosystem, five predator groups showed a relatively large dependence on menhaden prey: juvenile King Mackerel Scomberomorus cavalla, juvenile Spanish Mackerel Scomberomorus maculatus, adult Spanish Mackerel, Red Drum Sciaenops ocellatus, and Blacktip Sharks. The quantification of trophic linkages and key predators identified herein will be fundamental to future modeling efforts focused on the northern GOM ecosystem.

Received March 24, 2015; accepted September 3, 2015

Acknowledgments

We thank all of the researchers, students, and agencies who collected and reported diet data; J. Wrast and C.W.D. Gurshin for sharing their data; and D. Chagaris for sharing his method of weighting diet composition from multiple studies. This research was carried out in part under the auspices of the Cooperative Institute for Marine and Atmospheric Studies, a cooperative institute of the University of Miami and the National Oceanic and Atmospheric Administration (Cooperative Agreement NA17RJ1226). We appreciate J. Bohnsack, A. Chester, J. Buckel, and two anonymous reviewers, who helped to improve the quality of the manuscript.