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

Skyler R Sagarese,Matthew V Lauretta,Tess M Geers,John F Walter,Matthew A Nuttall,Joseph E Serafy

doi:10.1080/19425120.2015.1091412

Abstract

AbstractThe 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

Highlights

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
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
Events such as the Deepwater Horizon oil spill highlight the need for ecosystem-based fisheries management (EBFM) in the northern Gulf of Mexico (GOM), as the oil spill presented a significant threat to multiple organisms, habitats, and ecosystems and required an assessment of its ecosystemwide impacts (NRDA 2012)

Summary

Introduction

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. Events such as the Deepwater Horizon oil spill highlight the need for ecosystem-based fisheries management (EBFM) in the northern Gulf of Mexico (GOM), as the oil spill presented a significant threat to multiple organisms, habitats, and ecosystems and required an assessment of its ecosystemwide impacts (NRDA 2012). An Ecopath with Ecosim (EwE; Pauly et al 2000) model that was developed with Gulf Menhaden as the focal species highlighted this forage fish’s role in structuring the ecosystem but recognized the lack of available diet information, for higher-trophic-level organisms (Geers et al, in press). Menhaden have been identified as a more efficient energy transfer pathway to higher trophic levels than jellyfish, and increased forage fish harvest has led to reduced production of pelagic piscivorous fishes, seabirds, and apex predatory fishes (i.e., sharks; Robinson et al 2015)

Objectives

Methods

Results

Conclusion