Evaluating Ecosystem-Based Reference Points for Atlantic Menhaden

Abstract

Implementation of an ecosystem approach to fisheries management (EAFM) for forage fish requires methods to evaluate tradeoffs associated with competing management objectives that focus on supporting fishery yields or providing food for predators. We developed an Ecopath with Ecosim ecosystem model of the U.S. Northwest Atlantic continental shelf (NWACS) for the period 1982–2013 to inform an EAFM for Atlantic Menhaden Brevoortia tyrannus. The model (with 61 trophic groups and 8 fishing fleets) was parameterized and fitted to time series using data from stock assessments, surveys, and literature. Fifty-year simulations evaluated how Atlantic Menhaden fishing mortality rates (F) influenced different ecosystem indicators, including population biomasses, fishery yields, prey-to-predator ratios, and the proportion of trophic groups that were positively or negatively affected. We quantified tradeoffs associated with a range of alternative ecosystem-based reference points for Atlantic Menhaden F and biomass (B), including F for maximum sustainable yield (F_MSY), 0.5F_MSY, proxies for current single-species F reference points, 75% of virgin unfished biomass (B₀), and 40%B₀. Striped Bass Morone saxatilis were most sensitive to increases in Atlantic Menhaden fishing, largely due to their strong dietary reliance on this prey species, but other higher-trophic-level groups (birds, highly migratory species, sharks, and marine mammals) were also negatively impacted. Other commercially important predators of Atlantic Menhaden (e.g., Bluefish Pomatomus saltatrix and Weakfish Cynoscion regalis) had moderate to negligible responses at the highest levels of Atlantic Menhaden F. The alternative reference points considered resulted in (1) variable Atlantic Menhaden biomasses (40–75% of B₀) and yields (54–100% of MSY), (2) up to a 60% decline in Striped Bass B and yield, (3) negative impacts on the B of ≤13% of modeled groups, and (4) positive impacts on the B of ≤6% of modeled groups. Simulations demonstrated the varied responses, potential winners and losers, and tradeoffs resulting from alternative management strategies for Atlantic Menhaden. These results and the NWACS model can help to advance an EAFM for Atlantic Menhaden and other fishes.

Received April 4, 2017; accepted July 19, 2017

ACKNOWLEDGMENTS

We thank all of the researchers, employees, and volunteers who were responsible for developing, operating, and maintaining the numerous surveys and data collection programs we used. We particularly acknowledge scientists who have conducted the NEFSC trawl surveys (especially Sean Lucey and Brian Smith) and NEAMAP (especially Christopher Bonzek) for providing fish biomass and diet estimates. The work of many scientists on the EMAX project provided an excellent starting point for our research, and we thank everyone involved with that effort. We are grateful to the ASMFC Biological Ecological Reference Point working group for its assistance and consultation, particularly members David Chagaris, Howard Townsend, Micah Dean, Genny Nesslage, and Amy Schueller. Michael Frisk, Adrian Jordaan, and Bia Dias contributed through discussions and exchanges of ideas and data. Johanna Heymans, David Chagaris, and Howard Townsend provided helpful reviews of earlier model versions. Funding was provided by the Lenfest Ocean Program (Contract Number 00025536). This is Contribution 5389 from the University of Maryland Center for Environmental Science.