Ecosystem-Based Management of Menhaden

Atlantic menhaden (Brevoortia tyrannus) and Gulf menhaden (Brevoortia patronus) are an important component of the marine food web and key forage for a variety of resident and migratory fish species, as well as birds and marine mammals. However, menhaden also support the largest commercial fisheries in their regions, landing over 600,000 metric tons combined each year. Through the adoption of ecological reference points, managers are now seeking to account for menhaden's role in the ecosystem when setting harvest limits. Read below to learn how ecosystem models have been helping in this process.

Schematic representation of reference points. (A) FMSY is defined as the fishing mortality that results in maximum sustainable yield. (B) BThreshold and BTarget are defined as the biomass that corresponds to FMSY and 0.75·FMSY, respectively. (C) Ratios (color map) of scenario’s biomass relative to the target biomass (Btarget) for menhaden predators as a function of variation in fishing mortalities for Gulf menhaden and their predators. A contour value of 1 indicates a state in which the predators’ biomass equals Btarget. The x-value of the intersect between the “1” contour and the horizontal dashed line represents the ERP Ftarget. ERP FTarget is the multiplier of menhaden F that results in the BTarget of a given menhaden predator and is represented as a vertical red line. From Berenshtein et al. (2023).

What is an ERP?

An ecological reference point, or ERP, is generally defined as a target or threshold metric that accounts for some ecological or environmental process that may affect productivity of one or more fish stocks. In the case of menhaden , the ERPs were based on a tradeoff relationship with their predators. This is illustrated in the figure on the right, where we first define the target and threshold fishing mortality rate and spawning stock biomass of the predator. Then, equilibrium simulations are run under combinations of menhaden and predator fishing mortality rates. The ERP target and ERP threshold are defined as the menhaden fishing mortality rates that maintains the predator at its target and threshold biomass, when the predator is fished at its F target. Essentially, the menhaden ERPs are designed to adjust menhaden harvest so as not to compromise the single-species management objectives of the predator(s).

Using Ecosystem Models to Develop ERPs

For both Gulf and Atlantic menhaden, we used the Ecopath with Ecosim (EwE) modeling framework to develop the ERPs. In theory, these ERPs can be developed with any ecosystem or multispecies model as long as it represents bottom-up effects of prey on predators (i.e. food availability effects on predator productivity), and top-down predation effects. First, an ecosystem model is developed and calibrated to historical data in order to estimate the important predator-prey interaction parameters. Next, equilibrium projections are conducted on a species-by-species basis to estimate single species targets and thresholds. Then, equilibrium projections are run under combinations of predator and prey fishing mortality rates. Finally, predator biomass is plotted against predator and prey fishing mortality rates, and ERPs are identified for a given target F rate of the predator.

Atlantic Menhaden ERPs

Atlantic menhaden ERPs were developed using a Northwest Atlantic Continental Shelf model of intermediate complexity for ecosystem assessment, also known as a MICE model (Chagaris et al. 2020), and based on the tradeoff relationship with a single predator, Striped Bass. The menhaden ERP fishing mortality rates were approximately 30% lower than the single species reference points. The ERPs were approved for management by the Atlantic States Marine Fisheries Commission's (ASMFC) Menhaden Management Board in 2020, marking the first inter-dependent multispecies reference points ever adopted for a fishery system in the U.S. Work is ongoing to incorporate seasonal and spatial dynamics into the ERPs. Follow the links below to learn more about the process and history behind Atlantic menhaden ERP development.

Meeting Reports and Summaries

Publications:

Chagaris, D., K. Drew, A. Schueller, M. Cieri, &J. Brito, A. Buchheister. 2020. Ecological reference points for Atlantic menhaden using an ecosystem model of intermediate complexity. Frontiers in Marine Science 7:606417. https://doi.org/10.3389/fmars.2020.606417.
Anstead, K. A., K. Drew, D. Chagaris, A. M. Schueller, J. E. McNamee, A. Buchheister, G. Nesslage, J. H. Uphoff Jr, M. J. Wilberg, A. Sharov, M. J. Dean, J. Brust, M. Celestino, S. Madsen, S. Murray, M. Appelman1, J.C. Ballenger, J. Brito, E. Cosby, C. Craig, C. Flora, K. Gottschall, R. J. Latour, E. Leonard, R. Mroch, J. Newhard, D. Orner, C. Swanson, J. Tinsman, E. D. Houde, T. J. Miller, and H. Townsend. 2021. The path to an ecosystem approach for forage fish management: a case study of Atlantic menhaden. Frontiers in Marine Science. 8:607657. https://doi.org/10.3389/fmars.2021.607657.
Drew, K., M. Cieri, A. Schueller, A. Buchheister, D. Chagaris, G. Nesslage, J. McNamee, J. H. Uphoff. 2021. Balancing model complexity, data requirements, and management objectives in developing ecological reference points for Atlantic menhaden. Frontiers in Marine Science 8:608059. https://doi.org/10.3389/fmars.2021.608059.
Howell, D., A. M. Schueller, J. W. Bentley, A. Buchheister, D. Chagaris, M. Cieri, K. Drew, M. G. Lundy, D. Pedreschi, D. Reid, H. Townsend. 2021. Combining ecosystem and single-species modelling to provide ecosystem-based fisheries management advice within current management systems. Frontiers in Marine Science 7:607831. https://doi.org/10.3389/fmars.2020.607831.
2019 Atlantic Menhaden Ecological Reference Point Stock Assessment Report.

Press Releases:

7/11/2023 - NY Times article: A Tiny Fish That Fuels an Atlantic Ecosystem Now Fuels Industry Debates
Atlantic menhaden board adopts ecological reference points. ASMFC Press Release
Points of pride: Atlantic states commission takes bold step on menhaden. Article in the National Fisherman (Sep 2020)
In Major Policy Shift, Fisheries Commission Recognizes Value of Menhaden to East Coast Ecosystems. Article by Pew Charitable Trusts
Menhaden decision marks a new era in Atlantic fisheries management. Article in the Virginia Mercury.
Environmental groups, industry welcome new menhaden harvest rules. Article in Seafood Source

Gulf Menhaden ERPs

Beherenstein et al. (2023) recently developed a framework for developing ERPs for Gulf menhaden. Similar to Atlantic menhaden ERPs, an Ecosim model was used to identify the tradeoffs between menhaden harvest and predator biomass. Unlike in the Atlantic, there was no single menhaden dependent predator species identified for conservation. Therefore the ERPs were calculated as the mean F target and threshold across the 10 most sensitive (to menhaden harvest) species in the model. Results suggest the fishery is currently operating within the range of the ERPs, however there is considerable uncertainty in the model associated with bycatch and diet composition inputs. The Gulf menhaden ERPs have not been adopted for managemen. Future and ongoing bycatch and diet studies will help to improve the model so that one day it can be used to support ecosystem-based management of menhaden and its predators.

Web Links:

Publications:

Berenshtein I, Sagarese SR, Lauretta MV, Schueller AM and Chagaris DD (2023) Identifying trade-offs and reference points in support of ecosystem approaches to managing Gulf of Mexico menhaden. Front. Mar. Sci. 9:935324. doi: 10.3389/fmars.2022.935324
Berenshtein, I., S. Sagarese, M. Lauretta, M. Nuttall, and D. Chagaris. 2021. Technical documentation of a U.S. Gulf of Mexico ecosystem model. NOAA Technical Memorandum. NMFS-SEFSC-751. 229 p. https://doi.org/10.25923/zj8t-e656.