Flipping the Switch on Ecosystem Management
by Shanna Madsen, Research Scientist, Marine Fisheries Administration
With Jeffrey Brust, Chief, Bureau of Marine Fisheries
December 29, 2020
If you've attended a meeting for a fishery management council or commission in recent years, you'll have noticed that ecosystem management is a hot topic discussed at almost every meeting. Federal fishery policy through the National Marine Fisheries Service (NOAA Fisheries), "strongly supports implementation of Ecosystem-Based Fisheries Management (EBFM) to better inform and enable better decisions."1 Ecosystem management is a relatively new way of looking at fisheries management, but what does this mean for management of our marine resources as we know it?
Traditionally, fisheries management has implemented a single-species approach, which considers each species individually when making management decisions. If there is a change in the population of that species, the only variable that fisheries managers can change in this management scenario is how much we can fish for that species. However, we know there are factors outside of fishing that can cause a change in a fish population, and we know that fishing can affect more than just the species being targeted. Ecosystem management attempts to consider all aspects of the ecosystem holistically, rather than just focusing on a single fishery or species like traditional fisheries management. Ecosystem management incorporates the interactions between the fish species, protected species, habitat, and other ecosystem components (including our human reliance on them!), into management decisions. Ecosystem management not only investigates all the factors that impact fish populations, it also considers how the fishing itself impacts other parts of the ecosystem.
Ecosystem management obviously sounds great in theory, but it is challenging in practice. You can think of fisheries management like a switchboard. Traditional singles-species management has one lone switch, and managers can turn the fishing switch up or down. Ecosystem management has that same switchboard and switch, plus a host of other knobs and switches, which are all connected to each other. Flipping one switch or turning one knob may now change how all the others perform; in other words, changing harvest in one fishery may impact another species population and how much of that species we can harvest. Managers are left wondering what knobs, buttons, and switches to change and how those changes resonate through the rest of the ecosystem.
Ecosystem management is such a complicated issue that there are levels or tiers that managers can consider based on their management objectives, available data, etc. These levels vary in degree of complexity as far as looking at different ecosystem components and discussing trade-offs between management strategies. These levels are illustrated in the graphic from NOAA Fisheries (Figure 1).
- The simplest level is single-species management, which we discussed earlier, where only one species is considered, and outside influences are ignored.
- The next level, referred to as an ecosystem approach to fisheries management (EAFM), begins to consider ecosystem components beyond just fishing, but still focuses on a single species. For example, scientists and managers might consider habitat needs, predation, or climate change that affect a species, but still implement management decisions on a single species basis.
- The next more complex type is known as ecosystem-based fisheries management (EBFM). This framework considers multiple fisheries, non-target species, and environmental factors collectively to achieve some set of overarching management goals.
- Finally, the most comprehensive level, marine ecosystem-based management (EBM) incorporates all interdependent components of the ecosystem and all resource users (not just fisheries), into resource management decisions. At this level, anything happening in the ocean is considered to develop resource use policies across user groups.
Many fishery management Councils and Commissions have begun to incorporate some of these ecosystem considerations into their management process.
- Environmental data are considered for species managed by both ASMFC and MAFMC, such as how long-term trends in ocean temperatures affect recruitment, fish growth, and stock distribution, and how management decisions might respond to these trends (an example of EAFM).
- The Mid-Atlantic Fishery Management Council (MAFMC) incorporates ecosystem components into the Atlantic Mackerel, Squid, Butterfish FMP (an example of EAFM).
- The Atlantic States Marine Fisheries Commission (ASMFC) considers both horseshoe crab and shorebird abundance when setting annual harvest levels for horseshoe crabs (an example of two species EBFM).
Case study: Atlantic menhaden
The remainder of this article focuses on ongoing work to develop ecosystem management for Atlantic menhaden, or bunker (Figure 2) by the ASMFC Ecological Reference Points Workgroup (ERP). Menhaden live in coastal waters and estuaries from Northern Florida through Nova Scotia and support the largest directed commercial fishery on the US East Coast, with NJ as the second largest harvester. This fishery processes whole fish into products such as fish meal and fish oil and supplies whole fish as bait to other fisheries such as lobster, crab, and recreational hook-and-line fisheries.
Menhaden are an important link in the food chain, as they eat plankton and are themselves an important prey item for many species like striped bass, spiny dogfish, bluefish, and weakfish (Figure 3). These predators of menhaden are commercially, recreationally, and ecologically important, but menhaden also provide food for other charismatic species like birds and marine mammals. Because menhaden provide food to these predators, a decline in menhaden abundance may impact the abundance and diversity of predator populations, especially if other food sources are scarce or not available. Menhaden provide an important service by supporting valuable reduction and bait fisheries, but they also may provide additional services to fisheries of the predator species that depend on menhaden as a food source. Maintaining a healthy Atlantic menhaden population has benefits for the ecosystem as well as many different fishery stakeholders.
It is because of these species interactions that ASMFC has been working diligently to establish management measures that account for menhaden's role in the ecosystem. Predecessors to the current ERP Workgroup began work on multispecies models in the late 1990s. The result was a model that estimated annual consumption of menhaden by several of its key predators. This source of menhaden mortality was explicitly considered when estimating how large the menhaden stock was every year and determining how much was available for harvest after predation needs were accounted for (an example of EAFM). This model was a considerable step towards ecosystem management, but it was very cumbersome and only accounted for one-way interactions (how predators affect menhaden population size, but not how predator populations might be affected by changes in menhaden population size). To address these concerns, the ERP investigated several alternative models before selecting one that is more user friendly, accounts for two-way interactions, and incorporates additional trophic groups that the original model did not (such as birds and marine mammals). Model development occurred over several years, and a completed version was reviewed by a panel of independent experts in 2019. The panel determined that the framework and data sources used in the model were scientifically sound, and they recommended the model for use in management by ASMFC.
Another key step in the process was to shift our thinking from managing each species individually to managing them collectively. In 2015, ASMFC held a series of facilitated workshops to develop specific multispecies management objectives and priorities. For example, at a given population size of menhaden, the size of one predator population has the potential to affect population sizes of all other predators through prey (menhaden) availability, so tradeoffs must be considered for "acceptable" population sizes of the different predators. During the workshops, managers, stakeholder representatives, and scientists worked together to establish fishery priorities, population tradeoffs, and overall management objectives in a multispecies realm.
With an approved model, appropriate data, and an explicit set of management objectives, all the pieces were in place to develop multispecies management options. Early in 2020, the ERP Workgroup configured the model to answer the specific question: how much menhaden can be harvested each year and still sustain the menhaden population and provide enough menhaden to allow predator populations to attain their predetermined acceptable levels of abundance. The model was run numerous times to evaluate uncertainty in the data and various levels of risk of overharvesting menhaden. In October 2020, the options were presented to the ASMFC Atlantic Menhaden Management Board who ultimately adopted an annual menhaden harvest of 428.5 million pounds coastwide. This represents a 10% reduction in harvest from recent years but ensures enough menhaden are left in the water for the continued viability of the population, as well as sufficient forage to achieve the desired populations of striped bass and other predators.
The long road travelled
This new strategy is a significant accomplishment for ASMFC and a major step forward for fisheries management. It is one of only a handful of real-world implementations of ecosystem-based fishery management, where several species and fisheries are managed collectively to achieve a set of common goals, in the world. You may notice that it took nearly 25 years to implement this seemingly simple change in management strategy. Consider, however, that when this process began in the 1990s, there were no multispecies models available. Even if there had been, the data available on species interactions was limited and would not support such "data hungry" models. Over the years new models were developed to support this project, new surveys and sampling methods were initiated to support those models, and these surveys had to run for a decade or more in order to observe and understand trends over time.
Further, not only did we need to build the infrastructure to support this initiative, but multispecies management required a significant shift in mindset from traditional single-species management. It can be difficult enough to get commercial, recreational, and environmental groups to agree on management objectives for a single species; now we are asking them to agree on objectives for multiple species at once!
Adoption of these ecosystem reference points by ASMFC is a testament to the collaborative approach to fisheries management. Staff from the NJ Marine Fisheries Administration have been involved since the beginning and played a significant role in the development of the data sources, models, and management framework. But without the support and contributions from hundreds of other scientists, managers, and stakeholders over more than 20 years, we would not be celebrating this achievement. The product is the result of decades of hard work invested by countless individuals working together to achieve common goals that will benefit the individual stocks, the industries they support, and the ecosystem as a whole.
1 NOAA Fisheries: Ecosystem-Based Fisheries Management Policy: www.fisheries.noaa.gov/resource/document/ecosystem-based-fisheries-management-policy
Figure 1 - NOAA
Figure 3 - Pew Charitable Trusts