by Eyal Frank and Kimberly Oremus


Our global use of resources has increased threefold since 1970, leading to increasing wetland degradation, deforestation outpacing regrowth, accelerating biodiversity losses, and fisheries collapsing. Yet there is little causal evidence on the impact over time of laws that seek to rebuild and sustainably manage biological resources on a wide scale. Marine fisheries are a good example of the tension between utilizing and jeopardizing a biological resource. As of 2018, marine fisheries provided 84.4 million tonnes of fish, an important source of protein and food security, and 39 million jobs and livelihoods worldwide. In the United States alone, commercial fisheries employ 1.2 million people and generate more than $165 billion annually.

The Magnuson-Stevens Act (MSA) regulates all commercial marine fisheries in United States, which has the world’s second-largest marine jurisdiction. Its goal is to both conserve the fish population and maximize long-term catch by identifying stocks that are overfished and bringing them back to healthy levels. Under the policy, when a fish population falls below a predetermined scientific population threshold, total catch must be reduced until the population is rebuilt to a sustainable level. (The threshold is often set at one half of the biomass needed for maximum sustainable yield, the largest average catch that can be taken from a stock over the long term without depleting the stock.) Since the MSA’s reauthorization, other countries have adopted sustainable fishing policies with comparable provisions, and the policy has gained a reputation internationally as a gold standard in sustainable fishery management.

Even as countries increasingly adopt sustainable fishing policies, the MSA and its counterpart policies in other countries have been subject to controversy in recent years. Some blame the policy for being too stringent and leading to underfishing and yield losses (See Underfished or Unwanted? Much blame cast upon fisheries policy may be misguided). Others argue the policy is not doing enough to rebuild stocks, or that stocks would have rebounded even without it. As a result of the controversy, the MSA’s latest reauthorization has been held up in Congress since 2013. And such controversy could dissuade other countries from adopting sustainable fisheries policy.

Research Design

The researchers provided the first large-scale causal evidence for a policy’s effectiveness in recovering a depleted biological resource: fish stocks. They collected the largest dataset of its kind to study the requirement to rebuild overfished stocks under the 1996 reauthorization of the Magnuson-Stevens Act (MSA). A rebuilding plan aims to recover the fish population, measured by its biomass—the aggregated weight of all fish in a stock. Rebuilding plans take 10 years, on average. A successful rebuilding will lead to the recovery of the stock, allowing managers to increase the amount of fish they catch without jeopardizing the fish population.

The MSA’s requirement to rebuild stocks was implemented in the United States two decades before the European Union implemented comparable requirements. Because of this different policy environment and the fact that the US and EU fish stocks are otherwise very similar, the researchers used a natural experiment to compare the fish stocks in the US since 1996—subject to the policy—to those in the EU over the same period that would have met the rebuilding criteria had their policy been implemented. They additionally compared US stocks that were depleted before the rebuilding policy went into effect in 1996 to US stocks that were depleted after the policy went into effect.


Fish stocks subject to the policy had their biomass increase by more than 50 percent compared to their counterparts not subject to the policy. Comparing US fish stocks that went into rebuilding with EU stocks that met the conditions for rebuilding but weren’t subject to the policy, the researchers found that prior to entering rebuilding US and EU stocks were not very different. However, five to ten years after the US stocks met the criteria for rebuilding, their population began to improve. On average, ten years after a US stock fell below the threshold for rebuilding, its biomass was 52.2 percent higher than the average depleted stock in the EU.

Figure 1: US vs. EU Fish Stock Biomass Before and After Qualifying for Rebuilding

In the absence of a rebuilding policy, fish populations did not recover. With policy intervention, fish stocks significantly recovered. In addition to the EU comparison, the researchers also compared US stocks that were depleted before the 1996 law to US stocks that were depleted after the policy went into effect. During the period before the law, fish stocks that dropped to unhealthy levels continued to decline in the decade following, with their biomass dropping by an additional 44.9 percent. However, the researchers found that depleted stocks did recover after the rebuilding policy was required. Five to 10 years after falling to an unhealthy level, the stock population doubled—recovering, on average, by 97.9 percent relative to their population before it declined below the overfished threshold.  This aligns with the goal of the MSA policy, which in many cases aims to double the stock biomass within ten years.

Figure 2: US Fish Stock Biomass With vs. Without Regulations Before and After Qualifying for Rebuilding

As populations rebounded, fish catch and revenue also recovered to pre-rebuilding levels or higher a decade after the rebuilding efforts took effect. When comparing the US and EU stocks, the researchers found that catch levels were similar before the US stocks were subject to the policy. In the years after they entered rebuilding requirements, US stocks’ catch levels declined but returned to or exceeded pre-rebuilding levels by the ten-year mark. In the 10 to 15 years after being subject to the rebuilding efforts, our results suggest that rebuilt stocks had a 51.9% higher catch compared to stocks in the EU.

Figure 3: US vs. EU Fish Stock Catch Before and After Qualifying for Rebuilding

In the US, the researchers compared the revenue from fish catch for the fish stocks that were rebuilt. While there is some heterogeneity between stocks, on average, stocks recovered to their baseline revenue.

Figure 4: US Fish Stock Before and After Qualifying for Rebuilding

Policy Implications

The researchers concluded that the MSA fishing policy substantially increased fish stock populations that underwent rebuilding efforts.  In fact, for depleted stocks, the MSA result in 50 percent more fish in US waters compared to in the EU, where the fishing policies were not in effect or less stringent. Their findings have direct policy implications for domestic and global fishery management, emphasizing the important role rebuilding policies have played in improving fish populations, catch and revenue in the United States. Additionally, the findings provide clear support for the role of predetermined, scientific thresholds more broadly in biological resource management. For example, forest management could utilize tree-density or forest area thresholds; wetland areas could be preserved to buffer against various rain intensity thresholds; and conservation policies could predetermine viable population levels or habitat sizes.

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Areas of Focus: Environment
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Conservation Economics
Conservation Economics
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