Study spawns new method to curb overfishing

Man carrying fish

Man carrying freshly caught fish in Timor Leste. (© UN Photo/Martine Perret)

Editor’s note: A new paper in Conservation Letters offers a clearer picture of whether the ocean’s fisheries can continue to feed humanity into the future, providing a new method to help fisheries managers maintain healthy fish stocks and make the best use of the fisheries people depend on.

In this interview, Jack Kittinger, senior director of fisheries and aquaculture at Conservation International (CI) discusses the impact of the research with two of the paper’s lead authors, Andrew Rosenberg of the Union of Concerned Scientists and Elizabeth Selig of the Norwegian Institute for Water Research.

Question: Your research found that more than half of global fish stocks are overfished, or fished “too hard” to produce their maximum sustainable yield (the maximum level at which they can be routinely fished without being depleted). What were your key findings?  

Andrew Rosenberg (AR): A famous fishery scientist, John Gulland, once said, “Fisheries management is an endless argument over how many fish are in the sea until all doubt is removed, but so are all the fish.” In order to manage marine fisheries as a renewable source (i.e. one that we can continue fishing from in perpetuity), it’s important to get regularly updated information on the “status” of stocks of fishable species.  Managers need to know if they’re currently catching an excessive amount of a certain type of fish, what we refer to as “exceeding the productive capacity of the stock,” or, on the flip side, if a larger harvest is possible.  

Elizabeth Selig (ES): Previous attempts to estimate status have given us an incomplete picture of when management was needed. They would broadly tell us that a fish stock was “fully exploited,” which generally meant it was within safe limits and could continue to be fished, or it was “overexploited,” or in poor condition. Our work shows just how far a given stock is from achieving maximum sustainable yield. This is critical information because it tells us when management can increase yields. By giving a stock a “pass” or “fail,” we are missing an opportunity to deliver greater economic and nutritional benefits to people. Given that wild-capture fisheries are often discussed as having no room for growth, this information can tell us where we could be doing better.

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Q: There have been many recent assessments of global fisheries. How does the method you created more accurately assess fish stocks and in turn, how does it help managers more sustainably manage fisheries?

AR: While extensive data collection and the ability to measure the status of fisheries is happening in many developed countries, it’s not the case everywhere in the world. But data collection doesn’t change the simple fact that fisheries provide food for a lot of people regardless of how well monitored those fisheries are.

To improve the ability of fisheries to feed people and to provide food security, knowing the critical role monitoring and data collection and analysis plays, we set out to devise a consistent, repeatable method to estimate status from as many fish stocks as possible with data only on the amount of fish caught and a few details on the biology of the species. The upshot is that we were able to assess more fisheries, more accurately, with only basic levels of data. There are lots of ways to go about this, and to ensure the best chance of success, we applied an approach combining the results from several different methods into an “ensemble,” similar to what is done in other fields such as climate forecasting.

Ultimately, our goal was not to compete for the best method, but to use the best of the available methods. The “ensemble” allows us to take advantage of one model’s strength over another model, ensuring we are using the best predictions possible. We didn’t want to say “fisheries are okay” or “fisheries are a disaster,” we wanted to tease out the details in a way that can be applied over and over even when fisheries data are limited.  

Fish in Malaysia

Freshly caught fish being processed in Malaysia. (© Keith A. Ellenbogen)

Q: What does your research mean for marine conservation? 

AR: If you look at our results for regions around the world, in most places you can see that there are many fish stocks that are well below the level that could produce the best catches on an ongoing basis (so-called “maximum sustainable yield”). That means that if management actions could allow those fish stocks to grow, they would produce greater returns over time. For example, a 20 percent greater return might feed thousands of people with high-quality protein, not just in one year, but consistently, year afteryear into the future. In order to do this, fisheries managers need to know when to intervene, whether that’s  restricting catch to take pressure off fish stocks, opening up fishing access to a particular area or any number of other actions.

Having a big collaborative working group, such as the one that worked on this paper, helps us avoid the argument over who has the best method and that means the approach we ultimately come up can be used for many more fisheries. That benefits the people who rely on these fisheries for their livelihoods and for food security. While there is always room for improvement in methodology, the arguments over whether the overall picture is good or bad doesn’t motivate better management, they just motivate more arguments.  What we’ve done with this research is provide the information that people can use to improve management — and to keep eating fish sustainably.

Q: How could these research findings impact the average fish eater?

ES: Many of the world’s fish stocks are at or near their limit of exploitation. New stocks fish that haven’t traditionally been fished and consumed at the same levels as, say, tuna and salmon are now being exploited. There’s an opportunity for our work here. We can help make sure that all fisheries — not just the ones with the most data or most attention — are harvested in a sustainable way, ensuring that newly exploited stocks and perennial favorites make their way to people’s tables for a long time to come.   

Jack Kittinger is senior director of Conservation International’s Global Aquaculture and Fisheries program. Andrew Rosenberg is director of the Union of Concerned Scientists’ Center for Science and Democracy. Elizabeth Selig is senior scientist for the Norwegian Institute for Water Research.

Sophie Bertazzo is a staff writer for CI.

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