The science of sustainable seafood, explained

Fish populations around the world are improving

Let’s enjoy some unequivocal, inarguable good news: a paper published today in PNAS, Hilborn et al. 2020, shows that on average, scientifically-assessed fish populations around the world are healthy or improving. And, for fish populations that are not doing well, there is a clear roadmap to sustainability. With Australia on fire and scares of World War III, the start of 2020 and the new decade has been awful; hopefully Hilborn et al. 2020 can kickstart a decade of ocean optimism.

Hilborn et al. 2020 counters the perception that fish populations around the world are declining and the only solution is closing vast swaths of ocean to fishing. Instead, Hilborn et al. 2020 argues that increasing scientific, management, and enforcement capacity will lead to more abundant and sustainable oceans. The major takeaway of the paper is that fishery management works—when fisheries are managed, they are sustained. The key is following the science-to-management blueprint. Scientific data collection and fishery assessment comes first, then fishing regulation and enforcement of fishing policies. With the blueprint in place, most fisheries around the world are sustainable or improving.

The paper uses updates to the RAM Legacy Stock Assessment Database, a decades-long project to assemble data on fish populations that are scientifically assessed. As of 2019, the database contains data on 882 marine fish populations, representing about half of reported wild-caught seafood. In 2009, the database contained data on only 166, representing a much smaller proportion of global seafood. Researchers have spent the last 10 years adding to the database, and with today’s publication, update the global status of fish stocks. They found that, on average, fish populations are above target levels. Not every stock is doing well, but on average, things are much better than they were 2 decades ago. How nice: an environmental story where things are better now than they were in the past!

The paper describes the global status of fish stocks, but it also tells the story of fishery sustainability from the past 50 years.  

A brief history of commercial fishing and fishery science

A very general history of industrial fishing goes like this: before the 1950s, commercial fishing was a niche industry supplying a small proportion of the world’s protein. Then, starting in the 1950s, a global effort to increase food security led governments to invest heavily in fishing—often too heavily. Over the next few decades, it became clear that many fisheries were overcapitalized, meaning there were too many boats, too many fishermen, or some combination of the two. Put simply: fishing pressure was too high and eventually led to unsustainable, depleted fish stocks. In the 1990s, the collapse of several prominent fisheries and many high-profile media stories and scientific publications pressured governments to start taking action to protect their fish stocks. The U.S. in 1996 and the EU in 2002 began mandating their fishery policies to be based on fishery science. Take a look at the last 50 years of fish stocks:

You can see a big increase in fishing pressure and declining abundance through the mid-1990s, then a decrease in fishing pressure and recovery of abundance to the present day.

RAM Database: From Worm et al. 2009 to Hilborn et al. 2020

In 2009, Worm et al. was published. It was the first paper to put together and present global fish abundance data over time. It is now one of the most important and highly-cited fisheries paper in history. The data from that paper eventually became the RAM Legacy Stock Assessment database, where anyone could access information about specific stock assessments from around the world. When the paper was published, it showed a general trend of stabilization in the 166 fish populations it reported on. However, it was criticized for mainly including stocks from North America, Europe, and Oceania, painting a global picture with data from only a few regions. Hilborn et al. 2020 updates that work to 882 populations including a much broader global scope. The added decade of data also shows a more positive, upward trend: 78% of fisheries considered overfished in Worm et al. 2009 are improved in Hilborn et al. 2020.

Fish stock assessments

It all starts with stock assessments. Stock assessments are the backbone of fishery management. They involve fishery scientists first collecting and modeling various environmental and fishing data to estimate the biomass (a.k.a abundance) of a stock, then estimating how much fish can be harvested sustainably. Stock assessments are the information that governments and managers need to regulate fishing pressure to the level that leads to maximum sustainable yield (MSY), often the goal of fishery management.

Sustainability has two basic steps:

  1. Scientists perform a stock assessment to recommend how much fish should be harvested.
  2. Fishery managers and regulators follow and enforce that recommendation.

It seems simple, but the last 70 years of commercial fishing has shown it is anything but. Stock assessments are expensive. They require scientific and financial capacity that many countries do not have. The obvious reason Worm et al. 2009 had mostly North American and European stocks—those countries had resources to assess their fisheries. Hilborn et al. 2020 makes a point to recognize the global effort to increase fishery management capacity around the world.

Below is a Kobe plot over time, a fun way to visualize the complete history of fisheries assessments. On the x-axis is the ratio of biomass to biomass at MSY. On the y-axis is the ratio of fishing pressure to the right amount of fishing pressure (fishing pressure at MSY). The lines represent relative MSY targets with stocks closest to the intersection being closest to theoretical MSY. A stock would be above biomass targets and fished softly in the lower right quadrant (perfectly sustainable), below biomass targets and fished softly in the lower left quadrant (rebuilding), below biomass targets and fished too hard in the upper left quadrant (very bad), or above biomass targets and fished hard in the upper right quadrant (developing fishery and/or management needs to get it together). You can watch the egg-looking concentration move over time following the general trend of fishing hard and depleting stocks in the 1970s-1990s, then a slow rebuild over time. You can also see stocks getting added to the data as countries began performing more stock assessments. For a more detailed explanation of Kobe plots and the terminology used see Sustainable Seafood 101, a guide meant to explain every aspect of fishery science in an easy-to-understand way.

Stock assessment data on a Kobe plot over time
Data from RAM Legacy Database

What about stocks that are not assessed?

Fish populations that are not assessed and monitored are much more likely to be overfished, undermanaged, and unsustainable. This is almost certainly due to the correlation between a country’s financial and scientific capacity and its ability to effectively manage its fisheries. The RAM database is much improved, but still has very little data from Africa and Asia, the two poorest continents. Fish sustainability is most likely declining in those regions, though capacity-building is underway in many places.

Fishery management works

The main takeaway from Hilborn et al. 2020 is that fishery science and management works. If a fishery is assessed, proper decisions can be made on how to sustainably manage it. This is the roadmap for fisheries around the world:

  1. Build capacity to assess the stock
  2. Assess the stock
  3. Use the stock assessment to instruct fishery management

Stock assessment and strong management lead to sustainability. In 1996 the U.S. reauthorized the Magnuson-Stevens Act to require rebuilding plans and catch limits which lowered fishing pressure and raised abundance. Take a look at the Kobe plot over time of just U.S. stocks:

Gif of US stocks on a Kobe plot over time
U.S. Stocks: Data from Ram Legacy Database

The Common Fisheries Policy of Europe was similarly updated in 2002 and saw similar results. In 1997, Japan introduced total allowable catches (TACs) based on stock assessments and saw their TAC-based fisheries improve. Other countries have followed more recently, notably Chile in 2013.

With more and better fishery management, the future of sustainable seafood is on track.

Max Mossler

Max Mossler

Max studied environmental perception & policy in grad school. He thinks a lot about how other people think about the planet. He is the managing editor at Sustainable Fisheries UW.

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2 Responses

  1. It would be good to see the table going back pre 1970 so that we could see what the improvement is against what the abundance was before then. How to you decide which year to measure from? I’m just wondering about shifting baseline and how it might look like a greater improvement than it is when you are measuring it against an already depleted stock. Im sure some fisheries management works, but what happened to the NE Atlantic MSC certified Mackerel fishery that is no longer MSC certified as of 2019? I dont understand how a fishery that is labelled and sold as sustainable can become unsustainable.

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