Good Management can Lead to a More Sustainable Future

A new paper in the Proceedings of the National Academy of Science shows that there is a triple bottom line, that abundance, catch and profit can all be increased by reforming fisheries management in places where it has not been reformed. It provides the most comprehensive estimates of the status of global fisheries and shows that the large fish stocks of the world that provide 95% of global catch on average are at about the abundance that would produce long term maximum yield, and fishing pressure, on average is below traditional targets. Less than 20% of fish stocks appear to be overfished by U.S. standards.

Comment by Ray Hilborn, University of Washington, @hilbornr

The paper by Costello and others (including myself) Global fishery prospects under contrasting management regimes that appeared March 28 in PNAS, provides the most comprehensive assessment of the status and potential of global fisheries. Its key finding is that when stocks are overfished, most can recover within 10 years if the appropriate management measures are taken. This means that globally we could have more catch, more fish in the ocean and more profit. Most of the potential for this “triple bottom line” comes from Asia where fisheries are both large, and at present, mostly unmanaged. We must distinguish between fisheries that are reformed and those that are poorly regulated and remain in a race to fish.

Diving deeper into the estimated current status of fish stocks, we find it depends greatly on the size of the stock. Although the paper examined the status of 4,324 individual stocks, just 719 of them provide 96% of the catch. From the perspective of catch, profitability, and fish in the ocean, it is the 719 that are critical and feed us.

We find a very close relationship between the status of fish stocks and their size. One measure of stock status is their average size relative to their abundance that would produce long term maximum yield. Small stocks with potential yield of less than 1,000 T are at 76% of the level that would produce long term yield. The largest stocks (> 500,000 T potential yield) on the other hand, are at 1.34 times this target level. Essentially, small stocks are fished harder than large stocks.

Status of Global Fisheries

Potential Yield

(1000 MT)

Number of

stocks

Total potential yield of this group (1000 MT)

% of all potential yield

Abundance

Fishing

pressure

% overfished

0 – 1

2449

539

0.6%

0.76

1.04

19%

1-10

1184

4,303

4.9%

0.83

0.86

19%

10 – 100

553

   18,094

20.6%

1.00

0.79

15%

100-500

134

   29,354

33.4%

1.09

0.74

17%

> 500

32

   35,577

40.5%

1.34

0.60

19%

The large stocks with potential catch > 10,000 MT are, on average, above the biomass target and below the fishing mortality rate target – meaning they are generally in good shape. However, within each group there are stocks that are overfished (15-19%) and many that are fished harder than good management would dictate.

Why are big stocks in better shape than small stocks? One major reason is that governments, industry and NGOs devote more management effort to large stocks. A second possible reason is that the data available on small stocks are less reliable than for large stocks. We used the catch data provided to the Food and Agriculture organization of the United Nations by individual countries. FAO staff recommended not using stocks with less than 3,000 MT catch, which would eliminate a little over 3000 of the stocks in the analysis.

If we look at only U.S. fish stocks, the status is even better. Again large stocks are generally in better shape than small stocks, but abundance is higher, fishing pressure is lower, and the percent overfished lower. Again stocks with a potential yield of more than 10,000 tons constitute 96% of potential yield.

Of particular importance is the low fishing pressure for the larger stocks, so low that the U.S. as a country is giving up considerable potential yield by fishing so conservatively. This analysis suggests we could almost double U.S. harvest by fishing at a rate that would maximize long-term yield.

Status of U.S. Stocks

Potential Yield (1000 MT)

Number of stocks

Total potential yield of this group
(1000 MT)

% of all potential yield

Abundance

Fishing pressure

% overfished

0 – 1

142

29

0.4%

0.82

1.15

23%

1-10

75

256

3.5%

1.00

0.55

31%

10 – 100

62

2,059

28.3%

1.22

0.58

15%

100-500

12

2,627

36.1%

1.37

0.44

8%

> 500

2

2,301

31.6%

1.26

0.76

0%

A significant limitation in the analysis is that we assume that all stocks are independent and each could be managed to produce its maximum benefits. Many of the problems with U.S. fisheries, and indeed fisheries around the world, occur in mixed stock fisheries. Most U.S. mixed stock fisheries are limited by weak stocks. For example, catch of haddock and redfish in New England is limited by cod and yellowtail flounder; the catch of many species on the West Coast is limited by yelloweye rockfish; catch of pollock and groundfish in Alaska is limited by bycatch of halibut and salmon. So long as the U.S. insists on trying to minimize the number of overfished stocks, we will have to keep exploitation rates on many species low.

Ray Hilborn is a Professor in the School of Aquatic and Fishery Sciences at the University of Washington. Find him on twitter here: @hilbornr
Posted in Uncategorized.

3 Comments

    • Dave,
      Fishing pressure is a relative measure calculated for each stock, and then averaged across the stocks within each of these bins. The relative measure is the ratio of current exploitation rate (the % of the vulnerable population that is caught annually) to the exploitation rate that is expected to generate long-term maximum sustainable yield. So a value of 1 for a stock means that current exploitation rate is right on target, values greater than 1 mean the stock is fished harder than optimal for long-term yield, and values less than 1 mean the stock is fished at exploitation rates lower than those expected to yield MSY. Within each of these bins there is much variation among stocks (the same is true for abundance), but on average the smallest stocks (<1 t) are fished slightly harder than target levels and larger stocks (bins 2-5) are fished at rates lower than target levels.

  1. Thanks to the Daily Digest folks for putting up this article. There are many sides to most issues, and as many reasons to take those sides more often than not. I’m a fisherman, almost 40 seasons now, fishing many species with a number of gears over that time. So you might think that my slant is a given, and obvious. But a background in marine biology, and almost four decades of engagement in co-management processes which have included government, MENGOs, labour, processors, aboriginals, communities, and scientists have tempered a fisherman’s natural inclination to just catch fish. I don’t expect everyone to just accept that a leopard has changed its spots. I just hope that the fair minded folks on this site will take a look at the evidence. Dave Boyes

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