Can global fisheries yield more?

Popular opinion suggests today that we have reached the limits of what the ocean can provide, yet the available evidence doesn’t support this conclusion — getting more fish from the sea will be challenging, but it can be done.

There’s no doubt that we are overfishing many of the world’s fish populations. Of the 445 stocks currently included in the FAO’s global estimates, about 30 percent are over-exploited. That’s 148 of the stocks tracked by FAO that are providing less fish than they could because we are fishing them too hard. As the demand for fish rises, it becomes increasingly important that we address this problem.

Let’s assume we can fix it. How much more fish could we realistically expect?

One approach for arriving at an answer is to look at current yields from overfished stocks and compare them with potential maximum sustainable yields. This is the approach Ray Hilborn took for a subset of fisheries that accounted for about 18 percent of reported world catch. He concluded that restoring the overfished stocks would give an extra 15 percent yield (about 2 million tons). Using a different method, Uthara Srinivanasan estimated total global catch losses from overfishing in 2005 at between 4.5 and 20 million tons, with a mid-level estimate of about 10 million tons. With a total marine catch of 84.5 million tons in that year, this is an increase of about 12 percent.

Although there are lots of caveats to these calculations, expecting a 12-15 percent increase in yield by restoring overfished stocks and exploiting them at MSY seems reasonable. We also need to remember that these calculations describe the effects of fishing too hard — the alternative is not fishing hard enough. It turns out that fishing under-fished stocks harder will yield even more than restoring those that are overfished.

If we are to achieve such yield gains, investment to improve management in many large and small-scale fisheries across the world will be essential. With the right practices in place, fish supplies often increase within a few years. This is an important consideration in parts of Africa and other regions of the developing world where quick wins to increase fish supply for poor consumers are desperately needed.

A recent paper co-authored by Shije Zhou adds another twist: If we consider all of the fish species in an ecosystem they observed that our rates of fishing are, on average, even further below MSY. If we were to adopt a “balanced harvesting” approach, shifting pressure away from highly overfished stocks towards currently under-utilized species, we would both increase production and limit undesirable ecosystem effects. Calculations suggest that balanced harvesting could, in theory, yield between 50 to 125 percent more from the oceans than we obtain today.

If we are to move towards more balanced harvesting, however, we will need to:

1. Increase investment in fishing technologies and strategies that can identify and harvest in proportion to the biomass and productivity of fish species.

2. Institute policies that encourage balance harvesting.

3. Develop markets for the higher volumes of species for which there are currently none.

Although challenging, there seems no doubt that we can supply more fish by reducing pressure on overfished stocks, fishing many of the other stocks we currently fish harder, and better distributing moderate fishing pressure to a wider range of species. If we did so, we could potentially realize an extra 20 million tons of fish per year, a 20-25 percent increase. This would be a welcome addition to the world’s food basket.

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