Increasing fish stocks possible despite threat of climate change


Aaron Orlowski

Published on
March 13, 2017

Fishery management reforms could raise profits nearly 90 percent and increase fish harvests more than 10 percent by 2100, according to a group of researchers.

Fish stocks – and revenues in the seafood industry – are threatened by climate change, which will disrupt fisheries by forcing fish and shellfish populations to shift to more hospitable climes. But several key management reforms could mitigate the effects of climate change, the researchers said, and even make fisheries healthier and more productive, increasing the number of fish in the ocean by one-third.

The researchers – from the Environmental Defense Fund, Oregon State University and the University of Santa Barbara – previewed their results in February at a meeting of the American Association for the Advancement of Science in Boston.

They examined 780 species and 132 country-level fish stocks, representing a total of 4,424 fisheries and 74 percent of global yield. They assumed that climate change will cause average global temperatures to rise 2.2 degrees Celsius by 2100.

As the oceans warm, fish will migrate and equatorial regions will lose fish while cooler areas gain them, according to Jake Kritzer, who works in the Environmental Defense Fund’s Fishery Solutions Center.

“There could be some species that benefit from climate change if it produces conditions that are conducive to their biology,” Kritzer told SeafoodSource. “Many more will suffer.”

But with management reforms, equatorial regions could still see higher fish populations in the future than today, despite warming oceans, the researchers said.

Rights-based fishery management, which the researchers propose expanding, gives fishermen a stake in the fishery, usually in exchange for strict, science-based catch limits. The ownership stake incentivizes fishermen to care more for the fishery’s long-term health.

The other reforms include tying fish harvest limits more closely to population shifts and increasing international cooperation.
Regulators make a crucial decision when they set total fish harvest limits, Kritzer said. Those limits are calculated using a mathematical function that includes the estimated biomass of fish in the water and the expected mortality from fishing.

Usually, the proportion of a fish stock harvested from the sea remains the same year to year, Kritzer said, even as the total amount caught moves up and down. Kritzer proposes a different strategy: allow fishermen to catch a higher proportion when populations are booming, but reduce fishing even more when populations start to slide.

“You’re doing so with the confidence that because it’s healthy you’ve got some buffer against the risks of overfishing,” he said. “The flip side is if it’s going down, you back off even more.”

Forecasting models showed that in the face of climate change, such responsive management would work better than current management methods, Kritzer said.

Of course, estimates of fish biomass in the water can be wrong, hampering the ability of regulators to set effective catch limits. But Kritzer found that more responsive management kept fish populations healthier despite such uncertainty.

Kritzer wonders whether gradual responsive management could help avoid overfishing, and prevent drastic cuts to fishing that shock fishing communities and harm coastal economies. The results of responsive management in the mid-Atlantic region could help answer that question.

Climate change poses major management challenges for fish stocks that are shared between countries, or that will migrate because of changing ocean conditions, Michael Harte, a professor at Oregon State University and another of the researchers, told SeafoodSource.

Those climate impacts are already apparent: in Europe climate change-induced migrations of mackerel led to “fish wars,” with multiple countries competing for a shifting resource.

Such shared stocks must be managed collectively, lest one country deplete the stock, Harte said. But for international agreements to work, countries have to believe that they’re better off managing collectively than alone, that the other countries won’t cheat, and that outsider countries won’t benefit from their sacrifices, Harte said.

“In the long term, we can always show that by cooperating you have more sustainable fisheries and a more economically robust fishery,” Harte said. But, “people have to believe that no one else is cheating the system.” Electronic monitoring systems help with that, he added.

In addition to agreeing on sustainable catch limits, countries that cooperate can enforce limits on gear types and establish marine protected areas, Harte said. Also, implementing rights-based management across borders benefits fishermen by giving them more flexibility.

Harte said international cooperation is needed around the world, from Pacific Island countries that have both small-scale local fisheries and commercial-scale tuna fisheries, to developed countries in places such as northwest Europe, where shared stocks have long been jointly managed.

Though Harte is optimistic that countries can cooperate, he also believes “we’re seeing an increasingly nationalistic approach of watching out for the interest of your country and being less inclined to look at the bigger picture.”

Cooperation, he said, “depends on the political will of the countries.”

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