Uncharted Waters: fisheries managers tackle climate change

Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime—at least according to the old proverb. But what happens when the fish aren’t where they used to be? Climate change is rewriting the rulebook for natural systems and the ocean is no exception. Ocean waters are becoming more acidic, temperatures are increasing, and sea levels are rising. Marine fish populations, often managed by humans for harvest, are similarly under threat.

These changes jeopardize the health and livelihoods of people who depend on the oceans. Globally, Fish are a vital source of protein, accounting for nearly seven percent of all protein consumed globally, and support the livelihoods of 59.6 million people.

Researchers led by Dr. Steven Gaines of the University of California’s Bren School of Environmental Science & Management identified two main ways climate change will affect fish populations. First, as oceans warm, some fish will hightail it toward cooler waters, far from places fishermen have previously found them. Second, changing ocean temperatures will affect fish productivity, a measure of how quickly fish grow and reproduce. A decline in productivity could translate into a decline in maximum sustainable yield, or the amount of fish that fishermen can catch without depleting a fishery.

Under one climate change scenario, Gaines and his colleagues found that maximum sustainable yield would decrease by 5% and 50% of species would shift across national boundaries. Under a more extreme scenario, maximum sustainable yield would decrease by 25%, while 81% of species shift across national boundaries. 

Along the eastern seaboard, fishermen and scientists are already reporting changes in the ocean. Black sea bass, once living off the North Carolina coast, are now more commonly found near New Jersey. Lobsters have largely relocated from the Long Island Sound to the Gulf of Maine. For some fishermen, these unwelcome changes mean additional costs to catching the species upon which they’ve long relied.

However, Gaines’ new research in Science Advances offers a path forward for fisheries. The researchers analyzed 915 fish stocks under four different management scenarios, representing two-thirds of fish caught globally. In doing so, they hoped to understand how climate change—and resource managers’ response to it—could affect fishermen’s harvest and profit.

The four management scenarios represent different projected changes in fish populations’ ranges and productivity. The first scenario addressed both challenges, the second addressed only where the fish could be found, the third addressed only how many fish could be harvested sustainably, and the last addressed neither challenge. 

To address the issue of wandering fish, researchers looked at transboundary agreements. If a fish population straddles a national boundary, these agreements divide the number of fish that can be sustainably harvested among those nations. Without such agreements, fish are vulnerable to overharvesting.

To address declining maximum sustainable yields, researchers modeled a harvest policy that prioritized long-term economic benefits to each fish population over short-term profits. The policy was based on available fish biomass, or roughly the number of fish left in the ocean. This type of policy would naturally adjust for the fluctuating fish populations that will occur with climate change.

Gaines and his colleagues concluded that managing fish using both techniques—accounting for where fish are (or will be) located and how many there are—leads to the greatest difference in fisheries production, with 154% higher profits and 34% greater harvests in the future compared to the status quo. Their finding holds true even with the pressures of climate change. This is a game-changing result that gives some control back to fisheries managers confronted with climate change uncertainties.

While the authors’ results are promising, resource managers face significant hurdles in adopting such principles. In many cases, global interests might not align with interests of a particular country, region, or fisherman. As economically important fish migrate across political boundaries, some stakeholders will see their ocean resources decline, while others will benefit. Some fish species will thrive, while others are projected to disappear. 

Nevertheless, given the social, economic, and ecological importance of fish and the threats they face from climate change, this new research on adaptive fisheries management presents solutions for a hopeful way forward.