Closing the high-seas fishery could boost catches in coastal waters by 10 per cent, according to a new study.
The dramatic increase could be seen as soon as 2050 if humans stop catching fish beyond the 200-nautical-mile limit from shore that delineates exclusive economic zones, says the new work published Tuesday in the journal Fish and Fisheries. And it could help compensate for losses expected to accompany climate change.
“In this case, we look at the high seas as like a fish bank,” co-author William Cheung told Local Xpress.
“When the fish build up more in the high seas, it will spill over into the coastal countries, which benefits the coastal countries. Particularly, we are thinking those kind of benefits can compensate for the loss of fish because of climate change.”
His team devised a computer simulation model to project catches of 30 different fish stocks — including tuna, mackerel and billfish — as the oceans warm. They looked at scenarios where people do little to mitigate the carbon dioxide emissions that cause the planet to heat up, and another where humans clamp down on the greenhouse gases we pump into the environment.
Under the first scenario, the new model shows large catch drops in the South Pacific, Indo-Pacific, West African coast and west coast of Central America as fish swim toward cooler waters.
“We find that there will be substantial impacts on many coastal countries, particularly those that are in the tropics where the fish stocks will move away from the tropics and there will be a decrease in productivity of the oceans in those areas leading to a substantial — more than 30 per cent decrease — in fisheries catch by 2050 relative to now under a business-as-usual scenario,” said Cheung, a marine biologist at the University of British Columbia.
Some catches in Canada are projected to increase as fish swim away from the warm water, he said. “In fact, we are already seeing some of those effects when the waters in the Pacific or the Atlantic get warmer.”
Some fish stocks in Nova Scotia will increase, which could provide opportunities, Cheung said. But his team’s new study — dubbed “Transform high seas management to build climate resilience in marine seafood supply” — notes ocean acidification could throw a wrench in that potential boon.
“Then there’s also actually some risk because there will also be other species that may move into the water,” Cheung said. “So the risk is that may disrupt some of the ecosystem dynamics, which is quite difficult to predict.”
A load of shark sightings this summer off Nova Scotia might be a harbinger of things to come. “That’s what we actually expect,” Cheung said, “because a lot of those sharks are more warm-water-associated.”
Nearly two-thirds of the world’s oceans are considered high seas.
“There are a handful of countries that have big fishing fleets operating in the high seas,” Cheung said, noting those include Japan, South Korea, Taiwan, Spain, Chile and China.
The majority of the fishing fleets around the world are coastal fisheries, he said.
“For example, in many of the fisheries in Nova Scotia, they are actually fishing in Canadian water. They don't go out to the high seas to get lobster or things like that,” Cheung said.
Less than 0.1 per cent of the world’s catches come from the high seas alone. But stocks that straddle both sides of the border make up about 67 per cent of the world’s catch, he said.
“Those stocks that are only caught in the high seas is a really low number, but then there is a large amount of stocks that are caught both within and outside of the high seas.”
As in most things, rather than halting the high-seas fisheries altogether, achieving a middle ground might be the best anyone can hope for.
“If we say that we consigned the whole high seas from fishing, definitely that would be a really challenging political task to ask for,” Cheung said.
Instead, it might be more practical to set aside certain areas of the high seas where fishing is prohibited such as “particularly critical habitat or migration routes,” he said.
According to Cheung’s new study, there is no panacea.
“Large-scale transformation of international fisheries governance, through co-operatively managing the resources or closing the high seas, would help partially compensate for losses expected from climate change impacts on countries’ seafood production,” it says.
“High-seas closure is also effective in improving equitable sharing of straddling fisheries resources and enhancing fish stock resilience. Residual impacts in many tropical countries remain high even under the best-case scenario (low emission, good fisheries management) by the mid-21st century, highlighting the need for other adaptation measures in addition to transforming fisheries management.
“These may include diversifying the livelihoods undertaken in coastal fishing populations, as well as adaptation to fishing practices, through changing target species or gears. Adaptation funds to assist countries and coastal communities in these regions may be needed to facilitate the development of alternative adaptation pathways.”