Ocean migration

World’s fish have been moving to cooler waters for decades, study finds

Fish and other sea life have been moving toward Earth’s poles in search of cooler waters, part of a worldwide, decades-long migration documented for the first time by a study released Wednesday.

Washington Post,

16 May, 2013

The research, published in the journal Nature, provides more evidence of a rapidly warming planet and has broad repercussions for fish harvests around the globe.

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University of British Columbia researchers found that significant numbers of 968 species of fish and invertebrates they examined moved to escape the warming waters of their original habitats.Previous studies had documented the same phenomenon in specific parts of the world’s oceans. But the new study is the first to assess the migration worldwide and to look back as far as 1970, according to its authors.

The research is more confirmation that “global change is real and has been real for a long time,” said Boris Worm, a professor of marine biology at Dalhousie University in Halifax, Nova Scotia, who was not part of the study. “It’s not something in the distant future. It is well underway.”

The conclusions have important implications for fisheries and the people who depend on them. In developed nations, the fish migration poses costly challenges for the commercial fishing industry. In less-developed nations and the tropics, the movements could threaten a critical source of food.

In places such as Chatham, Mass., and the Gulf of Maine, fishermen who use small boats already are suffering severe economic consequences as cod and haddock that once lived close to the coast move north. While larger boats can reach those fish populations in cooler, deeper water farther offshore, smaller boats cannot, said Richard Merrick, director of scientific programs and chief science adviser for the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service.

“We’re seeing significant declines in the number of boats that can fish, for example,” he said. “The crews that go along with that, they’re out of work.”

Closer to home, the population of Atlantic surf clams has declined in the warmer and shallower waters off Maryland, Virginia and Delaware but thrived in cooler water off New England. The shift has caused the closure of a Virginia-based processing plant and forced fishing boats to move, according to a summary of the research prepared by the Pew Charitable Trusts, which helped fund it.

Glen Spain, northwest regional director of the Pacific Coast Federation of Fishermen’s Associations, said investment in boats, equipment and infrastructure are difficult to make when entire populations of fish move in a decade or two. Spain’s organization represents 1,000 fishing boats along the Pacific coast.

“Everything depends on some minimal level of predictability, and everything is becoming less and less predictable because of climate change,” Spain said. He called for more spending on fisheries management that would allow a “real-time” model of fish locations and populations.

“The biggest problem we have with fishery management is it assumes the future will look like the past,” he said. “That’s no longer the case.”

William Cheung, Daniel Pauly and their colleagues at the University of British Columbia looked at 52 distinct marine ecosystems that cover most of the world’s coastal and shelf areas. Even after accounting for the impact of fishing and wide variations in the oceans that cover 71 percent of the planet, water temperatures rose steadily each decade between 1970 and 2006.

The researchers used the fish themselves as a kind of thermometer to demonstrate the increase in water temperature. By looking at the size of the catch in species’ new habitats and comparing it with their preferred locations in 1970, the researchers calculated the “mean temperature of the catch,” which, they said, rose significantly each decade over that 36-year period.

The authors said the migration of sea life poses the greatest danger to people in the tropics. As sea life moves away from the equator and toward both poles, new species are not moving in to replace them in the planet’s warmest waters, the authors found.

“As the subtropical fish go away because it’s too warm for them, you don’t have hyper-tropical fish replacing them,” said Pauly, a professor of fisheries.

But Worm said he expected that some kind of fish population eventually would thrive in the warmest water. “Nature is very adaptable,” he said. “It always ­changes to something else. It never ­changes to nothing.”

Merrick said warming seas affect not only sea creatures but also the food web on which they depend. Warmer temperatures may have affected the zooplankton population upon which some species feed, forcing them to look elsewhere for food, he said.

“Fish are kind of the canary in the coal mine here, or the canary in the ocean,” Worm said. “They are showing you [climate change] is underway. It’s changing, and they are adapting. And the question is, how will we adapt? Or will we?”