Fish and other sea life have been heading toward the Earth's poles for more than three decades, a mass migration to cooler waters that provides more evidence of a rapidly warming planet and has repercussions for fish harvests around the globe, according to a first-of-its-kind study released Wednesday.
The study, in the journal Nature, found that significant numbers of 968 species of fish and invertebrates examined by University of British Columbia researchers moved to escape the warming waters of their original habitats. Previous studies had demonstrated the same phenomenon for specific places in the world's oceans. The authors said their research is the first to assess the migration worldwide and to look back as far as 1970.
The research is more confirmation that "global change is real and has been real for a long time. It's not something in the distant future. It is well under way," said Boris Worm, a professor of marine biology at Dalhousie University in Halifax, Nova Scotia, who was not part of the study.
The conclusions have important implications for fisheries and the people who depend on them, problems already being noticed by commercial fisherman. For example, as Atlantic mackerel have moved from Norway toward Iceland, a carefully negotiated treaty on the fish catch has been jeopardized, said William Cheung, the study's lead author.
In the mid-Atlantic region of the U.S., 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 the research.
Glen Spain, northwest regional director of the Pacific Coast Federation of Fishermen's Associations, said the shifts identified in the study are having a costly impact on people who earn their living catching and processing fish, which supply at least some of the protein for 3 billion people worldwide. Investments in boats, equipment and infrastructure are difficult to make when entire populations of fish move in a decade or two, said Spain, whose organization represents 1,000 fishing boats.
"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."
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 Daniel Pauly, a professor of fisheries at the University of British Columbia and one of the study's authors.
However, 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."
Richard Merrick, director of scientific programs and chief science adviser for National Oceanic and Atmospheric Administration Fisheries, 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.
In another aspect of their study, the researchers used the fish 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 between 1970 and 2006.