North Atlantic fish populations shifting as ocean temperatures warm

Southern species like Atlantic croaker may become common in New England waters

About half of 36 fish stocks in the Northwest Atlantic Ocean, many of them commercially valuable species, have been shifting northward over the last four decades, with some stocks nearly disappearing from U.S. waters as they move farther offshore, according to a new study by NOAA researchers.

Their findings, published in the journal Marine Ecology Progress Series, show the impact of changing coastal and ocean temperatures on fisheries from Cape Hatteras, N.C., to the Canadian border.

Janet Nye, a postdoctoral researcher at NOAA's Northeast Fisheries Science Center (NEFSC) laboratory in Woods Hole, Mass. and the lead author of the study, looked at annual spring survey data from 1968 to 2007 for stocks ranging from Atlantic cod and haddock to yellowtail and winter flounders, spiny dogfish, Atlantic herring, and less well-known species like blackbelly rosefish. Historic ocean temperature records and long-term processes like the Atlantic Multidecadal Oscillation and the North Atlantic Oscillation dating back to 1850 were also analyzed to put the temperature data into context.

"During the last 40 years, many familiar with have been shifting to the north where ocean waters are cooler, or staying in the same general area but moving into deeper waters than where they traditionally have been found," Nye said. "They all seem to be adapting to changing temperatures and finding places where their chances of survival as a population are greater."

Nye and coauthors Jason Link, Jonathan Hare and William Overholtz of NEFSC selected the 36 species to study because they were consistently caught in high numbers in the Center's annual spring bottom trawl survey. They also represented a wide range of taxonomic groups, and were known to be commercially or ecologically important. NEFSC, headquartered in Woods Hole, conducts annual spring and fall trawl surveys and has the world's longest time series of standardized fishery population data.

The researchers looked at where the fish were caught and their biomass, or the estimated total weight of the population, in each year of the survey. For each stock they estimated the center of abundance, average depth, the range or area that the stock occupied, and the average temperature at which each stock was found.

They also took into account fishing pressures on the species over time, as well as natural cycles in ocean temperature. Ocean temperatures have increased since the 1960s and 1970s, and the authors found significant changes in species distribution consistent with warming in 24 of the 36 stocks studied.