Study shows fish diverting north to cooler waters
By Doug Fraser
dfraser@capecodonline.com
November 03, 2009A new study by fisheries scientists in Woods Hole shows that about half of the 36 fish stocks they surveyed had shifted north or east toward cooler waters over the past 40 years, possibly in response to rising water temperatures due to global warming.
The study, conducted by scientists at the National Marine Fisheries Service Northeast Fisheries Science Center, requires further research to factor out the effects of decades of overfishing to get a true picture of the impact of warming seas, researchers said.
But the fish migration northward could mean that fishermen will have to travel farther to catch familiar species but might also see new opportunities in species coming up from southern waters.
Still, it could mean that some species, like cod, may not find the rich food resources available on a place like Georges Bank.
"Fish can shift into habitat that is suitable to them, and if there's enough food there and the water temperature is right, productivity of the fishery might not necessarily go down. But if they move into unsuitable habitat, we might expect the fishery to not be as productive," said Janet Nye, a post-doctoral researcher at the fisheries science center, and lead author of the study published in the journal Marine Ecology Progress Series.
"This is not good news if it translates into lower productivity," said New England Fishery Management Council Deputy Executive Director Chris Kellogg. But his agency deals primarily with the current size of a fish stock in making the fishery management plans that govern how much fish can be caught each year.
Nye, along with co-authors Jason Link, Jonathan Hare and William Overholz, looked at 36 species that were consistently caught on the NMFS annual spring fish survey, from North Carolina to the Canadian border. In an interview yesterday, Nye explained that fish tend to congregate around areas that have sufficient food and habitat, and the right environmental conditions like water temperature. Although fishing can reduce the numbers of fish, these population centers tend to thrive because they have optimal conditions for that fish species.
The NMFS researchers noticed that 24 of the 36 stocks had changes in distribution consistent with warming ocean temperatures. Ten of the 36 stocks had significantly expanded their territory, and 12 had reduced it. Seventeen stocks moved to deeper waters to find cooler temperatures.
Overfishing can also shrink the area that fish occupy, and so researchers looked at species, like blackbelly rosefish, that aren't targeted by commercial fishermen. From the 1960s through to the early 1990s, the greatest concentrations of rosefish were found in deep waters off the southern New England coastline. But from the mid-1990s to the present day, that population has shifted hundreds of miles to the northeast to deep waters off Georges Bank.
Cod and haddock, two commercially valuable local species also shifted north, although the distance was much smaller than rosefish.
Nye called the study a "broad overview" and said the next step will be to pick five species and look at them more closely. But she believes that fishery management would benefit from a more ecosystem-based system to account for things such as food availability in trying to protect and restore fish populations.
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