ROBERT SIEGEL, HOST:
Cod was once so plentiful in New England that legend had it you could walk across local waters by stepping on the backs of the fish. Well, now the species is in such trouble that cod fishing is practically shut down there. NPR's Nell Greenfieldboyce reports that scientists have a new idea about what happened.
NELL GREENFIELDBOYCE, BYLINE: Overfishing has taken a serious toll on cod in New England, and regulators stepped in. In recent years, they set increasingly restrictive fishing quotas, but it wasn't working.
ANDREW PERSHING: You know, year after year, as they looked at the population, they realized that there were fewer cod than they expected there to be. They thought that they should be rebuilding, but they were actually declining.
GREENFIELDBOYCE: Andrew Pershing is an oceanographer at the Gulf of Maine Research Institute. He says, at the same time the cod were mysteriously failing to rebound, strange things were happening on the shores of Maine. People were finding seahorses, which almost never go that far north.
PERSHING: We had lots of other things in 2012. We had squid we don't normally find here. We had species like black sea bass that are normally found around Long Island that were hanging out in the lobster traps here in Maine.
GREENFIELDBOYCE: These oddities were happening because the Gulf of Maine was warming. Today, in the journal Science, Pershing and his colleagues say the warming is also what's been hurting the cod.
PERSHING: In really warm years, every female cod produces fewer babies than we would expect, and we also see that the young fish are less likely to survive and become adults.
GREENFIELDBOYCE: He says ecosystems all around the world are warming up due to global climate change, but the Gulf of Maine is ahead of the curve. Over the last decade, it's warmed faster than 99.9 percent of the global ocean.
PERSHING: And that happened so fast that the people that were managing this very important fishery were not able to keep up with the changes.
GREENFIELDBOYCE: He says fishery managers tend to make decisions based on past experience. But when the environment is changing in truly unusual ways, that's not going to cut it. Patrick Sullivan is a fishery management expert at Cornell University. He says, it's tough to say what lessons managers should take from this experience with cod.
PATRICK SULLIVAN: Challenge, of course, is, should we have known this? Would we have known this? And in that sense, it's challenging to say that we should've done something different here.
GREENFIELDBOYCE: He says it's no easy job to predict how an environment will change or how the fish will react. Nell Greenfieldboyce, NPR News.
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