Are the embattled populations of Atlantic cod collapsing or making a comeback?
The answer varies according to whom you ask, and when you ask them.
Fishermen and fisheries officials were taken aback earlier this month by an initial assessment of Gulf of Maine cod populations conducted by the National Oceanographic and Atmospheric Administration (NOAA). Patricia Fiorelli, a spokeswoman for the New England Fishery Management Council, said in a phone interview following the announcement of the preliminary assessment results, "There is a lot of speculation that cod populations are dramatically lower than anyone expected."
The new findings fly directly in the face of an NOAA assessment conducted in 2008. That study presented an optimistic picture for New England cod, saying that the once-decimated population was no longer overfished and was rebuilding rapidly. The discrepancy may be explained by overfishing, or by lower-than-projected reproductive rates. Fisheries scientists are currently reviewing the new assessment and will issue their final report early in 2012. "We won’t know for sure until then," said Fiorelli.
Meanwhile, a group of Canadian researchers writing in the July issue of the journal Nature reported that the populations of cod and other bottom-dwelling predators on the Scotian Shelf, a shallow area east of Nova Scotia, are finally rebounding. In 1992, the Canadian government put in place what was to be a two-year moratorium on cod fishing after a sudden, catastrophic collapse in the 500-year-old commercial fishery. For some reason, even with fishing banned, the populations did not begin to recover for more than a decade. No one could explain why.
The answer to that mystery may provide an important lesson for American fisheries managers. "This recovery is about an entire ecosystem reestablishing itself, not just about the recovery of cod," William Leggett, a biology professor at Queen’s University in Ontario and one of four authors of the Nature paper, told me.
Leggett said that when overfishing dramatically reduced the population of cod, haddock, and other so-called groundfish, the smaller, minnow-like forage fish that they normally preyed on underwent an uncontrolled population explosion -- 900 percent over the ensuing decade. These small fish in turn ate the eggs and larvae of groundfish, consuming any young that the few surviving cod produced. Eventually, the population of smaller fish became so great that there wasn’t enough food to sustain them. Scarcity of food caused them to begin dying off, whereupon groundfish populations finally began to rebound. Today, cod have climbed back to 30 percent of their historical population levels. Haddock populations are even bigger than before the collapse.
"Fisheries management has to be evolving toward having a broader, ecosystem-wide approach," said Leggett, "not just focusing on individual species."
The good news is that the job of rebuilding fish stocks may be easier in waters off the United States than in those off Nova Scotia. Leggett noted that in New England, dogfish -- which are scarce in Canada -- are abundant and prey on smaller fish that would otherwise eat the juveniles of species like cod, improving the odds that the population will bounce back and do so in less time.
For the Gulf of Maine’s iconic Atlantic cod, recovery can’t come soon enough.
Image: Atlantic cod via Joachim S. Muller/Flickr