The first clue came in 2008, recalled George Rose, a marine biologist at Memorial University of Newfoundland, when he saw the cod aggregating in large numbers offshore during the spawning season. It was a sight he had sorely missed in 15 years. In the early 1990s, cod fisheries suffered such a dramatic collapse that they emerged as an aquatic poster child for fisheries mismanagement, according to Rose.
In a paper published yesterday in the Canadian Journal of Fisheries and Aquatic Sciences, Rose and his colleague, Sherrylynn Rowe, document the comeback of the Atlantic cod off Newfoundland and Labrador over the past decade. The fact that they have shown that the cod stock there is on the way to recovery is good news, Rose said, as “it shows that it is not all gloom and doom.”
Their study attributed the recovery to improved environmental conditions, better fish management and the availability of an important food source, capelin, whose populations also fell drastically in the early 1990s and have recently bounced back, too. The rebound of Atlantic cod in this region contrasts with their rapidly declining populations off the northeastern coast of the United States, where until last year the stocks remained significantly below sustainable levels. Previous research has associated this persistent population slump with the pressures of overfishing and also warming waters. The warming temperatures, however, seem to be favoring a cod fishery revival in Newfoundland and Labrador, or at least not hampering its recovery.
The authors relied on high-tech sonar technology to construct maps of cod distribution and abundance. They focused their surveys in habitats where cod are usually found during spawning, creating what Rose called “sound pictures” of cod aggregations. Sonar, once developed to hunt for submarines, has advanced in recent years to allow scientists to recognize the signature of a particular fish species. In this case, Rose and his team relied on the strength of the signal—they expected a stronger signal from the cod and signs of its peculiar group dynamics, and got it.
Still vulnerable off New England
The International Union for Conservation of Nature has identified the Atlantic cod as a vulnerable species. But Rose maintains that the stock in Newfoundland and Labrador is no longer imperiled, though he agreed that the favorable conditions are localized and may not exist for other cod stocks.
In the western Atlantic, the range of the cod stretches from the waters of Cape Hatteras, N.C., northward to both coasts of Greenland and the Labrador Sea off Canada’s east coast. The depletion of cod fisheries in New England, a coastal tract in the northeastern United States, is well documented and is also believed to have been precipitated by overfishing. According to recent reports, the current populations of the stock here are only 3 to 4 percent of sustainable levels.
While overfishing is seen as the primary culprit in most accounts, there is also recognition that depleted stocks are vulnerable to shocks like changes from climate variations. The important thing, experts pointed out, is that the changing climate is not affecting species and even different stocks of the same species in the same way.
As Andrew Pershing, who has been studying cod populations in the Gulf of Maine, explained, the Atlantic cod that inhabit the waters off the coast of Newfoundland and Labrador are in the northern reaches of their range, while those found in New England inhabit the lower end of the cod range.
“If you warm up both of these ecosystems, it is going to push Newfoundland squarely into the comfort zone of cod, and it is going to push the Gulf of Maine out of the comfort zone,” Pershing added.
Rose concurred that the warming temperatures in the last decade have helped fish off the northeastern coast of Canada while hindering the revival of fisheries in New England. The trajectory of both fish stocks is an indicator that the fish are adapting to changes in ocean temperatures, Pershing noted. However, the effect of climatic change on marine populations, including cod populations off the coast of Newfoundland and Labrador, is complex, Rose said. “It may not be a direct relationship; the increase in temperature has effects on the plankton, on the capelin, which are the food,” he said, and also affects the growth of the cod.
Rose was hopeful that the findings from Newfoundland and Labrador would serve as a lesson that better fishery management allows even the most hard-hit populations to better withstand other threats and eventually recover.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500