Geoscience Reference
In-Depth Information
The calamitous collapse of the 1990s has reduced the once great stocks to a minuscule fraction of their
former selves. The demise of the northern cod—a species of marvelous abundance and fecundity—can be
traced to both environmental and human causes. At first, the finger was pointed at environmental factors—in
particular, to unusually cold water temperatures, which might cause both high adult mortality and a low surviv-
al rate of juveniles. It is true that warmer conditions, on average, produce better recruitment for all of the major
northern cod stocks of the North Atlantic—off Norway and Iceland, as well as Newfoundland. Ultimately,
however, it was overfishing that delivered the coup de grace to the cod.
The decimation of northern cod began in the 1960s, during a time of high ocean productivity. Fishing fleets
from Canada, France, Poland, Spain, Portugal, and the Soviet Union hammered the burgeoning stocks well
beyond sustainable limits. To make matters worse, trawlers fished during the winter and the spring, when the
fish were gathering in dense schools on their spawning grounds. It was a frenzy from which the usually hardy
cod would never fully recover.
Stocks did rebuild to some extent in the 1970s and early 1980s, after the declaration by Canada of a
330-kilometer (200-mile) economic zone, which excluded foreign fleets from much of the Grand Banks. But a
decline in productivity in the ecosystem as a whole after the 1960s resulted in lower growth rates in individual
fish and, because there were fewer and smaller adults, a reduction in breeding potential. Then, in the late
1980s, the Newfoundland and Labrador waters turned bitterly cold, resulting in fast and furious changes to the
ecosystem.
It is a truism: where go the capelin, so go the cod. It was the arrival of the capelin in the North Atlantic that
originally allowed the explosion of the cod stocks that greeted John Cabot and subsequently sustained
European and North American fleets, as well as the culture of Newfoundland and Labrador, for five centuries.
Capelin disappeared from their northern ranges in the early 1990s, their numbers plummeting by 97 percent
during a period of the coldest weather ever recorded, which probably affected their plankton food source. Pre-
dictably, they began moving south in search of warmer waters and food, and their prime predator, northern
cod, followed.
In 1990 and 1991, acoustic surveys detected a huge migratory school of cod, estimated at 500,000
tonnes—perhaps the last great aggregation of the species—in the Bonavista Corridor, a funnel-like migration
route off Newfoundland's northeast coast. This motherlode was swimming at depths of 300 meters (1,000 feet)
and measured 30 by 20 kilometers (19 by 12 miles)— and probably represented 80 percent of the existing
stock. At the front of the pack were the bigger fish, so-called scouts that were leading the search for food.
They were likely following the cod's prime prey, capelin, but became prey themselves. Tragically, they swam
into the trawls and nets of domestic fishers and foreign fishers. This last great haul of cod spelled the end for
what had once seemed an inexhaustible resource.
Although the environment always plays a role in population fluctuations, some scientists reject the hypo-
thesis that attributes the collapse of northern cod to environmental change. Analysis of data going back a cen-
tury showed that water temperatures were indeed colder throughout the 19th century, up until the 1920s, when
the fishery harvest was as large or larger than that of the 1980s. In the more recent past, there were five years
(1972, 1973, 1974, 1984, and 1985) in which the water was particularly cold, but there was no consistent rela-
tionship between temperature and the recruitment of young fish to the adult stocks. In two of those years, in
fact, recruitment was greater than average. According to this view, overfishing was the only cause of the col-
lapse, which began in the north, where trawlers dragged up tens of thousands of fish as they formed dense
spawning schools, and worked its way south—a pattern called “fishing down”—until the predictable end
came.
Until recently, surveys showed that there was now less than 1 percent of the historical biomass of northern
cod. This stock spawned in early spring in selected areas throughout the continental shelf, from Hamilton Bank
in the north to the Grand Banks in the south and then undertook spring feeding migrations to inshore waters in
