Northwest Atlantic

## Northwest Atlantic Ocean

Long-term changes in fisheries production in the northwest Atlantic may be related to the physical environment, especially where a species is close to the extremes of its range. Warmer and colder periods in oceanic climate typically last for three to five years; a similar periodicity exists in northern cod stocks, and may also be found in shrimp, scallops, crabs, clams, and squid.

Some events in the fisheries of this region seem to be related to periods of local low coastal water temperatures. These cold-water anomalies could be due to the effect of increased ice break-up, which is believed to be correlated with the impact of climate change in West Greenland. The recent dramatic declines that have occurred in some northwest Atlantic cod fisheries may be a consequence of this climate change, although the severe fishing pressure experienced by these fish stocks in recent decades creates difficulty in assigning cause and effect to these declines.

U.S. GLOBEC scientists are involved in a major program of research off the coast of Massachusetts, in the Georges Bank area of the northwest Atlantic region. Georges Bank was selected for study because it is situated just north of a boundary which separates subtropical species from temperate species, and global warming could result in a northward shift of this boundary. Georges Bank also has a physical circulation, called an anticyclonic retention gyre, that enables populations of marine animals to develop and remain in the area for long periods of time. The species selected for study are cod, haddock, and tiny crustaceans called copepods, upon which these fish feed. From this research, U.S. GLOBEC scientists hope to determine whether global climate change may play a role in the decline of stocks of these fish. A challenge is to determine whether these fisheries declined as a result of overfishing versus the effects of climate-driven alterations in ocean circulation patterns, and associated changes in the marine ecosystem.