CLIMATE, COPEPODS AND COD - SOME THOUGHTS ON THE LONG-RANGE PROSPECTSFOR A SUSTAINABLE NORTHERN COD FISHERY

Cod Gadus morhua stocks on the Labrador Shelf and Grand Banks, NW Atla ntic, are apparently at an all-time low. While overfishing has undoubt edly occurred, it is probable that other factors are affecting stock r ecruitment as well. Water temperatures and salinity are also unusually low, which may have affected the abundance of cod in some way. Northe rn cod begin spawning in March in most stock management zones around N ewfoundland, Canada. First-feeding cod larvae survive in waters less t han 2 degrees C but require suitable prey, especially nauplii of the c opepod Calanus finmarchicus, to grow well. The 'match/mismatch' hypoth esis assumes that cod spawn at the same time each year, but spawning b y copepods may or may not 'match' depending on the stimulus provided b y the 'spring bloom' of phytoplankton, which can vary with environment al conditions by up to 6 wk. While C. finmarchicus is common in the At lantic waters of the Labrador Sea and Grand Banks, zooplankton in the Labrador Current, especially during this period of low temperature and salinity, are dominated by 2 arctic copepods, C, glacialis and C, hyp erboreus, which have different spawning seasons, and therefore probabl y would not provide a good nutritional match for young cod. Despite gl obal warming, sea water supporting important demersal fish on the cont inental shelf off northeast Canada is presently colder and fresher tha n normal. Global warming may have induced melting of glaciers and sea ice and increased runoff in rivers entering the Arctic Ocean and its c oastal drainage, reducing salinity at the sea surface, increasing stab ility and reducing deep convection, and hence upward heat transport. S everal cold, fresh 'anomalies' have been observed in the last few deca des and they have contributed to less favourable conditions at locatio ns around the North Atlantic. These anomalies may be part of an interd ecadal climate cycle of alternating warm and cold periods, the effects of which must be removed to clearly identify those associated with gl obal warming. Whatever the causes, periods of 'ocean cooling', with po tentially serious consequences for the cod fishery, may be predictable . Increasing amounts of ice in the eastern Arctic and Greenland Sea ar e easily monitored by satellite and appear to anticipate reduced tempe rature/salinity anomalies in the Labrador Sea by about 4 yr. Climatic impacts, whether cyclic or continuing, could be identified sufficientl y far in advance to enable modifications in management of the fishery toward at least mollifying their effects, thus improving the prospects for long-term sustainability.