Climate, copepods and cod: some thoughts on the long-range prospects fora sustainable northern cod fishery

Climate Research

Harding GCH¹  Wilson S¹  Vass WP¹  Conover RJ¹ 

关键词: Recruitment;    Calanus;    Copepod nauplii;    Cod Gadus morhua;    First feeding;    Spring bloom;    Sea surface temperature;    Salinityanomaly;    Banks;    Currents;    Polar front;   

DOI  :  10.3354/cr005069

来源: Inter-Research Science Publishing

【 摘 要 】

ABSTRACT: Cod Gadus morhua stocks on the Labrador Shelf and GrandBanks, NW Atlantic, are apparently at an all-time low. Whileoverfishing has undoubtedly occurred, it is probable that otherfactors are affecting stock recruitment as well. Water temperaturesand salinity are also unusually low, which may have affected theabundance of cod in some way. Northern cod begin spawning in March inmost stock management zones around Newfoundland, Canada.First-feeding cod larvae survive in waters less than 2*C but requiresuitable prey, especially nauplii of the copepod Calanusfinmarchicus, to grow well. The 'match/mismatch' hypothesis assumesthat cod spawn at the same time each year, but spawning by copepodsmay or may not 'match' depending on the stimulus provided by the'spring bloom' of phytoplankton, which can vary with environmentalconditions by up to 6 wk. While C. finmarchicus is common in theAtlantic waters of the Labrador Sea and Grand Banks, zooplankton inthe Labrador Current, especially during this period of lowtemperature and salinity, are dominated by 2 arctic copepods, C.glacialis and C. hyperboreus, which have different spawning seasons,and therefore probably would not provide a good nutritional match foryoung cod. Despite global warming, sea water supporting importantdemersal fish on the continental shelf off northeast Canada ispresently colder and fresher than normal. Global warming may haveinduced melting of glaciers and sea ice and increased runoff inrivers entering the Arctic Ocean and its coastal drainage, reducingsalinity at the sea surface, increasing stability and reducing deepconvection, and hence upward heat transport. Several cold, fresh'anomalies' have been observed in the last few decades and they havecontributed to less favourable conditions at locations around theNorth Atlantic. These anomalies may be part of an interdecadalclimate cycle of alternating warm and cold periods, the effects ofwhich must be removed to clearly identify those associated withglobal warming. Whatever the causes, periods of 'ocean cooling', withpotentially serious consequences for the cod fishery, may bepredictable. Increasing amounts of ice in the eastern Arctic andGreenland Sea are easily monitored by satellite and appear toanticipate reduced temperature/salinity anomalies in the Labrador Seaby about 4 yr. Climatic impacts, whether cyclic or continuing, couldbe identified sufficiently far in advance to enable modifications inmanagement of the fishery toward at least mollifying their effects,thus improving the prospects for long-term sustainability.

【 授权许可】

Unknown