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DFO Seminar: Why is northern cod biomass very low and Barents Sea cod biomass very high? The roles of scientific advice, management decisions and climate variability.


ABSTRACT:In the early 1980s, the northern (2J3KL) cod stock off southern Labrador and 
eastern Newfoundland was productive and recovering from the severe overfishing of the 
1960s-1970s, whereas the Barents Sea cod stock north of Norway and northwestern
 Russia was declining to an all-time low. The two stocks were at similar levels of total
 biomass at that time. By the late 1980s, management of both stocks was in crisis. For 
northern cod, the crisis resulted from recognition of scientific overestimation of stock size, 
whereas for Barents Sea cod, the crisis was ecological, stemming from a collapse of the 
capelin stock. In the early 1990s, the northern cod stock collapsed, whereas the Barents 
Sea cod stock rebounded strongly. Since the early 1990s, the northern cod stock has 
experienced low productivity, whereas the Barents Sea stock has been highly productive, 
despite fishery removals that were much too high during some years. In 2010, the northern 
cod stock was well below its biomass limit reference point. Total catch was uncertain, but 
perhaps about 4,000 t. In contrast, the Barents Sea cod stock was well above its 
biomass limit reference point and fished at 610,000 t. (The Barents Sea cod quota was
 increased to 703,000 t for 2011.) This talk will compare the dynamics of the two stocks. 
Primary focus will be on (i) the extent to which management decisions and climate
variability influenced the divergence in stock trajectories during the early 1990s and (ii) 
the contributions of exploitation, predators (seals), prey (capelin) and climate change to 
the different levels of productivity since the mid-1990s. 

Jan 30th, 2012

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