Research Document 2019/052

Changes in Productivity of Northern Cod (Gadus morhua) stock in NAFO Divisions 2J3KL

By Morgan, M.J.

Abstract

An extended period of low productivity could be a signal that a population may not return to productivity conditions that would allow it to grow to historic levels used to set a biomass limit reference point. Length at age, weight at age, condition, spawner per recruit, recruits per spawner, potential population growth rate and surplus production were all examined for evidence that Div. 2J3KL cod has been in an extended period of low productivity. All metrics of productivity showed variation over the time series. Short periods of low (and high) productivity are evident, particularly a low productivity period from the mid 1980s to mid 1990s, including 4 consecutive years with the lowest productivity in the time series. Since the mid 1990s there have been years of both high and low productivity. Overall, there is no evidence that Div. 2J3KL cod is experiencing a prolonged period of low productivity that would indicate that historic levels of biomass cannot be reached in the future under environmental conditions similar to the past.

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