Research Document - 2012/056

Updated life history parameters for northern Gulf of St. Lawrence (3Pn, 4RS) cod (Gadus morhua) and their impact on reproductive potential and projections of population growth

By Y. Lambert

Abstract

Updated time series of life history characteristics of cod in the northern Gulf of St. Lawrence indicate that important changes occurred in the age structure of the stock with 7+ fish only representing 13 to 19% of 4+ fish in the stock since 2008 compared to 25 to 32% in the early 2000’s. An apparent decrease in female age at 50% maturity is associated with this lower proportion of older fish. Decreasing trend in egg production per mature fish and low recruitment would also negatively affect the reproductive potential of the stock. Moreover, the higher natural mortality observed in the recent years has an important impact on the potential rate of population increase. While potential rate of population growth in the absence of fishing was estimated as ~ 15% per year in the early 2000’s it is now only estimated as ~ 3.3% per year with a declining trend since 2008. Projections of stock dynamics over 36 years using a demographic model assuming that current age-specific survival and reproduction were to be maintained in the future indicate a very slow recovery of the spawning stock biomass (SSB) in the absence of fishing and an absence of rebuilding of the stock if the fishing mortality level observed in 2011 was maintained or increased. In all scenarios, these extrapolations of the consequences of the present population productivity level indicate that SSB trajectory would not allow the stock to attain in the short and medium term the limit reference level of 116,000 t of SSB established for this stock. These results are in agreement with the conclusions of the recovery potential assessment of the stock done in 2011.

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