Science Advisory Report  2011/026

Recovery Potential Assessment for Laurentian North Designatable Units (3Pn, 4RS and 3Ps) of Atlantic Cod (Gadus morhua)

Summary

• The Laurentian North designatable unit of Atlantic Cod consists of two stocks or management units: northern Gulf of St. Lawrence cod (management units 3Pn,4RS), southern Newfoundland cod (management unit 3Ps).
• The northern Gulf cod population collapsed in the late 1980’s / early 1990’s. Abundance of mature cod has been stable at a low level since 1997. In contrast, the number of mature cod in 3Ps has been variable since the early 1980’s and near the long-term average in 2010.
• Natural mortality (M) and fishing mortality (F) of northern Gulf cod are approximately 0.4 each for a total mortality of approximately 0.8 in recent years. For 3Ps, estimates of total mortality (ages 4 to 11) over 2005-09 averaged 0.64; M is considered to be 0.2 and there is no evidence that it has changed.
• Seal predation is contributing to increased natural mortality of cod in the northern Gulf. Any reduction in natural mortality would promote recovery.
• Weights-at-age and maturity have declined in recent years for both stocks.
• A conservation limit reference point (LRP) has been established for both cod stocks. The LRP for northern Gulf cod is estimated to be 116,000 t. The estimated Stock Spawning Biomass (SSB) has been below the LRP since 1990 and stands at 16,000 t in 2010. For 3Ps cod, the limit reference point (LRP, BRecovery) is the 1994 level of SSB and the 2010 SSB is marginally above (7%) the LRP.
• The results of this RPA are mainly based on projections of stock size over 36 years (3 generations).  Long-term projections are dominated by process error (uncertainty in recruitment rates, mortality rates, etc.) so that their utility is not in providing probabilities of specific outcomes but rather in defining the uncertainty.  The entire range of uncertainty, particularly the lower limits, needs to be considered in any conclusion.
• Projections were undertaken for both stocks and at the DU level. These projections were not intended to be projections of stock status but rather used to estimate the probabilities of achieving the LRP.
• Assuming no fishing and future productivity conditions are similar to those previously observed, the northern Gulf population is projected to increase although 75% of the results remain below Blim after 36 years. For 3Ps, all results are above Blim, with results ranging from 2-4 times above the LRP in 36 years.
• If fishing mortality remains at current levels and future productivity conditions are similar to those previously observed, the northern Gulf population is projected to increase in the short-term but subsequently returns to the 2010 level after 36 years – 15% of LRP (ranging from 4-41% of LRP). In 3Ps, the SSB declines after 2025 and median SSB is 64% of the LRP. Further, the range of outcomes is relatively wide (30-130% of LRP).
• Projected status of the DU was inferred from combining the stock-specific projections. If fishing mortality is reduced to half of current levels or eliminated, the abundance of mature cod increases compared to current levels (with probability 0.60 or 0.98, respectively). If fishing mortality remains at current levels, the abundance of mature cod is 25% lower than current levels.

This Science Advisory Report is from the Fisheries and Oceans Canada, Canadian Science Advisory Secretariat, Zonal Advisory Process, February 21-25, 2011 on Recovery Potential Assessment (RPA) for Atlantic Cod (Newfoundland and Labrador, Laurentian North, Laurentian South, Southern Designatable Units).  Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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