Science Advisory Report  2011/062

Reference points consistent with the precautionary approach for northern shrimp in the Estuary and Gulf of St. Lawrence

Summary

• The main indicator of stock status is calculated from the male (recruitment to the female component) and female indices (spawning stock) obtained from the summer fishery (number per unit effort) and research survey (abundance). The adoption of the main indicator is used to replicate the informal method that was used to determine the status of the resource and recommend a TAC.
• Stocks increased from a relatively low abundance level in the mid-1980s and mid-1990s due to productive year-classes. In the first case, predator abundance was high and probably had a major impact on the maximum abundance level that stocks may have reached. In the second case, abundant cohorts were produced when predator abundance was decreasing. Thus, it appears that the spawning stock was sufficient to produce abundant cohorts which had a noticeable impact on stock condition. The stock status for these low abundance levels from which they have increased represents the limit reference point (LRP). The LRP for the Estuary fishing area is 0.65, for Sept-Îles, 0.53, for Anticosti, 0.60 and Esquiman, 0.45. Nevertheless, stock behaviour in the critical zone is uncertain since it has never been observed during the studied period.
• The production of very abundant year-classes has allowed stocks to increase again in the early 2000s when predation mortality was most likely low. However, stock status has gradually decreased in recent years and exploitation rate indices have increased. It is thus uncertain whether the abundance levels observed since 2003 can be maintained.
• The 1996-2002 period appears to represent a stable period during which catches proved to be sustainable. The average stock status for this productive and stable period represents a biomass approximation based on the maximum sustainable yield. The upper reference point (USR) value, in compliance with the fishery decision-making framework for incorporating the precautionary approach, could be equal to 80% of this value. The USR for the Estuary fishing area could be 1.12, for Sept-Îles, 1.33, for Anticosti, 1.18 and Esquiman, 1.34. However, the USR level was only observed in the absence of predators. If the biomasses of the large groundfish species return to the high values historically observed, it may be necessary to review the USR since it is not certain whether the shrimp stocks could reach abundance levels as high under maximum predation conditions.
• A target reference point (TRP) could be adopted based on socio-economic objectives. The mean indicator values between 1996 and 2002 could be used as a TRP. The TRP for the Estuary fishing area could be 1.40, for Sept-Îles, 1.66, for Anticosti, 1.48 and Esquiman, 1.68.

This scientific advice arises from the regional scientific advisory meeting held on November 2, 2011 on the «Precautionary approach reference points and Total Allowable Catch (TAC) adjustments rules for the Northern Gulf of St. Lawrence shrimp (Pandalus borealis) Stocks» of Fisheries and Oceans Canadian Science Advisory Secretariat. Any other publication arising from that process will be published when available on the site of the Canadian Secretariat of DFO Science sector.

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