Terms of Reference

Regional Framework Discussion on Stock Substructure of Northwest Atlantic Fisheries Organization (NAFO) Division 3NOPs4VWX5Zc Atlantic Halibut (Scotian Shelf and Southern Grand Bank)

Regional Peer Review – Maritimes Region

March 9-11, 2016
Dartmouth, Nova Scotia

Chairperson: Martha Krohn

Context

Atlantic Halibut (Hippoglossus hippoglossus) is a large and long-lived flatfish. It ranges widely in the waters off of Atlantic Canada. The management unit, the Northwest Atlantic Fisheries Organization (NAFO) Divisions 3NOPs4VWX5Zc (Scotian Shelf and Southern Grand Bank), is based largely on tagging results, which indicate that Atlantic halibut moves extensively throughout the Canadian North Atlantic. A new assessment framework for 3NOPs4VWX5Zc Atlantic halibut was accepted in November, 2014 (DFO 2015a). The last stock assessment was conducted December 8-9, 2014 (DFO 2015b). A stock update was completed December 3, 2015. The stock status of 3NOPs4VWX5Zc Atlantic halibut is in the healthy zone. Recovery of the stock has allowed for increased access by Canadian domestic and international fishing fleets. Continued sustainable exploitation of this resource would benefit from a collaborative approach between the three coastal states that have a primary interest in the stock: Canada; United States; and France.

Recent research has identified core areas of juvenile halibut that may be indicative of 3NOPs4VWX5Zc Atlantic halibut stock substructure on the Scotian Shelf and Southern Grand Bank. A better understanding of halibut substructure and connectivity between core areas would provide a basis for sustainable management. Multiple lines of evidence are necessary to evaluate stock structure and the appropriate management strategies in the face of this new data synthesis. This science framework discussion will support the development of a halibut research program and a common understanding of stock structure among the three coastal states. This common understanding will inform the development of management strategies that, if deemed appropriate, will take stock structure into account to achieve sustainable exploitation.

Objective

The objectives of this science framework discussion are to:

1. Examine work done to date on Atlantic halibut stock structure, specifically:
• history of the fishery and spatial pattern of landings;
• geographical extent of sub-stocks;
• connectivity between sub-stocks;
• range of demographic rates within sub-stocks; and
• implications for assessment model(s).
2. Examine the habitat in core areas (prey, sediment type, temperature, and depth) to explore what it is about these areas that make them so productive for Atlantic halibut.
3. If, upon examination, the Scotian Shelf and Southern Grand Bank stock appears to have significant substructure, there will be an evaluation of how stock structure could/should be taken into account in assessment and management (i.e., consider whether the one-stock assumption matters to the health of the population and explore methods of how multiple, connected populations could be managed safely). These questions on stock structure will not be definitive in the short-term; therefore, the discussion will consider how to manage the stock with incomplete information.
4. Recommend how future research should be focussed to further our understanding of Atlantic halibut stock structure and population dynamics more broadly.

The first three objectives above (1-3) will be addressed to the extent possible based on work completed to date, including all available evidence in the context of connectivity among core areas and how connectivity varies with total population size. Connectivity in other stocks has been shown to deteriorate as populations decline, and the distance between patches increases. In this context, approaches to ensure all high density core areas are sustained will be considered. Remaining gaps in our understanding will be identified and directions for future research to fill these gaps will be recommended for both the short- and long-terms.

Expected Publications

• Proceedings
• Research Document(s)

Participation

• DFO Science
• DFO Resource Management
• International (United States and France)

References

DFO. 2015a. Proceedings of the Regional Framework and Assessment of the Scotian Shelf and Southern Grand Banks Atlantic Halibut (Hippoglossus hippoglossus) in NAFO Divisions 3NOPs4VWX5Zc; November 3-6, 2014, and December 8-9, 2014. DFO Can. Sci. Advis. Sec. Proceed. Ser. 2015/040.

DFO. 2015b. 2014 Assessment of Atlantic Halibut on the Scotian Shelf and Southern Grand Banks (NAFO Divisions 3NOPs4VWX5Zc). DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2015/012.