Swordfish Stock Structure in the North Pacific

Stock structure scenarios for swordfish in the North Pacific. Top: Single stock scenario; Bottom: Two-stock scenario.

During November 12-14, 2008, the Billfish Working Group of the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC) convened a special session on stock structure. The goal of the meeting, held in Honolulu, was to develop plausible stock structure scenarios for populations of swordfish and striped marlin in the North Pacific for use in stock assessments. Participants included regular working group members from NOAA Fisheries, Japan's National Research Institute of Far Seas Fisheries, and the Inter-American Tropical Tuna Commission, and invited scientists from Texas A&M University and Hopkins Marine Station, Stanford University.

After carefully reviewing available data, the working group agreed that their upcoming swordfish stock assessment would explore two stock structure scenarios:

Single stock—a single North Pacific stock encompassing the entire North Pacific north of the equator.

Two stocks—a pair of stocks (Sub-area 1 and Sub-area 2) divided by a diagonal boundary extending from Baja, California (30°N x 110°W) to approximately 170°W at the equator, with the boundary following a step wise pattern. In the western and central Pacific the southern boundary is at the equator and in the eastern Pacific it is at 20°S.

A new stock assessment incorporating the two stock structure scenarios will be completed in time for the July 2009 ISC Plenary Session in Busan, Korea. Working group members will provide updated catch and effort statistics and life history data for the analysis. The assessment will be conducted collaboratively by ISC Billfish Working Group scientists using a Bayesian production model and Stock Synthesis models (SS2 or SS3).

For more information contact: Dean Courtney