International Team Launches Research on Pelagic Sharks in the North Pacific Ocean

The science needed for management of shark harvests and conservation of pelagic shark stocks has recently been given a higher priority by the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC).To advance the understanding of shark population dynamics in the North Pacific, the ISC's Shark Working Group (SHARKWG) recently convened its first intercessional workshop in Keelung, Taiwan. From 19-21 April 2011, scientists from Taiwan, Japan, Mexico, and the United States, including staff of the PIFSC Fisheries Research and Monitoring Division (FRMD) and colleagues from the Southwest Fisheries Science Center (SWFSC) met to accomplish several goals: 1) review available data for shortfin mako shark (Isurus oxyrinchus) and blue shark (Prionace glauca) in the North Pacific Ocean (NPO), 2) develop work plans for stock assessments of blue shark and shortfin mako shark in the NPO, and 3) elect a SHARKWG Chairperson.

A workshop was convened on the campus of National Taiwan Ocean University in Keelung, Taiwan, to develop plans for assessment of pelagic shark stocks in the North Pacific Ocean.

In its review of available data, the working group noted there is considerable uncertainty about biological parameters and stock structure of shortfin mako sharks in the NPO. Preliminary genetics work from U.S. scientists at the SWFSC, and tagging data, point toward a single North Pacific population of shortfin mako shark, distinct from subpopulations in the southeastern Pacific and southwestern Pacific. Moreover, life history parameters previously estimated for shortfin mako sharks differ substantially among geographic regions within the North Pacific. Uncertainties in life history and stock structure will be addressed in the final SHARKWG research plan. The plan will identify a suite of opportunities for potential collaborative studies on the life history and stock structure of shortfin mako sharks and blue sharks in the NPO.

The SHARKWG decided to conduct stock assessments of blue and shortfin mako sharks in the NPO over the next few years, starting with blue shark. In addition, the working group agreed to monitor ongoing research and fishery activities related to other ISC species of interest.

The next ISC SHARKWG workshop is scheduled for late 2011. The workshop will focus on preparing data for the North Pacific blue shark assessment and comparing two assessment models -Stock Synthesis III (SS3) and MULTIFAN-CL-using historic North Pacific blue shark data.