SCIENTIFIC COMMITTEE SEVENTH REGULAR SESSION 9-17 August 2011 Pohnpei, Federated States of Micronesia Analysis of North Pacific Shark Data from Japanese Commercial Longline and Research/Training Vessel Records WCPFC-SC7-2011/EB-WP-02

This paper analyses North Pacific longline operational data from research and training vessel surveys (1992-2008) and commercial longline logbook records (1993-2008) provided by Japan for onsite analysis in Shimizu during January-March 2011. Both data sets required filtering to remove records believed to under-report actual shark catches. The analysis was based on 7,974 sets representing 10 vessels in the research and training vessel surveys and 88,129 sets representing 112 vessels in the commercial longline fleet. Application of different filtering methods could result in larger sample sizes, but this benefit would need to be weighed against the probability of increasing the presence of under-reported catches in the filtered database. When considering the selection and application of data filters it is important to recall that if vessels began releasing/discarding (and not reporting) sharks in recent years, filtering may not fully correct for this effect, and declining catch rate trends would thus potentially be exaggerated. On the other hand, if reporting practices do not change but shark stock abundance actually does diminish over time, declining catch rates would be expected. The challenge is to apply a filter which removes those catch records which are under-reported, but retains those which are low but accurate. Filtered data were examined in terms of five potential indicators of fishing pressure: distribution, catch composition, catch rate, targeting and size. Blue sharks, which dominate the shark catch in the North Pacific, showed declining catch rates in research and training vessel surveys but a strong trend of increase in commercial records until 2005 and declines thereafter. Evidence of blue shark targeting was found in the increasing concentration of effort in areas of high catch rates. Mako sharks comprise a small proportion of the catch (<10%) but "effective" targeting may be increasing as a result of targeting of co-occurring blue sharks. Mako catch rates showed an increasing trend in both data sets until 2006 for the main commercial fishing grounds in the western North Pacific. Decreasing catch rate trends were shown for makos in both the central North Pacific and western North Pacific since 2006. Oceanic whitetip and silky shark catch rates showed declines in the research and training vessel data and were rarely recorded after 2005. There was also some evidence for a trend of decreasing size of both males and females of these species in recent years. Thresher sharks were analysed as a group and results are expected to mainly reflect the status of bigeye thresher. An increasing trend was found in the research and training vessel data and an inconclusive pattern in the commercial data. 1 Secretariat of the Pacific Community, BP D5 Noumea CEDEX 98848, New Caledonia 2 National Research Institute of Far Seas Fisheries, 5-7-1 Orido, Shimizu-ku, Shizuoka-ken, 424-8633, Japan