Species Composition and CPUE of Pelagic Sharks Caught by Japanese Longline Research and Training Vessels the Pacific Ocean

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  • Matsunaga Hiroaki
    Pelagic Fish Resources Division, National Research Institute of Far Seas Fisheries
  • Nakano Hideki
    Pelagic Fish Resources Division, National Research Institute of Far Seas Fisheries

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  • Species Composition and CPUE of Pelagic Sharks Caught by Japanese Longline Research and Training Vessels in the Pacific Ocean

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Scientific data collected by Japanese tuna longline research and training vessels during 1967-1970 and 1992-1995 were used for analyses of the historical change in species composition of pelagic sharks and CPUE by species between the two periods in the four areas into which the area 0°-20°N & 140°E-140°W in the Pacific Ocean were divided equally. To examine the long-term change of shark abundance, CPUE for sharks combined (total shark) was also analyzed from 1973 to 1993 which covered the majority of the missing period between the two periods. Blue shark Prionace glauca was the dominant species in these areas and the shark species composition in number changed somewhat in these areas between the two periods. Nominal CPUE of oceanic whitetip shark Carcharhinus longimanus and silky shark Carcharhinus falciformis decreased in three areas and that of thresher sharks Alopias spp. increased in all areas. However, levels of the CPUE adjusted with the effect of gear type did not change remarkably between the two periods. CPUE of total shark did not indicate any tendency in these areas from 1973 to 1993. Considering that there was no appreciable change in abundance of blue shark between the two periods or of total shark in the interim period between 1973 and 1993, the abundance of blue shark were inferred not to have changed significantly in these areas from 1968 to 1995.

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