Book excerpt: Catch data of the Japanese tuna longline fishery from 1964 to 1967 were analyzed to determine the distribution, abundance, and movement of skipjack tuna, Katsuwonus pelamis, in offshore waters of the Pacific Ocean. Large skipjack tuna, as well as larvae, were found to be concentrated mainly in the east central equatorial Pacific. Movement of skip-jack tuna stocks was determined by following the shifting of high-CPUE (catch per unit effort) cells from one quarter to the next. The apparent movement of skipjack tuna stocks in the Pacific appeared to coincide with the circulation of the major ocean currents; counterclockwise in the southern hemisphere and clockwise in the northern hemisphere, except in the eastern Pacific where the current flow is counterclockwise. The movement patterns of high CPUE suggested that skipjack tuna adults or their progeny could move from one area to the next. The movement pattern was used also to determine the probable migratory routes followed by skipjack tuna tagged in the eastern Pacific and recovered near the Hawaiian and Christmas islands.