speculative, it is reasonable to assume that the 

 potential yield of skipjack in the central and 

 western Pacific has not been reached and that 

 the resource is large enough for a sizable 

 expansion of the fishery. 



Distribution in Time and Space 



Our knowledge of skipjack distribution comes 

 primarily from the established fisheries in the 

 eastern Pacific, Hawaii, French Polynesia, and 

 the western Pacific, as reported by a number of 

 workers including Imamura (1949), Shimada 

 (1958), Shippen (1961), Calkins and Chatwin 

 (1967), Brun and Klawe (1968), Isa (in press), 

 and Tohoku Regional Fisheries Research Labo- 

 ratory (n.d.). Supplementing this information are 

 incidental catches of skipjack taken from tuna 

 longhne records (Kasahara, 1968; Miyake, 

 1968). Records are also available from research 

 and exploratory vessels scouting for skipjack 

 (Smith, 1947; Smith and Schaefer, 1949; Royce 

 and Otsu, 1955; Yoshida, 1960; McKenzie, 

 1961; Waldron, 1964; York, 1969; Hida, 1970a, 

 b). Currently an FAO development project has 

 been initiated in Fiji, and new fisheries 

 established in the Solomons and New Guinea 

 area are beginning to provide information from 

 the southwestern Pacific. 



Tag recoveries are beginning to contribute to 

 the understanding of the migration and seasonal 

 occurrence of skipjack (Rothschild, 1965; Fink 

 and Bayliff, 1970; Kasahara et al., 1971). From 

 such observations several summaries on their 

 occurrence have been published. These include 

 [U.S.] Bureau of Commercial Fisheries (1963), 

 Kawasaki (1965), Kasahara (1968), Rothschild 

 and Uchida (1968), and Kasahara et al. (1971). 

 These summaries led to hypotheses on the origin 

 and migration of skipjack in the Pacific, 

 including those by Rothschild (1965), Naga- 

 numa (in Kasahara, 1968), and Matsumoto^ . 



Following the formulation of distributional 

 and migration hypotheses, some attempts have 

 been made to generalize the distribution of the 

 skipjack and to relate them to their environ- 

 ment. In the eastern Pacific, their north-south 



Matsumoto, W.M. Distribution, relative abundance 

 and movement of skipjack tuna (Katsuwonus pelamis) in 

 the Pacific Ocean based on Japanese tuna longline 

 catches, 1964-67. Unpublished manuscript filed at 

 National Marine Fisheries Service, Southwest Fisheries 

 Center, Honolulu Laboratory, Honolulu, Hawaii 96812. 



distribution is believed to be limited between 

 surface isotherms of 20° and 29° C (Williams, 

 1969). In the central Pacific various attempts 

 have been made to describe the relation of 

 skipjack distribution to the various current 

 systems (Seckel and Waldron, 1960; Seckel, 

 1963) and in the western Pacific to seasonal 

 changes in water temperature and current 

 systems (Inanami, 1941; Kawasaki, 1965). For 

 the central and western Pacific, the general 

 pattern is one of a northward expansion from 

 near equatorial waters as the summer season 

 progresses and a contraction to the lower 

 latitudes with the onset of fall and winter. The 

 seasonal shift can best be seen in reports by 

 Kasahara (1968) and the Tohoku Regional 

 Fisheries Research Laboratory (n.d.). 



SKIPJACK FISHERY DEVELOPMENT 



Methods 



Until recently pole-and-line fishing with live 

 bait accounted for most of the skipjack landings. 

 Recently purse seining has begun to produce an 

 increasingly significant fraction of the catch. 

 These two methods have greatly exceeded the 

 small amounts taken by trolling and with gill 

 nets. Trolling is generally limited to nearshore, 

 small-boat subsistence fisheries and by research 

 vessels. In French Polynesia, however, this 

 method has been developed into a fairly pro- 

 ductive fishery (Van Campen, 1953; Van Pel 

 and Devambez, 1957; Brun and Klawe, 1968). 

 Some estimates of potential production by 

 trolling can be obtained from survey reports 

 such as Smith (1947), Smith and Schaefer 

 (1949), Bates (1950), Welsh (1950), Murphy 

 and Ikehara (1955), and Iversen and Yoshida 

 (1957). 



As with trolling, gillnetting until recently has 

 been limited to scientific surveys as an indicator 

 of the distributions of tunas (Matsumoto, 1952; 

 Shomura, 1963). In the last decade gillnetting 

 for tunas has been developed commercially in 

 Australia and New Zealand (Temple, 1963; 

 York, 1969; Avery, 1970). 



Purse seining is the preferred method for 

 taking tunas in the eastern Pacific, where in 

 1971 approximately 100,000 metric tons of 

 skipjack were taken. A review of this method is 

 given by McNeely (1961) and Green and Perrin 

 (1970). In the central Pacific purse seining has 



