FISHERY BULLETIN: VOL. 79, NO. 3 



fishery takes place on several adjacent fishing 

 grounds, and length-frequency data are available 

 separately for each ground, the movements of 

 groups offish through the fishery are investigated 

 where possible. Finally the availability of an in- 

 dependent estimate of skipjack tuna growth, from 

 the tagging data, makes possible the calculation of 

 probable date of birth of the fish comprising each 

 modal group, the results of which indicate possible 

 stock structure in the Papua New Guinea region. 



DATA COLLECTION 



Although skipjack and yellowfin tunas are 

 found throughout Papua New Guinea waters, the 

 fishery (Figure 1) is centered on baiting grounds 

 on the north coast of Manus Island, within the 

 extensive lagoon systems around and to the east of 

 the island of New Hanover, and in the barrier reef 



lagoons on the northwest coast of the large island 

 of New Britain. During the period of the present 

 study, these four areas were effectively separated 

 on both a fishing fleet and geographical basis. 

 Fleet A operated in the eastern Bismarck Sea 

 ( area 4, Figure 1) , fleet B operated throughout both 

 New Hanover fishing areas (2 and 3), and fleet C 

 also operated from New Hanover, but at any one 

 time fished either north (area 2) or south (area 3) 

 of the baiting grounds. The Manus-based fishery 

 (area 1) was exploited only occasionally and by few 

 vessels. 



Fifty-one Okinawan-type vessels (Tomiyama 

 and Hibiya 1976) operated throughout the fishery 

 in 1977, 47 in 1978, and 41 in 1979. Poor fishing 

 conditions caused by the northwest monsoon sea- 

 son from December through February preclude 

 intensive fishing in these areas, resulting in lim- 

 ited data being available for this period each year. 



Figure L— Pole-and-Une tuna fishing areas in the Papua New Guinea region (shaded): 1— north of Manus Island, 2— north of New 



Hanover Island, 3 — south of New Hanover Island, 4 — eastern Bismarck Sea. 



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