WANKOWSKI: ESTIMATED GROWTH OF SURFACE-SCHOOLING TUNAS 



quence of the absence of a swim bladder and rela- 

 tively small surface area of the pectoral fins, in 

 comparison with yellowfin tuna. 



Although over half of the tuna schools in Papua 

 New Guinea waters are pure skipjack tuna (West 

 and Wilson^''), about 40% contain a mixture of 

 yellowfin and skipjack tunas, and only about 5% 

 are pure yellowfin tuna. Length-frequency sam- 

 pling has demonstrated that yellowfin and skipjack 

 tunas taken from any single mixed school com- 

 prise a similar size range, although observations 

 indicate that larger yellowfin tuna (estimated to 

 be in the 70-130 cm size range) are frequently 

 present. Since yellowfin tuna grow so much faster 

 than skipjack tuna, the yellowfin tuna members of 

 a mixed school must, within a matter of a few 

 weeks, outgrow their skipjack tuna counterparts. 

 Such a situation would lead either to the break-up 

 of the school as a consequence of divergence in size, 

 or persistence of large-size yellowfin tuna in a 

 school comprising mainly smaller skipjack tuna. 

 Observations have indicated that the latter situa- 

 tion occurs during certain periods. 



ACKNOWLEDGMENTS 



I should like to thank the following for their 

 contributions to this study. A. D. Lewis originally 

 set up the length-frequency data collection scheme 

 and later contributed much essential comment 

 and discussion. The staff of the Fisheries Research 

 Laboratory in Kavieng and Fisheries Inspection 

 Offices in Kavieng and Rabaul collected the 1977 

 data. R Dalzell and L. F Cooper undertook much of 

 the field work, and R. Y. Lindholm of the Fisheries 

 Research Statistics Centre at Kanudi and B. 

 Richardson of the Department of Population Biol- 

 ogy, Australian National University, Canberra, 

 contributed toward the computer-based data pro- 

 cessing and manipulation. The manuscript was 

 reviewed by J. Munro, D. Gwyther, K. R. Perry, 

 and three anonymous reviewers whose comments 

 greatly contributed to the final form of the paper. 



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