UCHIYAMA and STRUHSAKER: AGE AND GROWTH OF SKIPJACK AND YELLOWFIN TUNAS 

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Figure 6. — Age determinations (points) of skipjack tuna from Papua New Guinea and comparison with the von 

 Bertalanffy growth curve of central Pacific skipjack tuna derived in this paper. 



fishes than can be gleaned using traditional an- 

 nual techniques. Data presented here suggest 

 three stanzas of linear growth for central Pacific 

 skipjack tuna ranging in size from 3 to 80 cm FL, 

 and that central Pacific yellowfin tuna from 7 to 93 

 cm FL have at least one stanza of linear growth. 



Our assumption that the growth increments on 

 the sagittae of skipjack and yellowfin tunas are 

 deposited daily was supported by the deposition of 

 experimentally induced increments on the sagit- 

 tae of captive fishes and the relatively good agree- 

 ment of our skipjack tuna and yellowfin tuna 

 growth curves with those of previous studies 

 utilizing other growth estimating techniques such 

 as progression of modes in length-frequency dis- 

 tributions and interpretation of other hard parts. 

 Growth studies on tunas based on tagging experi- 

 ments have usually slower growth rates. 



Otolith readings on specimens from three dif- 

 ferent areas suggest that there are geographical 

 variations. 



Estimation of growth rates from daily growth 

 increments on sagittae is subject to at least two 

 possible sources of error. One is that increments 

 may not be deposited due to variables such as an 

 inadequate ration, diet, temperature, age of fish, 

 or during some physiologically stressful activity, 

 such as reproduction. This is apparently the case 

 for three species of boreal gadoids investigated by 

 Pannella (1971). Another source is differential 

 error during increment counting. If fewer rings 

 are counted than actually exist, this, in addition to 

 nondeposition of daily increments, would result in 

 overestimation of growth rate. 



ACKNOWLEDGMENTS 



We thank Edward B. Brothers, Gary T. 

 Sakagawa, Robert A. Skillman, Richard N. 

 Uchida, and Jerry A. Wetherall for reviewing this 

 manuscript and for their suggestions for improv- 

 ing it. We also wish to thank Wilvan G. Van Cam- 



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