HILL ET AL.: ANALYSIS OF GROWTH ZONES IN PACIFIC BLUE MARLIN 



30 



•E 25 



20 



15 



B 10 



30 



« 25 



c 



3 

 O 

 O 20 



~ 15 - 



(0 



.t: 10 



O) 

 CD 

 CO 



5 



30 



25 



20 



15 



10 



5 10 15 20 25 



Anal Spine Band Count 



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5 10 15 20 25 



Dorsal Spine Band Count 



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10 15 20 25 



Anal Spine Band Count 



30 



Figure 9. — Correlations between coresponding sagittal 

 ridge counts (SO, corrected dorsal spine band counts (DC), 

 and corrected anal spine band counts (AC) for male and 

 female Pacific Makaira nigricans. Slopes of the regi'essions 

 did not differ significantly from parity (P < 0.05). SC = 

 2.2905 + 0.8077(AC) r = 0.84; SC = 0.2069 + 

 0.9300(DC) r = 0.86; DC = 1.7682 + 0.8779(AC) r = 

 0.95. 



than reader 2 for both anal (D = 0.85) and dorsal 

 (D = 0.55) counts, while reader 2 assigned 

 higher counts to otoliths (D = 1.5) (Fig. 10). 

 None of these count differences differed signifi- 

 cantly when compared with a Wilcoxon Signed 

 Ranks test {P < 0.05). The greatest difference 

 between mean counts was 8 for otoliths. Overall, 

 there was a greater percentage of age estimates 

 within ±1 and ± 2 years for anal and dorsal 

 spines than for otohths. 



Mean Length at Estimated Age 



Based on estimated ages from anal fin spines, 

 there was a pronounced difference in gi'owth 

 between male and female marlin (Fig. 11). Males 

 appear to grow to an average length of 202 cm 

 LJFL at an estimated age of six years, after 

 which gi-owth is determinate. Growth of female 

 marlin, more variable than males, is steady and 

 does not level off as rapidly. 



DISCUSSION 



Growth patterns observed in dorsal and anal 

 fin spine sections were similar to those described 

 by Jolley (1977) for sailfish. Prince et al. (1984) 

 for Atlantic blue and white marlin, and Wilson 

 (1984) for Pacific blue marlin. Sagittal otolith 

 morphologies were also similar to those from 

 previous studies of Pacific blue marlin (Radtke 

 1981; Wilson 1984), and rostral ridges were anal- 

 ogous to those validated in one tag-recaptured 

 sailfish specimen (Prince et al. 1986). 



Three basic assumptions of the ageing theory 

 are that 1) the growth of a structure used is 

 proportional to growth of the animal, 2) the 

 number of gi'owth increments increase with the 

 growth of the structure, and 3) the observed 

 increments follow a discernible time scale e.g., 

 one year of life (Bagenal 1974). In this study, 

 growth of each hardpart was, to some degree, 

 proportional to growth of the animal's length or 

 weight. Increment counts increased with size of 

 each hardpart, providing further support for the 

 use of these structures for age estimation 

 studies. With the exception of the comparison 

 between SW and LJFL, females had higher coef- 

 ficients of determination for the relationships 

 between hardpart and somatic gi'owth. This was 

 probably due to the fact that a greater size range 

 of females was sampled. The variable relation- 

 ship between otolith weight and body size is not 

 surprising since otoliths are so small, relative to 



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