FISHERY BULLETIN: VOL. 87, NO. 4, 1989 



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Anal Fin Spines 



Mean Ditf. = -0.85 ± 0.33 year 

 Percent ± 1 year = 65% 

 Percent ± 2 year = 80% 



— I — 

 10 



— I — 

 20 



— I — 

 30 



— I — 

 40 



— I 

 50 



10 



20 



30 



40 



50 



% of Paired Observations 



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Sagittae 



. Mean Ditf. = +1 .5 ± 0.65 year 

  Percent ± 1 year = 40% 

 Percent ± 2 year = 55% 







— r- 



1 



20 



— I — 

 30 



40 



— I 

 50 



Figure 10. — Comparison of differences of mean age estimates between readers (1 minus 2) for anal spines, dorsal spines, and 



sagittae. 



body size. It was expected that fin spines, much 

 larger in size than otoHths, would have a closer 

 relationship to body size. Prince et al. (1984) 

 found a similar relationship between female 

 and male size and hardpart gi-owth for Atlantic 

 blue marlin. The relationship between spine 

 radius and body size may, therefore, be more 

 useful than sagitta weight for back calculation of 

 early growth in marlin. While the first two 

 assumptions of ageing theory have been met, the 

 most important assumption, that increments ob- 

 served in spines and otoliths of blue marlin rep- 

 resent one calendar year of life, has yet to be 

 proven. 



While validation (or, confirmation of the 

 temporal meaning of a gi'owth increment) was 

 not within the scope of this study, partial ver- 

 ification was achieved. Wilson et al. (1983) 

 defined verification as "the confirmation of a 

 numerical interpretation", usually used in refer- 

 ence to the precision of estimated age. Precision 

 was determined by means of comparisons of age 

 estimates from corresponding fin spines and 

 sagittae as well as by means of measurement of 

 error in age estimates within the data and 

 between the data of both readers. In general, 

 there was good agreement in age estimates 

 between sagittae, anal spines, and dorsal spines 

 from the same fish. Prince et al. (1984) de- 

 scribed similar relationships between otoliths 

 and dorsal spines of Atlantic blue and white 



marlin. While the variability of our counts be- 

 tween otoliths and their con'esponding spines 

 was greater than between corresponding 

 spines, much of this variation was based on 

 several cases in which the counts of sagittae 

 were as much as 5-10 counts above or below 

 those of corresponding spines. Neither the sta- 

 tistical tests of regression slopes nor the non- 

 parametric tests were able to detect significant 

 deviations from parity; these three structures 

 may deposit increments in relation to similar 

 environmental or gi'owth stimuh. 



Comparisons of age estimates, within the data 

 and between the data of both readers provided 

 information on the precision of each technique. 

 Average percent error values of both reader 

 estimates were lower for fin spines than for 

 sagittae, which suggests that fin spine estimates 

 produce a higher degi'ee of precision than sagit- 

 tae. Similarly, comparisons of differences in 

 mean age estimates between readers revealed 

 greater variability of age estimates resulted 

 from sagittae compared to spines. Variabihty of 

 sagittal age estimates may be due in part to 

 problems involved with calcium overlayering, 

 and the overlapping, successive ridges, or multi- 

 ple smaller ridges on these structures. Wilson 

 (1984) reported a similar individual variability in 

 the general morphology and clarity of gi-owth 

 features of Atlantic blue marlin otoliths, and it is 

 reasonable to assume that the interpretation of 



840 



