444 



Fishery Bulletin 89(3), 1991 





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Figure 1 



Juvenile Atlantic blue marlin Makaira nigricans. (A) Photomicrograph of the video image of a whole otolith. White lines indicate 

 the preferred counting paths on the anterior (a = antirostrum) or posterior (b) axis of the dorsal lobe of the sagitta. Black bar = 200pm. 



(B) Primary increments formed during the first few months of life in a sagitta from a 139.7cm LJFL specimen. White bar = lOjjm. 



(C) General location of the core on a sagitta from a 136.6cm LJFL specimen. White bar = 100pm. (D) Location of the margin of 

 the antirostrum on a sagitta from a 139.7cm LJFL specimen. White bar = 10/jm. B-D are SEM micrographs of transverse sections. 



Precision of age-determination technique 



The repeatability or precision of otolith microstructural 

 analysis applied to juveniles and young adults/adults 

 (for increment counts 21-495) was assessed using the 

 average percent error (APE) approach of Beamish and 

 Fournier (1981). Three nonconsecutive blind counts 

 were made by the same reader. Computation of APE 

 for individual samples was: 



/ R 



APE = 100 1/R 



IXjj-XjI/Xj 



i=l 



(1) 



// 



where Xjj = the ith count for the jth fish, Xj = the 

 average count for the jth fish, and R = the number of 

 counts for each fish. 



The index of APE for all fish in this sample (N 77) 

 using a single reader was: 



APE = 100 



lulls. \\ 



1/N X I/R Zl x ij- X jl /X 



ii-1 



i = l 



\ \ 



// 



(2) 



where N = the total number of juvenile and young 

 adults/adults aged. 



