Fujinami et al.: Age determination and growth of Prionace glauca in the western North Pacific Ocean 
1 1 1 
Table 1 
Monthly numbers of vertebrae used for age determination of blue sharks (Prionace glauca) captured in 2010-2016 in the 
western North Pacific Ocean. 
Month 
Sex 
Jan. 
Feb. 
March 
April 
May 
June 
July 
Aug. 
Sep. 
Oct. 
Nov. 
Dec. 
Total 
Male 
51 
31 
25 
66 
107 
74 
39 
15 
29 
65 
85 
72 
659 
Female 
25 
44 
42 
65 
61 
61 
29 
0 
22 
69 
97 
105 
620 
Total 
76 
75 
67 
131 
168 
135 
68 
15 
51 
134 
182 
177 
1279 
were converted to binomial data (non- 
maternal conditional), maternal condi¬ 
tion^). The logistic function was fit¬ 
ted to these data in the same way as 
it was fitted to the maturity data for 
estimating age at 50% maturity. 
Results 
Age determination and verification 
Cervical vertebrae were collected from 
1347 blue sharks (688 males, 645 fe¬ 
males, and 14 sex undetermined). Of 
these sharks, for growth analysis, we 
used data for 1279 individuals (659 
males and 620 females; Table 1), 
which had PCLs of 33.4-258.3 cm for 
males and 33.4-243.3 cm for females 
(Fig. IB). The sex-specific relationship 
between CR and PCL trended in a lin¬ 
ear fashion, with no significant differ¬ 
ence between sexes (ANCOVA: F- 3.70, 
P=0.06). The sex-combined equation 
for the relationship of CR and PCL 
was PCL=15.96CR+20.85 (coefficient 
of determination [r 2 ]=0.920, n=1279). 
Counts of growth bands were 1-18 
for males and 1-17 for females. There 
was a high level of both inter- and 
intrareader agreement in band counts 
(Fig. 3, A and B). However, errors as¬ 
sociated with age estimates of older 
sharks were larger than those asso¬ 
ciated with ages for younger sharks, 
although sample sizes were small. In 
repeat counts by reader 1, the counts 
for 710 samples (55.5%) agreed com¬ 
pletely and the counts for 467 sam¬ 
ples (36.5%) differed by one band. 
For inter-reader comparison of counts 
of 200 vertebrae, the counts for 86 
samples (43.0%>) agreed completely 
Figure 3 
Age-bias plots of pairwise comparison of vertebral counts (A) by reader 1 
(intrareader: first counts versus mean counts) and (B) by separate readers 
(inter-reader: reader 1 versus reader 2) for blue sharks (Prionace glauca) 
captured between 2010 and 2016 in the western North Pacific Ocean. Er¬ 
ror bars represent 95% confidence intervals. The diagonal line indicates 
1:1 equivalence. Numbers at the top of the graph denote the sample sizes 
for each count. 
