Fujinami et at: Age determination and growth of Prionace glauca in the western North Pacific Ocean 
1 15 
ymptotic length is less than that reported for the North 
Atlantic Ocean (Skomal and Natanson, 2003; Table 5), 
possibly because a greater size range of individuals was 
examined in that study. Although we cannot discount 
the possibility of underestimation, we can assert that, 
at least for blue sharks in the North Pacific Ocean, our 
estimation of growth parameters used more specimens 
of a greater size range than that of any previous study. 
Another possible reason for variation in growth pa¬ 
rameters among studies could be differences in aging 
technique and precision (Tanaka et al, 1990). Where¬ 
as most previous studies on blue sharks of the North 
Pacific Ocean have used silver nitrate impregnation 
to age specimens (Table 5), we simultaneously used 2 
complementary techniques (burn and thin-sectioning 
methods) to effectively age sharks of different lengths 
(Fujinami et al., 2018a). As discussed previously, 
growth bands apparent from the use of a burn method 
and silver nitrate impregnation are comparable; there¬ 
fore, we consider any effect of technique to be slight. 
Furthermore, because we used the thin-sectioning 
method on older sharks, we minimized underestima¬ 
tion of age. The aging precision (IAPE and CV) that 
we achieved by combining techniques is comparable to 
that from the use of a single technique like thin sec¬ 
tioning (Lessa et al., 2004), silver nitrate impregnation 
(Blanco-Parra et al., 2008), or X-ray imaging (Joung et 
al., 2017; Joung et al., 2018). Consequently, our aging 
