118 
Fishery Bulletin 11 7(1-2) 
Because a compensatory response can take a long time 
(e.g., Carlson and Baremore, 2003), the second of these 
explanations is more plausible. 
Blue sharks have a considerable geographic range, 
from coastal to pelagic waters and from temperate re¬ 
gions to the tropics (Nakano and Stevens, 2008) in sea 
temperatures of 5.6-28.0°C (Nakano and Seki, 2003). 
This species is also an opportunistic feeder, with a diet 
that reflects abundance of local prey, such as fish and 
squid (e.g., Preti et ah, 2012; Fujinami et ah, 2018b). 
As such, blue sharks are likely tolerant of fluctuations 
in food resources, buffering the species from anthropo¬ 
genic stress and changes in environmental conditions, 
such as water temperature (Levitus et ah, 2005; Levi- 
tus et ah, 2012) and prey abundance (Chavez et al., 
2003). In addition to its high adaptability, this species’ 
relatively fast growth and high productivity probably 
explain why it has been able to maintain high biomass 
levels, outnumbering other shark species in pelagic 
waters. 
We establish that growth parameters of blue sharks 
of the North Pacific Ocean have not changed remark¬ 
ably from levels observed from the 1980s to the present 
day, despite changes in stock abundance or environmen¬ 
tal conditions. Because male blue sharks grew larger 
than females, and after the age of about 7 years had 
growth rates different from females, we believe a sex- 
specific approach for assessing stocks of blue sharks in 
the North Pacific Ocean is necessary. Given the num¬ 
ber of samples in our study, their size range, and the 
accuracy of our aging technique, we believe the growth 
parameters that we report are appropriate for future 
stock assessments and management of blue sharks in 
the North Pacific Ocean. Bomb radiocarbon dating and 
tag-recapture techniques would further clarify growth 
rates of these sharks, given that current methods and 
structure-based aging techniques might underestimate 
age, especially for larger and older individuals (Harry, 
2018; Natanson et al., 2018). 
Acknowledgments 
We appreciate the prolonged help of M. Sakai, H. Kido- 
koro, S. Suyama, J. Abo, K. Ishida, T. Oyama, M. On- 
odera, and S. Onodera, Japan Fisheries Research and 
Education Agency, and of M. Nemoto, Tokyo University 
of Marine Science and Technology, for assistance with 
sampling. Helpful comments on this manuscript were 
provided by S. Ohshimo and Y. Hiraoka, Japan Fish¬ 
eries Research and Education Agency. This study was 
supported by the Japan Fisheries Agency. 
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