107 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
established In 1881 
Spencer F. Baird 
First U S Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Age determination and growth of the blue shark 
(Prionace glauca) in the western North Pacific 
Ocean 
Email address for contact author: y.fuji925@gmail.com 
Abstract —Accurate estimation of 
growth parameters is vital for stock 
assessments and management of 
exploited species. To determine if 
changes in sex-specific growth pa¬ 
rameters of the blue shark f Prionace 
glauca) have occurred in the North 
Pacific Ocean following population 
declines in the 1980s and 1990s, we 
analyzed data obtained from the ver¬ 
tebrae of 659 male and 620 female 
sharks that had precaudal lengths 
(PCLs) of 33.4-258.3 cm and were 
captured over a wide geographic 
area between 2010 and 2016. Maxi¬ 
mum counts of growth bands were 
18 for males and 17 for females. 
Significant (P<0.001) between-sex 
differences were detected in growth 
parameters. We estimated param¬ 
eters of the von Bertalanffy growth 
function: for males, the theoretical 
asymptotic length (L„) was 284.9 cm 
PCL, the growth coefficient ( k ) was 
0.117/year, and the theoretical age 
at zero length (t 0 ) was -1.35 years, 
and, for females, was 257.2 cm 
PCL, k was 0.146/year, and t 0 was 
-0.97 years. Sexual discrepancies in 
growth rates are likely a function of 
differences in energy allocation re¬ 
lating to reproduction between sex¬ 
es. Given that no remarkable change 
in growth parameters was observed 
over 3 decades, life history param¬ 
eters of this population do not ap¬ 
pear to have been affected by shifts 
in stock abundance or environmental 
fluctuation. 
Manuscript submitted 2 June 2018. 
Manuscript accepted 18 April 2019. 
Fish. Bull. 117:107-120 (2019). 
Online publication date: 30 April 2019. 
doi: 10.7755/FB. 117.1-2.12 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Yuki Fujinami (contact author) 1 
Yasuko Semba 1 
Sho Tanaka 2 
1 National Research Institute of Far Seas Fisheries 
Japan Fisheries Research and Education Agency 
5-7-1, Orido, Shimizu 
Shizuoka 424-8633, Japan 
2 School of Marine Science and Technology 
Tokai University 
3-20-1, Orido, Shimizu, 
Shizuoka 424-8610, Japan 
The blue shark (Prionace glauca) is a 
large pelagic species found worldwide 
from temperate waters to the trop¬ 
ics, from 60°N to 50°S (Nakano and 
Stevens, 2008). This species is one 
of the most prolific and resilient of 
all sharks (Smith et al., 1998; Cortes 
et al., 2010) and the most abundant 
pelagic shark globally (Nakano and 
Stevens, 2008). Blue sharks are also 
a valuable fisheries resource that is 
commonly caught in pelagic longline 
fisheries both as a target species 
and as bycatch (Nakano and Ste¬ 
vens, 2008). Their meat, liver (oil), 
cartilage, and fins are used in many 
countries (Clarke et al., 2006; Camhi 
et al., 2008). Consequently, stock as¬ 
sessments of this species have been 
conducted by several regional fisher¬ 
ies management organizations to im¬ 
plement appropriate regional conser¬ 
vation and management strategies. 
Accurate age and growth informa¬ 
tion is essential for sustainable man¬ 
agement of exploited species. Such 
basic life history parameters are nec¬ 
essary to estimate population growth 
rates, age at recruitment, mortality 
rates, and longevity (Campana, 2001; 
Goldman et al., 2012; Yokoi et al., 
2017). Because sexual dimorphism 
is common in shark species—with 
females being typically larger than 
males (Sims, 2005)—life history pa¬ 
rameters should be based on sex- 
specific growth equations for proper 
stock assessment and management 
(Punt and Walker, 1998; Chang and 
Liu, 2009). Estimates of param¬ 
eters, such as “spawning biomass” 
(the term spawning biomass is used 
in stock assessment reports to rep¬ 
resent the biomass of reproductive 
organisms), maximum sustainable 
yield, and fishing intensity, can be 
strongly biased when an assessment 
does not take sexual dimorphism into 
consideration (Wang et al., 2005). 
Several studies have reported 
age and growth information for blue 
sharks of the North Pacific Ocean 
(Cailliet and Bedford, 1983; Tanaka 
et al., 1990; Nakano, 1994; Blanco- 
Parra et al., 2008). However, varia¬ 
tion in growth parameters reported 
in these studies could be caused by 
differences in sample size and size 
range (e.g., Cailliet and Bedford, 
1983; Henderson et al., 2001; Blan- 
co-Parra et al., 2008) and in aging 
technique and precision (Tanaka et 
