116 
Fishery Bulletin 11 7(1-2) 
Table 5 
Estimates of growth parameters of the von Bertalanffy growth function for blue sharks (Prionace glauca) from previous 
studies. Total lengths (TLs) and fork lengths (FLs) from studies were converted to precaudal length (PCL) by using conver¬ 
sion factors of Fujinami et al. (2017). The parameters are the theoretical asymptotic length (L„), measured in centimeters; 
the annual growth coefficient (k)\ and the theoretical age, measured in years, at zero length ( t 0 ). n=sample size used in the 
age determination. 
Region 
Sex 
n 
Size range 
(cm PCL) 
L 
k 
t 
0 
Max. 
age 
Aging method 
Study citation 
N Pacific 
Male 
43 
_ 
284.8 
0.10 
-1.38 
11 
Stained thin section 
Tanaka et al. (1990) 
Female 
152 
- 
233.4 
0.16 
-1.01 
8 
N Pacific 
Male 
148 
- 
289.7 
0.13 
-0.76 
10 
Silver nitrate staining 
Nakano (1994) 
Female 
123 
- 
243.3 
0.14 
-0.85 
10 
NE Pacific 
Male 
38 
18.1-192.9 
226.6 
0.18 
-1.11 
9 
Silver nitrate staining 
Cailliet and Bedford 
Female 
88 
184.9 
0.25 
-0.80 
9 
(1983) 
NE Pacific 
Male 
122 
59.4-206.9 
230.1 
0.10 
-2.44 
16 
Silver nitrate staining 
Blanco-Parra et al. (2008) 
Female 
62 
66.5-192.8 
181.5 
0.15 
-2.15 
12 
NW Pacific 
Male 
659 
33.4-258.3 
284.9 
0.12 
-1.35 
17 
Burn method and 
This study 
Female 
620 
33.4-243.3 
257.2 
0.15 
-0.97 
16 
stained thin section 
Central S 
Male 
173 
87.5-242.0 
290.0 
0.13 
-1.48 
15 
X-ray image 
Joung et al. (2018) 
Pacific 
Female 
86 
82.1-227.9 
254.0 
0.16 
-1.29 
11 
N Atlantic 
Combined 
411 
44.9-286.8 
263.6 
0.17 
-1.43 
16 
Thin section 
Skomal and 
Male 
287 
259.5 
0.18 
-1.35 
16 
Natanson (2003) 
Female 
119 
285.7 
0.13 
-1.77 
15 
NE Atlantic 
Combined 
159 
46.2-174.1 
289.9 
0.12 
-1.33 
6 
Unstained whole 
Henderson et al. (2001) 
S Atlantic 
Combined 
742 
74.3-249.8 
270.9 
0.13 
-1.31 
15 
X-ray image 
Joung et al. (2017) 
SW Atlantic 
Combined 
236 
131.8-238.1 
270.9 
0.16 
-1.01 
12 
Thin section 
Lessa et al. (2004) 
precision was greater than reference IAPE and CV val¬ 
ues (Campana, 2001) that are considered acceptable. 
Our findings indicate that male blue sharks grow 
larger than females and that the difference in growth 
rate occurs after females reproduce (after the age of 
approximately 7 years). This fact is widely supported 
by previous studies for blue sharks of the Pacific Ocean 
(Table 5). However, although the occurrence of sexual 
differences in growth is well known in elasmobranchs, 
females typically grow larger than males (e.g., Cortes, 
2000). Skomal and Natanson (2003) provided the only 
previous report of female blue sharks growing larger 
than males, but they considered the extremely large 
female (286.8 cm in calculated PCL, Table 5) in their 
study to be very rare given natural mortality. Skomal 
and Natanson (2003) also reported that differences in 
female growth began at ~7 years of age. Therefore, 
sexual differences in growth rates of blue sharks are 
likely attributable to differential energy allocation be¬ 
tween sexes, as has been reported for several other 
shark species (e.g., Semba et al., 2009; Joung et al., 
2018). In general, the onset of maturity results in 
reduced energy allocation toward growth and in in¬ 
creased allocation toward reproduction (Jensen, 1985) 
because mating, gestation, and parturition in female 
sharks consumes considerable energy (Francis and 
Duffy, 2005). Blue sharks are one of the most produc¬ 
tive (high fecundity and annual reproductive cycle) vi¬ 
viparous sharks (Fujinami et al., 2017), unlike others 
in the family Carcharhinidae, indicating that females 
may expend more energy than males on reproduction 
(e.g., mating, gestation, pupping, and migration related 
to reproduction) and more energy on reproduction than 
on somatic growth following sexual maturation. 
Whereas the male asymptotic length from our study 
is similar to that from Nakano (1994), the asymptotic 
length for females from our study is slightly greater 
(257.2 cm PCL, Table 5), possibly because we examined 
a greater number of large-sized females. Nevertheless, 
our growth parameters do not differ remarkably from 
those of Nakano (1994), indicating that shark growth 
rates have not changed demonstrably with shifts in 
stock abundance from the 1980s to the 2010s. 
The most recent stock assessment of blue sharks in 
the North Pacific Ocean reported a prompt recovery 
of spawning biomass (ISC, 2017). Estimated female 
spawning biomass exceeded 300,000 metric tons (t) in 
the early 1980s, decreased to approximately 200,000 t 
in the 1990s, and began recovery from the late 1990s 
to reach 300,000 t in the 2010s. This upward popula¬ 
tion trend has been attributed to a decrease in fishing 
pressure following prohibition of high seas drift nets in 
1992 and subsequent decrease in the numbers of long- 
line vessels (Hiraoka et al., 2016). Although the dif¬ 
ference in spawning biomass of blue sharks from the 
North Pacific Ocean between the early 1980s (Nakano, 
1994) and the 2010s (our study) is not great, the bio¬ 
mass in the intervening years fluctuated considerably. 
