84 
Fishery Bulletin 1 1 7(1-2) 
120 n A 
100 - 
80 
CT) 
c 
c 
o 
c 
CD 
o 
c 
o 
o 
60 - 
40 - 
20 - 
M 
Short 
Elongating 
Completed 
E 
CD 
c 
c 
o 
"cS 
c 
CD 
o 
c 
o 
o 
CL 
5 i B 
4 - 
3 - 
2 - 
1 - _* 
0 - -'— 
i 
Short 
i i 
Elongating Completed 
Figure 6 
Comparisons of concentrations of the hormones (A) testoster¬ 
one (T) and (B) progesterone (P4) from May 2008 to December 
2013 in a male whale shark (Rhincodon typus) at the Okinawa 
Churaumi Aquarium, Japan, during the 3 developmental periods 
of the clasper: short, elongating, and completed. The box indi¬ 
cates the 25th and 75th percentiles, the whiskers indicate the 
minimum and maximum values, and the line within each box 
indicates the median value. A circle indicates an outlier. 
The results of this study indicate that morpho¬ 
logical and functional changes in the claspers dur¬ 
ing maturation occurred over a relatively short time, 
less than 1 year, in our shark. The animal began to 
display new clasper movements during the period of 
rapid clasper growth, behavior that has hitherto not 
been reported. These movements have been observed 
during the mating season in other elasmobranchs, in¬ 
cluding the tawny nurse shark ( Nebrius ferrugineus), 
zebra shark ( Stegostoma fasciatutn), bull shark (Car- 
charhinus leucas), sandbar shark (C. plumbeus), and 
dasyatid rays (senior author, unpubl. data), and they 
sometimes occur in the absence of females (Ritter 
and Compagno, 2013). Moreover, a white milky flu¬ 
id, which we suspect to be semen, was released from 
the tip of the claspers as the claspers crossed. Based 
on these observations, it is likely that the function¬ 
al maturation of the claspers occurs in parallel with 
morphological changes. 
In summary, observations of a captive male whale 
shark made over a period of 20 years have improved 
our understanding of the process of sexual matura¬ 
tion in this species. Maturation was associated with 
increased plasma concentrations of T and P4 and the 
rapid morphogenesis and functioning of claspers. Addi¬ 
tional studies involving both captive and wild individu- 
