108 
Fishery Bulletin 109(1) 
Table 5 
Summary of demographic parameters and elasticities estimated during this study for Triakis megalopterus and four other tri- 
akid shark species from Cortes (2002). Values in parenthesis denote lower and upper 95% confidence intervals calculated from 
1000 Monte-Carlo simulations. A=annual population growth rate, r=conditional intrinsic rate of increase (calculated as r=lnl), 
T = average age of mothers of newborn individuals in a population with a stable age distribution, f? 0 =average number of female 
offspring per female during her lifespan (calculated as R 0 = exp (rT ) ). 
Elasticity (%) 
Species 
X 
r 
T 
R 0 
Fecundity 
Juvenile 
survival 
Adult 
survival 
Triakis megalopterus 
1.000 
0.000 
18.76 
1.00 
5.4 
78.3 
16.4 
(0.976-1.041) 
(-0.024-0.040) 
(14.44-19.86) 
(0.63-1.83) 
Mustelus californicus 
1.132 
0.124 
4.6 
1.77 
18.5 
34.7 
46.8 
Mustelus manazo 
1.096 
0.092 
6.6 
1.83 
13.3 
52.4 
34.3 
Mustelus antarcticus 
1.082 
0.079 
11.5 
2.48 
8.0 
50.6 
41.3 
Triakis semifaseiata 
1.016 
0.016 
18.5 
1.34 
5.1 
63.9 
31.0 
25 
8 
20 
• Jr * 
CT) 
♦ y# • 
• • 
15 
aJ 
0 
• 
; IAPE=5.02% 
• Ml 
1 io 
• JSr y=0.97x+0.58 
o 
0 
c n 
5 
: n=84 
Vi* r 2 = 0.97 
0 ■ 
■u • 
0 5 10 15 20 25 
First reading 
Figure 2 
Age-bias plot of estimated ages from Triakis mega- 
lopterus vertebrae. Sharks were sampled on the 
southeast coast of South Africa. The age-bias 
plot regresses the age estimates from a second 
reading against the age estimates from the first 
reading. IAPE=index of average percent error. 
Figure 3 
Observed total lengths of male and female Triakis meg- 
alopterus sampled from the southeast coast of South 
Africa. Length data were overlaid with the predicted 
von Bertalanffy growth model (solid line) and its 95% 
confidence intervals (dotted lines) estimated by using 
parametric bootstrapping. 
not (see McFarlane and King, 2009) be related to the 
slow growth and low levels of calcification of the ver- 
tebrae of these long lived sharks. Absolute age was 
validated up to 25 years. Oxytetracycline was shown 
to be an effective growth marker for T. megalopterus, 
which, like its congener T. semifaseiata, exhibits slow 
growth and a maximum age of at least 25 years (Smith, 
1984; Smith et al., 2003). 
Female T. megalopterus were found to grow larger 
than males — a finding similar to that of Kusher et 
al. (1992) for T. semifaseiata. In both studies, males 
grew to a similar size but female T. megalopterus were 
considerably larger. Kusher et al. (1992) found that 
their growth coefficient estimates of 0.07/yr for females, 
0.09/yr for males, and 0.08/yr for both sexes combined 
were lower than what would be predicted from Holden’s 
(1974) method of estimation with the ratios of length at 
birth to maximum observed length (range = 0.1-0.2/yr). 
Using a birth size of 435 mm and a female maximum 
observed length of 2075 mm TL together with a gesta- 
tion period of 1.7 years (Smale and Goosen, 1999), Hold- 
en’s (1974) estimated the growth coefficient at 0.12/yr, 
which corresponds well with the growth curve estimate. 
Our estimate of age at maturity for T. megalopterus 
exceeds that of T. semifaseiata (7 years for males, 10 
