Booth et al.: Age validation, growth, mortality, and demographic modeling of Triakis megalopterus 
107 
Table 3 
Age-length key showing the number of fish aged within different length classes for Triakis megalopterus 
sampled 
on the south- 
east coast of South Africa. TL=total length. Sexes were combined. 
Length class 
Age 
(mm TL) 
0 12 3 4 
5 
6 
7 
8 
9 10 11 
12 13 
14 
15 16 17 
18 19 20 
21 22 
23 24 25 
200-399 
6 
400-599 
5 
600-799 
3 2 
1 
800-999 
1 3 
1 
2 
1 
1000-1199 
1 
1 
1 
1 
3 
1 
2 
1 
1200-1399 
1 
1 
2 1 
2 
2 
1 
1 
1400-1599 
1 
2 2 
3 
4 5 4 
2 11 
1 
2 1 
1600-1799 
1 
1 
2 4 
1 1 
Table 4 
Estimates for von Bertalanffy growth model parameters (and their associated variability and correlation matrices) for male, 
female, and combined-sexes of Triakis megalopterus sampled on the southeast coast of South Africa. L M =theoretical maximum 
size, £=growth coefficient, t 0 =theoretical age at zero length, SE = standard error, CV= coefficient of variation, 95% CI = 95% con- 
fidence intervals, TL=total length. 
Parameter 
Estimate 
SE 
CV 
95% Cl 
k 
*0 
Males (72=26) 
(mm TL) 
1667.89 
103.35 
6.1% 
(1517.25 to 1909.17) 
-0.95 
-0.63 
k (/yr) 
0.12 
0.02 
17.4% 
(0.09 to 0.17) 
0.79 
t 0 (yrs) 
-2.15 
0.42 
19.4% 
(-3.07 to -1.39) 
Females (71 = 60) 
(mm TL) 
1738.93 
90.60 
5.2% 
(1618.95 to 1969.19) 
-0.95 
-0.70 
k (/yr) 
0.10 
0.02 
16.2% 
(0.07 to 0.14) 
0.85 
t 0 (yrs) 
-2.67 
0.59 
21.4% 
(-4.02 to -1.75) 
Combined (n = 86) 
(mm TL) 
1711.07 
56.42 
3.3% 
(1615.79 to 1844.95) 
—0.93 
-0.65 
k (/yr) 
0.11 
0.01 
10.7% 
(0.09 to 0.13) 
0.82 
t 0 (yrs) 
-2.43 
0.35 
14.2% 
(-3.18 to -1.80) 
female offspring per female during her lifespan was 
estimated at 1.00 (Table 5). 
Over half (50.6%) of the female stable-age distribu- 
tion of this population was accounted for by sharks 
less than four years of age. Age-1 sharks contributed 
16% of the female stable-age distribution, and only 8% 
of the female stable-age distribution was mature (>15 
years of age). 
The elasticity of A, the annual population growth 
rate, was relatively low for both fertility (5.5%) and 
adult survival (14.4%) and the highest for juvenile sur- 
vival (80.2%) (Table 5). 
The conditional intrinsic rate of increase parame- 
ter, r, exhibited a nonlinear response when calculat- 
ed for a variety of combinations of fishing mortality 
and age-at-capture scenarios (Fig. 5). In general, the 
conditional intrinsic rate of increase declined as fish- 
ing mortality increased and the rate of decline was 
inversely proportional to age at first capture. When 
the conditional intrinsic rate of increase was mod- 
eled as a function of fishing mortality at the current 
natural mortality rate and age at 50% selectivity, 
a zero rate of increase was observed at F=0.04/yr. 
Discussion 
In this study, T. megalopterus exhibited annular 
growth zone ftormation, depositing one band pair 
per year, as was also found in T. semifasciata (Smith, 
1984; Kusher et ah, 1992). The ratio of the number of 
sharks that exhibited fluorescence in their vertebrae 
(n- 7) to the number of sharks injected (n= 23) was 
unfortunately low and may (see Smith, 1984) or may 
