Vital Rates (Life History Parameters)
of the Sevengill Shark, Notorynchus cepedianus
Vital Rates (Life History Parameters)
of the Sevengill Shark, Notorynchus cepedianus
| Parameter | Female | Male | References |
|---|---|---|---|
| Largest specimens (Total length and mass) | 2.96 m, 170 kg; 2.91 m, >182 kg; 2.86 m (a), 130-160 kg (A8, MBA) | 2.43 m, 75 kg; 2.42 m, 79,5 kg; 2.28 m (b), 65.2 kg (A7, MBA) | Ebert 1986; Ebert 1989; Mollet 1995 (unpublished data); |
| Mean TL and mass of mature fish (TL > 2 m for males) | 2.54 m (n = 24, s.d. = 0.24 ), 103 kg ( n =23, s.d. = 37) | 2.24 m (n = 9, s.d. = 0.14 ), 56.6 kg (n =9, s.d. = 18.4) | Mollet 1995 (unpublished data); |
| Size at maturity | 2.18 - 2.44 m | 1.55 m | Ebert 1989; |
| Smallest mature | 2.215 m (80.5 kg) | 1.515 m (13.5 kg) | Ebert 1989; |
| Largest immature | 2.44 m (57 kg) | 1.71m (17.8 kg) | Ebert 1989; |
| Sizes at which 10, 50, and 90% are mature (c) | 2.2 m, 2.4 m, 2.6 m (n = 282) | 1.45 m, 1.55 m, 1.65 m (n = 289) | Mollet 1995 (unpublished data); |
| Estimated age at maturity | 11 - 21 yr (assuming VBGF (d)) | 4.3 - 5.0 yr | Van Dykhuizen and Mollet 1992; |
| Gestation time estimate | 12 months | Ebert 1986 | |
| Reproductive cycle | 2 years | Ebert 1986 | |
| No. of eggs >50 mm in ovary (litter size estimate) | 79 (s.e.= 2, n = 16), range 67 - 96, no correlation with TL nor W could be established | Ebert 1989; Mollet 1995 (unpublished data); 6 | |
| Size of largest egg | 77 mm (diameter) | Ebert 1986 | |
| Birth size estimate | 0.35 - 0.45 m TL (16% of 2.5 m) | Ebert 1989; Mollet 1995 (unpublished data); | |
| Smallest free-swimming (California) | 0.44 - 0.53 m TL, 0.384 - 0.5 kg | Ebert 1986, Van Dykhuizen and Mollet 1992; | |
| Smallest free-swimming (Argentina) | 0.34 - 0.42 m TL, 0.133 - 0.254 kg | Menni and Garcia 1985 | |
| First year growth | 0.35 - 0.45 m TL (16% of 2.5 m) | Van Dykhuizen and Mollet 1992; Mollet 1995 (unpublished data); | |
| VBGF (d) parameters for captive juveniles | TLoo = 2.02 m, Woo = 40.5 kg , k = 0.26 yr-1, sexes combined | Van Dykhuizen and Mollet 1992; | |
| M-TL relationship for captive juveniles (e,f,g) | M(kg) = 4.05* TL^3.333(m), sexes combined | Van Dykhuizen and Mollet 1992; | |
| M-TL relationship for wild sevengills (f,g) | M(kg) = 3.44* TL^3.315(m), sexes combined | Van Dykhuizen and Mollet 1992; Mollet 1995 (unpublished data); | |
| Parameter | Female | Male | Ref. |
a) calculated from 2.98 m over the curve measurement;
b) calculated from 2.37 m over the curve measurement;
c) logit maximum log likelihood calculation based on field data;
d) VBGF = Von Bertalanffy Growth Function;
e) over the curve TL;
f) GM power regression;
g) the pre-exponential constant gives the weight of a 1 m TL sevengill shark
because meter wasused as length unit.
Vital rates needed for demograhic analysis are age-specific
mortality rate M (can be estimated from longevity), age-at-first reproduction
(alpha = age-at-maturity + gestation period), longevity estimate w (can
be estimated from Von Bertalanffy growth curve), and fertility m (number
of female pups born per year). I suggest the following values for a preliminary
demographics analysis:
M ~-ln(0.01)/45 = 0.1023 yr-1;
Alpha ~15 yr;
w ~ 45 years
m ~ 79/(2x2) ~ 20