Vital Rates (Life History Parameters) and Elasticities

of the Porbeagle, *Lamna nasus *in the western North Atlantic

a) The pre-exponential constant gives the weight of a 1 m FL porbeagle because
I converted the reported equation using cm for FL to meter.

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). The following values were used by Campagna
et al. (in press) in a demographics analysis (but I have suppliedthe elasticities):

A) M(pups) = 0.2 yr-1, M(juveniles) = M(adults) = 0.1 yr-1. (M = -ln(0.01)/45
= 0.1023 yr^{-1} is almost the same);

Alpha = 13 yr; w = 45; m ~ 3.9/2 = 1.95

Results: Lambda = 1.085, Ro = 4.87, Abar = 17.94 yr, T = 19.4 yr, mu1
= 21.2yr

Elasticity results for comparison with estimates given above: E(m) = 0.056;
E(JS) = 0.725, E(JS)/E(m) = 13.0; E(AS) = 0.275, E(AS)/E(m) = 4.94 (Sum
= 1.056). Normalized values: E(m) = 5.3%, E(JS) = 68.6%, E(AS) = 31.4%.

B) M(pups) = 0.2 yr-1, M(juveniles) = 0.1 yr-1^{;} M(Adults) =
0.2 yr-1

Alpha = 13 yr ; w ~ 30; m ~ 3.9/2 = 1.95

Results: Lambda = 1.0523, Ro = 2.33, Abar = 16.31.yr (Abar is simalar
to value obtained in A, thus elasticities should be similar), T = 16.6
yr, mu1 = 17.07 yr. Elasticity results for comparison with estimates given
above: E(m) = 0.0613; E(JS) = 0.736, E(JS)/E(m) = 13.0; E(AS) = 0.264,
E(AS)/E(m) = 5.9 (Sum = 1.061). Normalized values: E(m) = 5.28%, E(JS)
= 68.6%, E(AS) = 26.1%.

Created October 2002; updated November 2002. Back to previous page Please send comments or corrections to henry@elasmollet.org