Fróðskaparrit - 01.01.1991, Page 39

STUDIES ON THE LONG-FINNED PILOT WHALE
43
Fig. 4. The average composition of 5 schools of long-
finned pilot whales from the Faroe Islands from the
period 1978 - 1985; N=388. 1 = 118 immature males;
2 = 50 mature males; 3 = 69 immature females; 4 =
64 mature females without any further information; 5
= 36 pregnant females; 6 = 2 pregnant and lactating
females; 7 = 42 lactating females; 8 = 7 resting fema-
les.
include some lactating females which have
not been recorded as such, thus underes-
timating the number of lactating females.
Half of the population (48.2°7o) is composed
of immature animals, 38.9% of mature fe-
males, while only 12.9% is made up of phys-
iologically mature males. Of these, only a
part will be functionally mature males which
migrate between schools (Andersen, in print;
Amos et al, 1991; Desportes, Saboureau and
Lacroix, in print).
Age. Of the 267 sampled mandibles, the age
of 139 was determined, with a maximum age
of 27 years for the males and 32 years for the
females (Fig. 5, a and b). The age of an aver-
age whale was found to be 11.4 í 0.7 years
for both sexes (N = 139), 10.0 t 0.9 years for
males (N = 58), and 12.5 t 0.9 years for fe-
males (N = 81). The material from the Faroes
from the period 1986-1988 recorded maxi-
mum ages of 46 years for males and 59 years
for females (Bloch et al, in print, c). From
New Foundland the oldest male was 36
years, and the oldest female 57 years after
the reexamination (Kasuya et al, 1988b). But
even with the above-mentioned reservations,
it is also clear from this present material that
females exceed males in age, as a result of a
higher natural mortality rate in males (Bloch
et al, in print, c).
Examinations of growth patterns of the
long-finned pilot whale (Fig. 5) show a high
growth rate until the beginning of sexually
maturity (at the age of 8 for females; 16 for
males, Bloch et al, in print, c; Desportes et
al, in print). After that, the growth rate slows
down approaching an asymptotic length L^.
Included in the male and female growth
curve in Fig. 5 is the fitted line from the
Laird/Gomertz growth model (Laird, 1969)
calculated from the material from 1986-1988
(Bloch et al, in print, c). Taking into account
Dentine layers, years
n 35 immature male; + 23 mature male; X 26 immature female; X 55 mature female
Fig. 5. Length at age, determined from tooth dentine
GLG's, in the long-finned pilot whales off the Faroe
Islands. The Laird/Gomertz growth formula is inclu-
ded. N=139.