Fróðskaparrit - 01.01.1991, Blaðsíða 45

STUDIES ON THE LONG-FINNED PILOT WHALE
49
Sex ratio
Sex ratio in different schools: 10 entire
schools (range: 24-318 animals) were sexed
(Table 4). The sex ratio was biased towards
females, comprising on average 58.2 t 1.8%
females (N = 931). The range was 45.2-64.4%
females, and the difference in sex ratio is sig-
nificant (p< 0.001). Only a single school
contained more males than females (18. Sep-
tember 1984, Table 4), but especially this
school is known to be a part of a bigger one.
The sex ratio of 58.2% females recorded in
the present study agrees with that observed
in other studies from the Faroes, 60% (Joen-
sen, 1962; Moore et al, 1978; Bloch et al, in
print, a), and compares with the ratio found
from Orkney, 55% (Kock, 1956), British
strandings of 62% (Martin et al, 1984),
Iceland of 68% (Sigurjónsson, Víkingsson
and Lockyer, in print) and from New Found-
land of 65% females (Sergeant, 1962).
From the drive fishery and small-type
whaling off Japan of the short-finned pilot
whale, G. macrorhynchus, it has been shown
that the two species of Globicephala differ
from each other in some biological
parameters. Nevertheless, these schools also
contain more females than males with 67.3%
females (Kasuya and March, 1984; Kasuya,
in print; Kasuya and Tai, in print, a; in print,
b).
But this was quite the opposite of the sex
ratio in landed schools of another small
cetacean, the porpoise (Phocoena phoco-
ena), where the proportion of females is
24% (Møhl-Hansen, 1955), which indicates
that different species seem to have different
school structures.
Neo-natal sex-ratio: 57 foetuses were sexed,
showing an equal sex distribution of 50% fe-
male foetuses, (Table 3 and 5). The number
of foetuses from this material is too small to
examine any trend in sex ratio changes dur-
ing gestation.
Post-natal sex-ratio: The sex-ratio of 8
schools was recorded (N = 541, Table 6),
where the sexual maturity was fixed at a
length of > 480 cm on average for the males,
and > 375 cm for females following Ser-
geant (1962) and confirmed by Desportes et
al (in print). The number of histologically
sexually mature males in the schools was on
average 15.0 + 2.8% (4.2-29.0%), and 41.4
í 1.0% for females (35.8-45.8%). On aver-
age, there were 2.8 t 1.2 times more mature
females than males in the schools (range:
1.4-11.0, N = 541). The proportion of func-
tionally mature males is considerably smaller
(Desportes et al, in print).
Sex frequency at age: When the whales were
distributed according to age (Table 5), the
difference in male percent decreased with
age in the post-natals, while the foetuses had
an equal ratio at birth, as also shown in the
material from New Foundland (Sergeant,
1962: 67).
Sex ratio over time: Since 1884 (Miiller, 1882;
1884), sex frequency has been calculated
several times in investigations from the
Faroes and New Foundland (Table 7). It ap-
pears that male frequency has not changed
in the period 1952-1985, but is significantly
higher than in 1883 (z = 6.2; p<0.001).
According to Faroese whaling statistics
dating back to 1584, pilot whales occur in
the Faroese waters periodically with a cycle
of about 120 years (Joensen and Zacharias-
sen, 1982; in print; Bloch, Joensen, Hoydal