Fróðskaparrit - 01.01.1992, Side 20

24
THEINTERNATIONAL RESEARCH .. .
The sex ratio was at parity close to con-
ception, but the proportion of males
decreased significantly with increasing
gestational age and reached 35% at the time
of birth. After birth the proportion of males
increaseđ and reached 50% at age 3. There
is thus a differential foetal mortality fol-
lowed by a subsequent differential mortali-
ty in the opposite direction in postnatal
individuals. Parity is maintained until age
10, and from the period of male puberty the
male proportion decreased by stages with
increasing age until it reached 0 at age 50.
Male-only schools are uncommon in the
fishery (Bloch, 1992), though one was
landed during the project, and it is not clear
whether the decreasing proportion of males
from puberty onwards is solely the result of
the stronger selection operating on males or
whether it is also partly due to some segre-
gational pattems.
The proportion of male foetuses de-
creased with gestational age and was also
significantly lower among older pregnant
females. These results suggest strongly that
the foetal mortality might be important in
pilot whales, as it is in other mammalian
species, and should be taken in account
when calculating reproductive parameters.
The Faroese sample included a dispro-
portionate number of female foetuses while
the Newfoundland sample (Sergeant,
1962a) included a disproportionate number
of male foetuses. Variation in foetal sex
ratio between Newfoundland and the
Faroes may point to the existence of more
than one population in the North Atlantic
or/and to changes in environmental condi-
tions or population density.
Further analyses are being carried out to
examine variations in foetal and post-natal
sex ratios between schools and between
geographical areas, and their relatedness to
biotic and abiotic parameters. Future stud-
ies will try to analyse the factors leading to
the higher mortality of male foetuses, and
of juvenile females, to address the link
between the results on sex ratio variation in
pilot whales and some theoretical predic-
tions conceming sex ratio trends, and to
explore the demographic consequences of
these effects
Andersen, L.W., Desportes, G. and Friedrich, U. 1989. Sex
determination in long-finned pilot whale foetuses of the
Faroe Islands. Paper SC/41/SM12 presented to the IWC
Scientific Committee, May 1989 (unpublished). 1-6.
Andersen, L. W., Desportes, G. and Friedrich, U. 1992. Sex
identification of long-finned pilot whale foetuses off the
Faroe Islands. Maríne Mammal Science 8/2: 184-187.
Andersen, L. W. and Friedrich, U. 1988. The karyotype of
the long-finned pilot whale, Globicephala melaena.
Hereditas 109: 245-251.
Andersen, L. W. and Gradl, G. 1989. Sex determination of
5 Odontocetes species. Paper presented to IWC work-
shop on the genetic analysis of cetacean populations”
(Califomia, Sep 1989) under the title “Sex determina-
tion of Phocoena phocoena” (unpublished). 1-5.
Bloch, D., Lockyer, C. and Zachariassen, M. In press. Age
and growth parameters of the long-fmned pilot whale
off the Faroe Islands. Rep.int.Whal.Commn (Special
Issue 14).
Desportes, G., Andersen, L.W., Aspholm, Bloch, D. and
Mouritsen, R. 1993. A note about a male-only pilot
whale school observed in the Faroe Islands.
Fróðskaparrit 40: 31-37.
Desportes, G., Bloch, D. and Andersen, L.W. in press.
Variation in foetal and neo-natal sex ratio in long-fmned
pilot whales off the Faroe Islands. Ophelia. 38(3).
Desportes, G. Saboureau, M. and Lacroix, A. In press.
Reproductive maturity and seasonality of male
long-fmned pilot whales off the Faroe Islands.
Rep.int.Whal.Commn (Special Issue 14).