Náttúrufræðingurinn - 1992, Blaðsíða 54

SUMMARY
Sex hormones, puberty and
relative frequency of
pregnancy in fin whales caught
off
the coast of Iceland
by
Matthías Kjeld, Jóhann Sigurjónsson
and Alfreð Árnason
Landspítalinn (The University Hospital,
Department of Clinical Chemistry),
Endocrine Unit,
Hafrannsóknastofnunin
(Marine Research Institute),
Blóðbankinn (The Blood Bank),
Dept. of Genetics
IS-101 REYKJAVÍK
Iceland
The blood levels of testosterone and
progesterone in 718 fin whales (Balaenop-
tera physalus) caught during the summer
seasons 1981-1988 have been measured.
To our knowledge, such measurements
have never been carried out on these giant
cetaceans before. The whales were caught
off the coast of Iceland, and samples tak-
en immediately post mortem from a fluke
vessel. The hormones were measured by
highly specific radioimmunoassays after
solvent extraction from serum or plasma.
The animals were aged by the ear plug
method.
Testosterone levels in the 319 males av-
eraged about 2 nmol/I, or 10 times lower
than in man and 2.5 times lower than in
stallions. About 12% of the males had lev-
els of 0.1 nmol/1 or lower, indicating sex-
ual immaturity. Eighty-five percent of
these were distributed in a gaussian way
between the ages of 2 and 14, suggesting
that sexual maturation (elevation of lev-
els) was at its highest rate at the age of
8-9, when the number in the immature
group decreased fastest.
During the summer whaling season
mean testosterone levels in the males in-
creased more than four-fold from the be-
ginning of June until the earlier part of
August (Fig. 2).
The frequency distribution of the blood
progesterone levels in the females is
shown in Fig. 3. The levels fell into three
groups: group I with 0.1 nmol/1 or less;
group II with intermediate values of more
than 0.1 but less than 10 nmol/l; group III
with high levels, 10 nmol/1 or rnore.
Females of group I were young (Fig. 4)
and probably consisted of sexually imma-
ture animals. Group II had scattered
levels, probably comprising mature but
resting females. Group III presents a
gaussian distribution of the highest pro-
gesterone levels, and when a foetus was
found in a female, it always belonged to
this group.
Group I levels were mostly found in ag-
es from 2 to 14 with a clear peak in the 6
to 8-year olds (Fig. 4). This distribution
and the age distribution of group III sug-
gests that the age of puberty occurs chiefly
between 7 and 10 years, which is in agree-
ment with results of biological studies on
the reproduction of this species.
The relative frequency of pregnant fe-
males (pregnancy rate) in the catch was
determined by the proportion of high ser-
um progesterone levels (&10 nmol/1) in
the measured females. During the hunting
period the pregnancy rate was found to
start at 60% in the beginning of June and
to decrease to 25% in early August. The
fall in the relative number of pregnant fe-
males during the summer season may be
related to a long mating time, or to differ-
ent migratory behaviour of pregnant and
non-pregnant females off the coast.
Group II had intermediate values of un-
known significance. We have measured
serum oestradiol levels in fin whale fe-
males and found them to be Iow and with-
out any relation to pregnancy or maturity.
It would seem possible that the whales
have different oestrogens, for instance
equine oestrogens, which are found in
horses, the measurement of which might
throw further light on the data presented
and the reproduction of the species.
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