Translation 2783

260
and females (usually sexually mature) stay in pairs, either a pair
of one sex or a male and a female; in other cases they form groups
of from six to eight animals of one sex. I% has been obserVed that
the males show a greater tendency to congregate together, and form
larger groups.
From April to June groups of females predominate in the Gulf
of Alaska; from July on there are more groups of males and mixed
groups. That indicates that the females that have already mated are
the first to arrive in the Gulf; then come the males, and the migration
is completed by the rest of the animals.
During the fattening period there is a reMarkable change in
the state of nutrition: the-thickness of the subcutaneous blubber
layer increases from 3-5 cm to 7-10 cm and even 13 cm.
Most of the males attain sexual maturity on attaining an
average length of 17.4 to 17.6 metres, the weight of the testes
Icing not less than 2.6 kg, and the length of the penis not less
than 1.3 metres. The females become sexually mature at a length of
18.2 to 18.6 metres. The w_:.e of such whales is from four to six
years. The fin whales in the Uast China Sea, which do not go beyond
the boundaries of the Sea of Japan, are more "early-maturing" and
begin to take part in reproduction at the following average lengths:
males about 17 metres, and females about 18 metres.
Mating takes place mostly from November to january, with a
peak, apparently, in the middle of December; it is consummated under
the water, sometimes on the surface, .A few cases of coitus have
been observed in summer on the fattening-grounds.
Gestation lasts for about 11.5 months. The average length
of new-born calves is about six metres (from 5.0 to 6.9 metres:).
As with other rorquals, parturition takes place in warm water, as
the new-born calf does not have a protective layer of blubber. For
its firs% hours of life the calf is very sluggish, and then it gradually
begins to move. For more than six months it feeds exclusively
on its mother's milk . The fat content of the milk is from 20% to
45%, with an average of about 35.
The lactation period ends when the calves have attained a
length of 12 or 15motres, somet,ies even 13.5 metres'. The calves
l'eed for some time on both .Milkaiid crustaceans, after which they
advance to the regular diet of the srecies.