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62
APPENDICES.
northern humpbacks is well-founded and that it applies to the South Georgia herds; I have further assumed that the length at birth is fifteen feet and that the rate of growth is equal throughout pregnancy. The possible dates for the pairings so found range from 8th November to 7th December, and eight of these dates occur in November. The highest number of corpora lutea found was three in a female pregnant with a 6-inch foetus, taken on 20th December. One may provisionally fix the beginning of the sexual season of the humpbacks at the beginning of Novem ber, or two or three months later than the opening of the sexual season of the finners -a difference in time which accounts for the evidence of the partial overlapping of nursing and renewed pregnancy given above.* How long the sexual season of this species lasts is not known, but the corpora lutea show it to be polycestrous. The calf is probably weaned before, or immediately after, re-impregnation of the dam; and the rate of propagation is probably the same as in the finners and blue whales, viz., a calf in alternate years after the birth of the first one. Sperm Whales :-
Total number captured and examined at South Georgia, three males,
namely
Whale No. 1, 14th November; length 53-25' (King Edward's Cove).
6, 15th November; length 54.3' (Leith Harbour). Whale No. Whale No. 291, 16th January; length 51.5 (Leith Harbour). These may
be young bulls or "bachelors." In the proof of Mr. J. Erik Hamil- ton's Report to the British Association, on the Belmullet (Co. Mayo, Ireland) Whaling Station, for the season of 1913, which Professor J. Stanley Gardiner has most kindly allowed me to peruse, it is said that according to the whalers "In the southern seas each adult male is the leader of a herd of females, and, as the young These bulls approach maturity, they are driven off by the old leader.
are inferior in young bulls do not become leaders of herds, as they strength and size to the fully adult males. But when fully grown, they will return to the herd, and contend with the leader for possession of the females. If the old male is then driven off, he becomes a solitary wanderer, and frequently travels up into the North Atlantic. In connexion with this theory, it may be mentioned that the sperm whales taken at Blacksod and Inishkea are all males, and of great size for sperm whales, which never appear to exceed 60 feet, the average for the ten Blacksod specimens being 57 feet 3 inches, while the smallest was 53 feet." The latter figure, allowing for the different method of measuring the total length of whales employed at Belmullet, is at least equal to the length of the largest male from South Georgia.
to
The accompanying comparative table (p. 63) has been drawn up show some important differences in the character of the individuals which compose the herds of each of the three principal species of South Georgia, between the middle of November and the middle of January. In the first part of the table it is shown that of the total number taken, males were largely in excess of females in the case of finners; of blue whales, on the other hand, the females were 4 per cent. more numerous than the males; and in the case of the humpbacks the females were nearly twice as numerous as the males. Of the total catch of finners, 3-3 per cent. are immature males, while no immature females were obtained; of the total catch of blue whales, 10 per cent. were immature males and 20 per cent. were immature females. Deducting these immature whales, we find in the second part of the table that the adults of both finners and blue whales consist of about 55 per cent. of males and 45 per cent. of females. The humpback catch similarly treated, still shows a preponderance of females over males of nearly two to one. Major Barrett- Hamilton was not able to examine all the adult cows for pregnancy, but, taking those that were examined as a fair sample of the herds, the total number of females in various stages of pregnancy must amount to about 40 per cent. of all the adults in the finners and blue whales, and to 60 per cent. of all adults among the hump- backs. Nursing females account for little more than 1 per cent. of the mature stock of finners; they seem to be absent from the herds of blue whales; and they amount to about 8 per cent. of the adult stock of the humpbacks.
*As a result of further work the view expressed in this paragraph is modified in the complete report. The age of the small fœtuses is greater than was supposed. Some of the hump. backs appear to pair on the African coast about July, while others appear to pair at later dates down to about September or October in the neighbourhood of South Georgia.
APPENDICES. ·
63
COMPARATIVE TABLE OF STATISTICS RELATING TO FINNERS, BLUE WHALES, AND HUMPBACKS OF SOUTH GEORGIA, DURING THE PERIOD BEtween 15th NOVEMBER, 1918, AND 15TH JANUARY, 1914.
Finners.
Blue Whales.
18-84-% 25=65·8% 8=7·9% 16-89-5*/
Humpbacks.
Total number
184=100
*
of males
females
106=57%
Immature males
79=48%.
6=3·3%.
females
0=0
50=1 0 24=48%. 2652/ 6=10% 10=20%,
57=100 90-85*, 87=86*/.
7=12·8% 12=21·1%%
Total mature
+1
"J
malea females
178=100
99=55.5°/ 79=44.3%
E
19
10
19
nursing
TJ
11
"
16
J
pregnant (observed)
(estimated)
8?=1.12% 8519.0%. 78=41%
85=100 19-54.8*/ 16:45-7.
0=0 9=25·7% 18-87.2%
88=100
Dates of capture of immature males
Deo. 29- Jan. 12
Dec. 8
1
Nov. 5
6
Jan. 2-8
4
Deo 18-28
2
Jan. 5-16
4
6
6
7
Doc. 1-12
2
Nov. 18
1
Den. 22-29 ...
8
Doo, 8-18
2
Jan. 6-16...
8
Jan. 6-16
9
10
12
Dates of capture of immature females
Percentage of all mature females pregnant
92
81
If length of largest female... That of largest male measured
100 88
100
95.8
28-80-5/
92
100
95.8
The following scheme is intended to give an idea of what appears to be the rate
of propagation in normal circumstances: the period allowed for growth from birth to sexual maturity is almost certainly not too long but may be too short.
Period of gestation Length at birth ...
First year, suckling, and grows to Second year, weaned, and grows to
Finner, (Female.)
Humpback.
(Female.)
10-12 months 20-25 feet
About 11 months
11
15 feet
45-50
85
2)
21
11
61
41
"
E
#1
Ready for breeding in nezt sexual season. Third or fourth year, gestation; fourth or fifth year, calf born; and so on in alternate years.
The rate of propagation is thus a slow one, and though nothing is definitely known of the subject it is not improbable that the natural rate of mortality among infant and adolescent whales is a high one.
It has been shown above that the sexual season of the finners and blue whales and Major of South Georgia probably opens as early as the month of August," Barrett Hamilton's observations prove that it continues at least to the middle of January. Assuming the sample examined by Major Barrett-Hamilton to be a fair one, and that estimates based upon it are reliable, it appears from the com- parative table above, that in the period mid-November to mid-January 92 per cent. of the mature finner cows and 81 per cent. of the mature blue whale cows are pregnant.
*It is now believed that the principal months for pairing are either June, July, and August, or July, August, and September in the case of the southern finners; the season" of the blue whales appears to correspond. Some pairing takes place in other months also. (Bee complete report.)
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