Fróðskaparrit - 01.01.1991, Page 49

Fróðskaparrit - 01.01.1991, Page 49
STUDIES ON THE LONG-FINNED PILOT WHALE 53 with a mean of 7.2 t 1.8 (r=1.0) was shown. The testes grow slowly until a body length of about 480cm at 12 years of age and a testes weight of about 300g, at which point the testes begin to increase rapidly in weight (Fig. 10). Histological examinations of the present material display a range of 446-520cm and 12-18 years of age at the at- tainment of sexual maturity (Desportes, per. comm.). The males were therefore defined as sexually mature at about the time when their testes began to grow rapidly. This oc- curred on average with a body length of 480cm and age of 11 years. This is in agree- ment with the findings of Sergeant (1962:45) from New Foundland of 490 cm and 12 years (see also Perrin and Reilly (1984: 103)), as well as the findings by Desportes et al (in print). Females: In the females, both ovaries from 158 animals were weighed and examined in order to find the corpora. The females were defined as mature when at least one corpus (luteum or albicans) was found (Perrin, Brownell and Myrick, 1984; Perrin and Reil- ly, 1984: 101). But to establish the range length for attainment of sexual maturity, fe- males with only one corpus luteum are con- sidered in the present study. On average it occurred with a body length of 375 cm (range 375-445cm, N = 58, Fig. 11) and an age of 6 years (Fig. 3), with a range from 6-13 years. The wide range in length and age could perhaps indicate that the attainment of female maturity is more a question of weight than age, as pointed out for the por- poise (Møhl-Hansen, 1955: 380) and in con- nection with further examination of the pi- lot whale (Bloch et al, in print, c). Studies in New Foundland showed that Fig. 11. Number of ovarian corpora at body length in long-finned pilot whales off the Faroe Islands. N=158; r=0.57; t=4.83. the females of the long-finned pilot whale were mature on average at a length of 365 cm and 6 years (Sergeant 62: 42). The short- finned pilot whale is not directly comparable since it grows larger, so here the females reach sexual maturity at an age of 9-9.5 years (Kasuya and Marsh, 1984; Kasuya and Tai, 1991b). Pregnancy: The number of pregnant fe- males in 7 schools was recorded (Table 8). The numbers found represent a minimum figure because not all females were exa- mined, and it was sometimes difficult to find the smallest foetuses in the time availa- ble for examination. The length of 61 foetuses, all from July to September, was measured (Table 3). Nearly all the foetuses were placed in two distinct groups, one comprised of 15 very big > 140 cm foetuses, and 30 in another group of small foetuses up to about 100 cm. If the gestation time is known, the expect- ed time of birth can be calculated. The length of gestation is said to be 10-14
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