Aspects of Reproduction in the Male Humpback Whale, Megaptera nodosa (Bonnaterre)

Abstract

At puberty, male humpback whales off the Western Australian coast have an average body length of 36 ft 9 in. From histological examination of the testes, the extreme range of lengths at puberty is from 33 ft 4 in. to 40 ft 10 in. The mean testis weight at puberty is 2000 g. Following puberty, males are of low fertility for a period (possibly 1 yr) during which testis weight, tubule diameter, and spermatogenetic activity increase, before the attainment of full sexual maturity.

The mean length of the penis at puberty is 3.5 ft, but owing to considerable individual variation the penis length alone is not a reliable criterion of puberty. In sexually mature males the penis length ranges from 3.2 to 6.2 ft.

The proportion of fully physically mature males amongst those examined was very low (1.4 per cent.). The mean body length of those defined in this paper as approaching physical maturity was 41.90 ± 0.35 ft, and that of the fully physically mature males was 42.97 ±1.59 ft. The largest male examined (46.42 ft) showed no sign of epiphysial fusion.

Changes in mean testis weight, mean diameter of testis tubules, and number of sperms in testes and vas deferens fluid have been followed at various stages of the life cycle. The variations of these characters in mature individuals have been examined for evidence of a seasonal cycle in male humpback whales; increasing testis weight and more active spermatogenesis are exhibited during winter months off Western Australia.