Humpback whales Megaptera novaeangliae in the Arabian Sea

Abstract

The population identity of humpback whales Megaptera novaeangliae in the Arabian Sea has long been a matter of dispute. New information is presented from this region, based upon whaling and observations conducted by the Soviet Union, primarily in November 1966. In that month, a total of 238 humpbacks were killed off the coasts of Oman, Pakistan and northwestern India; 4 others were killed in 1965. Biological examination of these whales showed that they differed significantly from Antarctic humpbacks in terms of size, coloration, body scars and pathology. In addition, analysis of the length distribution of 38 foetuses indicates that the reproductive cycle of the Arabian Sea whales was unequivocally that of a northern hemisphere population. Mean lengths were 12.8 m for males (range: 95 to 14.9 m, n = 126) and 13:3 m for females (range: 9.5 to 15.2 m, n = 112). All whales 12.5 m or more in length were sexually mature. Among 97 females examined, 12 (12.4%) were immature. Of the 85 mature females, 39 (45.9%) were pregnant, 3 (3.5%) were lactating, and 43 (50.6%) were resting. A more plausible pregnancy rate, adjusted for underrepresentation of lactating females, was estimated at 39%. A majority of stomachs examined contained food, including euphausiids and fish. Overall, the data presented here argue strongly that Arabian Sea humpbacks constitute a discrete population which remains in tropical waters year-round, a situation which is unique for this species.