Seasonal distribution, abundance, habitat use and population identity of humpback whales in Oman

Abstract

Previously published data on the occurrence of humpback whales (Megaptera novaeangliae) in the Arabian Sea suggests that the region hosts a
non-migratory population that adheres to a Northern Hemisphere breeding cycle. In order to investigate the distribution and abundance of this
population, twelve small boat surveys were conducted in three main locations off the coast of Oman between February 2000 and November 2004.
Humpback whales were observed during surveys in Dhofar and Gulf of Masirah on Oman’s Arabian Sea coast, but not during surveys in the Muscat
region in the Gulf of Oman. An even ratio of males to females was observed and sampled during surveys in the Gulf of Masirah, which was surveyed
in October and November (n = 38), while almost all whales sampled in Dhofar in February/March were male (n = 28). Song was detected frequently
in the bay surrounding the Halaniyat Islands (formerly known as the Kuria Muria Bay) in February/March, but observations of mother-calf pairs
were sparse, and competitive groups were absent. Feeding was observed in both October/November and February/March, but behavioural and
environmental observations indicate that the Gulf of Masirah is primarily an important feeding ground, while the Dhofar region, particularly the
Halaniyat Bay, may be a breeding area. However, limited survey effort and a lack of recent observations of mother-calf pairs or competitive groups
raises the possibility that the primary mating, calving and nursing areas are yet to be identified. Sixty-four individual whales were identified using
photographs of dorsal fins or tail flukes. A high rate of re-sightings between years and between survey areas at different times of the year indicates
year-round residence off the coast of Oman. A Chapman’s modified Petersen estimator was applied to various data pairings to calculate abundance.
All pairings yielded estimates of less than 100 individuals, but sample sizes were small and there were various sources of possible bias. Analysis
of scarring on the caudal peduncle region of identified individuals in Oman indicates that between 30 and 40% are likely to have been involved in
entanglements with fishing gear. Comparison of the Oman photo-identification catalogue with those from Zanzibar, Antongil Bay (Madagascar)
and Mayotte and the Geyser Atoll (Comoros Archipelago), yielded no photographic matches. These data are consistent with the hypothesis of a
discrete population. The distribution of fluke pigmentation rankings from the Oman catalogue, which varied significantly from those of Madagascar
and Mayotte, provides further evidence for this theory. The evidence presented here provides a strong underpinning for the recent IUCN Red List
classification of the Arabian Sea sub-population of humpback whales as Endangered. In light of ongoing coastal development and other threats to
this population’s habitat and future survival, urgent research and conservation measures are recommended.