Preliminary Report on Long-term Detection of Arabian Sea Humpback Whale Vocalizations off Oman

This report presents an overview of the progress to date on the humpback whale detection component of the Arabian Sea Humpback Whale Acoustic Research program off Oman. Three archival acoustic recorders were deployed at sites in two regions for approximately one year each, in Hallaniyats Bay during 2011/2012, and the Gulf of Masirah during 2012/2013. Performance of recorders varied among deployments, but despite some challenges due to equipment failures we succeeded in documenting spatiotemporal patterns in the presence of humpback whales in a large dataset. Several key findings broaden our understanding of the Arabian Sea humpback whale population off Oman. There appears a strong seasonal component to the use of song by this population, primarily from November through May, which is congruent with the Northern Hemisphere breeding cycle and singing season. Throughout this period, singing was heard in both Hallaniyats Bay and the Gulf of Masirah, separated by approximately 400km, indicating that the population utilizes both of these regions. However, there was a much stronger presence in Hallaniyats Bay, with song heard nearly 24 hours/day during the peak months, and song detected simultaneously at multiple sites across the Bay. Previous boat-based survey data indicated similar trends, however, given limitation in the duration of this fieldwork the current acoustic dataset provides a more reliable indication of this population’s breeding related activity. This suggests that the Hallaniyats Bay might serve as a more important habitat for breeding activity than the monitored region of the Gulf of Masirah. There also appeared to be a subtle northward shift in distribution of detections as the singing season progressed, both within Hallaniyats Bay, and from Hallaniyats Bay to the Gulf of Masirah, suggesting a seasonal shift in distribution for singing males. During the summer and autumn months, very little song was detected, however sparse detections indicate that whales are present in both regions during at least some of this period. It is recommended that similar acoustic monitoring be conducted in all range states of the population to elucidate spatiotemporal distribution throughout the Arabian Sea.