by Rochelle Constantine, School of Biological Sciences, University of Auckland
Every year humpback whales undertake one of the longest migrations known to man, which takes one population from their feeding grounds in Antarctic waters to their Tongan breeding grounds. These whales form part of an Antarctic feeding population south of New Zealand and Australia but little is known about the migration path of this small population and their movements between the Southwestern Pacific Islands.
The pre-whaling population of humpback whales south of New Zealand and East Australia was estimated to be 10,000 animals but when commercial whaling stopped in 1963, this population had been reduced to less than 500 whales. With such low numbers the increase in population size frequenting Tongan waters has been slow whereas the East Australian population has recovered to over 2000 whales. The reasons for this are unknown.
In 1994, the South Pacific Humpback Whale Project began research on the humpback whales in the Southwest Pacific Ocean. The research involves photo-identification of flukes, DNA analysis and song profiles in order to establish the recovery rate and migration patterns of the Tongan humpback whales. To date there have been some very interesting findings. We have a low resight rate of the 100 whales we have photo-identified in Tongan waters. This leads to the question of where do the whales go when not in the Vava'u group of islands in Tonga? We have one whale photo-identified in Tonga which has been photo-identified in East Australia and there are elements of their song which are similar but even so, the Tongan whales' song is least like East Australian whales when compared to New Caledonia and New Zealand.
As the population came so dangerously close to extinction and the recovery is slow, it will no doubt take a few years before we know the exact status of the Tongan whales. The research will continue and we hope to collect data in neighboring Pacific Islands such as Niue and the Cook Islands to determine whether the Tongan whales range to these other areas of the Pacific. If so, then the possible future implementation of the South Pacific Ocean as a whale sanctuary will be even more valuable to afford protection to these whales from threats to their future survival.
This research would not be possible without the generous support of the South Pacific Regional Environment Program, the Whale and Dolphin Conservation Society and Cetacean Society International.
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