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Genetic and demographic assessment of dolphins taken in live-capture and traditional drive-hunt in the Solomon Islands

 

Principal Investigator: Marc Oremus, Opération Cétacés

Funding year: 2011

Main objectives:

 

  • To gain an improved understanding of the population status and dynamics of Tursiops aduncus in the Solomon Islands and to contribute to a robust science‐based assessment of the sustainability of current authorised levels of live‐capture removal.

  • To determine the species of dolphins taken by traditional drive‐hunts in the Solomon Islands and to investigate the population status of these species using molecular tools.
     
  • To provide, through objectives 1 and 2, the Government of Solomon Islands with capacity building in marine mammal surveys and scientific advice, based on robust data, to inform management decisions on the removal of dolphins from their wild populations.

 

Main outcomes:

 

  • Extensive small boat survey effort (350 h, 7,126 km) yielded sightings of 126 groups of marine mammals (1.77 groups per 100km effort). These included nine species (8 cetaceans, and the dugong), including sightings of possible Omura's whales. A total of 71 biopsy samples collected, mostly from Stenella longirostris and Stenella attenuata, but including Tursiops aduncus, Tursiops truncatus and Globicephala macrorynchus.
     
  • Surveys allowed for assessment of habitat use, encounter rates, individual movements and site fidelity, particularly for T. aduncus and S. longirostris. Data indicate year round occurrence of T. aduncus in coastal waters, although reduced rates of encounter at Guadalcanal and Malaita reflect recent captures. T. aduncus are likely distributed amongst local sub-populations or communities, and are likely demographically isolated from one another.
     
  • The abundance of T. aduncus within the study area was estimated to be between 700-1300 individuals using a range of capture-recapture models. Using a Potential Biological Removal  approach, the annual  'safe removal level' is estimated to be between two and nine per year  for each study site. This is well below the quota of 50 animals per year valid at the time of the survey.
     
  • Captive holding facilities were visited and an assessment made of captures, deaths, releases and exports. Photo-identification images were also collected. Tissue samples from 33 dolphins were collected from two different facilities.
     
  • Genetic analyses indicate that Solomon Islands T. aduncus populations are highly differentiated from neighbouring populations off New Caledonia, China/Taiwan and East Australia. Extensive assessment of markets and drive-hunting communities, led to the collection of teeth (used for jewellery), some fresh tissues, numerous interviews with hunters and elders and collection of catch statistics for selected areas and hunts.
     
  • A summary of available catch records for the drive hunt showed that a minimum of 15,444 dolphins were killed by villagers (mean annual catch 813 dolphins, SD = 464). This is considered an underestimate given data gaps.
     
  • DNA analyses of sampled teeth and tissues confirmed that S. longirostris and S. attenuata are the primary targets of drive hunts.
     
  • This work contributed to Solomon Islands Government decision to ban dolphin exports in 2014. This measure is still in place as of March 2015.

Reports/Papers:

Oremus et al. 2014. Genetic and demographic assessment of dolphins taken in live-capture and traditional drive-hunt in the Solomon Islands. A contribution of the South Pacific Whale Research Consortium. Final Report for the Small Cetacean Conservation Fund of the International Whaling Commission, January 2014. 87 pp. Click here to read.

Oremus et al. in press. Phylogenetic identification and population differentiation of bottlenose dolphins (Tursiops spp.) in Melanesia, as revealed by mitochondrial DNA. Marine Mammal Science.