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  • Humpback whale
  • The humpback whales in the South Pacific

    Humpback whales were abundant in the South Pacific ocean but in the first part of the XXth century their number have been reduced to 5% of the original population because of the commercial exploitation.
    Thousands have been killed in the whaling stations of Australia, New Zealand on the migratory corridors between their tropical breeding grounds and their polar feeding grounds. Numerous have been hunted in the Antarctic feeding grounds.
    More 46000 humpback whales have been illegally taken by URSS after that the spcies was declared protected by the International Whaling Commission in 1963. At that time the population have been estimated to be in between 200 and 500.
     

    Study area

     
    Humpback whale have been studied since 1993, however, since 1995, we have undertaken to spend 2 to 3 months every year observing and photographing the whales in the South of Grande Terre (New Caledonia, main island). The animals are located with the aid of binoculars from a land-based observation site. Their passage and behavior  is observed more closely with a telescope. 

    Permanent contact between the land-based observatory and the researh vessel enables observations to be carried out both from land and sea.
    Observation have also been carried out at Lifou one of the Loyalty islands in August 1998, in the northern lagoon to the Surprise atoll in 2000 and 2001.
     

    Extensive information is gathered from each group of whales encountered at sea
    • date
    • position,
    • duration of the observation,
    • number of animals in group,
    • the group's behaviour.
    Each animal is individually identified by photo of the caudale and flank types.

    Individual identification

    Photo-identification is the method used to individually identify each animal. This method involves using natural marks on the body of each animal to recognise it. For humpback whales, the tail flukes, and sometimes the flanks, of each individual present a unique pigmentation. This "tail print", the equivalent of our fingerprint, serves to identify each individual. Flukes have been classed into five types.
     

    type 1

    type 2

    type 3

    type 4

    type 5
     
    Southern hemisphere humpback whales, and particularly those from the south west Pacific, are particular in that the flanks can show varying amount of white pigmentation. The flanks, classed into four types, can be used to recognise an individual.

    Research carried out since 1993 has allowed us to individually identify 250 humpback whales in New Caledonia ( Garrigue et Greaves, 1999 ).
     

    Population estimation

     
    In biological terms, the identification of an individual in year X is called a "capture", it's re-identification in a subsequent year is a "recapture"; this type of information is indispensable for estimating the size of the population of the whales that frequent the lagoon. Population size have been estimated at 314 individuals (Garrigue, Greaves et Chambellant, 2000).

    Life history and migratory exchange

     

    HNC009, 1999
    Comparison of photographs allows the recognition of individually identified animals. This is used to establish the life history of each animal. As an example : 

    HNC009, 1997
     a whale numbered HNC009 and named Caterpillar was observed for the first time in 1993. It is a female. She was seen again in 1997 accompagnied by a calf and then in 1999 in a reproductive group. In 2000 she was observed with a new calf.

    HNC009, 2000
    The photo-identification is also used to study the migratory exchange into the South Pacific ocean.The scientists from the South Pacific Whale Research Consortium share their photographic catalogue of humpbacks in order to study the migratory exchange in the South Pacific Ocean.
    Some whales were observed in Tonga and New Caledonia, in Tonga and Cook island, in French Polynesia and Cook island. (Garrigue et al., 2000, Garrigue et al., 2001).

    Acoustic behavior

    On the breeding grounds the sexually mature male humpback whales sing. These songs differ from one population to an other, and analysis of them enables researchers to establish the population to which the study animals belong (Gill et al., 1995). We use a hydrophone linked to an amplifier to listen the songs and record them onto cassettes.
    In collaboration with Dr Cato (Australia) and Dr Helweg (USA) songs recorded in New Caledonia have been compared to those recorded in Tonga and east coast of Australia (Helweg et al., 1998 , Helweg et al., 2000).
    Spatial and temporal behavior of singers have been studied in the aouthern part of New Caledonia (Dodemont et al., 2001).

    Genetic analysis of the population
     
    From a small piece of tissu, it is possible to extract and study the DNA found in the chromosomes. For this purpose, biopsies are carried out on whales. The biopsies are colleted by using a crossbow to shoot a specially adapted boilt, the tip of the bolt has been modified to take a small plug of skin and fat. On hitting the dorsal area of the animal the bolt rebounds taking with it a sample of about 1cm3. The bolt has a float attached that makes it easy to pick up.  The skin and the fat are separated using a sterile blade. The skin is placed into a tube containing 70% alcohol, while the fat is wrapped in aluminium foil previously sterilised.
     
    The samples are stocked in a freezer. These samples enable us to establish the genetic identity of the animals, the diversity of the population and the kinship. The sex of each whale is also established. The comparison of samples from different localities will enable us to establish the links between individuals and know whether they are part of the same stock (Rosenbaum et al., 1998).
    This work is carried out in collaboration with the Laboratory of Ecology and Evolution of the University of Auckland (New Zealand), Dr S. Baker.

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