Bumper Year for the Southern Right Whale calves

Posted on October 27, 2014

  • Over 1000 Southern Right Whales were observed during the survey including 459 cow and calf groups and 88 single adults or adults in groups without calves
  • The annual surveys, carried out over the last 36 years have shown the population along the southern Cape coast to be increasing strongly at about 7 percent per annum

The Mammal Research Institute of the University of Pretoria has recently flown their 36th consecutive annual helicopter survey of the Southern Cape’s Right whale population.  The survey carried out between Nature’s Valley and Muizenberg in the Western Cape was sponsored by four offshore oil and gas companies namely;ExxonMobil Exploration and Production South Africa Limited, Impact Africa Limited, PetroSA, and Thombo Petroleum Limited PetroSA, and Thombo Petroleum Limited.

The Southern Right whales so called because they were the ‘right’ whales to hunt and relatively an easy target because they were predictable in their distribution and floated when dead. They were hard hit by historical whaling particularly from the “Moby Dick style” open-boat whalers between 1780 and 1835, when the bulk of the population is believed to have been taken from three whaling centres on the Southern African coastline.

By the time of international protection in 1935 the global population is estimated to have been reduced from between some 70,000 and 80,000 individuals to probably less than a few hundred, with illegal Soviet whaling fleets continuing to take whales up until the 1960s.

The annual surveys have shown the population along the southern Cape coast to be increasing strongly at about 7 percent per annum (which is close to the maximum biologically plausible increase rate) and now in the region of 5,000 to 6,000 individuals (out of a total global population of some 15,000 individuals).

It took approximately 50 hours of flying in a Bell Jet Ranger helicopter, a total of 22 survey flights of up to three hours each over the prime right whale habitat between 500 to 800 m offshore along the Southern Cape coast with surveys commencing on each flight at the end position of the previous flight’s searching.

Over 1000 Southern Right Whales were observed during the survey including 459 cow and calf groups and 88 single adults or adults in groups without calves. These totals may contain around 25% duplicate sightings as we believe southern right whales generally move westward during the two week survey period and so tend to be resighted if surveying is delayed by poor weather.  Such duplicates are identifiable in the analyses of the survey results through the whale marking patterns. The westward whale movement is also the reason for the westward flying of the survey as it leads to duplicate rather than missed sightings.

All encountered groups of Southern Right Whales that comprised a cow and calf pair or animals with distinctive brindle colouration markings were photographed from the helicopter as vertical images of the heads and the backs of the animals allow for individual identification from the patterns of the wart - like callosities on their heads and in some cases from the pigmentation patterns on their backs.

Initial sorting of images will be done using a computer-based image recognition system, followed by final matching of whales by eye. These analyses provide a suite of information on the vital parameters of the population including abundance estimation, population growth rate, survival, calving intervals and age at first parturition (the age at when a female calf first returns with her calf) which are used to model the population for comparison with and verification of the raw survey counts. Furthermore known individuals may be tracked over time providing information on movement and migration patterns.

Once filtered to extract the best identification images of each encounter, the collected identification photographs will be added and compared to the Institute’s catalogue of identification photographs of some 1700 recognisable adults from previous surveys.

Despite such a strong increase in the population size, research has detected a marked decline and probable change in the distribution of animals without calves (the so called “unaccompanied adults”) in recent years.

Whereas field counts of “unaccompanied adults” were roughly equal to the number of cow and calf sightings in the years prior to 2010, the counts of these animals have dropped significantly in recent years. This can probably be attributed to results from a change in the distribution patterns of “unaccompanied adults” towards the west coast (in association with increasing sightings in Namibian waters) and the plan is to have surveys across the West Coast area in future years.

In addition to the generous support of the survey sponsors, the MRI Whale Unit acknowledges the De Hoop Collection, CapeNature and the Dyer Island Conservation Trust for logistic support, accommodation for the survey crew, and for access to the survey areas.

All surveying was carried out under a permit from the Department of Environmental Affairs to approach whales and under specific Marine Protected Area permits from conservation authorities. Further information may be obtained from Ken Findlay or Meredith Thornton of the Mammal Research Institute on 0825708212 or 0827465579 respectively.

- Author DUR

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