Statistics have been based on 12 years' worth of sightings, drawn from systematic whale shark research off Western Australia's Ningaloo Reef.
The records provide a pointer to trends in overall numbers as well as relative numbers of younger and older whale sharks. Analysis is helped by the existence of photographs of many of the recorded creatures.
According to the Australian researchers, the decline appears to be progressing at a rate somewhere between gradual and a more serious 10 per cent.
Ningaloo Reef is a regular meeting ground for whale sharks and a good area in which to build a representative regional picture. The sharks migrate over distances of up to 7500 miles, so that those sighted off Australia are among populations extending through South-east Asia and India.
Researcher Dr Corey Bradshaw, of Charles Darwin University, highlighted the problem that scientists remain in the dark over key aspects of the animal's life cycle, saying: 'A big gap in our understanding of whale sharks is how often they breed and how many offspring they produce.' |
