Up to 20 meters long and weighing as much as 20 tons, its enormous size gives the whale shark (Rhincodon typus) its name. Known as the gentle giant for its non-predatory behavior, this fish, with its broad, flattened head and minute teeth, eats tiny zooplankton, sieving them through a fine mesh of gill-rakers. Listed as a rare species, relatively little is known about whale sharks, which live in tropical and warm seas, including the western Atlantic and southern Pacific. However, a new study combines computer-assisted photographic identification with ecotourism to study the rare species and suggests whale shark populations in Ningaloo, Western Australia are healthy. The study appears in the Ecological Society of Americas January issue of Ecological Applications.
West Australian marine scientist Brad Norman (ECOCEAN/Murdoch University) began the study in 1995. Photographs were taken while swimming alongside each whale shark and photographing or video-taping the white lines and spots along the flanks of the animal. Norman teamed up with U.S. computer programmer Jason Holmberg (ECOCEAN, Portland, Oregon) and astronomer Zaven Arzoumanian (USRA/NASA, Greenbelt, Maryland) who adapted software originally used with the Hubble space telescope. The pattern-recognition software developed by Holmberg and Arzoumanian allowed the group to positively identify individual whale sharks. Like a human fingerprint, the speckles and stripes pattern on the skins of whale sharks are believed to be unique to each individual.
Ningaloo Reef, in Western Australia, is one of the best locations to find whale sharks, especially between April and June. The authors found that more whale sharks are returning to the northern area of Ningaloo Marine Park from season to season, suggesting the population is growing. In addition, they found that about two-thirds of the sharks were repeat visitors while one-third were sighted only once during the study period.
|Contact: Nadine Lymn|
Ecological Society of America