whale shark

n contrast to most sharks from the same order (Orectolobiformes), which are benthic (live on or near the bottom) species, the whale shark is a pelagic (open sea) species. Studies reveal that this shark prefers warm waters, with surface temperature around 21-30º C, marked by high primary productivity (much plankton). It is often seen offshore but commonly comes close inshore, sometimes entering lagoons or coral atolls.

The whale shark is thought to be highly migratory but currently there is no direct evidence to support this hypothesis. Their movements might be related to local productivity and they are often associated with schools of pelagic fish that are probably feeding on the same prey organisms.

Different geographic locations appear to be preferred at various times of the year. Whale sharks alternatively may undertake either fairly localized or large-scale transoceanic migrations, the movements governed by the timing and location of production pulses and possibly by breeding behavior. Seasonal migrations have been postulated for various areas but more information is needed to confirm these patterns. Each March and April, whale sharks are known to be aggregate on the continental shelf of the central western coast of Australia, particularly in the Ningaloo Reef area. A study was done in this area to provide information on the short-term movements and behavior of this species of shark. Whale sharks are thought to migrate to Ningaloo Reef each year to take advantage of the high zooplankton (microscopic animals) concentrations associated with large-scale coral spawning events occurring during the March and April full moons. A few whale sharks were tracked and some behavioral observations were made while snorkeling in the area. The reaction of the sharks to snorkellers varied between ignoring them to slowly diving. At times when water was flowing out from the reef lagoon, possibly transporting potential prey outside the reef, the tracked sharks swam in large circles adjacent to passes in the reef. The whale sharks also made numerous dives throughout the observation period. It appears that these movements, up and down through the water column, were associated with feeding. Whale sharks have smaller livers than most sharks and could conceivably control their buoyancy by swallowing some air as do the sand tiger sharks (Ondontaspis taurus).

Whale sharks were also observed near La Paz, Mexico. Researchers reported that when these sharks were not feeding at the surface, they swam practically without the head turning, gulping, and rhythmical opening and closing of the gill slits, seen during feeding behavior. The mouth was held slightly open, and the skin over the gill openings was quivering as water flowed steadily out the gill slits in the typical ventilation of pelagic sharks. Generally, whale sharks are encountered singly but loose aggregations of over 100 animals have been seen, which suggests that schooling activity does occur. Scientists do not know whether sexual segregation, either locally or geographically, occurs.