Whale Shark Aggregation in Red Sea Sheds Light on their Movements

A newly discovered juvenile whale shark aggregation in the Red Sea is shedding light on the movements of these gentle giants, as described in a new study published in the journal PLOS ONE.

Whale sharks (Rhincodon typus) - which can grow more than 30 feet long - may be the largest fish in the ocean, but their overall movements and patterns still remain a mystery. During fieldwork in 2009, researchers found hundreds of juvenile whale sharks gathering on coral reefs near Al-Lith on the central coast of the Saudi Arabian Red Sea, providing scientists with a rare glimpse into the lives of these giant fish.

"The fact that there were so many whale sharks in such a small area gave us an opportunity to begin an unprecedented study to answer some of the basic questions," co-author Simon Thorrold, a biologist at the Woods Hole Oceanographic Institution (WHOI), said in a news release. "The discovery of the site provides a window into the movements and ecology of the species in a region that we were not necessarily expecting to see them in such high numbers."

The research was conducted by WHOI and colleagues from the King Abdullah University of Science and Technology (KAUST) and Massachusetts Division of Marine Fisheries.

Using three types of satellite transmitting tags, the research team tracked the movements of 47 whale sharks from 2009 through 2011. The tags - which measured temperature, depth and light levels of the waters the fish swim in - showed that most of the whale sharks remained in the southern Red Sea throughout the study period.

Although, some of them roamed waters in the Indian Ocean - scientists suspect these movements were driven by an abundant food supply related to seasonal upwelling. Whale shark diets vary both seasonally and geographically, but they are thought to feed mainly on zooplankton as well as algae, small fishes, fish eggs and cephalopods.

"Interestingly, while some individuals that we tagged left the Red Sea and headed into the Indian Ocean, most remained relatively close to where they were tagged, suggesting that the area represents a critical juvenile habitat for this population," Thorrold added.

Researchers did not see any adult whale sharks in the area, and believe the site may serve as a "staging ground" for juveniles before they move on to regional aggregations of larger sharks.

The International Union for Conservation of Nature (IUCN) ruled whale sharks "vulnerable" in 2000 after small-scale harpoon and entanglement fisheries starting eating away at their population numbers. According to the IUCN website, whale sharks are valued for their meat and liver oil, which was traditionally used for water-proofing boat hulls.