Newly discovered juvenile whale shark aggregation in Red Sea
Woods Hole Oceanographic Institution
Whale sharks (Rhincodon typus) — which grow more than 30 feet long — are the largest fish in the world’s ocean, but little is known about their movements on a daily basis or over years. A newly discovered juvenile whale shark aggregation off Saudi Arabia is giving researchers a rare glimpse into the lives of these gentle giants.
Scientists from the Woods Hole Oceanographic Institution (WHOI) and colleagues from the King Abdullah University of Science and Technology (KAUST) and Massachusetts Division of Marine Fisheries report on the movements of whale sharks tagged at the site in a study published July 30, 2014, in the journal PLOS ONE.
During fieldwork in 2009, the research team found hundreds of juvenile whale sharks gathering on coral reefs near Al-Lith on the central coast of the Saudi Arabian Red Sea.
The research team utilized three types of satellite transmitting tags to track the movements of 47 whale sharks from 2009 through 2011. The tags, which are placed just below the dorsal fins, measure temperature, depth, and light levels of the waters the fish swim in. After several months, the tags pop off, float to the surface and beam data via the ARGO satellite system back to computers on shore.
Diving data from the tags revealed the sharks made frequent deep dives to at least 500 meters (1,640 feet). Three of the tagged sharks made excursions below 1,000 meters (3,281 feet), with a maximum-recorded dive depth of 1,360 meters (4,462 feet).
Most of the sharks remained in the southern Red Sea throughout the time the tags were on. Some of the tagged individuals headed into the Indian Ocean, which may have been motivated 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.