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whale-sharks Simon Thorrold Woods HoleSimon Thorrold, Woods Hole Oceanographic Institution

Scientists have discovered a juvenile whale shark aggregation site in the Red Sea

Researchers from the Woods HoleOceanographic Institution and from the King Abdullah University in Saudi Arabia discovered hundreds of young whales sharks gathering on an isolated reef - unusually for such aggregation they were a 50/50 mix of males and females.

The research team started tagging the sharks in 2009 and tracked 47 individuals most of whom stayed in the southern Red Sea suggesting the area is an important habitat for juvenile whale sharks.

‘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,' said Simon Thorrold, a biologist at Woods Hole and co-author of a paper recently published in PLOS ONES. ‘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 team used three types of satellite transmitting tags to track the movements of the 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 500m (1,640 feet). Three of the tagged sharks made excursions below 1,000m (3,281 feet), with a maximum-recorded dive depth of 1,360m (4,462 feet).

‘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 said.

Adult whale sharks were not seen at the site near Al-Lith on the central coast of the Saudi Arabian Red Sea.

To date, 12 whale shark aggregation sites have been identified globally.

‘While all other juvenile whale shark aggregations are dominated by males, we found a sex ratio of 1:1 at the site in the Red Sea. The presence of so many female juvenile sharks may be of considerable significance to the global whale shark populations,’ Thorrold said.

‘Our research on whale sharks in the Red Sea clearly shows that much remains to be learned about the species,’ said co-author Greg Skomal. ‘This newly discovered aggregation off Saudi Arabia likely plays an integral role in the natural history of this species in this region and, perhaps, well beyond.’


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