A few months ago, researchers from the King Abdullah University of Science and Technology discovered a gathering site for whale sharks off the Saudi Arabian red sea coast. But that was not the first such site discovered in the relatively warmer waters of the Middle East.
For years, workers in offshore oil rigs in Al Shaheen, the largest offshore oil field in Qatar, have noticed whale sharks aggregating around the platforms. When one of the workers took a picture of dozens of whale sharks swimming around the platform, it ended in the formation of the Qatar Whale Shark Project by the ministry of environment to study the patterns and habits of these vulnerable species.
“In the beginning we had no clue when and where to find the sharks so we had the offshore workers report sightings to us,” said Steffen Sanvig Bach from the Maersk Oil Research and Technology Centre, which has joined the Qatari ministry of environment’s research effort.
Later, they started attaching tracking devices to the whales to try to monitor their habits and movements. “Sometimes we saw over a hundred of them in a group. They start to appear in April, peak in the summer months and disappear in October, said Bach. “We don’t really know where they go after October, they simply disappear and we can’t know where they go except if they are close to the surface. They just return every year in April.”
Whale sharks (Rhincodon Typus) are the biggest fish in the world, with reports of individuals over 20 tonnes in weight. The whale sharks that aggregate at the Al Shaheen location are mostly juvenile, however. The average age of the fish found there is around six. Whale sharks can live up to 60-100 years, and are only mature and sexually active by the age of 30.
Aggregate sites are often important spots to understand the fish and plan for conservation efforts. “We have identified over 300 whale sharks in the Arabian Gulf and will continue to monitor, but it would take us five years to know the final count and determine if they are decreasing or not.”
But why are these young whale sharks gathering in this location? The researchers have several theories why the fish love this place. The site is rich in tuna mackerel, whose eggs is a favourite food for the whale sharks. The site contains a large amount of these fish, who make their home in the artificial reef created by the offshore rigs.
This is coupled by the warmer waters of the Arabian Gulf, which Bach thinks creates a favourable habitat for the whale sharks. “The area is probably a good feeding spot for the mbecause the water is warm, there’s plenty of prey to feed on and no predators. This is particularly important because these are relatively young fish,” he added.
During Qatar’s Annual Research Conference (ARC14), Bach discussed his the new technologies his team are using to learn more about the fish that aggregate at Al Shaheen every summer, before disappearing again. One such technology they are now using is eDNA, where they take a sample of water and study it to identify all the species that interacted with that sample recently.