Discovering a New Whale Shark Hotspot… In an Arabian Oil Field?
Written by Marine Megafauna Foundation
Whale sharks. Oil. Not topics that normally go together in a positive way.
So, finding myself on an oil company vessel, in the middle of an oil field, staring out at 100 large whale sharks charging back and forth on the surface, was… unexpected. Unlikely, even. But there I was, 90 km off the coast of Qatar, looking at the largest group of whale sharks I’d ever seen.
But why on Earth are they there? That’s what David Robinson is trying to find out over the course of his PhD at Heriot Watt University. David is working with a team of experts from the Qatar Ministry of Environment, Maersk Oil, and a few other scientists (including myself) to learn more about the ecology of sharks at this site, and how they can thrive in this extreme environment.
The Arabian (Persian) Gulf is shallow, sloping gently to a maximum depth of only 90 metres. In practical terms, that means it heats up or cools down quickly, and significantly. Temperatures reach a roasting 39°C in summer, making the Gulf the hottest sea body in the world. Because it is surrounded mostly by desert there is little freshwater input into the system, so the Gulf is also highly salty. The intricacies of how whale sharks use this area gives us insight into their physiology, and may help us understand how they will be affected by ongoing climate shifts. Whale sharks are a globally threatened species, so these results have a much broader relevance around the world.
Aside from this, the sheer numbers of sharks present make this an important hotspot in global terms. The first year of research took place at the site in 2011, and these results have just been publishedin the open-access journal PLOS ONE. Workers on the oil platforms actively helped the research team by logging whale shark sightings on a daily basis, which told us that sharks are present within the Al Shaheen field from at least May to September.
David towed a plankton net through the midst of feeding sharks to see what they were eating. Each time, the net came up full of fish eggs – up to an estimated 56 thousand per cubic metre. These eggs appear to be released at depth, but their oily composition means they float gradually upwards to carpet the surface. The sharks wait there, mouths agape, to welcome in this highly nutritious food.
Egg samples collected for genetic analysis showed they were from mackeral tuna, a species found widely through the Indian Ocean. The limited boat access into the oil field affords some protection to the tuna, supporting both their spawning ground and the whale sharks’ food source.
I first visited Al Shaheen last year to help David and team deploy satellite-linked and acoustic ‘pinger’ tags on the sharks. Satellite tags can give a useful picture of how sharks use the environment, both in terms of where they swim and how they use the water column. To accomplish that, they continuously record pressure, light and temperature data to establish depth and position. More advanced tags incorporate a GPS or GPS-like system to transmit their location to satellite, allowing the sharks to be tracked until the tag is shed or runs out of battery. Pinger tags are much simpler, emitting an intermittent pulse of sound that travels around 500 m through sea water. This transmission is recorded by special receivers when the shark swims within range, allowing us to establish which sharks are present in the area, and when.
While we were hard at work, two great TV crews were busily filming this natural spectacle, and our research work. The first feature from this work was shown as part of a BBC series, Wild Arabia. You can view some of the beautiful footage they shot here, and some photos of the sharks and area here. The second documentary, filmed for Qatari TV by a crew from Myriad, has just been posted online in its entirety.
I’ll be heading back to Qatar in the next couple of months to deploy some more tags, and hopefully to see a few hundred more sharks. I’ll report more from this amazing site soon!
Thanks to the Qatar Ministry of Environment and Maersk Oil for supporting this work, and the Shark Foundation for funding the equipment I was using in the field.