Whale sharks. Oil. Not topics that usually go together… at least in a positive way.
So finding myself on an oil company vessel, in the middle of an oil field, staring out at 100 huge 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 had ever seen.
Whale sharks feeding in the Al Shaheen oil field. Photo by Mohammed Jaidah.
Why are the sharks there? Good question! That’s what David Robinson is trying to find out for 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 the Al Shaheen field. Its a neat model, too: theres a strong capacity-building element to the project, with a five-year knowledge transfer strategy for the Qatar MoE to build their internal technical expertise. Environmental scientists from Maersk Oil work are also key collaborators. There’s a website on the project here.
Sharks in hot water
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 39C in summer, making the Gulf the hottest sea body in the world.
Because it is surrounded mostly by desert, with little freshwater input into the system, evaporation leads to the Gulf also becoming very salty. The intricacies of how whale sharks use this area provides an insight into their physiology, and may help us understand how they will be affected by ongoing climate change.
Whale sharks are a globally threatened species, so these results have broad resonance around the world.
Qatar – a global hot-spot for whale sharks
The first year of research took place in 2011, and the results have just been published. Workers on the oil platforms actively helped the research team by logging whale shark sightings on a daily basis, proving that sharks are present within the Al Shaheen field from at least May to September.
Large numbers of sharks feeding of a Qatari oil platform. Photo by Soren Stig.
Nom nom nom
During field surveys, David took the opportunity to tow a plankton net through the midst of the feeding sharks to see what they were eating. Each time, the net came up packed 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 calorific food.
Without actually seeing the fish, it can be difficult to work out which species are involved in these enormous spawning events. Egg samples collected for species identification (through genetic analysis) showed they are primarily 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.
Spying on the sharks
I first visited Al Shaheen last year to help David and the team deploy satellite-linked and acoustic ‘pinger’ tags on the sharks. Satellite tags 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 this, 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.
Satellite-tagged whale shark off Qatar. Photo by David Robinson.
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 if the shark swims within range, allowing us to establish which sharks are present in the area, and when.
Pinger-tagged whale shark off Qatar. Photo by David Robinson.
Fortunately David and myself were joinedon this trip by Katie Lee-Brooks, who can process whale shark IDs and say intelligent things to camera… at the same time!
While we were hard at work, two great TV crews were busily filming both this natural spectacle and our research escapades. The first feature was shown as part of a BBC series, Wild Arabia. You can view some of the beautiful footage they shot here, and photos from the shoot here.
You can watch the second documentary, filmed for Qatari TV by a crew from Myriad, right here!
Thanks to the Qatar Ministry of Environment and Maersk Oil for their support, and the Shark Foundationfor funding the equipment I was using in the field.