Our previous work with Dr David Robinson and the Qatar Whale Shark Project team found that the Arabian Gulf, unexpectedly, hosts a large, seasonal feeding aggregation of whale sharks within the Al Shaheen gas field off Qatar.
Why was that a surprise? Well, the Gulf is the world’s warmest sea. Temperatures reach over 35°C on the surface in summer months – which is when whale sharks are on the surface, sometimes feeding for more than six hours daily. Crazy sharks.
Whale shark at Al Shaheen (from the paper)
Al Shaheen is an extreme environment. It’s also one of the few places around the world where adult male whale sharks are common. The Gulf is a major international shipping route too, and our field observations have made it clear that whale sharks are threatened by vessel strikes. There were a lot of good reasons for us to do some follow-up work!
This new paper looked at 59 whale sharks, tracked via satellite to follow their movements around the Arabian region – the largest sat-tagging study on the species so far.
David tagging a whale shark at Al Shaheen (from the paper)
The sharks used a small 66 km2 “hotspot” in Al Shaheen as their core habitat. A likely second feeding area, based on the amount of time the sharks spent there, was identified off Al Jubail in Saudi Arabia (see below). Most of the sharks stayed close to these two areas over the summer months.
This enthusiasm for hanging around Al Shaheen over the tuna spawning season suggests that the production of eggs is enough to support the dietary needs of sharks for several months. That’s pretty impressive, as whale sharks like to eat. A lot.
Whale shark “hotspots” of activity in the Arabian region
Although the sharks were feeding in genuinely hot water, the local oceanographic characteristics do help them out. The water in the Gulf is poorly mixed so, even at just 60 metres, the water temperatures remain a cool 18°C over summer. We didn’t examine the sharks’ vertical habitat use in much depth (guffaw) in this paper, but this access to cooler water is probably a requirement for them to deal with the high surface temperature.
We even included a graph (above), because science. The squiggly lines show the sharks’ average depth profiles at various stages during their movements around the Gulf. If you look at the blue line you can see that, when the sharks were at Al Shaheen, they’d feed at the surface in the mornings, then retreat to cooler waters at 30-40 m. That seems like a sound plan to avoid being fried.
Chillaxing – literally – in cooler water could also be a useful way for the sharks to slow down their digestion. That would help them to maximise the energy intake from the tuna eggs they’ve eaten. The eggs are incredibly calorific, with Mexican sharks potentially eating the energy equivalent of 8 kg of milk chocolate per day, so cooler temperatures would help the sharks to get full value from their time in the hot surface water.
Over winter, when a precipitous drop in temperature occurs, the majority of satellite-tagged sharks dispersed from Al Shaheen and Al Jubail, but remained in the region. One shark stayed inside the Gulf over the whole winter period, where it had to contend with temperatures of below 22°C for more than a month.
I hadn’t thought that whale sharks could function well at such a cool temperature, so that was interesting. Going forward, the Gulf area provides us with a useful “natural experiment” to examine their ability to cope with the world’s changing oceanographic conditions.
We tagged both adult and juvenile sharks. While all of the sharks moved among the Gulf countries, only nine moved out into the Gulf of Oman. There were no obvious differences between the movements of adult males and juveniles, but the one (presumed) pregnant female David tagged was the only shark to travel further afield. This 9 m female swam an estimated 2, 644 km over 37 days to near the Somalian coast, where the tag popped-off (see below).
Can’t make conclusions from a single track, but it would certainly be nice to tag a few more big female sharks in the Gulf to see if they make similar movements.
Fifty-five of the tagged sharks were also photo-identified, and 58% of those swam back to Al Shaheen the following or in later years, some repeatedly. It’s clearly an important site for them.
In the region, whale sharks are only afforded species-specific protection within the UAE, although all sharks are protected from fishing in Saudi Arabia and Kuwait. Whale sharks are still targeted by Omani fishers, and appear to be routinely hit by shipping vessels. The protection that existing conservation legislation offers them is, therefore, fairly limited.
David and I contributed to a regional IUCN Red List assessment for whale sharks in early 2017 that determined the species to be endangered in the Arabian Sea. They were already listed as endangered in the broader Indo-Pacific.
To reverse that decline, our next step is to use these tagging data, combined with records of whale shark deaths and injuries from fishing, and information on shipping traffic, to create a threat map and effective protection plan for whale sharks in the Gulf and surrounding areas. That can’t come too soon, unfortunately.
Thanks to the Qatar Ministry of Environment and Maersk for their support of this project, and for the two private trusts and Aqua-Firma that support MMF’ whale shark program.
Interested in more whale shark science? Check out Connecting The Dots: Whale Sharks In The Western Atlantic.
Like geeky animal facts and dad jokes?
I write a few articles just for my mailing list. They normally focus on something interesting, and possibly hilarious, that I've learnt about sharks (or other random animals) that week. There may also be groan-inducing jokes.
Real talk: there will be groan-inducing jokes.