I did an interview recently for a New Scientist article, “Whale sharks’ secrets revealed by live-tracking aquatic drones“, written by Alex Matthews-King.
It’s a neat story, so I thought I’d expand on my answers (below). I’ve pulled some information and quotes from both the New Scientist article and a separate feature written by Stuart Philpott for Sport Diver UK.
Konrad Madej (above left) was the research director at the Whale Shark & Oceanic Research Centre in Utila, Honduras. He led the work featured in the New Scientist article: tracking whale sharks with autonomous “Wave Gliders” from Liquid Robotics.
The Wave Glider is a pretty awesome piece of kit. It’s the solar-powered surfboard-type doohickey in the photo above.
Here’s a video on how they work:
Whale sharks at Utila
I’ve spent bit of time looking for whale sharks off Utila myself, so I was really interested to hear about this study. Between 2011 and 2013 I spent six weeks on the island hosting “whale shark research weeks” for Deep Blue Resort (and, unsurprisingly, obsessing over the endemic Utila iguanas).
While I was there, I helped Steve Fox from Deep Blue / Utila Whale Shark Research write a scientific paper: “Population structure and residency of whale sharks at Utila, Honduras“.
That study, based on photo-identification of Utila whale sharks between 1999 and 2011, found that sharks were usually sighted in conjunction with tuna schools. Both the sharks and the tuna were thought to be feeding on the same small baitfish.
Whale sharks can turn up in any month of the year off Utila, so my suspicion was that their presence was related to the movement of productive oceanic fronts rather than any specific biological event.
These sightings data suggested that the sharks weren’t sticking around: 78% of them were only seen in a single calendar year.
But what if the sharks simply weren’t visible?
I’m not (just) being pedantic here. The seafloor off the northern coast of Utila drops rapidly to over a kilometre depth. Whale sharks can dive to at least 1, 928 m, and tagging data have shown that they often go long periods without approaching the surface.
The sharks could easily be hanging out deeper, only approaching the surface when they’re attracted by something – perhaps the sound of tuna jumping around while they feed.
Remotely tracking whale sharks
My last blog article was about the whale sharks at Mafia Island in Tanzania. There, the sharks move inshore to feed on shrimps from around October to February.
When we started tracking the sharks’ movements using pinger tags, recording their presence via passive acoustic sensors, we learned that the whale sharks weren’t leaving the area outside those months. They were just moving a bit further out from the island, and rarely coming to the surface.
It turns out that the sharks are so resident, we’ve been able to give many of them names.
That technique, deploying an array of passive acoustic sensors, worked fine in a shallow bay like Mafia. Installing receivers was easy, either by freediving or using basic scuba equipment. It’s much more complex in deep water. At Utila, that’s where the Wave Gliders come into play.
Konrad’s team set two Wave Gliders to patrol 5 km off the north coast of Utila. Each one carried a passive acoustic receiver, “listening” for whale sharks that had been tagged with high-frequency pinger tags. These sounds (inaudible to people) carry well through the clear oceanic waters off Utila. I’m guessing that the receivers would hear a tagged shark if it swam within around 800-1000 m of a Wave Glider.
The Wave Gliders can transmit real-time information on the depth and position of tagged sharks while they are in reception. Konrad told New Scientist that the drones detected one shark at a depth of 90 metres in July, when the team thought all the whale sharks had migrated north toward Mexico.
“With the turbulent weather during these months, it’s difficult to find whale sharks feeding as rough waters prevent the plankton, roe and coral spore they feed on from settling at the surface,” he says. “So it’s great to see they’re still swimming at depth, for the first time, via the Wave Glider.”
The Wave Glider can move at about three knots at maximum speed, around 5.5 km per hour – pretty quick. For the sake of random comparison, Michael Phelps swims the 100 m butterfly at a bit over 7 km per hour. Whale shark tracks of up to 25 minutes at a time were achieved.
All well and good, but let’s focus on me.
Alex did a quick email interview with me for New Scientist, so I’ve added that here:
What do you see as the big challenges in whale shark conservation at present?
A big challenge for whale shark conservation has been our inability to locate and follow adult whale sharks. Truly large whale sharks – over 12 m length – are regularly seen at just a handful of remote offshore seamounts. These areas are difficult and expensive to access.
Juvenile male sharks, from around four to nine metres in length, often feed in coastal waters, so we know a lot more about that age group. The problem is, we don’t know how much of that knowledge remains relevant as the sharks grow up.
It’s a worry for us. Whale sharks are an endangered species, but we know little about where the breeding-age sharks are, or what they get up to.
Do you think the insight provided by current or future drone technologies can help address some of these?
Drone technologies have the potential to provide insights on movement and behaviour that currently elude us. Tracking the movements of these sharks over long periods, while simultaneously sampling oceanographic data, would provide us with improved insight into the habitats they use and the human threats they might be exposed to.
I think there will be some interesting technologies converging over the next few years, such as solar-powered autonomous vehicles like Wave Gliders and the global internet access that companies like SpaceX and Google are working on.
The ability to transmit real-time high-bandwidth data, like video streams, would be huge for us.
Can it be applied to other species?
I think long-term monitoring of adult whale sharks is probably a stretch goal at the moment. These sharks are one of the deepest-diving fishes, to around 2 km depth, and swim 10-15, 000 km a year through the open ocean. They’re not easy to keep up with.
Some of the slower-moving, more coastal species will be a lot easier to track. There have even been some interesting initial studies done on basking sharks and white sharks.
That being said, I’ll be hugely interested to see what comes out of these initial whale shark studies. The species is constantly surprising us, so any new insights into their behaviour are very welcome.
< Interview ends >
Some quality time with Google has since revealed some neat footage of white sharks trying to eat drones:
Want more shark geekery? Many Utila sharks head north to join the world’s largest whale shark aggregation off Mexico each summer. I’ve written about that here.
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