By Simon Pierce
Madagascar isn’t just about lemurs and chameleons. Although to be fair, it’s quite a bit about lemurs and chameleons.
Chameleon. He comes and goes.
And a giant day gecko, because OMG.
Now that I’ve got them out of my system…
Madagascar is a global biodiversity hotspot. After separating from what is now Africa about 160 million years ago, Madagascar split from the Indian subcontinent about 66-90 mya. Madagascar’s land species have had a long, long time to evolve independently, and around 90% of the country’s wildlife is found only on the island.
Okay, so the lemurs aren’t entirely out of my system yet.
Marine life of Madagascar
Madagascar is pretty special below the water, too.
The South Equatorial Current carries water from Indonesia right across the Indian Ocean. The current hits Madagascar and splits. The northern branch accelerates around the tip of the island, and instabilities in the current lead to gyres and eddies (large, whirling water masses) forming in the northern Mozambique Channel, between Madagascar and continental Africa.
NASA released a very, very cool visualisation of this physical process. Check out the Madagascar region from about 47 seconds in.
That mixes up all the water in this area, leading to high connectivity in the marine fauna between these countries. There are around 300 reef-building coral species in the region, making this “Western Indian Ocean Coral Triangle” the second-most biodiverse coral ecosystem in the world.
Nosy Be, an island off the north-west coast of Madagascar, is in the eastern corner of the Triangle (see the red marker above). The ocean area around Nosy Be is a global hotspot for large planktivorous animals, including manta rays, mobula rays, Omura’s whales(!) and… whale sharks.
Whale sharks in Madagascar
The first information on whale sharks in Madagascar was published in 2007. Researchers from the Wildlife Conservation Society surveyed fishers and dive operators from various parts of the country and discovered that Nosy Be was a hotspot for sightings.
Dr Rachel Graham from WCS (now at MarAlliance) followed up on this information in the mid-2000s, conducting two seasons of research at Nosy Be. Then the country went through a period of political instability, and the work became untenable.
Everything went quiet for a decade.
Then, in 2015, Stella Diamant got in touch with me. She had volunteered in Madagascar with a WWF fisheries project, living in a local village for several months, and fallen in love with the country. On a second trip, she saw her first whale shark. As they are totally amazing (I’m not remotely biased, it’s science), she became determined to start a research and conservation project on the Madagascar sharks.
I invited her to come over to Mafia Island in Tanzania for our 2015 field season so she could learn MMF’s research techniques, and apply them to work at Nosy Be.
Shortly after that initial contact, Dr Jeremy Kiszka from Florida International University emailed me about Madagascan whale sharks. Jeremy, who is massively experienced in shark and marine mammal research in the region, was planning a big new shark and ray project in Nosy Be. I introduced him to Stella, and he linked her up with Arthur and Tanguy Guillemain from Les Baleines Rand’eau, who had started a marine conservation non-profit, Les Baleines Ass’eau, based in Nosy Be.
Together, in true Captain Planet style, we formed… the Madagascar Whale Shark Project!
Why study whale sharks in Madagascar?
Tanguy and Arthur spent a lot of time collecting whale shark photo-identifications over 2015. When Stella started processing these photos, along with others contributed by Scuba Nosy Be, she discovered they had seen over 100 individual sharks through the year.
To put that in perspective, after working in Tanzania since 2012, we’ve identified 130 sharks. Over 100 in a season… suffice to say they had my attention.
Whale sharks are not doing well. Last year, Brad Norman from ECOCEAN and myself updated the IUCN Red List assessment for whale sharks and determined that their populations have seriously declined, to the extent that they are now a globally endangered species.
These declines have been particularly pronounced in the Indian Ocean. In southern Mozambique, where I’ve been working on whale sharks since 2005, we documented a 79% decline in sightings between 2005 and 2011, which has continued to the present. in the Mozambique Channel, between Mozambique and Madagascar, Dr Ana Sequeira and colleagues used tuna fishery data to identify a 50% decline in peak monthly whale shark sightings between 1991 and 2007.
We really need to determine whether the Madagascar population is a separate unit to the surrounding countries or, alternatively, whether these “disappearing sharks” have reappeared in Madagascan waters.
The 2016 whale shark season
Stella flew down to Nosy Be in September 2016 to start her first full field season. In late October, I flew over for my first visit to the country.
It’s a tough old life.
So very tough.
But it wasn’t all sun and beaches. There was also the swimming with whale sharks. Muhaha.
I did do some work. Stella learnt how to take tissue samples from the sharks, allowing us to pursue some neat upcoming studies, and I brought over eight SPOT5 satellite tags from Wildlife Computers. We’d been using these for a study in the Philippines with the Large Marine Vertebrates Project. Their team had been able to recover a few tags that had detached from the sharks early, so we had some new and several recycled tags ready for another adventure.
Satellite tags can only transmit through air. That means we have to get them to the surface somehow. There are two different general categories of tags, which vary in their approach to this challenge.
Pop-up satellite tags, http://www.marinemegafauna.org/tagging-amazingly-huge-whale-sharks-galapagos/, are programmed to release themselves from the shark and float to the surface after a predetermined interval. We often use six months, as it seems to optimise our data recovery. The longer they stay on, the better the data… but the higher the chance that algal grow on the tag which will reduce their buoyancy, resulting in a $4, 000 tag sinking uselessly into the depths. Sad face.
Pop-up tags provide excellent information on temperature and depth. However, because they are constantly submerged during the track, we can only estimate geographical movements via a light sensor on the tag. The sensor allows us to infer the time of sunrise, sunset and midday, which is then used to generate a rough latitude and longitude. It still provides a useful track, but the results are indicative rather than exact.
Tethered tags, as we used on this project (shown in the photos above and below), float on a short length of Dyneema spear-fishing line. If the shark isfeeding or loitering near the surface, the buoyant tag will float up, a wet / dry sensor detects that the antenna is in air, and the tag will try to communicate with the ARGOS satellite network.
If the shark spends a lot of time near the surface, we can build a very detailed track of its movements. This information can then be combined with data on sea temperature, ocean currents and phytoplankton concentration, among other things, to work out which factors influence the sharks.
The downside is that these tags do not provide depth information, and we usually get shorter retention times than with pop-off tags. The tether means they can pull out easily, and predatory fish try to eat the towed tags. Pesky fish.
Fortunately, we had no problems finding eight sharks to tag. Most spent a lot of time near the surface; Dr Chris Rohner, principal scientist at MMF, put together this map based on the first few weeks of tracking:
As he’s a bit of a science ninja, he also created a “heat map” from the results above. That helps to point out the overall high-use areas – darker colours represent a high density of satellite transmissions:
Most sharks stayed fairly close to the tagging area off the southwestern coast of Nosy Be. Interesting that there’s a secondary hotspot to the south, though. We’ve continued to get good results from these tags, so we’ll update and publish these maps at a later stage.
Sharking with the sharkies
Swimming with the whale sharks is becoming increasingly popular off Nosy Be. I can see why – it’s a beautiful place, and the water was an amazing deep blue while I was there. Spending time with the whale sharks is amazing, too.
Having a good code of conduct in place for tourism operations helps to minimise the potential downsides of tourism, from the whale sharks’ perspective, while also improving client satisfaction. The operators trialed these recommendations, and most seemed to be working well.
There are increasing numbers of informal tourism operators, however, so continuing work will be required to ensure that everyone works to the same high standards.
All in all, it was a great start to the project. Stella is currently busy processing all the photo-identification data the team gathered last year (she stayed until December), and has been posting project updates on the Madagascar Whale Sharks Facebook page.
I’ll be heading back to Nosy Be in October 2017. Want to come? I’ll be hosting a public trip from the 10-17th October 2017 for my regular travel partner company, Aqua-Firma. I can’t wait!
This post was originally written for www.simonjpierce.com.