Why research whale sharks?
Way back, in 2005, my long-time friend and colleague, manta ray researcher Dr Andrea Marshall, suggested that I should come over to Mozambique and start up a whale shark research program. She was seeing lots of these huge sharks, but didn’t have time to study them herself.
I’d never actually seen a whale shark at that stage but, hey, it sounded fun.
It turned out to be a life-changing opportunity. Africa is amazing. Whale sharks are big, spotty, and thoroughly endearing.
Unfortunately, they’re also at serious risk of extinction. It’s our fault. People have killed them for their livers, to waterproof boats with the liver oil, then dumped the bodies. They kill them for their fins, to make shark fin soup. People eat them. Hit them with boats. Accidentally catch them in nets.
This stuff is still happening.
Our global conservation assessment for whale sharks, published in 2016, estimates that people have killed more than half of the world’s population of these gentle giants since the 1980s.
We’re working to stop whale sharks from being killed, and to help their populations recover. Unfortunately, we still don’t know very much about the sharks, so it can be hard to know the best way to achieve those goals.
That’s why we research whale sharks.
Who are we?
Well, there’s me. As I said above, I started working on whale sharks in 2005, in Mozambique. These days I’m a Principal Scientist at the Marine Megafauna Foundation, Science Advisor to Wildbook for Whale Sharks (the global whale shark photo-identification library), and a regional Co-Chair of the IUCN Shark Specialist Group.
There’s more about me here, on the site.
Dr Chris Rohner, a fellow Principal Scientist at MMF, finished his doctoral thesis on Mozambican whale sharks in 2013 and has been leading our project at Mafia Island in Tanzania since 2012.
Chris is an expert on… well, lots of things these days, but particularly dealing with satellite-tagging data. He’s also a great underwater videographer.
Clare Prebble (MSc) joined MMF as a Project Manager in 2011. She was running day-to-day operations in Mozambique from 2012 until she started her PhD project, on the biochemical ecology of whale sharks, through the National Oceanography Centre at the University of Southampton, UK.
Clare’s an expert on stable isotope and fatty acid analysis, and consistently gets slightly better photos than me when we shoot together. It’s annoying.
Alexandra Watts (MSc) took over from Clare in Mozambique, and in 2017 started her PhD on the conservation genetics and genomics of whale sharks at Manchester Metropolitan University, UK.
Alex is a geneticist, and has also worked as a vet nurse and horse-riding safari guide in South Africa.
Stella Diamant (MSc) founded the Madagascar Whale Shark Project in 2015 and leads research activities in Nosy Be. She’s also a talented wildlife artist, and her photography is coming along too.
Another competitor. Le sigh.
How do we study whale sharks?
Identifying individual sharks
Every whale shark has a distinctive pattern of white spots on their skin. These spots make them identifiable (like every person has a unique fingerprint). By taking photographs of each side – the area just behind the gills – we can reliably identify individual sharks for at least 22 years (the current ‘record’). That allows us to count how many sharks we see, and to track their movements and behaviours over time.
Of course, we can only use the photos to track the sharks’ long-distance movements if everyone takes the same kind of photographs, and then shares them with one another.
Fortunately, we have Wildbook for Whale Sharks, an online global photo-ID library that acts as a central database for whale shark researchers and the interested public. Over 8700 individual whale sharks have been identified from more than 50 countries (I looked this up alphabetically… they’ve been identified from Angola to Yemen 🙂 ). Over 5000 people have submitted photos.
Getting personal: whale shark size, age, and sex
Once we know who the sharks are, we try to learn a bit more about them.
We can distinguish male from female sharks based on the presence (males) or absence (females) of claspers, the male reproductive organ – a rolled-up extension of the pelvic fins, underneath the shark. Once the shark becomes an adult, at around 8-9 m length, the claspers become larger and more obvious.
Adult male whale shark with large claspers
At this stage, we can’t tell if a female is an adult or not, unless she is very obviously pregnant. While the sharks can have a noticeable bulge in the right area, as in the photo below, absolute confirmation is still a work in progress. Teams working in the Galapagos Islands and offshore Mexican islands, respectively, are trying to use waterproofed ultrasound machines to prove that the sharks are indeed pregnant.
A “presumed pregnant” whale shark in the Galapagos Islands
Determining the age of whale sharks has proven to be a challenge. Most sharks have annual growth rings in the centre of their vertebral column; a bit like a tree stump has concentric annual rings. However, because whale sharks don’t stop swimming, and can cover huge distances each year, they aren’t necessarily subject to seasonal variations in temperature. The rings may not reliably correspond with a year in the shark’s life.
To get around that, we’ve been trying to measure free-swimming whale sharks to see how fast they grow over time.
We started off using parallel-mounted green lasers, which project two laser ‘dots’ onto the side of the whale shark, giving us a measurable scale. While that kind of worked, our initial results suggest that whale sharks grow so slowly that a very slight change in their body position (which we can’t necessarily pick up in photos) can make the measurements unreliable.
More of that story here:
Ultimately, we need to use a more repeatable method, and over much longer time periods (so the sharks will have grown more). In 2018 we’ll be working with stereo-video units, which should be an improvement.
At this stage we don’t really know how fast they grow, and what their maximum age might be. They’re probably long-lived, though. Possibly longer than people.
Just keep swimming…
We also need to understand whale shark movement patterns. Once we know where they like to live at different points in their life, we can help to ensure that they are effectively protected.
There are several different techniques we’re using to work that out.
Whale shark DNA encodes the species’ whole evolutionary history within their cells. Genetic data makes it clear that whale sharks in the Atlantic are an isolated population, at least for practical purposes (like assessing their conservation status and threats).
The whale shark genome has now been sequenced, which should allow us to have a more detailed look at their population ecology over the next few years. That’s part of what Alex Watts will be studying for her PhD.
Alex taking a tissue sample in Galapagos
As I said earlier, photo-identification has allowed scientists to keep tabs on individual whale sharks for up to 22 years (and counting). It’s also a relatively cheap way to monitor populations (compared to expensive satellite tags, for instance), so photo-ID is a great way to conduct long-term studies.
Because we can track resightings of whale sharks through the Wildbook system, we’ve been able to show that, for instance, whale sharks in the Caribbean and Gulf of Mexico routinely swim between countries (see a map of shark movements below).
Over shorter time-scales (months, to a few years) we can use biochemical techniques, like stable isotope analysis – which gives us information on habitat use and general diet – and fatty acid analysis, which gives us more specific insight into whale shark diet. That’s what Clare Prebble is working on for her PhD. We take a small sample of whale shark skin, and from that we can collect enough tissue for both these analyses, along with the genetic and genomic work.
Electronic tags can give us a very detailed short- to medium-term (days, to 1-2 years) look into the life of a shark. Unfortunately, their expense means we often have to assume that a small number of tagged sharks are representative of the population.
Satellite tags allow us to track the sharks over large geographical distances, and get information on temperature preferences and diving behaviour. Acoustic “pinger” tags are good for looking at the residency and return migrations of whale sharks to specific areas over time. 3D “behavioural” tags can give us a highly detailed look at the shark’s movements and behaviours over a few hours to a few days, so long as the tag can be physically recovered afterwards.
Jonathan Green checking a fin-mounted satellite tag
What are our main objectives?
How many subpopulations are there?
Genetic work, supported by photo-ID and tagging results, show that Atlantic whale sharks rarely move into the Indian or Pacific oceans. But do Galapagos whale sharks swim to Mozambique? Probably not, but the techniques used so far haven’t had the discriminatory power to tell. It’s a really important question though.
We need to work out the large-scale population structure of whale sharks to effectively protect them. For instance, there are no current targeted fisheries for whale sharks in the southwest Indian Ocean (there are other threats, but bear with me). Are those sharks affected by the big Chinese fishery though? At the moment we’re not sure. Our photo-ID results suggest they aren’t, as we haven’t seen any whale sharks swim across the Indian Ocean, but since the adults rarely approach the coast it’s tough for us to tell.
That’s why Clare and Alex are working on techniques that don’t require us to physically follow the sharks to tell us what they’re up to. No one technique gives us all the answers; they just give us another puzzle piece.
What are the key threats to each subpopulation?
Whale shark with propeller scar off Mexico
To prioritise conservation activities we need to determine the most lethal threats to the largest number of sharks. Then, for each geographical “unit” of sharks, we can work to remove the most important threat, one by one, allowing that population to start recovering.
Protection efforts can have a disproportionately positive impact if we focus on high-use areas, such as, for instance, Al Shaheen off Qatar.
Are whale sharks in decline, or recovering?
Whale sharks swim around. A lot. That makes it really hard to tell if a decline in sightings in one country, such as Mozambique, is meaningful – are the sharks in trouble, or are they just not coming close to shore due to changing environmental conditions? We don’t know.
In the same way, 2017 was a great year for (smallish) whale shark sightings in Thailand. Does that mean shark populations are recovering in Southeast Asia? We don’t know.
Most of the countries or regions for which we have long-term sightings records show a decline, which is the basis of their globally Endangered conservation status. It would be great to be able to answer the questions above, though.
We’ll be working on that question a lot more this year.
Understand whale shark biology and ecology
As I said earlier, there’s still a lot we don’t know about whale sharks. We don’t know where the babies are. We don’t know where most of the adults are. Most feeding areas are dominated by juvenile males, so we don’t really know where the females are either.
When we’re “missing” such a large proportion of the population, it makes it tough to conserve the sharks effectively.
Similarly, at the moment we don’t have enough information about their biology to determine what level, if any, of deaths from fishing or boat strikes that their populations may be able to absorb. We don’t know how fast their populations can bounce back from overfishing, either.
To answer this, we need to build a demographic model for the species. The key parameters we need are (1) the average age of adulthood for females (age at maturity), (2) how often they have babies (reproductive frequency), (3) their reproductive lifespan, and (4) the level of human-induced mortalities they’re having to deal with.
Help whale sharks to recover as fast as possible
All that research is for nought if it doesn’t make things better for the sharks. We’re working with governments to protect whale sharks in key countries, along with their key habitats. We’re working with fishers to reduce accidental catch and injuries. We’re working with shipping companies to avoid areas where whale sharks are feeding on the surface. We’re working with tourism operators to promote ecotourism while avoiding impacts on the sharks, providing an economic benefit from shark conservation efforts.
Where do we work?
As of 2018, we’re working at field sites in…
Darwin Island, the northernmost of the Galapagos archipelago, is frequented by large female sharks from around July to October each year. We’re working with the Galapagos Whale Shark Project team to track these massive sharks with satellite tags, collecting photos to look at how often the females get pregnant, and collecting tissue samples for genetic and biochemical studies.
Madagascar (Nosy Be)
Nosy Be, in northwest Madagascar, is a major “new” hotspot in the Western Indian Ocean. We’re part of the Madagascar Whale Shark Project team and have been tracking the sharks’ movements, investigating what the sharks are doing there, and helping to develop best-practice standards in the (admirably good!) tourism industry there.
Mexico (Quintana Roo)
Chris and I have been hosting trips to Mexico (through Aqua-Firma) with Ch’ooj Ajauil AC each year since 2013. This is one of the world’s largest whale shark aggregations. I’ve personally seen over 200 sharks in a day, and 100 is common.
We’ve published a couple of papers on whale shark movements between countries in this region, and overall population size in the western Atlantic.
Mozambique is where it all started for me, and Chris did his PhD here between 2009 and 2012. We’ve published papers on tourism development and sustainability, regional movements, population structure, diet, and we’ve still got at least one more big population ecology paper to work on.
Unfortunately, we’ve also seen a pronounced decline in sightings off Tofo over the last few years, so we’ve got conservation efforts underway to address the main local threat: floating gill nets. The good news is that whale sharks were protected in Mozambique in 2017.
The Philippines (Tubbataha Reefs Natural Park and elsewhere)
We’ve been working with the Large Marine Vertebrates Research Institute in the Philippines since 2014, first on whale sharks and now also on reef-associated sharks and marine protected area monitoring. Publications coming soon!
Tanzania (Mafia Island)
We started working at Mafia Island in 2012, after getting a contract from WWF Tanzania, partnering with TAFIRI and KAUST on the research itself. After the KAUST team deployed a bunch of acoustic tags, we found out that the sharks here are highly resident, uniquely so. That has provided us with the opportunity to track individual sharks over time, which is hugely valuable for learning more about their biology and ecology.
We’ve published papers on their movements, diet and population structure, and there’s plenty more to come.
The United Kingdom (St Helena Island)
Alex will be joining Dr Al Dove and his Georgia Aquarium whale shark research team at St Helena this year.
How are these results useful for conservation?
I’m really proud of the results we’ve got from our small team.
A lot of our work was used to inform the most recent (2016) IUCN Red List global conservation assessment for whale sharks, which I wrote with Dr Brad Norman from ECOCEAN. The big population declines seen around the world meant their status was downgraded to globally Endangered.
Following on from this, a regional IUCN assessment of whale shark conservation status in the Arabian Sea region, which I also contributed to, similarly classified them as Endangered in 2017.
The global assessment was used as a basis for the successful nomination of whale sharks to Appendix I of the UN Convention on Migratory Species in 2017, which obligates all 120+ signatory countries to ensure that whale sharks are protected in their waters. I led the technical proposal for that, with lots of other research groups adding in information too. A CMS Appendix I listing is the closest thing we have to “global protection” at this stage, policy-wise, so that was a great result.
On a national level, we’ve been working on species-level protection, habitat protection and monitoring, ecotourism development and sustainable fisheries, in many of our study areas.
Whale shark off Mafia Island, Tanzania
Where to learn more
I try to keep up a running commentary on our fieldwork on my shark biology blog. If I’m behind on that material (and I always am) there’s still a good chance that I’ve been procrastinating on Instagram, Facebook or Twitter at some point, so you can get an update from there.
You can also download any of our scientific publications from here on the site.
Want to join us in the field?
If you’d like to see some whale sharks with us, I host a few public research expeditions each year. I’ll be taking people to Madagascar and Tanzania in 2018, and there’s an additional trip to the Galapagos in 2019.
Interested in supporting this work?
That would be hugely appreciated! Please do get in touch.
Thanks for reading!
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