Two days of non-stop rain means no diving and no new manta sightings but it also means that we have time for a much needed blog post. Today I’m going to talk about the thrilling topic of databases! Also known as “what we spend our evenings doing”. Bear with me here...
Every single manta ray has a unique spot pattern on their ventral surface (scientific word for belly). It means that if you can get a photo of it then you can ID that specific manta again and again whenever and wherever it shows up. They work just like our fingerprints. The best way of cataloguing the population of manta rays in an area is to photograph the belly of each one you see and then use the Manta Trust’s database to work out if it has been sighted before, how many times, where-abouts etc. And that is exactly what we have been trying to do in Bora Bora. The database of Bora Bora mantas goes back to 2002 when some of the original research was done on the population here so we have been comparing our belly photos to these. Some of the mantas we have encountered are new to the Manta Trust so we have given them new numbers like our most recent individual ST-MA-0137 (catchy right!)
The photo above is straight from the database gallery and shows you that ST-MA-0137 is a female with a long tail. Here we would also be able to log if she has any damage to her fins, tail or body which thankfully she doesn't! Spreadsheets within the database then tell us info like when they were first seen and where, if they've ever been sighted pregnant, their size, life stage and all sorts of other info. It's all very useful and we're excited to be able to contribute to something like this.
Some of the mantas we're seeing though have been encountered before. This week we have had two dives with a manta called ST-MA-0003. For those of you that haven’t guessed how the numbering system works this means that this particular ray was the third manta added to the database for Bora Bora. She was first seen way back in 2002, already as an adult and since female mantas reach maturity at around 15 years old then it stands to reason that she is around 30 now! She’s known as Blacky, she travels regularly between Bora Bora and Maupiti (another nearby manta spot) and is well known to manta scientists here.
On to Tikehau which is an island (or a motu as they're known in Tahitian) near to Bora Bora and part of an island group called the Tuamotus. We recently met a man called Vincent who has been working with and photographing the mantas in Tikehau for years and had hundreds of belly shots dating back to 2011. He offered us the photos to catalogue and add to a new Tuamotus database and we eagerly accepted. After a few long evenings of staring at photos of manta stomachs we have 71 new individuals logged already! Vincent has some stunning manta photos from Tikehau which we hope to share with you soon as well as persuading him to write a little guest too.
Thanks for reading,
Today marks exactly a month in Bora Bora for Graham and I and I’m pleased to say that the manta rays got the message and decided to join us for a one-month celebration! After a week of barely being able to see the end of our own noses underwater, we haven’t exactly had a great manta to dive-time ratio. That’s not to say that the mantas weren’t there, we’ve certainly seen a few dark shadows in the gloom (Cue internal dialogue: ‘Arrhh! What-the? Please be a manta, please be a manta. What else could it be...? don’t think about that! Please be a manta.’), but we stood no chance of photographing and identifying them. Today however, following a storm free Saturday afternoon and minimal rain in the night, the visibility was far better at over 10m. Clear enough for us to spot manta rays but still misty enough for them to make a dramatic entrance; like cloaked magicians appearing from a cloud of smoke.
Here is a little clip of a manta ray gliding over our heads and nearly blocking out the sun. Please excuse the shaky images, the camerawoman was a little overexcited.
As each couch-sized ray casually swooped past we did our best to capture as much data as possible: size, gender, visible injuries, tail length, species, spot patterns… thank goodness for underwater cameras. There was one ray on this dive, however, which stood out from the others for an exciting reason. A big, beautiful and incredibly pregnant female! This heavy, hampered lady was swimming around in the shallow corals and looked absolutely fit to burst; reminding me of some of our friends when they hit the ‘I just want to get this thing out of me’ phase of their pregnancy. We have our fins and fingers crossed that we might spot her new-born on another dive very soon.
Manta rays have a long gestation period of 12-13 months and only produce one baby at a time. They are ovoviviparous reproducers which means that an egg develops and hatches within the womb and the female later gives birth to a fully formed, mini-manta. It is believed that female mantas only reproduce once in every 5-6 years so they are not at all fast at replenishing their numbers. Not enough is known yet about manta reproduction but what is clear is that with few natural predators, mantas haven’t evolved to cope with the pressure of heavy predation making them very vulnerable to overfishing.
Tonight perhaps a new baby manta will be born somewhere nearby? A comforting thought before bed.
Thanks for reading,
Most of our posts recently have been manta ray info and travel adventures; fascinating but it’s probably time for a project update!
We arrived at the tail end of the rainy season here in Bora Bora…a tail that ended up being longer than we thought…in fact it’s still going. I mentioned before that when it rains heavily the manta dive site gets pretty washed out with silt making the visibility quite poor. This week though we have been able to get there more regularly and got some dives in which has been great. We have seen a manta or two and we’re persevering despite the milky water and hope that it will clear up soon! Obviously the clearer the water the easier it is to see mantas and identify them. Hopefully as the water clarity improves the number of dives will continue to go up as will the number of manta photos we have to share with you.
Oh and it’s a 20 mile round trip on our newly purchased bikes in 30°C heat to the manta dive site, so we’ll be fitter than ever in no time. The things we do for science!
On to cleaning stations! A few weeks ago I said I’d talk a bit more about them, what they were and why animals like manta rays use them. Well, that day has come! Cleaning stations are areas of the ocean, usually part of coral reefs, where large marine animals like mantas but also sharks, turtles, other species of ray and large fish come for a good clean up. When they arrive they sit almost stationary in the water and usually open their mouths or behave in some other way to indicate that they would like to be cleaned. At this point a little task force of specialist shrimps and fish (mostly wrasse and gobies) descend and eat any parasites, dead skin, bacteria and mucus off of the body surface and gills of the larger fish, even going inside the mouths of sharks to clean.
This process is called mutualistic symbiosis. A fancy way of saying that both parties (the manta ray and the cleaner team) get something out of the experience. Cleaning helps keep the mantas healthy as they stay parasite free and any dead or infected skin gets removed from wounds which helps them to heal faster and prevents infection. At the same time the cleaner team are provided with a regular and easy dinner. Manta rays are known to spend hours each day at cleaning stations and return again and again to the same ones; not only day after day but also year after year. This makes them really useful places to study manta ray populations and health.
As the cleaning stations are fixed locations they are also popular places for snorkel and dive operators to take guests to see these amazing animals. It is really important that codes of conduct are adhered to by everyone at these stations so that the natural behaviours of the mantas are not altered. If you’re lucky enough to be going on holiday to somewhere where you might get to see these animals, please take a look at the Manta Trust’s guide for ‘Swimming with Mantas’ before you leave.
Cleaner fish are very eager to clean any animal that seems in need, as I found out on a dive yesterday. We were doing our safety stop (which is just hanging in the water for 3 minutes at 5 meters at the end of the dive to let any excess nitrogen slowly leave our bodies) and a cheeky little cleaner wrasse swam over. It started nibbling on my legs and giving me a good old clean! I don’t think I have much in the way of parasites on my legs but maybe a little bit of peely sunburn – enough for a snack for a cleaner fish anyway. Check out the little video that Bex shot below.
All for now, thanks for coming by and reading.
Being a magnificent, ethereal ocean giant that traverses the deep and mysterious blue like a BOSS does not, alas, protect you from the reaches of industry and human impact on the environment. Far from it! Along with countless other marine species, manta ray populations around the world are now fighting for survival against man-made pressures including fishing, habitat loss, pollution and climate change and both Oceanic and Reef manta species are listed as Vulnerable by the IUCN.
One particularly worrying and relatively new threat to these colossal, briny beasts is that of the gill plate trade. I have mentioned in a previous post that manta rays have specialised gills which they use to filter feed. Inside each of a manta’s ten gill slits is a set of feather-like gill plates (a circle of thin cartilage filaments) which trap planktonic food as water passes through a manta’s mouth and out of through the gills. Manta and mobula rays are now being hunted specifically for their gill plates which are extremely valuable for their use in Traditional Chinese Medicine.
Gill plates are dried and usually eaten in a soup (see image below). The soup may not look all that appetising to our Western tastes (yup, it's garnished with pipefish) but retailers promote that consumption of the plates can treat all manner of health issues ranging from asthma to chicken pox to cancer and that their filtering properties help to boost the immune system and detoxify the blood... all of which helps to explain why so many people are slurping down this 'wonder-drug', pipefish and all! However there is of course no scientific evidence to back up any of these claims, as is the case for so many of these Traditional Medicines made from desperately endangered and ill-treated animals.
What makes this story all the more frustrating is that research into traditional literature has revealed no mention of gill plates. It seems they are not actually a true Traditional Medicine but a remedy invented in recent years by Chinese retailers seeing an opportunity to market new products as 'revived' ancient medicines, playing on the fears of consumers over disease outbreaks such as Bird Flu and SARS. The result: big new manta and mobula rays fisheries popping up in India, Sri Lanka and Indonesia.
That alone sounds like enough for a big, flappy, cartilaginous fish to have to deal with but sadly there is more to tell. Further posts to follow soon on other threats to mantas and what you can do to help protect them. You can read more about the gill plate trade on the Manta Trust's website.
Thanks for reading!