Not much is known about smalleye stingrays. They are rare, elusive, and likely to be endangered. Off Mozambique, Marine Megafauna Foundation founder Andrea Marshall recently tagged the world’s largest ocean stingray for the first time ever. Will tagging help protect the species?
As a bare minimum you are going to need an armoured breast plate to protect you,” one of my research associates said. I mulled the statement over for a minute. Perhaps, I thought. I was incredibly nervous about what we were proposing. The idea of tagging the world’s largest marine stingray, free-swimming in the wild, was intimidating to say the least. With massive stingers the size of a human forearm and the tail musculature needed to deploy it mid-water into anything that presents a threat, these rays can certainly defend themselves. As no one had ever tried to tag this species before, it was unclear how they would react.
I am a shark and ray expert. I have been researching different species in the field for more than 20 years. Along the way I have personally tagged more than 100 individual sharks and rays and I feel extremely comfortable doing so. I also have been working with this specific species of ray in the wild for years in Mozambique and have always found them to be docile, slow moving and relatively unperturbed of our presence.
Known commonly as the smalleye stingray, these rays can reach up to ten feet in length and have extremely small eyes relative to their body size. They give the impression they can’t see very well – we often see them bumping into soft coral sea whips or sponges as they track around the inshore reefs to visit cleaning stations. In fact, when another species accidentally bumps into them, it seems to elicit a disproportionately strong response, almost as if they had not seen the animal at all. These observations were worrying as I was unsure how these specific rays might respond to me prodding them with my tagging pole. Different species of sharks and rays have wildly different responses to tagging. Whale sharks barely react. However, given the fact that they have the thickest skin of any animal, they simply may not feel it. Giant oceanic manta rays, on the other hand, know I have done something to them, but they often act like they are not bothered by it. An animal that feels like tagging is a threat to them might react by trying to defend itself. In the case of the smalleye stingray, this kind of reaction could result in them deploying their stinger.
The development of sophisticated animal-borne tags has been a gamechanger for marine researchers, particularly those of us needing to track rare, elusive or highly mobile species. We have learned so much about manta rays, whale sharks and marine predators like bull sharks by tagging them. Tagging a smalleye might be our best and only opportunity to learn more about one of the world’s rarest and most elusive species of rays – a species that has never been studied before, and is likely to be endangered. Given all that, the potential reward outweighed the potential risk.
We only discovered we had smalleye stingrays in Africa in 2008. Dr Simon Pierce, the other co-founder of the Marine Megafauna Foundation (MMF), and I had been regularly encountering a huge species of stingray that we were unfamiliar with on our deep reefs in southern Mozambique. After some sleuthing we determined it was an extremely rare species, occasionally seen in fisheries on the other side of the Indian Ocean. It was not known from Africa, and it turned out to be a whopping 5,000km range extension from the Maldives, the furthest west they had previously been seen in the Indian Ocean. We continued to encounter them regularly and it did not take us long to realise that we were sitting on the largest identified population in the world, and the only known location where they could be studied reliably.
Fast forward a decade and we were now faced with the daunting challenge of tagging some representative individuals in an attempt to learn more about their movement patterns, habitat preferences and daily habits. Even with the highest rates of encounters in the world, our researchers were not seeing them very often and interactions were limited to inshore cleaning stations. If we wanted to know more about this intriguing animal, tagging them with satellite and acoustic tags was the only way to find out more.
I had some theories. Seeing them only on deeper reefs led me to believe they might be a deep-water species, one that would only come up to shallower waters periodically for a clean. We also believed them to be pelagic or at least semi-pelagic, meaning that they may, like manta rays, be in constant motion – never resting on the sea floor like a typical stingray. We believed this because we had never come across one stationary on the seabed. Plus, their body shape is designed for swimming, with elongated wing-like pectoral fins that enable them to swim more efficiently than their more rounded counterparts. If they were highly mobile like mantas, they might travel far distances as well – another possible explanation for why we were not encountering them regularly on our reefs.
Then there were the impossibly tiny eyes. There had to be an explanation for those. Sharks and rays, or at least those that live in the shallows, typically rely heavily on vision and generally have good eyesight. This ray was different. Did it live in a deep-water environment where vision was not needed? Had its other senses heightened, making sight less important? What on earth could be the explanation for miniature eyes on such an enormous body and was the development of their super-sized stinger related? Poor vision resulting in the need for an over-the-top defensive system?
My preferred tagging tool is a Hawaiian sling, a simple pole with elastic on one end that, when pulled, launches the pole at speed toward its target with enough force to place a small anchor under the skin of the target animal. The tags themselves sit outside the animal and eventually come off. Some tags are programmed to release after a set amount of time, others simply work their way out of the animal over time like a splinter.
Different types of tags provide researchers with different types of information. Acoustic tags work in conjunction with ‘listening’ receivers affixed to the seabed. They provide highly accurate information about how animals are using specific areas or habitats. The animal must be in close range to the receivers to log its presence at a site. It helps us to understand how often they visit these specific areas of interest, how long they spend once there and ultimately how important these environments are to them. Satellite tags are helpful in other ways. They collect data independently as the animal moves along, recording things like water temperature, depth, and the animal’s physical location as it travels through time and space. The location data are often not precise, as GPS does not work underwater, but generally you still get a good idea of what the individual animal has been up to for up to a year.
As novel and exciting as this research seemingly was, it took us a long time to get support for the project and the necessary funding. Then, even after everything was secured and the necessary planning had taken place, I still had to find some individuals to tag. This turned out to be a lot harder than we had anticipated. While we encounter smalleye stingrays here in Mozambique more than anywhere else in the world, we do not see them regularly. The first day I went out prepared to tag a smalleye I was incredibly nervous. If I only had an indication of how the ray was going to react. Then it dawned on me – as a tester, I could try to genetically sample one first and see what happened. We use the same pole for this, just with a different modified tip which extracts tissue rather than placing a tag. I could sample the animal from the underside as it was swimming, well away from where it could deploy its stinger, and I could see how it reacted. After a few weeks I found one, tried it and was pleasantly surprised to see that while the ray did have a small reaction, it swam away from me without any retaliation.
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