New Study Reveals Long Distance Migration of Largest Stingray
A new study from the Marine Megafauna Foundation (MMF) has revealed much about the life of the smalleye stingray, the world's largest, but one of its least known species of stingray.
Smalleye stingrays (Megatrygon microps) are part of the Dasyatidae family, more commonly known as 'whiptail stingrays', which includes more familiar species such as the southern and blue-spotted stingrays. Smalleye stingrays are the largest members of the family, reaching disc widths of over 2.2m, yet almost nothing is known about the species. They are patchily distributed through the Indo-Pacific region and thought to be semi-pelagic, but appear to be most commonly encountered around Mozambique, where the MMF study was conducted.
'We reported the first sightings of smalleye stingray in 2004 and have since been racing against the clock to learn more about their ecology before it is too late,' said Dr Andrea Marshall, co-founder and principal scientist of the Marine Megafauna Foundation. So little is known about the smalleye stingray that the species is listed as 'data deficient' by the IUCN's Red List of threatened species, however, 31 per cent of the world's sharks and rays are listed as threatened. 'This species of ray is likely in trouble too,' said Dr Marshall, 'but we can’t protect what we don’t know much about. Our study is an important first step in understanding more about the animal’s ecology and behaviour'.
In order to learn more about the elusive stingray's behaviour, the team of marine biologists first studied if the stingrays’ white dorsal spots could be used as a means of identification, in the same way that the ventral markings of a manta ray or a whale shark's spots can be used to identify an individual. To aid their studies, the scientists called on local dive centres asking for tourists to provide any images of the smalleye stingray they might have captured.
'Southern Mozambique and its rich marine life attract many passionate scuba divers, most of which own GoPros or other lightweight cameras and will happily make their images and footage available for research,' said Atlantine Boggio-Pasqua, a Tofo-based MMF volunteer 'Their contributions proved immensely valuable, we managed to gather more than 140 photographs suitable for comparison and identification, with some images dating as far back as 2003.'
The team identified 70 different individuals from their spot patterns, including 15 that had been seen on several occasions in the area. The stingrays were often encountered at cleaning stations where small fish appeared to be removing parasites from the rays’ skin. 'Smalleye stingrays may look intimidating at first glance with their large, razor-sharp tail spines, but they’re actually really charismatic and easy to approach,' said Boggio-Pasqua. 'We hope to receive many photo and video contributions from citizen scientists in future. They could tell us more about the species’ habitat preference as well as feeding and cleaning behaviour.'
The photographic study also provided a glimpse into the migratory behaviour of Megatrygon microps. Some individuals travelled hundreds of kilometres along the coastline, including a pregnant female which travelled from Tofo to the Bazaruto Archipelago and back, a 400km round-trip, apparently giving birth at some point along the way. This proved to be the longest straight-line distance ever recorded for any species of whiptail stingray.
By studying the smalleye stingray, scientists hope to address the current lack of data and aid the formal assessment of the species’ conservation status in the IUCN Red List. Smalleye stingrays are thought to be under threat from increasing fishing pressures, where both targeted and incidental catches by coastal gillnets and industrial purse seiners are an ongoing issue in Mozambique.
'There are so many questions that remain unanswered about this rare species,' said Dr Marshall. 'Where do they live, how fast do they mature and how do they reproduce? Filling these knowledge gaps is crucial to figuring out how to protect them properly in Mozambique and other parts of the Indian Ocean.'
The study by Atlantine Boggio-Pasqua, Anna Flam and Andrea Marshall, titled ‘Spotting the “small eyes”: using photo-ID methodology to study a wild population of smalleye stingrays (Megatrygon microps) in southern Mozambique’ was published in the journal PeerJ on 11 June 2019 and is freely available at https://peerj.com/articles/7110/