Marine Megafauna Foundation Formally Describes African Zebra Shark Hotspot
A new study by Marine Megafauna Foundation (MMF), in collaboration with Swansea University and All Out Africa, has described a population of endangered zebra sharks in Africa for the first time. The study, centred around Barra and Tofu in Mozambique but ranging as far north as Pomene and as far south as Sodwana Bay in South Africa, suggests that not only is the region a hotspot for zebra shark populations, but is also a potential mating area.
Zebra sharks (Stegostoma tigrinum) – also commonly called leopard sharks due to the spot patterns present on a mature animal's skin – are currently listed as Endangered on a global level by the IUCN Red List of Endangered Species. The new study has led scientists to recommend species-level protection for zebra sharks, and an expansion of Marine Protected Areas (MPAs) to ensure their preservation.
The study used a range of data collection methods to describe the population, including structured underwater surveys and identification photographs taken by both scientists and recreational scuba diving citizen scientists. Like whale sharks and manta rays, individual zebra sharks have unique spot patterns which can be used to track their movements over time.
Photographs taken between 2010 and 2018 identified 90 individual sharks of both sexes, 38 per cent of which were seen in multiple years, indicating an affinity for the area. More than 62 per cent of the sharks were mature, and the high frequency of both male and female adult sharks indicate that the area may be used for mating.
In addition to the photo ID, interviews with 100 local fishers helped to identify a number of other potential zebra shark habitats, although unfortunately, encounters were most commonly reported as bycatch in gillnets. Further modelling also identified the possible locations of several new hotspots that merit future underwater surveys.
Based on MMF's interviews with local fishers, one site of particular interest called Morrungulo, approximately 100km north of Barra, is believed to have another population of zebra sharks, or an extension of the Barra/Tofo population. Although the site has not been regularly dived before, it has generated enough interest that MMF is currently setting up a new research centre in the area.
'This study adds credibility to using a multi-faceted approach to collect baseline data for marine species,' said the study's lead author, Saoirse Pottie. 'When used in combination, fishers’ observations and dive surveys can complement each other. Fisher surveys can collect sightings information at a wider spatial scale than underwater surveys, yet dive surveys are capable of providing more in-depth information on the movement and behaviour of individuals.'
The study's authors hope that their approach to the research will inspire other scientists to look at expanding their data collection methods in data-deficient locations. 'This approach could be applied in other regions to highlight areas of interest, prioritize research activities, and inform conservation actions,' said Pottie. 'The inclusion of local knowledge also provides an opportunity to enrich our understanding of social-ecological systems, engage local communities, and make environmental decisions that are more inclusive.'
Zebra sharks lack formal protection in Mozambique, and the majority of the suitable zebra shark habitat identified in this study remains unprotected. Anna Flam, MMF scientist and one of the study's co-authors said: 'this is one of the world’s largest identified populations of zebra sharks and we should protect them, otherwise, we could see them disappear, as has happened in parts of Southeast Asia.'
Citizen science is becoming an increasingly valuable tool for data collection. With many marine megafauna identified by spot patterns or fin shapes, photographs contributed by scuba divers allows researchers to greatly increase the scope of the data captured. During the course of this study, contributions from citizen scientists led to the creation of the Wildbook for Leopard Sharks, a global online database that allows scuba divers to submit their photos to support research around the world.
In light of the current paper, we wrote to Anna Flam to ask her for tips on how best to report zebra shark sightings if you should encounter them while diving. They tend to be fairly docile creatures often found resting on sandy patches on the sea bed, and can make fantastic photographic subjects if you approach them with care.
Tips for Citizen Scientists
(courtesy of Anna Flam, MMF researcher)
- Approach calmly and slowly from one side. Stay low to the ground as you approach.
- We recommend maintaining two metres distance from the shark to avoid disturbing them.
- We use the unique spot pattern on the leopard shark's side to identify them.
- Identification photos should cover the area from the pectoral fin to the pelvic fins, as shown in the photo below, or if possible the entire side of the shark. Take the photo as perpendicular to the shark as possible.
- Try to take the left side photo first, as that's what is used to add a new shark to the database. If you can get photos of both sides, even better. If you only can get the right side, that's still helpful, as we can match it to sharks that are already in the catalogue, or add it to the catalogue later when we receive paired ID photos.
- Any ID photos can be submitted here on the Wildbook for Leopard Sharks. You do not need a login to upload a shark (those are currently only for researchers).
- You just need to submit a date and location together with the photo
- Additional information such as behaviour, sex, and estimated size is not required, but helpful if known.
- You will receive email updates when the shark you saw is matched or added to the catalogue.
For more information about MMF, visit www.marinemegafauna.org. The complete study 'Quantifying the distribution and site fidelity of a rare, non-commercial elasmobranch using local ecological knowledge' by Saoirse Pottie et al is available in the online journal Ocean and Coastal Management.