In this way, we are currently tracking more than 100 different sharks of various sizes and species, including blacktip reef, sicklefin lemon, grey reef and tawny nurse sharks, among others. To date we have more than two years’ worth of track data, which give us unique insight into the sharks’ private lives. One of our main discoveries is just how important the coastal habitats of D’Arros and St Joseph appear to be for these sharks. In particular, I can now identify the access-restricted refuge of the St Joseph lagoon as a crucial nursery habitat for several species: juvenile sicklefin lemon, blacktip reef and tawny nurse sharks shelter in the lagoon all year and for several years. The lagoon is an idyllic nursery for young, vulnerable sharks, providing both shelter from predators, because of the access-restricted shallows, and an abundance of prey, such as juvenile reef fish, rays and crustaceans. Although not in the lagoon, juvenile grey reef sharks appear to live just along the shallows of the atoll’s outer reef.

This year-round residency of various shark species highlights St Joseph as an invaluable nursery, which may be critical for recruitment into the regional shark populations. In contrast to the tracked juveniles, the adults of most species tend to range more widely. For instance, we have recorded sicklefin lemon sharks moving to other islands up to 80 kilometres away from D’Arros, and adult grey reef sharks seem to range predominantly along offshore reefs.

So how can we use these data to plan and inform potential management strategies? One way is to assess how effective certain MPA designs might be. D’Arros and St Joseph are relatively small and isolated, so it is feasible that an MPA of moderate size could be enforced with relative ease. Aldabra, the World Heritage Site with the most comprehensive protection in the Seychelles, possesses a no-fishing exclusion zone that extends one kilometre from the high-tide mark. Using this as a reference, a similar MPA at D’Arros would provide reasonable coverage of overall shark movements, ranging from 40 to 90%, depending on the species. However, the large reef flats associated with St Joseph mean that a boundary measured one kilometre from high tide would not even cover all of the lagoon, and wouldn’t fall far beyond the reef edge. Consequently the sharks, including the juveniles, would continue to cross the boundaries and remain vulnerable to fishing, even within the lagoon.

To combat this, we tried setting the boundaries at one kilometre from the low-tide mark, when the reef flat is exposed, instead of the high-tide mark. Although it’s only a small variation in definition, it provides a large boost to the protection afforded: now 70–99% of overall shark movements would be encompassed by the MPA, with all tracked juveniles spending at least 95% of their time within its boundaries. However, the larger sharks tend to range more broadly so they would still be frequently exposed to fishing pressure, a risk starkly realised by the capture of a tagged individual 80 kilometres from D’Arros at the island of Marie-Louise. Consequently, any MPA must be coupled with broader fisheries management strategies, such as catch quotas, size limits and time/area closures, if it is to be effective. There would be limited benefit in protecting juveniles to maturity, just for them to be caught as they start to range more widely.

Our work is ongoing and there is still much to learn, but it is becoming clear that D’Arros and St Joseph play an important role in the nursing of juvenile sharks to maturity and that this role is jeopardised by ongoing fishing pressure. Through the stewardship of the D’Arros Research Centre and the development of an MPA, D’Arros can become a true sanctuary for sharks in the Seychelles: a bastion from which a broader, regional recovery can be seeded, enabling the islands to aspire to their former majesty.