(Seychelles News Agency) - Curieuse is a small granitic island lying just one kilometre north and only fifteen minutes away by boat from the Seychelles second most populated island of Praslin.

Used in the past as a quarantine station for people suffering from leprosy, today the island boasts a large population of Aldabra giant tortoises, relocated in the late 1970's from the Aldabra atoll, one of Seychelles UNESCO World Heritage site.

Designated a national park since 1979, Curieuse is also the only other location aside of Praslin where the Coco de Mer, the largest nut in the world grows naturally.

For several years now, the island which covers an area of more than 4 kilometre square and the surrounding ocean has been frequented by international volunteers working with Global Vision International, GVI, a not-for-profit organisation that runs conservation and community development programmes in numerous locations around the world.

Getting up close with lemon sharks is one of GVI’s latest project adding to its list of monitoring and conservation efforts on the island that has involved giant tortoises, birds, sea turtles, the coco-de-mer and even mangrove systems.

Turtle pond-turned lemon shark sanctuary

Baie Laraie, one of the main beach on the island is where all the excitement surrounding the lemon shark population on Curieuse is taking place.

Back in 1910, a sea wall was built across the beach forming an enclosed 40 acre pond as part of efforts to raise Hawksbill Turtles (Eretmochelys imbricata) or ‘Kare’ as it is widely known in the native Creole language.

The idea was nevertheless abandoned after it quickly proved to be unsuccessful, which in turn allowed several species of mangroves to flourish in the protected lagoon it had created.

Unfortunately, large sections of the seawall did not withstand the aftermath of the earthquake which struck the Aceh Province in Indonesia on December 26, 2004 as the tsunami that followed reached the coasts of most landmasses bordering the Indian Ocean, including Seychelles.

The unfortunate incident has nevertheless paved the way for something good as the 'turtle pond' has since become a sanctuary for female lemon sharks to birth their offspring, turning the enclosure into a perfect laboratory for GVI volunteers at the organisation’s permanent research station on the island.

While there are two species of lemon sharks globally, the species found in Seychelles is the Sicklefin lemon shark, (Negaprion acutidens), which is found in the tropics and subtropics throughout the Indian Ocean, extending into the western Pacific, to Taiwan and the Philippines in the north, northern Australia in the south, and recently discovered as far east as Palmyra Atoll in the central Pacific.

The other species is simply the lemon shark, (Negaprion brevirostris), which inhabits the shallow waters of the tropical and subtropical West Atlantic, West Africa, and Western Mexico.

A young lemon shark swims in the shallow waters of Curieuse. (GVI Curieuse) Photo License: All Rights Reserved

GVI-SNPA tagging and monitoring project entering second year

The study of lemon sharks frequenting Curieuse started in September last year and according to a report compiled by GVI’s science officer on the island, James McClelland, the project has provided the group with “a sampling rate of less than 50”.

“...Recapture rates suggest a population in excess of 200 sharks frequent the area...” states McClelland.

Although juvenile lemon sharks have been observed to be resident year round on Curieuse, the adult females come into the shallows to give birth roughly between September and December each year.

The pups make use of the former turtle pond and mangrove system during the first stages of their life as they offer protection from larger sharks and provide a rich feeding ground. This makes it easy for the project to track growth rates of individuals throughout the first stage of their life.

The GVI project, which is being done in collaboration with the Seychelles National Parks Authority, SNPA aims to establish how many juveniles there are around the island, how fast they grow, what their natural rate of mortality is, and what habitats they are using.

“We are doing this by catching the juveniles and implanting electronic identification tags (Passive Integrated Transponder, or PIT tags) before releasing them again. This means we can identify each individual shark, and if we catch the same shark again we can then measure how much it has grown and we will know it is still in the area,” Alan Grant, GVI’s Base Manager on the island explained to SNA in an email interview.

“We are also collecting genetic data which will allow us to see the relatedness of the juveniles, and hopefully identify and quantify the breeding population of adult males and females. The genetics should also show us how related the individuals are to each other, and how related the Curieuse population is to other populations of Sicklefin lemon sharks.”

Last year the project captured, measured, tagged and released 97 distinct individuals, which according to GVI has seen many of them recaptured providing useful growth rate data.

Extra funding allows extension of project and visitors' education

With the month of September fast approaching GVI has been receiving some support for the ongoing project including funding from British High Commission in Seychelles. The money has been used to purchase research equipment as well as for education initiatives.

“Public information boards were created and are now displayed in the Curieuse mangroves. These are to give visitors a basic understanding of Lemon sharks and the type of research being done on them here. A film is also to be produced in the near future to be aired on television in the Seychelles. This will be an educational production covering the basic biology of lemon sharks and the Curieuse population, and the research being done on them,” Grant explained to SNA.

Curieuse is a popular stop over among tourists, as it is one of 115 islands of the Seychelles archipelago where giant tortoises are seen roaming free.

“..We have one of the most diverse and interesting biodiversity including the mangrove habitat which is an important ecosystem for many species of marine life...” Anto Suzette, a Senior Ranger working for the Seychelles National Park Authority, (SNPA) told SNA in an interview.

SNPA is responsible for managing the island and its surrounding marine boundaries with Curieuse being a national park.

One of the new lemon shark information boards within the mangroves (GVI Curieuse) Photo License: All Right Reserved

Valuable data should benefit Seychelles and global community

With the lemon shark monitoring and conservation efforts entering its second year, the GVI volunteers are planning to extend the original basic tagging project, especially with the acquisition of an acoustic tracking equipment.

“With the tracking equipment we will be able to follow them and find out if they also use other habitats around the island in addition to the mangroves. We should also be able to tell how much area each individual needs and therefore how many juveniles the area can support. Furthermore, we have other monitoring equipment to measure salinity and temperature, which should allow us to determine their preferences with regard to those two parameters,” said Grant.

The research is being viewed as one which will go a long way in helping conservation efforts of the species in Seychelles as well as in the wider Indian Ocean region.

"Locally, Curieuse is a very special place, with many charismatic plants and animals on land and in the sea, and the Lemon sharks form part of that ecosystem. The island and its surrounding waters are a national park, and it's important to know what species are here and what their status is, whether their populations are healthy, and whether they are changing in either a positive or a negative way.”

According to Grant few studies have been carried out on the Sicklefin lemon shark in Seychelles and on a wider scale in contrast to the relatively well studied Atlantic species.

"...Any research showing that Curieuse is home to a relatively healthy population of Lemon sharks will underline the importance of continuing to protect the area. This will also contribute to global efforts to conserve shark populations in general.” 

Deputy British High Commissioner Dave Jones on a recent trip to Curieuse, tries out the acoustic tracking equipment with GVI Science Officer James McClelland. ( GVI Curieuse) Photo License: All Rights Reserved

The GVI researchers are also collaborating with another not-for-profit organisation Save Our Seas Foundation, which is running a project of similar nature, at its D’Arros Research Centre.

The project is being run by Ornella Weideli at the St Joseph Atoll, some 250 km south west of the Seychelles main island of Mahé, to assess populations of sicklefin lemon and the blacktip reef sharks investigating the way they share natural resources found in a remote coastal ecosystem.

“Ornella has visited us on Curieuse and we are in touch with them. We hope there may be some collaboration over the course of the two projects, and to compare results from these two very different habitats,” concludes Grant.

Both lemon shark species, the Sicklefin lemon shark, (Negaprion acutidens), and the lemon shark, (Negaprion brevirostris) are featured on the International UUnion for the Conservation of Nature, IUCN’s red list of threatened species.