After the exciting news of the silky sharks on the Saba Bank two weeks ago, this time we move a bit Southeast from Saba to the Caribbean island of Sint Eustatius (better known as Statia) for another shark-story. Throughout Spring 2015 and Summer 2016, multiple observations were made of a, for Statia’s waters, undocumented shark species: the lemon shark. And when life gives you lemons..
It all began when I joined a trip organized by Save Our Sharks NL, a project of the Dutch Caribbean Nature Alliance to conserve sharks in the waters of the Dutch Caribbean. The trip brought us to Statia, where I met up with two of the owners of the Scubaqua Dive Center, Mike Harterink and Menno Walther. Mike shot a couple of pictures of a young shark in the shallow waters near the dive center. In addition, Menno shot a short video of two young sharks cruising in the same area. The young sharks observed on both occasions happened to be young lemon sharks (Negaprion brevirostris), a species that has not been documented before in the waters of this Caribbean island.
Figuring these observations were interesting, as no adult lemon sharks were observed during any of the dives of Scubaqua, I came into contact with Erik Boman. Erik lives on the island and focuses on the hu(uuu)ge (and awesome) marine snail, the queen conch (Lobatus gigas) for his PhD. at Wageningen University. Fortunately, Erik and his wife also observed young lemon sharks in shallow waters over multiple occasions. This time, however, the sharks were observed on the other side of the island. We teamed up with Paddy Walker (University of Applied Sciences Van Hall Larenstein) to write a short research note on the observations, to stimulate local conservation efforts towards shark species and to document this species for the island.
All of the observed lemon sharks were estimated to be between 50 and 65 cm. This is close to the size at birth for lemon sharks, which is a length of 60 to 65 cm. Throughout their life, these sharks can grow to a whopping length of 3.40 meters (although individuals of 2.40 meters are more common) and reach an estimated age of at least 25 years. Like many other shark species, lemon sharks reach maturity relatively late in their life, at an age of 12 to 16 years. Female lemon sharks give birth every other year to a litter of 4 to 17 pups, after a gestation period of 10 to 12 months. The pups will remain in the area of where they were born for several years. This behavior is known as natal philopatry (i.e. tendency to return to a specific area).
Where do these little sharks come from?
Good question! These are only observations only indicate that the shark seem to use the waters of Statia. Where they come from remains speculation. There are two possibilities: (1) the sharks were born in these waters and remained in the vicinity of the island, (2) the sharks were born elsewhere and visit Statia now and then. Before going into detail on both possibilities, I would like to stress that these observations are merely an indication for future research and do not prove that Statia’s waters act as a nursery or vital area for this species. For this, more research is needed!
If the sharks were born in the vicinity of Statia, you would expect existing observations of adult lemon sharks within the area. However, no adult lemon sharks have been observed on any of the dives of the dive center. Part of the island is rough, and not a lot of diving occurs there, so one possibility remains that the adults hang out on that side of the island. Young lemon sharks do exert natal philopatry, which means they normally have a tendency to return to their birth ground, which could explain the repeated sightings of a small number of young individuals within the same general areas.
However, the lack of observations of adult lemon sharks opens up the possibility that parturition did not take place around Statia. This means the sharks swam over from nearby reefs or islands. The closest island, Saint Kitts, is located on the same bank as Statia at a distance of approximately 13 km. The closest islands of which we know lemon shark occur in local waters is Sint Maarten (and the French Saint-Martin) (56 km), located on a different bank than Statia, with deep water separating both islands. Studies focusing on young lemon sharks in the Bahamas showed that these little guys have a limited home range of approximately 0.68 km2, making it less likely that the young sharks swam all the way from nearby islands. In other words, more research is needed to study the role of Statia’s waters in the lifecycle of lemon sharks (Super interesting!).
Publishing observations like this.
So why would we publish observations like this? I believe understanding biodiversity is one of the cornerstones of conservation science, and even small observations like this can contribute to that knowledge. Now we know that a specific life stage of this species frequents these waters, we can continue studying this species within the region. Information like this can also benefit local nature conservation NGO’s like STENAPA, St. Eustatius National Parks in their efforts to conserve local natural areas. In addition, a digital age asks for open access of observations and knowledge sharing. While writing up these observations, we heard of the new platform Science Matters. This all-digital, open access journal lets authors publish short notes about small observations that are worth sharing within their field. And, unlike many conventional journals, the reviewing process does not take months. Which is great!
Want to feed your inner-sharknerd? Read our paper!
Leurs, G., Boman, E. M., & Walker, P. A. (2018). Range extension of the lemon shark (Negaprion brevirostris) within the Dutch Caribbean: First records of young individuals in the waters of Sint Eustatius. Science Matters, 1–6. http://doi.org/10.19185/matters.201803000002
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