Sun, sand and apex predators: taking the plunge with oceanic whitetip sharks

shark

Dr. Lauren Smith—a marine biologist for Marine Scotland who runs conservation and research organization named Saltwater Life—explores the population of the oceanic whitetip shark (Carcharhinus longimanus) around Cat Island in the Bahamas. Here are excerpts from her article—access full article, photos, and bibliography via The Guardian:

[. . .] I’m here to dive with the oceanic whitetip shark – Carcharhinus longimanus, the migratory circumtropical pelagic apex predator. Historically, the oceanic was a highly abundant species, but more recently it has undergone severe population declines. Globally across its range, it is listed by the International Union for the Conservation of Nature (IUCN) red list as vulnerable, and critically endangered in the north-west and western central Atlantic. This reduction in numbers is a result of fishing pressures, most likely related to the global shark fin trade, for which it is targeted and highly prized due to its large pectoral fins, from which the shark gets its name: “longimanus”, meaning “long hands”.

[. . .] Despite being critically endangered in the north-west Atlantic, the oceanics that come to the waters around Cat Island from April through May each year are highly site-specific. [. . .] The reasons behind why oceanics return to the Bahamas, and in particular show high site fidelity to the waters around Cat Island, was investigated in a study in 2015. This showed that gatherings consisted of adult individuals, that females were more common and more than half were pregnant. Dietary analysis showed that the oceanics were predating on more large pelagic teleosts (72%) than in the sharks’ long-term diets (47%). This suggests that the availability of these large prey is something that keeps bringing the oceanics back to Cat Island.

It was this level of site fidelity which drew me to the Bahamas in search of this once-abundant top predator, and I’m not the only one. A study in early 2017established that the Bahamas dive industry is the largest in the world, contributing approximately US$113.8m annually to the Bahamian economy. Elasmobranch tourism generated 99% of the total revenue, and the balance came from film, television and research. The Bahamas is a unique refuge for sharks in the Caribbean, largely due to a ban on longlining in the early 1990’s, followed by the establishment of the Bahamian shark sanctuary in 2011.

As I walked along the shoreline at Cat Island the following day, I thought about how the stewardship shown by the Bahamian government ensured that their waters remained a carefully managed habitat for many shark species, and how there is also a real need for regional Caribbean-wide commitment to the management of highly migratory species. Of course with current estimates indicating that approximately 24% of all chondrichthyan species are threatened with some risk of extinction , this undoubtedly needs implementing on a global scale.

For full article, see https://www.theguardian.com/science/blog/2017/jun/20/sun-sand-and-apex-predators-taking-the-plunge-with-oceanic-whitetip-sharks

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