Modern Caribbean reefs: where are the sharks?

Sharks aren’t easy to spot on many, if not most, Caribbean reefs these days so figuring out what species remain and in what amount is a daunting task. Even though sharks are rare, they still leave traces behind — dermal denticles, their tiny tooth-like scales. Finding these can tell researchers like STRI fellow Erin Dillon what a shark community looks like, no matter how small it is.La Caleta (1 of 4)

But finding dermal denticles is only slightly less difficult than seeing a shark on a reef dive. They are so small that most can only be seen under a microscope and even relatively large concentrations are equivalent to about 25 per 10-kilogram sack of sediment. So identifying the correct site to sample is essential. These spots are often what scientists call low-energy sites, meaning they are not subject to strong wave action or currents, which sweep tiny particles like denticles away.

When a potentially apt site is identified, it’s time to get to work. Today, Erin and Mauro Lepore dug up some 100 kilograms of sediment. Doing so required that they carry more La Caleta (3 of 4)weight than usual in order to stay put on the sea floor when pushing into the hard surface. Otherwise, each thrust of the trowel would push them up from the bottom. It’s also important to avoid losing any fine sediments by digging too vigorously. When each sample bag is full, Félix Rodríguez, the O’Dea lab manager, drops a line down with a mesh bag and hoists the bags to the surface.

Erin, Mauro and Félix are just beginning their trek around the reefs of the Dominican Republic. Over the next few days they aim to gather another half ton of sediments. And while that might sound like hard work, once the samples are back at the lab of STRI scientist Aaron O’Dea in Panama, it will take a solid year (and an intern or two) to digest all the material (a process that involves copious amounts of acid). This, they hope, will get us one critical step closer to learning just how drastically shark communities on Caribbean reefs have changed since humans became the major driver of their decline.


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