The Galapagos Islands of the Pacific are home to many wonders and are often linked to Darwin’s seminal studies. The waters around the islands are also rich with life and diversity, and new research has identified that two of the Galapagos’ northern islands are home to the world’s largest shark biomass, making them an important target for conservation efforts.

Sharks around the world are currently under siege from over-fishing, persecution and illegal hunting. An estimated 100 million sharks are killed every year and some species are thought to have dropped by over 90% in the last 30 years alone. Whilst the designation of new marine sanctuaries serves to protect sharks and their habitats, scientists need more information on shark numbers and distributions to identify the most important hot-spots for marine predators.

“The islands of Darwin and Wolf are jewels in the crown of the Galapagos because of the sheer abundance of sharks and other top predators,” said Pelayo Salinas de Leon, lead author and senior marine ecologist at the Charles Darwin Research Station (CDRS).

A team from the CDRS and the National Geographic Society (NGS) recently completed an expedition through the Galapagos Marine Reserve that surveyed the underwater habitats surrounding the two islands, with the goal of informing the government on the designation of marine sanctuaries. By conducting diver-controlled video surveys at seven sites around the island reefs, the researchers were able to quantify the abundance and diversity of the fish species they observed.

Sharks accounted for over 70% of the fish biomass in these marine areas and identified four major contributing species, including hammerheads, blacktips and, unsurprisingly, Galapagos sharks.

Previously, Costa Rica’s Cocos Island National Park and the Chagos Marine Reserve in the Indian Ocean were home to the largest biomasses of sharks, but with a remarkable 12.4 tonnes of shark per hectare, these two islands are now thought to home the densest population of sharks in the world.

Why the Galapagos Islands? What do the sharks love about the area? The Galapagos are thought to attract such a large number of sharks because the oceanographic features surrounding the northern islands in particular provide great habitats for many communities of fish, which, of course, serve as a rich food source for sharks and other large predators.

However, excessive fishing has led to dramatic declines in the numbers of reef fishes, which in turn can impact on the area’s shark populations. In March 2016, the Ecuadorian government finally designated the area surrounding Darwin and Wolf as a fishing-restricted marine sanctuary, but lasting damage to fish populations may already have been done.

As a global biodiversity hot-spot and a significant contribution to Ecuador’s tourism industry, it is important for both humans and wildlife to protect all of the Galapagos Islands’ ecosystems, not just those on the surface. “Charles Darwin made the Galapagos Islands famous, but for the underwater world to be so full of life is something he probably never imagined,” said Enric Sala, NGS explorer-in-residence.

The researchers believe that they have gathered useful data on shark populations and habitats that will help inform scientists and conservation organisations on the interactions between marine predators and their environments. They conclude by proposing that the data will hopefully prove useful for other researchers: “The study published today adds to the growing body of literature highlighting the ecological uniqueness and the irreplaceable value of Darwin and Wolf — not only for Ecuador but for the world.”

Below: Watch a school of hammerhead sharks in the waters surrounding Wolf island, Galapagos Islands.

Reference

Pelayo Salinas de León, David Acuña-Marrero, Etienne Rastoin, Alan M. Friedlander, Mary K. Donovan, Enric Sala. Largest global shark biomass found in the northern Galápagos Islands of Darwin and Wolf. PeerJ, 2016; 4: e1911 DOI: 10.7717/peerj.1911

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