The northern Galápagos islands of Darwin and Wolf are home to a world record when it comes to sharks, according to a new study. The Charles Darwin Research Station (CDRS) and the National Geographic Society investigated the remote Ecuadorian islands made famous by naturalist Charles Darwin, and found a shark biomass of 12.4 tons per hectare.
Biomass? That's essentially the collective mass of some living thing — in this case sharks — in a designated area. Imagine scooping up the ocean with a giant bucket, picking out all the sharks and weighing your haul. Biomass is a slightly different measurement than the sheer number of sharks, as one large hammerhead shark could weigh more than the combined weight of three smaller nurse sharks, for instance. So that amount of 12.4 tons, if translated just to scalloped hammerheads, for instance, would equate to about 380 sharks per hectare, weighting 65 pounds (30 kilograms) each when full grown. A hectare is equal to about 2.5 acres, or 10,000 square meters.
"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, the paper's lead author and senior marine ecologist at CDRS, in a press release announcing the findings.
Overfishing has dramatically depleted the world's population of sharks and other large predatory fishes by up to 90 percent. The paper, published in the journal PeerJ, underscores the ability of government action to have a positive impact on preservation efforts. Darwin and Wolf Island, the two northernmost islands in the Galapagos Archipelago, are located within Ecuador's Galapagos Marine Reserve, but until March 2016 did not enjoy as full a legal protection as the rest of the sanctuary. Overfishing has had a significant impact on the islands' grouper population, for instance, which was a motivating factor in instituting the protective measures.
"The current protection should ensure the long-term conservation of this hotspot of unique global value," the paper concludes.
The team surveyed seven rocky reef sites around the islands, using stereo-video equipment over a period of two years. The researchers actually found the largest biomass of reef fish ever, with the majority comprising shark species.
"While Galapagos giant tortoises, Darwin's finches, and mocking birds have received much of the attention since Darwin's visit," the authors write," the underwater Galapagos remains under-studied and largely unknown compared to terrestrial ecosystems."