Galápagos Islands home to largest global Shark biomass

Overfishing has dramatically depleted sharks and other large predatory fishes worldwide except for a few remote and/or well-protected areas. The islands of Darwin and Wolf in the far north of the Galapagos Marine Reserve (GMR) are known for their large shark abundance, making them a global scuba diving and conservation hotspot.

Researchers from the Charles Darwin Research Station (CDRS) and the National Geographic Society revealed this week that the northern Galapagos islands of Darwin and Wolf are home to the oceans largest shark biomass reported to date (12.4 tons per hectare). The Galapagos Islands are known worldwide for its iconic terrestrial fauna and flora, due in large part to a young Charles Darwin who sailed to these islands in 1835

Published in the journal PeerJ, the study which was conducted over two years of rigorous research, is significant as the presence of these top predators indicates a healthy marine ecosystem. However, worldwide overfishing has reduced the biomass of most sharks and other large predatory fishes by more than 90 percent.

The shark biomass research team collected data using stereo-video surveys at seven sites in collaboration with the Galapagos National Park Directorate. The quantitative surveys recorded at Darwin and Wolf are considerably larger than those reported at Costa Rica’s Cocos Island National Park and the Chagos Marine Reserve in the Indian Ocean, home to the world’s next largest shark biomasses.

The team’s results showed that sharks, mainly hammerhead and Galapagos sharks, dominated the fish assemblage, but other predators like the bluefin trevally, black jack (Caranx lugubris) and bigeye jack (C. sexfasciatus) were also common at several of the sites surveyed.

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(A) A large school of hammerhead sharks (Sphyrna lewini); (B) A group of Galapagos sharks (Carcharhinus galapagensis), including a couple of pregnant females; (C) A large female whale shark (Rhincodon typus) swims among a school of hammerhead sharks. All photos by Pelayo Salinas-de-León.

However despite the large shark biomass at Darwin and Wolf, the team’s surveys also revealed a low overall biomass of predatory reef fishes such as the leatherbass (Dermatolepis dermatolepis) and the sailfin grouper (Mycteroperca olfax), both endemic to the Eastern Tropical Pacific (ETP). These species are highly prized by Galapagos artisanal fishermen, but their life histories (e.g., long lives, slow growing) make them extremely vulnerable to overfishing.

A total ban on the capture, transport, and trade of sharks within the GMR was established in 2000. However, illegal fishing within GMR boundaries and recent efforts by local artisanal fishermen to expand longline fishing, a practice banned since 2005 due to large by-catch, threaten shark and predatory reef fish populations.

This study adds to the growing body of literature that highlights the ecological uniqueness and the global irreplaceable value of Darwin and Wolf. The government of Ecuador created a 40,000 km2 no-take reserve (the ‘Darwin and Wolf Marine Sanctuary’) in March 2016, expanding levels of protection around Darwin and Wolf, including some of the numerous seamounts located around these islands. This conservation move is critical to ensure the recovery and long-term preservation of one of the most extraordinary marine ecosystems on the planet—and an economic engine for Ecuador.

JK


 

Header Photo credit: Galapagos Conservation Trust

Article reference: Salinas de Leon P, Acuta-Marrero D, Rastoin E, Friedlander AM, Donovan MK, Sala E. (2016) Largest global shark biomass found in the northern Galapagos Islands of Darwin and Wolf. PeerJ 4:e1911 https://doi.org/10.7717/peerj.1911

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