Where is the largest shark biomass in the world?

Cocos Island National Park and the Chagos Marine Reserve might be considered to be contenders for the largest fish biomass on the planet, but a new location has been found to have an even larger biomass and it consists almost entirely of sharks!

The islands of Darwin and Wolf in the Galapagos have recently received full protection from fishing from the Ecuadorian Government (see The Shark Post: New marine sanctuary in the Galapagos will protect a variety of fish species). This change was partly driven by the conclusion that these islands support a large amount of shark species; now publishing in the journal Peerj a team of researchers have presented their evidence that Darwin and Wolf support the largest biomass of sharks reported to date. 

Using underwater cameras to conduct stereo-video surveys the researchers recorded and measured the fish around Darwin and Wolf islands. This data was then used to convert length measurements to biomass and the fish were classified as apex predators, lower level carnivores, planktivores and herbivores.

Primarily consisting of the scalloped hammerhead (Sphyrna lewini) (48.0%), the Galapagos shark (Carcharhinus galapagensis) (19.4%) and the blacktip shark (Carcharhinus limbatus) (5.1%), the shark biomass made up almost 73% of the total fish biomass at these 2 sites. Interestingly the majority of the fish observed were found in the south-east section of both islands; the researchers hypothesised that this might be owing to the unique currents which flow through these islands or possibly the south eastern part of these islands are used as a cleaning station or a location for nightly foraging excursions. 

Sharks are incredibly important to the Galapagos and to Ecuador; not only do sharks help regulate the ecosystem as apex predators but an individual shark in the Galapagos has been estimated to be worth USD$360,000 per year through tourism, whilst a fisherman may receive a one off payment of USD$158 for the same dead shark.  

Whilst veteran divers have reported larger abundances of sharks at Darwin and Wolf 30 years ago, there exists a real lack of long term studies in the area to quantify these observations. Owing to the fact that these islands are home to the last true coral reef in the Galapagos Marine Reserve, are important waypoints for whale shark migrations in the region and have now been proven to support the largest shark biomass ever recorded it is important that studies such as this continue in order to ensure ongoing protection of this biologically significant region.   

Salinas de León P, Acuña-Marrero D, Rastoin E, Friedlander AM, Donovan MK, Sala E. (2016) Largest global shark biomass found in the northern Galápagos Islands of Darwin and Wolf. PeerJ Preprints 4:e1872v1 https://doi.org/10.7287/peerj.preprints.1872v1