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At Swim With Five Tons of Shark Per Acre in the Galapagos

Posted by Richard Conniff on May 11, 2016

(Photo: Enric Sala/National Geographic)

(Photo: Enric Sala/National Geographic)

Yep, that’s how many sharks researchers found living in the northern Galapagos Islands, according to a new study in PeerJ. And of course the researchers found out by diving and swimming transects to count the fish they saw en route.  Not sure this would qualify as “nice work if you can get it.”

They did the research around Darwin and Wolf Islands, in part of Ecuador’s newly designated Galapagos Marine Reserve.

The results:

Nearly 73% of the total biomass (12.4 ± 4.01 t ha−1) was accounted for by

sharks, primarily hammerheads

(Sphryna lewini—48.0%), Galapagos (Carcharhinus galapagensis— 19.4%), and blacktips (Carcharhinus limbatus—5.1%). Hammerheads occurred on 92% of transects at SE Darwin, 59% at SE Wolf, and 9% at both NW Darwin and Wolf. Gringos (Paranthias colonus) were the third most abundant species by weight, accounting for an additional 18.3% of the total biomass. They were 2.2 times more abundant by weight in 2013 (3.8 ± 4.1) compared with 2014 (1.7 ± 2.4). Gringos were 48% more abundant in the SE (3.5 ± 3.5) compared with the NW (2.4 ± 3.7) exposures.

 

That figure, 12.4 ± 4.01 t ha−1, works out to a little more than five tons of shark per acre.   The abundance is partly a result of a unique confluence of ocean currents:

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