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September 2016    Download the Entire Issue (PDF) Available to the Public Vol. 31, No. 9   RSS Feed for Undercurrent Issues
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Why You Can Dive with 700 Sharks in Fakarava

from the September, 2016 issue of Undercurrent   Subscribe Now

Those of you who have ridden the current into the lagoon of Fakarava in the Tua Motus of French Polynesia will have marveled at the huge number of gray reef sharks that aggregate there -- up to 700 at one time. But, where are there enough prey fish to feed so many?

Turns out, they survive year-long by feasting every winter on the huge number of grouper that swim into the channel to spawn.

A study published in the journal Current Biology says it is an example of an 'inverted trophic food pyramid,' with the average biomass skewed towards predators rather than prey. This seasonal meal delivery of spawning groupers into the southern pass sustains the extraordinary concentration of gray reef sharks, the highest density of the species ever recorded.

Dr. Johann Mourier of Macquarie University in Sydney says, "We went there to study groupers because we heard about these spawning aggregations happening every year. [Then] we found this huge population of sharks, about three times higher in density than found in any other reef, worldwide."

The channel is just 300 feet wide by 100 feet deep but the winter peak coincided with the spawning grouper, up to 17,000 fish at a time, from habitats as far away as 30 miles.

Instead of having to forage outside the area, the sharks simply stay at the reef and save their energy, taking aggressive advantage of this convenient meal delivery system, their very own room service.

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