Reef Shark Toll Overestimated?

New research suggests we've hurt reef shark populations much less than previously assumed.

by David Shiffman, Hakai Magazine

To restore shark populations to their natural abundance—levels held prior to overfishing by humans—the first step is to answer a question: how many sharks should there be? Researchers thought they had answered that question for coral reef sharks about a decade ago, and since then many shark advocates have been using the data to focus their conservation efforts. The only problem: it turns out the population target they've been using was wrong.

Sharks are under intense pressure from overfishing and ecosystem degradation, and many species are threatened with extinction. But as University of California, Santa Barbara, ecologist Darcy Bradley shows in a new study that calculated the shark population at Hawai'i's Palmyra Atoll, previous estimates of how many sharks should be living in the reef ecosystem were grossly inflated. With her newly revised estimate of what constitutes a healthy shark population, conservationists' goals should now be much easier to reach.

Researchers turn to the Palmyra Atoll because, as a coral reef system that's largely free from human interference, the location offers as close as can be found to a truly natural environment. Hence, the density of sharks swimming there represents what would have been found elsewhere before humans took their toll.

Through her study, Bradley found that there are approximately 20 reef sharks per square kilometer in the Palmyra Atoll.

Read the rest of the story in Hakai Magazine here: