Quantifying the decline for the first time, the analysis published online Friday in the journal Conservation Biology demonstrates that shark populations fare worse the closer they are to people — even if the nearest population is an atoll with fewer than 100 residents.

 

The team of eight scientists examined the results of a decade of underwater surveys across 46 Pacific islands and atolls, and found densities of reef sharks — gray, whitetip and blacktip reef sharks as well as Galapagos and tawny nurse sharks — “increased substantially as human population decreased” and the productivity and temperature of the ocean increased.

“Our results suggest humans now exert a stronger influence on the abundance of reef sharks than either habitat quality or oceanographic factors,” the authors wrote.

Near populated islands such as the main Hawaiian Islands and American Samoa, the study found, there were roughly 26 sharks per square mile. Remote reefs such as the Northwestern Hawaiian Islands or Johnson Atoll, by contrast, boasted 337 sharks per square mile.