Populations smaller than previously thought.

• Position: Sharks

Many shark populations around the world are known to have declined over the past several decades, yet marine scientists lack important baseline information about what a healthy shark population looks like. A clearer picture now is coming into focus--thanks to a team of scientists who investigated the size of an unfished community of reef sharks.

Researchers from the University of California, Santa Barbara, and colleagues conducted an eight-year study of a healthy shark population on Palmyra, a remote, uninhabited atoll in the central Pacific Ocean. This pristine ecosystem is part of a marine refuge that extends 50 nautical miles from its shores. No fishing is allowed within these borders, which protect a diverse array of species, including grey reef sharks. The investigators were surprised to find far fewer sharks than expected. The study results appear in the journal Scientific Reports.

"We estimated a population size of between 6,000 to 8,000 grey reef sharks at Palmyra, which works out to a density of about 20 sharks per square kilometer," says lead author Darcy Bradley, a postdoctoral researcher in the Sustainable Fisheries Group, a collaboration of the campus' Marine Science Institute and School of Environmental Science &amp...