Mysterious Shark Killer (Partially) Identified

Scientists have discovered a surprising culprit behind a rash of shark strandings in California and elsewhere, but many questions remain.

SHARKS: On Assignment with Brian Skerry opens at the National Geographic Museum on May 24, 2017. Catch SharkFest on Nat Geo Wild starting July 23.

The leopard shark was still alive when it washed ashore on a San Francisco Bay mudflat a few hundred feet south of the runway of the San Francisco International Airport. A state game warden found it there, lolling in shallow brown water, dying.

The warden called the Pelagic Shark Research Foundation, a shark conservation group based in Monterey, California. The group’s executive director drove up, packed the now-dead shark in a cooler, and FedExed it to Mark Okihiro.

Okihiro is a California Department of Fish and Wildlife senior fish pathologist whose day job is to assess disease in white seabass hatcheries. But lately he has become, in his spare time, a leading expert on what causes sharks to die where

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