When Predators Become Prey

How the same adaptation can make a shark deadly and vulnerable

Hammerhead sharks’ oversize fins allow them to maneuver underwater with incredible control. The fish evolved this and other traits over the span of 10 million years, turning them into one of the ocean’s most agile hunters. “But today, the rules of the game have changed,” says University of Miami biologist Austin Gallagher. “People are now in the picture.” In a paper published in June, he describes how adaptations that make the sharks so deadly to sea creatures also leave them vulnerable to humans.

Hammerheads, like sports cars, are built to accelerate in short, energy-intensive bursts, Gallagher says, which means encounters with fishhooks are often fatal. Once caught, a super-high stress response causes the shark to fight furiously, often until it dies of exhaustion. Between accidental bycatch, recreational fishing, and a booming shark-fin industry, some populations have plummeted 99 percent in the past century.

Another adaptation could help. Electrosensory organs in the sharks’ heads detect prey in wide swaths of seawater. Lanthanide hooks, which create an electromagnetic field in saltwater, could signal sharks to steer clear.

_This article originally appeared in the August 2014 issue of _Popular Science.