By 1550, sixty percent of all fish eaten in Europe was cod ... being indestructible. Cod do find lots to eat, swimming with their huge mouths open, ingesting whatever goes in.

"Fish have swim bladders that resonate like bells," Makris explains. "Cod have large swim bladders that have a low resonance, ...

Can sharks be kept at bay without harm? A scientist is testing an electromagnetic barrier off Cape Cod to find out.