In 2006 scientists were mapping the bottom of the York River, one of the Chesapeake Bay's many tributaries, when they came across something odd. “We started to see these little squares all over the place,” says Donna Bilkovic, a biologist at the Virginia Institute of Marine Science. “They were clearly man-made.”
The squares turned out to be hundreds of loose crab traps, escapees from the bay's large blue crab fishery. Every year crabbers around the world set millions of these cagelike traps, known as pots, and sometimes a high percentage go missing. In Maryland and Virginia alone, crabbers set out around 800,000 pots annually, and as many as 30 percent break free of their lines and drift away only to stick in the mud, sometimes for years. But just because the pots are derelict does not mean they no longer work: each one can catch more than 50 crabs a year, as well as several other species, including the diamondback terrapin, a threatened species.