Stonington — As Alan Chaplaski, captain of the fishing boat Neptune, was trawling for red shrimp on the morning of Aug. 25, his vessel suddenly came to a dead stop 95 miles southeast of the Town Dock. At first Chaplaski thought his net had snagged on the bottom, 1,200 feet below. Then something began pulling the 150-ton steel boat backward, causing it to shake violently. Chaplaski raced to the winch to release the brakes on the five-eighths-inch-thick steel wire attached to the net and the twin 1,000-pound “doors” that keep the net open. That prevented the boat from capsizing. He...