It has become increasingly unlikely that the dozens of migrants whose boat capsized over the weekend in the Florida Straits will survive. Search operations began at 8 a.m. on Tuesday when a capsized 25-foot boat was sighted. A man was found on the hull of the boat and taken to the hospital, where he told authorities that he and 39 people had left Bimini, in the Bahamas, on Saturday night. “The longer they remain in the water, without food, without water, it’s cold, with the marine environment, the sun, the conditions. Every moment that passes, and it becomes much more dire and unlikely that anyone can survive,” said Capt. Jo-Ann F. Byrdian, the commander of the Coast Guard’s Miami district. At least one dead person has been spotted in the water.