The number of blue crabs in the Chesapeake Bay is down slightly from last year, to 317 million, but researchers said the numbers are manageable and they see “no serious reason for concern.” The population estimates come from the annual winter dredge survey released last month by the Maryland Department of Natural Resources and the Virginia Institute of Marine Science. It estimated that the overall number of crabs this year is down from the 323 million estimated in 2023.