Maryland is offering to buy back more than half the state’s commercial crabbing licenses, hoping to protect Chesapeake Bay’s crab population. The state Department of Natural Resources announced it wants to retire almost 3700 of the licenses through what is called a reverse auction. The bay’s crab population bounced back last year, but scientists say it has not fully recovered and is still vulnerable. Although the state issued about 6000 commercial crab licenses, less than a third of those are actively fished. The buyback would be funded from $10-million in federal disaster-relief funds.