A large turnout is likely Monday when a legislative committee holds a public hearing on a proposed law to allow fishermen to keep lobsters they inadvertently snag in their nets in offshore waters and bring them to Portland. It’s now illegal for boats that go after cod, haddock and other groundfish to bring their lobster by-catch to shore in Maine, although it’s legal to do so in Massachusetts. Bill supporters say allowing fishermen to keep lobsters would bring more fishing boats to Portland and help maintain port businesses that serve the fishing industry. Similar bills in past years have been defeated in the face of strong opposition from lobstermen. Lobstermen say giving net fishermen a few lobsters isn’t going to save Maine’s fishing fleet.