Illegal taking of shellfish will cost perpetrators $300 in Marshfield if Town Meeting votes on Monday to add waterway fines to the bylaws. Harbormaster Michael DiMeo said fines have previously existed in the harbormaster’s regulations and have changed over the years — including a reduction in 2008 — but have not always been clear. Article 6 on the warrant would make waterway fines part of the town bylaws, establishing fines of $150 for a first violation of the harbormaster’s regulations, $250 for a second offense, and $300 for a third offense. Illegal taking of shellfish would bring a $300 fine for each offense. The article would also prohibit houseboats — defined as non-motorized vessels designed for human habitation — from mooring or anchoring within town waters, except at marinas that would allow direct access from land and have sewage, water, and electricity. Town Meeting starts at 7 p.m. at Furnace Brook Middle School.