50 CFR § 648.104 - Summer flounder size requirements.
(a) Moratorium (commercial) permitted vessels. The minimum size for summer flounder is 14 inches (35.6 cm) TL for all vessels issued a moratorium permit under § 648.4(a)(3), except on board party and charter boats carrying passengers for hire or carrying more than three crew members, if a charter boat, or more than five crew members, if a party boat.
(b) Party/charter permitted vessels and recreational fishery participants. The minimum size for summer flounder is 19 inches (48.3 cm) total length for all vessels that do not qualify for a summer flounder moratorium permit under § 648.4(a)(3), and charter boats holding a summer flounder moratorium permit if fishing with more than three crew members, or party boats holding a summer flounder moratorium permit if fishing with passengers for hire or carrying more than five crew members, unless otherwise specified in the conservation equivalency regulations at § 648.107. If conservation equivalency is not in effect in any given year, possession of smaller (or larger, if applicable) summer flounder harvested from state waters is allowed for state-only permitted vessels when transiting Federal waters within the Block Island Sound Transit Area provided they follow the provisions at § 648.111 and abide by state regulations.
(c) Measurement. The size limits in this section apply to whole fish or to any part of a fish found in possession, e.g., fillets, except that party and charter vessels fishing exclusively in state waters possessing valid state permits authorizing filleting at sea may possess fillets smaller than the size specified if all state requirements are met.