"had butchered their marlin out and carried them laid full length across two planks"
Atlantic blue marlin
Public DomainAtlantic blue marlin

The Atlantic blue marlin can reach almost twenty feet in length. Marlin "are incredibly fast swimmers, reaching speeds of about 110 kilometres per hour (68 mph)."

Swordfish
Public DomainSwordfish
People sometimes use the terms "marlin" and "swordfish" interchangeably, since both fish have a sharp, elongated snout; however, they are two different kinds of fish.