Dictionary of Ichthyology
otter board = 1) a large, heavy, flat piece of wood and metal on each side of the mouth of an otter trawl; the boards plane or shear through the water and keep the net mouth open. Also called otter door, trawl door, trawl board. The term is also used for any shearing device used to separate lines or drive a line deeper in the water. Various models and designs exist.