The otter trawl is a mesh net used to collect organisms from a sandy bottom.  "Otter boards"  help hold the mouth of the net open. 

Organisms living at different depths can differ radically from shallow water species in terms of both biology and behavior.  The otter trawl is used to collect organisms from about 90 meters (50 fathoms/300 feet) as well as 9-18 m (5-10 fath/30-60 ft).

For a diagram of the otter trawl in use, click here.