(Fairbairn 1981) found some small independent populations of Witch flounder in the Newfoundland region but no recent studies could be found so the stock structure is considered as unknown (DFO 2016). Different assessment units are therefore assumed by Fisheries and Oceans Canada (DFO): 

• Southern Grand Banks (3NO), St. Pierre and Miquelon (3Ps) and Southern Labrador/Eastern Newfoundland (2J3KL) in the Newfoundland and Labrador Region (DFO 2005)(DFO 2014)(DFO 2014)(DFO 2016)(Maddock Parsons and Rideout 2014);
• Gulf of St. Lawrence (4RST) in the Gulf region (DFO 2017).