Stock structure of edible crab populations along the coasts of Ireland and Northern Ireland is not well understood. There is some evidence that the stock inhabiting northwest Ireland waters between 54.50°N and 57.0°N and from 6.0°W to 11.5°W (which would contain the Malin assessment unit) is a biologically or functionally distinct unit (Tully et al. 2006). However, a recent genetic study of brown crab populations within the Irish Sea and across the Northeast Atlantic did not find strong evidence of distinct population structure at the local or regional scale (McKeown et al. 2018).

For purposes of stock assessment, four units are defined: Malin, SW Ireland, Celtic Sea, and N Irish Sea (ICES 2013).