Most northeast Atlantic skates occupy broadly continuous shelf habitat. The undulate ray does not. It occurs in discrete concentrations, including parts of the English Channel and Channel Islands, the Bay of Biscay, Portuguese and Moroccan coasts, and limited areas of the western Mediterranean, with long stretches of apparently suitable coast in between where it is rare or absent.
That pattern complicates management. A survey inside a pocket can find plenty of rays and suggest a healthy stock; a survey across the whole range finds a fish that is uncommon and easily removed patch by patch. European management measures for the species have been revised more than once as this became clearer.
The markings are diagnostic and stable: dark undulating lines bordered by small pale spots across a brownish disc. No other ray in the region carries them, which makes catch identification unusually reliable for this species.