Reduced landings, smaller average size and general observations indicate that populations have declined considerably since the 1970's, in south-west Britain at least. Numbers in the Mediterranean have also been reduced (Campillo & Amadei, 1978). Reasons for the decline include possible over-fishing through use of more efficient capture mechanisms such as tangle nets. Environmental conditions may also play an important role (Hiscock, pers. comm., based on observations in Russell, 1973 and Wilson, 1951). Their presence only on coasts bordering the Atlantic suggests a confinement to oceanic waters (Hepper, 1977). Successful recruitment of decapod larvae may be dependent on incursions of more oceanic water (Russell, 1973).

Several observations suggest that the species makes active annual migrations to and from deeper water (e.g. Hunter, 1999). The populations, at least off the west of Ireland, (except perhaps for large males), move offshore into deeper waters late in the year to over-winter with the movement back inshore occurring in spring (Mercer, 1973, cited in Hunter, 1999). Migrations may be triggered by seasonal changes in sea temperature.