The Shellfish sampling programme undertaken each year collects data on the size (and where applicable age composition) of the landings of whelk, scallop, crab and lobster. These are sampled at ports, at processing plants or at live fish holding facilities. Catches of these species are also sampled on board commercial vessels through an at sea observer programme. Catch rate indicators are developed from logbook data and from a sentinel fleet of about 80 vessels which report information on catch, fishing effort and fish size composition mainly in the lobster and crab fisheries.
A number of mollusc species (oyster, clams, cockles) are assessed by survey on inshore commercial fishing vessels or on foot in the case of intertidal species and provide estimates of biomass and size and age composition on an annual basis.