King Scallop (Pecten maximus)

Fishery

King scallops are the Isle of Man’s most commercially valuable fishery with a total of 1233 t landed (~£2.5 million first sale value) during the 2019/2020 fishing season (source: DEFA Electronic Daily Catch Returns and EU Logbooks). The fishery is targeted using Newhaven dredges by vessels from the Isle of Man and other nations around the Irish sea,  with 79 vessels licenced to fish for king scallops in the territorial sea in 2020/2021. The minimum landing size for king scallops in Isle of Man territorial waters is 110 mm.

Life Cycle

The king scallop is a large bivalve that can grow up to 15 cm long. The right valve is highly convex and off-white, yellowish, or light brown in colour. The left valve is flat and light pink to reddish brown in colour. Both valves have 15-17 radiating ribs. Their lifespan can be up to 20 years and they reach sexual maturity between 3 and 5 years. King scallops are hermaphrodites (i.e. they have both male and female reproductive organs) and fertilization takes place externally with release of male and female gametes into the water column. Their larvae develop in the water column and are dispersed in the currents. After ~30 days they settle to the sea floor and attach to a suitable surface using their byssal threads (strong, silky fibres). Young scallops usually remain attached by byssal threads until they are between 4 and 13 mm in length and then settle on the seabed. Adult king scallop are not known to migrate and only move when disturbed. Therefore, their distribution relies heavily on larval dispersion and consequently the local environmental conditions, such as sediment type, currents and temperature.

Habitat & Distribution

King scallops are usually found in shallow depressions in the seabed. They prefer clean, firm sand, fine or sandy gravel, but are occasionally found in areas of muddy sand. They are found along the European Atlantic coast from northern Norway and south to the Iberian Peninsula, but have also been reported off West Africa, the Azores, Canary Islands and Madeira. King scallops are filter feeders and eat micro-organisms in the water column.