Molluscan Research in D&S IFCA's District

Molluscs or Mollusca are the second largest phylum of invertebrates in the animal kingdom.  There are around 75,000 different living species, which are recognised as molluscs.  Molluscs are the largest marine phylum comprising about 23% of all named marine organisms.  The phylum is divided into eight extant classes of which five are found within north west European waters.   These include cephalopods such as squid, cuttlefish, and octopuses; gastropods which included sea snails and slugs such as whelks and winkles; bivalves which include many commercially harvested species such as mussels, oysters, cockles, clams, and scallops; scaphopods - the tusk shells; and polyplacophorans - the chitons.

Within the D&S IFCA’s District molluscan fisheries include very important wild and cultivated species.  The most important wild capture species are scallops, whelks, and cuttlefish.  In 2018 landings of scallops into Devon’s ports for all UK vessels (both under 10m and over10m in length) equated to 4,527 tonnes worth £9.56 million.  These figures will include scallops caught outside the IFCA’s District by the larger vessels over the 15.24m limit allowed within the District.  For the under 10m vessels the landings were 615 tonnes worth £751,000.  Whelks are another important molluscan species largely fished within the D&S IFCA’s District and landed into Devon’s ports.  In 2018, 1,155 tonnes were landed worth £1.49 million.  Cuttlefish are mainly targeted outside the 6nm boundary of the District extending out to the Mid English Channel. However, there is a trawl fishing within the District and an inshore pot fishery between March and June each year.  The landings into Devon’s ports, in particular Brixham and Plymouth, are significant for the local economy.  In 2018 landings for all sized vessels into Devon’s ports were 2,975 tonnes of cuttlefish worth £11.32million.  The under 10m vessels landed 126.7 tonnes worth £533,040.

Molluscs are also important cultivated and harvested species within the D&S IFCA’s District.  The Mariculture section of the website District details the important species and shellfish businesses that exist within the inshore coastal areas and estuaries within the District.  Mussels are of particular importance, being harvested from intertidal areas and from rope grown mussel farms.  Oyster cultivation too is economically significant being grown and harvested from several of the estuaries in the District including the Teign Estuary, Exe Estuary, Yealm Estuary, Dart Estuary, Avon Estuary and at Porlock Weir in Somerset.  Other species harvested commercially are surf clams and winkles and recreational gathering of molluscs include the following species: cockles; clams; winkles; and razor clams.

Research undertaken in the D&S IFCA’s District includes stock assessments of intertidal mussel and cockle beds; developing scallop stock assessment methodologies with Cefas; Salcombe scallop stock assessments; size of sexual maturity and reproductive seasonality of whelks; mapping wild shellfish beds; cuttlefish fishing effort studies, trialling egg laying media and fishery impacts.  The research work undertaken by D&S IFCA is detailed below for the different molluscan species.

Page reviewed: 3rd July 2020

Cockles

Mussels

Whelks

Scallops

Cuttlefish