TABLE OF CONTENTS 1 INTRODUCTION .........................................................................................................1 2 ECOLOGY AND POPULATION DYNAMICS ........................................................3 2.1 Pecten maximus ........................................................................................................3 2.1.1 Habitat ................................................................................................................3 2.1.2 Life cycle ............................................................................................................3 2.1.3 Spawning and settlement of P. maximus in Mulroy Bay ...................................6 2.1.4 Growth ..............................................................................................................10 2.1.5 Recruitment ......................................................................................................10 2.1.6 Exploitation and mortality rates: North Irish Sea .............................................12 2.2 Aequipecten opercularis: North Irish Sea ...............................................................13 2.3 Chlamys varia .........................................................................................................15 2.4 Chamelea gallina in the Northern Adriatic ............................................................17 2.4.1 Habitat ..............................................................................................................17 2.4.2 The Northern Adriatic ......................................................................................17 2.4.3 Life cycle ..........................................................................................................22 2.4.4 Status of clam resources: North Adriatic .........................................................26 2.5 Portuguese clam species: ........................................................................................28 2.5.1 Species ..............................................................................................................28 2.5.2 Habitat ..............................................................................................................28 2.5.3 Life cycle: General considerations ...................................................................29 2.6 Spisula solida ..........................................................................................................30 2.7 Ensis siliqua ............................................................................................................32 2.8 Chamelea gallina: Portuguese waters .....................................................................33 2.9 Donax trunculus ......................................................................................................35 2.10Clam species in French waters ...............................................................................38 3 DREDGE DESIGN .....................................................................................................50 3.1 European dredge designs ........................................................................................51 3.1.1 Manual dredges ................................................................................................51 3.2 Box designs ............................................................................................................54 3.2.1 Flexible designs ................................................................................................57 3.2.2 Hydraulic dredges ...........................................................................................70 3.3 Dredge designs elsewhere .......................................................................................77 3.3.1 Rigid Box dredges ............................................................................................77 3.3.2 Flexible dredges ..............................................................................................80 3.3.3 Hydraulic dredges ...........................................................................................84 4 EUROPEAN DREDGE FISHERIES ........................................................................89 4.1 England and Wales .................................................................................................89 4.1.1 Pectinid group .................................................................................................90 4.1.2 Oyster Fishery ..................................................................................................91 4.1.3 Clam fisheries ..................................................................................................93 4.1.4 Mussel Fisheries ...............................................................................................95 4.1.5 Management measures UK dredge fisheries ....................................................96 4.1.6 Dredge Fishing Effort for Pecten maximus in England and Wales .................98 4.2 Scotland .................................................................................................................102 4.2.1 Pectinid Group ................................................................................................102 4.2.2 Aequipecten opercularis ................................................................................107 4.2.3 Other local novel bivalve dredge fisheries ....................................................110 4.3 Isle of Man ...........................................................................................................112 4.3.1 Pectinid group ................................................................................................112 4.3.2 Management measures Isle of Man fisheries ................................................120 4.4 Ireland ...................................................................................................................122 4.4.1 Pectinid group ................................................................................................122 4.4.2 Oyster group ..................................................................................................125 4.4.3 Management measures ...................................................................................126 4.5 France ...................................................................................................................129 4.5.1 Pectinid group ................................................................................................129 4.5.2 King scallops (Pecten maximus) ................................................................... 129 4.5.3 Queen scallops (Chlamys varia and Aequipecten opercularis) .....................136 4.5.4 Clam group ....................................................................................................138 4.5.5 Warty venus (Venus verrucosa) .....................................................................139 4.5.6 Small bivalves: Palourd, Bittersweet and Thick trough shell ........................142 4.5.7 Mussels ...........................................................................................................143 4.6 Italy ......................................................................................................................147 4.6.1 Chamelea gallina fishery ................................................................................147 4.6.2 Razor clam fishery .........................................................................................152 4.6.3 Callista chione fishery ...................................................................................154 4.6.4 Management measures ...................................................................................155 4.7 Portugal .................................................................................................................157 4.7.1 Management measures ...................................................................................162 5 ENVIRONMENTAL EFFECTS .............................................................................165 5.1 Physical effects .....................................................................................................165 5.1.1 Scallop dredging ............................................................................................165 5.1.2 Hydraulic dredging ........................................................................................166 5.2 Chemical Effects ...................................................................................................168 5.3 Biological effects ..................................................................................................168 5.4 Ecological effects ..................................................................................................174 6 SELECTIVITY .........................................................................................................183 6.1 Species selection ...................................................................................................183 6.2 Size selection ........................................................................................................185 Introduction 1 INTRODUCTION Dredge fisheries face stock and environmental management pressures. Size and species selectivity and non-catch incidental mortality are important issues concerned with technical measures. Environmental issues are likely to become increasingly