Conservation of the Native Oyster Ostrea Edulis in Scotland
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COMMISSIONED REPORT Commissioned Report No.251 Conservation of the Native Oyster Ostrea edulis in Scotland (ROAME No. F02AA408) For further information on this report please contact: David Donnan Scottish Natural Heritage Battleby Redgorton PERTH PH1 3EW E-mail: [email protected] This report should be quoted as: University Marine Biological Station Millport. (2007). Conservation of the Native Oyster Ostrea edulis in Scotland. Scottish Natural Heritage Commissioned Report No.251 (ROAME No. F02AA408). This report, or any part of it, should not be reproduced without the permission of Scottish Natural Heritage. This permission will not be withheld unreasonably. The views expressed by the author(s) of this report should not be taken as the views and policies of Scottish Natural Heritage. © Scottish Natural Heritage 2007. COMMISSIONED REPORT Summary Conservation of the Native Oyster Ostrea edulis in Scotland Commissioned Report No.251 (ROAME No. F02AA408) Contractor: University Marine Biological Station Millport Year of publication: 2007 Background Native oyster (Ostrea edulis) populations in Scotland have declined significantly in abundance and distribution since the 19th century, mainly as a result of over-exploitation. Most of the remaining populations are thought to exist in west coast sea lochs. The native oyster is the subject of a UK Species Biodiversity Action Plan, the Native Oyster Species Action Plan (NOSAP), so there is a requirement to consider what conservation measures are appropriate. This project aimed to develop advice on the conservation management of the native oyster in Scotland, based on an assessment of the current status of extant populations, reviews of the history of oyster exploitation in Scotland, and conservation and fisheries management practices in the UK and elsewhere. Sites throughout the west and north coasts of Scotland were surveyed for oysters and detailed population studies were carried out at three of these sites. Main findings • Native oysters occur mainly in small, scattered populations fringing sea lochs around the west and north coasts of Scotland, usually at low population density. The only managed fishery is in Loch Ryan, which appears to have a large, self-sustaining population. There is evidence of unlawful gathering of oysters on a wide scale having a severe impact on small populations. • Population density and abundance at the Argyll sites were within the range of estimates for other British and European populations, but were much lower than in Loch Ryan at present and in the Firth of Forth historically. • Native oysters were attached to all hard materials surveyed, but with an apparent preference for oyster shell and other shell types (‘cultch’). However, shell material was sparse and patchy. There was no evidence of competition for space with other sessile species surveyed. • Detailed analysis of the small-scale distribution of oysters indicated a potential for limited reproductive success, owing to the distances between adult oysters. Sparseness and patchiness of oysters is probably exacerbated by a lack of cultch and by unlawful gathering. • Genetic analyses indicated that past translocations of oysters have probably masked any former local differences, but more-widely separated populations can still be differentiated. A Skye population appeared very distinctive, but was represented by only a small sample, so further studies are desirable to ascertain whether this population is deserving of special conservation status. A range of management measures were reviewed in relation to their applicability to conserving native oysters in Scotland. Low population densities and unlawful gathering are the two key issues to be addressed. Effective control of unlawful gathering is essential if remaining populations are to persist. Measures to increase broodstock density or habitat availability may also be required to sustain some populations. For further information on this project contact: David Donnan, Scottish Natural Heritage, Battleby, Redgorton, Perth, PH1 3EW Tel: 01738–458664 For further information on the SNH Research & Technical Support Programme contact: Policy and Advice Directorate Support, Scottish Natural Heritage, Great Glen House, Leachkin Road, Inverness IV3 8NW. Tel: +44(0)1463 725067 or [email protected] CONTENTS Part Title Page CONTENTS iv LIST OF FIGURES vii LIST OF TABLES ix ACKNOWLEDGEMENTS xi 1 INTRODUCTION 1.1 The Native Oyster Species Action Plan 1 1.2 Current status of Ostrea edulis stocks in the United Kingdom 2 1.2.1 England and Wales 2 1.2.2 Northern Ireland 2 1.2.3 Scotland 3 1.3 Conservation & restoration of Ostrea edulis stocks in Europe 4 1.4 Research Aims and Objectives 5 1.5 Study sites 6 1.5.1 West Loch Tarbert 6 1.5.2 Linne Mhuirich (Loch Sween) 8 1.5.3 Loch Ailort 11 2 THE SCOTTISH OYSTER FISHERIES: AN HISTORICAL REVIEW 2.1 Introduction 12 2.2 The west coast fisheries 12 2.2.1 Loch Ryan, Ballantrae district 12 2.2.2 West Loch Tarbert, Inveraray district 14 2.2.3 Linne Mhuirich (Loch Sween), Campbeltown District 15 2.2.4 Orkney and Shetland 15 2.3 The east coast fisheries 16 2.3.1 The Firth of Forth, Leith district 18 2.4 Exploitation of oyster populations 20 2.5 The decline of the oyster fisheries 22 2.6 Other potential factors 24 2.7 The wider experience 24 2.8 Conclusion 25 3 POPULATION ESTIMATES OF SELECTED WILD OSTREA EDULIS POPULATIONS IN SCOTLAND 3.1 Introduction 27 3.2 Methods 29 3.2.1 Sites surveyed 29 3.2.2 Population surveys 29 3.2.2.1 Multi-level surveys 29 3.2.2.2 Belt-transect surveys 31 3.2.3 Unlawfully gathered oysters 31 3.3 Results 31 3.3.1 Multi-level transect survey: habitat and species data 31 3.3.2 Population surveys 32 3.3.3 Unlawfully gathered oysters 45 3.4 Discussion 47 3.4.1 General status of wild populations 47 3.4.2 Sampling design 47 3.4.3 Population estimates and unlawful exploitation 48 i 3.5 Current status of Ostrea edulis populations 51 3.6 Observations and local information from around Scotland 53 3.6.1 Dumfries and Galloway 53 3.6.1.1 Loch Ryan 53 3.6.2 Argyll and Bute 53 3.6.2.1 Loch Melfort 53 3.6.2.2 Loch Fyne 53 3.6.2.3 West Loch Tarbert 53 3.6.2.4 Linne Mhuirich (Loch Sween) 53 3.6.2.5 Loch Sween 54 3.6.2.6 Bute 54 3.6.2.7 Loch Ceann Traigh 54 3.6.3 Mull and Ulva 54 3.6.3.1 Loch Tuath 54 3.6.3.2 Sound of Ulva 54 3.6.3.3 Loch na Keal 55 3.6.3.4 Ulva (other areas) 55 3.6.3.5 Loch Scridain 55 3.6.4 Mull (other areas) 56 3.6.4.1 Loch a’ Chumhainn 56 3.6.4.2 Tobermory Bay 56 3.6.4.3 Broadford Bay 56 3.6.5 The Highlands and Islands 56 3.6.5.1 Loch Ailort 56 3.6.5.2 Loch Moidart 57 3.6.5.3 Loch Kishorn 57 3.6.5.4 Skye 57 3.6.5.5 Uist 57 3.6.6 Sutherland 57 3.6.6.1 Loch Eriboll 57 3.6.6.2 Kyle of Tongue 57 3.6.7 Shetland and Orkney 57 3.6.7.1 Shetlands 57 3.6.7.2 Orkney 58 3.6.8 Other Areas 58 4 SETTLEMENT SUBSTRATUM AVAILABILITY AS A LIMITING FACTOR FOR THE ABUNDANCE OF OSTREA EDULIS POPULATIONS IN SCOTLAND 4.1 Introduction 59 4.2 Methods 60 4.2.1 Analysis 60 4.3 Results 62 4.3.1 Substrata 62 4.3.2 Ostrea edulis 62 4.3.3 Potential competitor species 75 4.3.4 Settlement tiles 79 4.4 Discussion 81 4.4.1 Substrata availability and Ostrea edulis 81 4.4.2 Competitive interactions 82 4.5 Conclusions 83 ii 5 DO ALLEE EFFECTS POTENTIALLY LIMIT THE RECRUITMENT SUCCESS OF OSTREA EDULIS IN SCOTLAND? 5.1 Introduction 84 5.2 Methods 85 5.2.1 Experimental investigation of the factors influencing fertilisation 87 5.3 Results 89 5.3.1 Manipulated plots 97 5.4 Discussion 97 5.5 Conclusions 100 6 GENETICS OF SCOTTISH POPULATIONS OF THE NATIVE OYSTER, OSTREA EDULIS: GENE FLOW, HUMAN INTERVENTION AND CONSERVATION Author: A.R. Beaumont. University of Wales, Bangor 6.1 Introduction 101 6.2 Methods 104 6.3 Results 108 6.4 Discussion 118 7 REVIEW OF FISHERIES AND CONSERVATION MANAGEMENT MEASURES 7.1 Introduction 121 7.1.1 Invertebrate fisheries 121 7.1.2 The conservation and fisheries importance of Ostrea edulis 121 7.1.3 Current fisheries management measures 122 7.2 Management measures 122 7.2.1 Minimum landing sizes 122 7.2.2 Legal rights 123 7.2.3 Temporal fisheries closures 124 7.2.4 Marine protected areas 125 7.2.5 Stock enhancement 127 7.2.5.1 Species biology and stock enhancement 128 7.2.5.2 Stock enhancement and national and international policy guidelines 129 7.2.6 Habitat enhancement 130 7.3 Additional legal aspects 131 7.4 Financial considerations and potential management strategies 131 8 THE APPLICABILITY OF MANAGEMENT MEASURES FOR OSTREA EDULIS POPULATIONS IN SCOTLAND 8.1 Introduction 133 8.1.2 Summary of findings 133 8.2 Population assessments 133 8.3 Enhancement techniques 134 8.3.1 Broodstock enhancement 134 8.3.2 Habitat enhancement 136 8.4 Marine protected areas 137 8.5 Fisheries 138 8.6 Unlawful gathering 141 8.7 Concluding remarks 142 REFERENCES 144 APPENDIX I – RIGHT TO GATHER OYSTERS IN SCOTLAND 159 APPENDIX 2 – NATIVE FLAT OYSTER, OSTREA EDULIS: MICROSATELLITE DATA SET FOR TFPGA 165 iii Figure Title Page 1 INTRODUCTION 1.1 Map of Scotland showing the location of main research sites 7 1.2 Mean monthly temperatures in 2004 and 2005 10 2 THE SCOTTISH OYSTER FISHERIES: AN HISTORICAL REVIEW 2.1 Map of Scotland showing the location of the principal oyster fisheries and 13 cultivation sites in Scotland from the 18th – 20th century 2.2 Map of the Firth of Forth oyster beds showing the boundaries of ownership 17 2.3 Annual landings of O.