Port of Truro Oyster Management Group

Slipper Limpet Utilisation and Management

Final Report

Andy FitzGerald January 2007

FINANCIAL INSTRUMENT FOR FISHERIES GUIDANCE

Acknowledgements

Many thanks to Mr Paul Ferris and Captain Andy Brigden of the Port of Truro Harbour Authority for their assistance in this study. I am grateful for the provision of the harbour vessel Two Castles with her crew that allowed us to collect slipper limpet stocks for this study.

On the ground, information from the oystermen of the fishery has proved invaluable with appreciated input from Tim Vinnicombe, Frank Vinnicombe, Jon Bailey, Colin Frost, Dennis Laity and Mike Parsons. Martin Laity’s input with the extraction trial using the winkle sorter was particularly useful as was Sam Laity’s assistance with the translation of the French report.

Potential partners for a trial to implement the study findings are thanked for their assistance to date and indications of future input. Representatives and companies include:

-Malcolm Gilbert (Ammodytes of St Ives) -Nigel Ellis (Cornish Cuisine of Penryn) -Peter Tierney (Ciamar of Falmouth) -Rob Furse (Contac of St Austell) -Sam Evans (Kildavanan Seafoods of Fleetwood)

Many thanks to Gary Cooper and Colin Bates from Port of Falmouth Health Authority for the microbiological examination of the slipper limpet samples.

Particular thanks are due to Mr Martin Syvret of SEAFISH and Dr Clive Askew of SAGB for their comments and suggestions regarding the Draft Report. In addition, Martin Syvret’s input in the 8th International Conference of Shellfish Restoration 2005 and subsequent discussions with workers on slipper limpets was most useful.

A vast number of other people have helped in discussions relating to this project as listed in Appendix E. Of all those who participated Msr. Michel Blanchard of IFREMER was particularly helpful. Many thanks to all of the above for their assistance.

This report was produced on behalf of the Port of Truro Oyster Management Group.

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Executive Summary ...... 8 Section A - Slipper Limpet Population Status...... 9 A.1. OVERVIEW...... 9 A.2. IMPACT OF THE SLIPPER LIMPET...... 9 A.2.1 Impact on Commercial Fishing Activities...... 9 A.2.1.1 Oysters...... 9 A.2.1.2 Mussels...... 10 A.2.1.3 Scallops ...... 11 A.2.1.4 Finfish...... 12 A.2.2 Impact on Environment...... 12 A.2.2.1 Biodiversity...... 12 A.2.2.2 Water Quality ...... 13 A.2.2.3 Geochemical Cycling...... 13 A.3. POPULATION SUCCESS...... 14 A.3.1 Reproductive Advantage ...... 14 A.3.2 Feeding Regime ...... 15 A.3.3 Environmental Tolerance...... 16 A.3.4 Absence of Predators ...... 17 A.3.5 Distribution Strategies...... 17 A.4. EXTENSION OF RANGE...... 17 A.4.1 Natural Range and the US...... 17 A.4.2 UK and Europe ...... 18 A.4.3 The World...... 20 A.5. COMPARATIVE ASSESSMENT ...... 20 A.5.1 European Status...... 20 A.5.1.1 Bay of Brest ...... 21 A.5.1.2 Mont St Michel Bay ...... 22 A.5.1.3 Arcachon Bay ...... 22 A.5.1.4 German Wadden Sea ...... 23 A.5.2 UK Status...... 24 A.5.2.1 Essex...... 24 A.5.2.2 Solent...... 25 A.5.2.3 English Channel ...... 25 A.5.2.4 South Wales ...... 26 A.5.3 Carrick Roads / Fal System Status...... 26 A.5.3.1 Historical Slipper Limpet Levels ...... 26 A.5.3.2 Potential Reasons for Population Growth...... 27 A.5.3.3 Population Density...... 28 A.5.3.4 Carrick Road ‘Hot-Spots’...... 28 A.5.3.5 Population Growth Rates ...... 30 A.6. SUMMARY...... 31 Section B - Management Options...... 33 B.1. OVERVIEW...... 33 B.1.1 Eradication ...... 33 B.1.2 Control Population...... 33 B.1.3 Do Nothing...... 33 B.2. MANAGEMENT TECHNIQUES...... 34 B.2.1 Destruction by Chain Harrowing ...... 34 B.2.1.1 Theoretical Impact on Slipper Limpets...... 34 B.2.1.2 Potential Risk of Technique...... 34 B.2.2 Collection by Fishermen...... 34 B.2.3 Collection by Harbour Authority ...... 36 B.2.4 Collection by Suction Dredge...... 37 B.2.4.1 The ARVAL Programme...... 37 B.2.4.2 Technique Limitations ...... 37

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B.2.4.3 Extraction Costs ...... 38 B.2.5 Stock Storage...... 39 B.2.5.1 On the Seabed...... 39 B.2.5.2 On the Land...... 39 B.2.5.3 On a Barge...... 39 B.2.6 Stock Destruction...... 40 B.2.6.1 On the Seabed...... 40 B.2.6.2 On the Land...... 41 B.2.6.3 On a Barge...... 41 B.2.7 Removal by Pheromone Traps...... 41 B.3. INTEGRATED MANAGEMENT ...... 42 B.3.1 Appropriate Assessment...... 42 B.3.2 Slipper Limpet Removal...... 43 B.3.3 Targeted Chain Harrowing/Laying of Cultch...... 44 B.3.4 Modeling of Fishery Value vs. Fishery Maintenance Costs...... 45 B.3.5 Long Term Measures...... 45 B.4. SUMMARY...... 45 Section C – Extraction/Treatment Techniques ...... 47 C.1. OVERVIEW...... 47 C.2. SEPARATION ...... 47 C.2.1 Manual Shucking ...... 47 C.2.1.1 Pre-treatment Blast Freezing...... 47 C.2.1.2 Pre-treatment Brine Dipping...... 47 C.2.2 Ensilage...... 48 C.2.2.1 Acid Ensilage...... 48 C.2.2.2 Fermentation Ensilage ...... 48 C.2.2.3 Alkaline Ensilage...... 49 C.2.3 Freezing and Knocking...... 49 C.2.4 Cooking and Knocking ...... 49 C.3. WHOLE SHELL ...... 50 C.3.1 Simple Crushing...... 50 C.3.2 Crushing and Drying...... 50 C.4. SUMMARY...... 51 Section D – Utilisation ...... 52 D.1. ANIMAL CONSUMPTION ...... 52 D.1.1 Poultry Applications ...... 52 D.1.2 Cattle Applications...... 52 D.1.3 Aquaculture Applications...... 53 D.1.4 Pet Food Applications...... 54 D.1.5 Aquarium / Leisure Fishing Bait Applications...... 54 D.1.6 Commercial Fishing Bait Applications ...... 55 D.2. HUMAN CONSUMPTION ...... 55 D.2.1 Previous Applications ...... 55 D.2.1.1 Early European Applications ...... 55 D.2.1.2 Current European Applications...... 55 D.2.2 Trial Preparations...... 56 D.2.2.1 SAGB Dinner...... 56 D.2.2.2 Rick Stein / The Seafood Restaurant...... 56 D.2.2.3 PESCA Trials ...... 56 D.2.2.4 This Study ...... 57 D.3. SOIL AMENDMENT APPLICATIONS...... 59 D.3.1 Lime Soil Conditioner...... 59 D.3.2 Organic Fertiliser...... 59 D.4. SHELL AGGREGATE APPLICATIONS ...... 59 D.4.1 Bound Blocks and Surfaces...... 59 D.4.2 Loose Shell Uses ...... 60

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D.4.3 Cultch for Oyster Settlement ...... 61 D.5. LIMITATIONS...... 62 D.5.1 Flesh Yield ...... 62 D.5.2 Flesh Quality...... 63 D.5.3 Processing Costs...... 63 D.5.4 Perception and Market Inertia ...... 64 D.5.5 Unknown Product Availability ...... 64 D.5.6 Access to Overseas Markets ...... 65 D.5.7 Competition from Existing Established Products ...... 65 D.5.7.1 Shellfish Products...... 65 D.5.7.2 Shell Products...... 65 D.5.7.3 Fertiliser Products ...... 66 D.6. LEGISLATION ...... 66 D.6.1 Shellfish Hygiene/Classification...... 66 D.6.2 Animal By-Product Regulations ...... 68 D.6.3 Animal Feed-Stuff Regulations...... 68 D.6.4 Habitats Directive ...... 69 D.6.5 Water Framework Directive ...... 69 D.6.6 Waste Disposal ...... 69 D.7. SUMMARY...... 70 Section E - Proposals ...... 72 E.1. FISHERY STATUS PROPOSALS ...... 72 E.1.1 Ongoing Monitoring ...... 72 E.1.2 Slipper Limpet Biomass...... 72 E.2. MANAGEMENT PROPOSALS ...... 73 E.2.1 Combined Slipper Limpet Removal of 25t/yr...... 73 E.2.1.1 Oysterman By-Catch Collection During Season (12.5t/yr) ...... 74 E.2.1.2 Harbour Authority Collection Following Season (12.5t/yr)...... 74 E.2.2 Slipper Limpet Handling...... 74 E.2.2.1 Collection Monitoring ...... 74 E.2.2.2 Live Slipper Limpet Storage ...... 74 E.2.3 Business Model...... 75 E.3. UTILISATION PROPOSALS...... 75 E.3.1 Human Consumption...... 75 E.3.1.1 Economics of Shucking...... 76 E.3.1.2 Legislation...... 76 E.3.1.3 Marketing ...... 76 E.3.1.4 Fresh Food Market...... 76 E.3.1.5 Prepared Food Market...... 76 E.3.1.6 Production Facilities...... 77 E.3.1.7 Trial Season...... 77 E.3.2 Animal Consumption...... 77 E.3.2.1 Processed Material...... 77 E.3.2.2 Un-processed Material...... 77 E.3.3 Shell Applications...... 78 E.3.3.1 Bound Shell...... 78 E.3.3.2 Loose Shell ...... 78 E.3.3.3 Cultch ...... 78 E.4. SUMMARY...... 78 E.4.1 Short Term Actions Prior to Trial...... 80 E.4.2 Medium Term Actions During October-March Trial ...... 80 E.4.3 Long Term Actions Following Trial...... 80 Section F – Trial Season Financial Assessment...... 81 F.1. OVERVIEW...... 81 F.2. COLLECTION AND MONITORING ...... 81 F.3. STORAGE / CLEANING AND HANDLING...... 81

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F.4. SHUCKING AND PROCESSING ...... 82 F.5. UNPROCESSED FLESH APPLICATIONS...... 82 F.6. PROCESSED FLESH APPLICATIONS ...... 83 F.7. SHELL APPLICATIONS...... 83 F.8. SUMMARY...... 84 F.8.1 Baseline Overheads...... 84 F.8.2 Scenario 1 –Processed, High Utilisation, Full Costs...... 84 F.8.3 Scenario 2 –Processed, High Utilisation, Limited Costs ...... 85 F.8.4 Scenario 3 – Unprocessed, Low Utilisation, Limited Costs ...... 85 Section G - Conclusions...... 89 Appendix A - References ...... 91 Appendix B - French Case Study Plots ...... 96 Appendix C - CEFAS Survey Results for the Port of Truro Fishery...... 98 Appendix D - Automated Extraction Trial Output...... 100 Appendix E - Contact Listing ...... 101

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LIST OF FIGURES

Figure 1 – Oyster dredging under sail in Carrick Roads ...... 10 Figure 2 – Slipper limpet coverage on scallop shells ...... 11 Figure 3 – Slipper limpet complete coverage of seabed ...... 12 Figure 4 – Slipper limpet ‘chain’...... 14 Figure 5 – Slipper limpet natural range on US Atlantic Seaboard...... 18 Figure 6 – Slipper limpet range in Europe ...... 18 Figure 7 – Slipper Limpet Distribution along French coastline...... 19 Figure 8 – Slipper limpet UK range ...... 19 Figure 9 – Slipper limpet range Worldwide...... 20 Figure 10 – Slipper limpet population growth Bay of Brest ...... 21 Figure 11 – Slipper limpet 2006 survey of Carrick Roads...... 29 Figure 12 – Sorting table for oysters with a haul of slipper limpets...... 35 Figure 13 – Small oyster dredge used for slipper limpet collection ...... 36 Figure 14 – Slipper limpet removal using suction dredge ...... 37 Figure 15 – Diver Surveys of Suction Dredge Operation ...... 38 Figure 16 – Smoked slipper limpets in vacuum sealed pack...... 57 Figure 17 – Whelk Processing – Possible Model for slipper limpets? ...... 58 Figure 18 – Resin Bonded Aggregate Surfaces...... 60 Figure 19 – Oyster Settlement of slipper limpet shell...... 61 Figure 20 – Schematic Diagram of Slipper Limpet Process Stages and Market Outlets...... 79

LIST OF TABLES

Table 1 – Slipper limpet Tonnage in French ‘Hot-Spots’ ...... 20 Table 2 – Carrick Roads Port of Truro Fishery Historical Slipper limpet ‘Chain Recovery’ ...... 27 Table 3 – Carrick Roads Slipper Limpet Density (2006)...... 28 Table 4 – Carrick Roads, Port of Truro Slipper Limpet Stock Biomass ...... 30 Table 5 – Slipper Limpet Collection Costs – French Experience (Ref. 5) ...... 38 Table 6 – Review of Slipper Limpet Flesh Yields...... 62 Table 7 Microbiological Quality of Slipper Limpets in Carrick Roads (E. coli counts/100g MPN) ...... 67 Table 8 – Trial Season - Collection Cost ...... 81 Table 9 – Trial Season – Handling and Cleaning Cost for 25t...... 82 Table 10 – Trial Season – Slipper Limpet Processing Cost for 25t ...... 82 Table 11 – Trial Season – Bait Production for 25t ...... 83 Table 12 – Trial Season – Processed Flesh, Costs and Sales...... 83 Table 13 – Trial Season – Processed Shell, Costs and Sales...... 84 Table 14–Processing Cost under Full Utilisation and Cost Basis...... 84 Table 15 – Processing Cost under Full Utilisation and Limited Cost Basis...... 85 Table 16 – Low Value Utilisation with Limited Costs...... 85 Table 17 – Trial Season – Scenario 1, Financial Summary for Complete Processing ...... 86 Table 18 – Trial Season – Scenario 2, Financial Summary for Complete Processing and Limited Cost Basis ...... 87 Table 19 – Trial Season – Scenario 3, Financial Summary for Low Value Utilisation with Limited Costs ...... 88

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Executive Summary

The Port of Truro Oyster Management Group has identified the slipper limpet as a major potential threat to the continued viability of the native oyster fishery (Ref. 1). In the first step to establish the level of threat posed by this non-indigenous invasive species CEFAS was commissioned to monitor population levels in association with oyster stock surveys in 2004, (Ref. 6), 2005 (Ref. 7) and 2006 (Ref. 8). This report aims to assess the information provided by these previous studies and put them into context with experience elsewhere in order to provide options for the management and utilisation of slipper limpets in this region. Although the various sections of this report have been cross referenced, each unit is designed to be self contained.

A major source of information for this project has been kindly provided by French workers who have studied slipper limpet invasion, management and utilisation over a number of years. The findings of French research (Ref. 2, Ref. 3, Ref. 4) have been incorporated into this report and the recent Bay of Brest report translated (Ref. 5).

The Port of Truro slipper limpet population has only undergone slow population growth since the 1950’s. However, in the last few years a tipping point appears to have been reached and growth has been rapid. Comparison with other areas shows that a similar pattern of population explosion has occurred in other settings such as the Bay of Brest in France and Poole Harbour in the UK. Where population levels have taken-off, slipper limpets can dominate the sea bed fauna with negative impacts on both the environment and fisheries.

This report reviews the slipper limpet population status elsewhere to put the local problem into context. The level of infestation in the Port of Truro fishery is serious enough to impact working of some beds (e.g. East Bank). In absolute terms the degree of coverage (average of ~20, peak of ~60 individuals/m2) is still well below peak levels in other UK and France areas where coverage exceeds 1,000’s ind/m2. Once this high level of coverage has been reached population control is both difficult and expensive as demonstrated by the French ARVAL programme which is publicly funded to remove 30,000t/yr and yet still cannot limit population growth.

Two major components of this study are to review management and utilisation options – both of which are inextricably linked. The large scale extraction and utilisation options currently undertaken in France are not appropriate for the Port of Truro where the total slipper limpet stock is <1,000t. Instead it is proposed to remove the slipper limpets primarily with the assistance of the oystermen and to utilize the stock for a variety of ‘added-value’ niche market applications. A trial season has been proposed to remove 25t/yr of slipper limpets and aim to utilize material with a number of local partner companies with complimentary interests. The project will endeavor to stimulate market interest in products in order to provide a business plan for a self sustainable scheme in future years.

The success of the proposed trial will be dictated by the handling of material between the various partner companies in order to provide some income at all stages of the supply chain. If the utilisation options do not provide sufficient income to support an ongoing scheme then another business model or public financial support will need to be addressed. Failure to act will ultimately result in a significant impact to both the fishery and the Special Area of Conservation.

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Section A - Slipper Limpet Population Status

A.1. OVERVIEW

The Port of Truro Oyster Management Group has identified the slipper limpet as a major potential threat to the continued viability of the native oyster fishery (Ref. 1). In the first step to establish the level of threat posed by this non-indigenous invasive species the group commissioned CEFAS to monitor population levels in association with native oyster stock surveys in 2004, (Ref. 6), 2005 (Ref. 7) and 2006 (Ref. 8). This section assesses the information provided by these previous studies and puts them into context with experience elsewhere in both the UK and Europe.

The Port of Truro Oyster fishery is unique in that it is the largest natural oyster fishery still using traditional dredging techniques and a commercial sailing fleet in Europe. This fishery is also very ancient having operated since Roman times (Ref. 1).

A.2. IMPACT OF THE SLIPPER LIMPET

A.2.1 Impact on Commercial Fishing Activities Impact on commercial fisheries can be significant in reducing income and ultimately threatening fishery viability. Generally, slipper limpets are not perceived as a direct pest as they do not visibly kill commercial species, unlike drills or tingles. Instead they are widely viewed as a competitor species. This is outlined by the current project performed by Ifremer in Argenton (Ref. 9) which seeks to assess the trophic balance between 5,000t oysters, 10,000t of mussels and 100,000t of slipper limpets (now increased to 150,000t).

In addition to the competition issue the impact of slipper limpets upon different commercial species varies. A review of different species is provided below:

A.2.1.1 Oysters Oysters are not directly threatened by slipper limpets and their attachment does not immediately impact on oyster survival in the same fashion as for mussels and scallops. Immuno-competence studies performed on oyster spat in the presence of slipper limpets showed no specific detrimental effect relative to the presence of adult oysters (Ref. 10). One study conducted field trials with a variety of slipper limpet and Pacific oyster (Crassostrea gigas) concentrations and concluded that there was no negative impact in terms of growth, condition index or survival (Ref. 11). However, it should be noted that the experiment only tested comparable wet masses of test animals in an area with high phytoplankton production where food was therefore unlikely to be a limiting factor. Furthermore, slipper limpets were in ‘free’ chains not attached to host oysters and therefore not adjacent to the oysters inhalant siphon.

The main area of conflict with oysters is with the competition for space and food (see Section A.3.2). Economic impacts are also felt by the oystermen through all aspects of handling:

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-Dredging is hard work in areas where slipper limpets outweigh oysters i.e. creates difficulty when hauling by hand.

-The high level of slipper limpets increases sorting time.

-Knocking slipper limpets off oysters can damage stock.

-Market acceptance of oysters can be compromised by the presence of attached slipper limpets meaning they must therefore be removed incurring more time costs.

Figure 1 – Oyster dredging under sail in Carrick Roads

Source: Port of Truro Oyster Management Group

Note: Manual hauling of oyster dredge

The Port of Truro oyster fishery has experienced large fluctuations in its landings as a ‘boom and bust’ fishery. Licence uptake in the last 20 years peaked in the early 1980’s prior to the outbreak of Bonamia, with 154 licences taken out. Licence numbers then dropped between 1988-1993 to 23 licences/year, before recovering back to 70 licences in the 1999/2000 season, employing 56 men (Ref. 1). Numbers have since dropped markedly partially as a result of slipper limpets which are stated to be the “single biggest problem faced by the Oyster Fishery” (Ref. 1).

A.2.1.2 Mussels Ref. 12 reports that slipper limpet attachment in the Waddenzee reduces mussel survival and growth rates (Section A.5.1.4). Reduced growth was attributed to disruption of the benthic boundary layer by slipper limpets thus affecting feeding rates. Growth and mortality levels were also possibly compromised by the increased resources needed in byssus production as the stressed shellfish struggle to maintain attached due to the weight of slipper limpet chains on their backs.

Conversely, the same workers in this area showed that the presence of slipper limpets on mussels could actually reduce the rate of loss through predation (Ref. 13). This was attributed to the shielding of the mussel by the slipper limpets, (although the workers accepted that on a commercial bed if a starfish struggled to open a mussel with a slipper limpet chain on its back it

Section A – Slipper Limpet Population Status Andy FitzGerald Page 10 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study could just move onto an adjacent mussel).

Ref. 14 showed that although increasing numbers of slipper limpets may seem to correspond to decreasing numbers of mussels, both trends were in fact related to increasingly mild winters and that climate change was the function effecting both trends.

As with oysters the removal of slipper limpets increases processing time.

A.2.1.3 Scallops Scallops occur on sandy bottom sediments where they can partially bury themselves in the sediment but can also escape if attacked. Slipper limpets can adversely effect scallop survival as they become attached on the scallop shell by compromising the escape response. Furthermore, once the seabed is covered with slipper limpets there is nowhere for the scallops to hide leaving them exposed. In consequence, their habitat is reduced and their density drops.

Slipper limpets are considered to have a major impact on scallop fisheries once a significant level of bed coverage has occurred (Ref. 15, Ref. 16 and Ref. 17).

Figure 2 – Slipper limpet coverage on scallop shells

Source: Ref. 15

Impacts to the fishing/processing industry include:

-Increased time required to sort the catch.

-Reduced quality of catch. Scallop landings can be adversely affected by the presence of slipper limpets. Scallop divers in Lyme Bay have reported ~10kg of slipper limpets to every 50kg of scallops in some areas (Paul Fivian pers. comm.).

-As with oysters and mussels the presence of slipper limpets on scallops can increase processing time as slipper limpets need removing if the animal is to be sold on the half shell (Peter Tierney pers. comm.). This is the situation in the Bay of Brest (Ref. 15 and Ref. 16) where a shell cleaning time of 15.5hr/t was estimated.

-Slipper limpets on scallop shell increase the mass (and odour problems) of waste requiring expensive disposal following processing.

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-Loss of fishing areas. The Bay of Brest (Ref. 15) is estimated to lose 25% of harvestable area/yr. This represents a 97% loss of harvestable area in 12 years. Heavily infested beds with pseudofaeces deposition convert a soft sandy bed into cohesive sediment as solid as concrete that is impossible to dredge.

A.2.1.4 Finfish Slipper limpets have been implicated as a threat to finfish nursery grounds through the loss of habitat. Ref. 18 describes the threat of slipper limpets on the Bay of Biscay sole fishery which is valued at 40M Euros with a 2003 landing of 4,000t. This paper considers that slipper limpets reduce the availably of soft homogenous sediments for the young sole to feed on and bury themselves in. Trawl studies show that 60% of annual recruits for this fishery have nursery grounds in three shallow (<5m) coastal areas in southern France which are all infested with slipper limpets.

A.2.2 Impact on Environment Environmental impact can be viewed from a variety of perspectives depending on the measure used and the timescale considered. Although options on the type of impact are varied, all workers seem to agree that slipper limpets are a major influence.

A.2.2.1 Biodiversity Slipper limpets can add to the biodiversity and biological abundance of an area and could in consequence, by some measures, be considered no threat. This observation has been repeatedly observed in many French estuaries and bays infested by slipper limpets. Ref. 19 considered the muddy and medium sandy sediments of the Bay of Marennes-Oléron, France, and compared biological indices in similar environments with and without slipper limpets. This study concluded that diversity and abundance were increased by the presence of slipper limpets. Another study by the same worker in Arcachon Bay showed by field trials that varying levels of slipper limpets did not impact on diversity (Ref. 11). The impact of high slipper limpet densities on biodiversity within the Bay of Brest is also reviewed by Ref. 20 which again showed that slipper limpets can add to diversity and abundance.

This result is not surprising as the presence of slipper limpets can add a variety of new niche habitats. For example, on a fine sandy seabed slipper limpets will provide shelter for other benthic species, a hard substrate to epizootes and ultimately fine organic sediment species types once pseudo-faeces starts to be deposited. This ability to be an ‘ecosystem engineer’ and its implication to 3D sediment structure is reviewed in Ref. 20.

Figure 3 – Slipper limpet complete coverage of seabed

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Source: Ref. 15 (Photo: Erwan Amice) www.issg.org/database

In some already biologically rich environments seabed coverage with slipper limpets can be expected to reduce biodiversity with the change in habitat. Slipper limpet beds in Brittany have been identified as a threat to maerl beds due to smothering from deposited pseudo-faeces (Ref. 21). Maerl beds are considered an important marine habitat as the open matrix between the calcified seaweed allows many species to thrive allowing a high level of biodiversity. A high level of slipper limpet coverage in Carrick Roads could likewise offer a significant threat to the maerl bed habitat a protected species within the designated Special Area of Conservation (SAC).

A.2.2.2 Water Quality The University of Brest (Ref. 22) investigated the environmental impact of the spread of the slipper limpets in the Bay of Brest. Ref. 20 assimilates many of the geochemical flux impactions of Ref. 23 and Ref. 24 on the water quality. This work explains the relationship between slipper limpet population and the overlying water body in a revised approach to a benthic/pelagic relationship. The increased level of filter feeding has been implicated in a reduction in primary productivity with a resultant increase in nitrate levels. There is even evidence to suggest an increased frequency of dinoflagellate blooms.

A.2.2.3 Geochemical Cycling Once a high level of seabed coverage is achieved slipper limpets have been mooted to have a major influence on benthic fluxes and geochemical cycling in the case of carbon and nitrogen cycles (Ref. 23) and silicon cycles (Ref. 24).

Extensive slipper limpet beds are reported to transform sediments from coarse grained to fine silts with shell. This process is achieved through the rapid deposition of pseudo-faeces which contains an extremely high carbon content (Michel Blanchard pers. comm.). Ref. 20 provides model results for the Bay of Brest which indicate bio-deposits of 21,019 ± 5,360t/d (dry weight) of which 5,255 ± 1,340t/d (dry weight) is organic.

The ability to fix significant carbon amounts in sediments which is not subsequently resuspended through bioturbidation is unusual. Large scale deposition along continental shelf areas could, with time, provide a significant carbon sink through natural sequestration. Ironically, global warming could well be one of the features that increase slipper limpet success in European waters.

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A.3. POPULATION SUCCESS

It is perceived that non-indigenous species enjoy success purely because they are removed from their home environment where checks and balances are in place. In reality it is somewhat more complex than this as the majority of non-indigenous species are not successful (Ref. 54) and those that are could be equally as successful in their natural range because they are well adapted generalists. Ref. 25 provides an excellent review of biological parameters. Ref. 26 provides a detailed account of the invasive process.

A.3.1 Reproductive Advantage The reproductive habits of the slipper limpet have been well studied over the years. A good review and summary can be found in Ref. 25 with details of the Bay of Brest case study in Ref. 27. The slipper limpet initially matures into a small male before eventually undergoing a sex change to a female by protandry. Unusually fertilisation is internal which means that the sedentary adults need to form a chain for reproductive viability. Although the timing and sequence of sex change in a chain is influenced by the status of adjacent adults in the group, a number of studies (Ref. 27, Ref. 28 and Ref. 29) have shown that the majority of adults below 30mm are likely to be male or inter-sex whilst animals >30mm are more likely to be female.

Figure 4 – Slipper limpet ‘chain’

Note: small males at top, large females at bottom

Slipper limpets have a number of key reproductive advantages over bivalves:

-Maximum reproductive efficiency with large eggs only produced by large females. In contrast, even large numbers of sperm can be produced by small males. This and other reproductive strategies for different Crepidula species are reviewed in Ref. 28. -Less biological resources required for reproduction by virtue of internal fertilisation which means that unlike broadcast spawners (such as bivalves) less sperm and eggs are needed. By forming a sedentary ‘chain’ with males positioned on top of the females the males’ penis can reach adjacent females (Figure 4). This maximises the fertilisation rate of eggs. -Reduced risk in the planktonic phase is achieved by the brooding of egg pouches by the

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mother. A female will lay ~11,000 eggs which are held in ~50 yellow egg pouches beneath her shell for around a month as they develop (Ref. 25). Ref. 25 indicates 4,000 larvae/female although other papers (Ref. 27) show reproductive potential may be much greater. Larvae are released into the water column for the dispersal phase of 2-3 weeks. Although this method only gives limited planktonic dispersion it avoids the massive losses of a long planktonic life stage. Ref. 30 indicates that larval dispersion is sufficiently effective to prevent isolation of colonisation communities. -More broods/year as the reduced level of resources needed for reproduction allow the animal to quickly return to condition. Ref. 27 studied intensively the reproductive condition in the Bay of Brest between 2001-2004 and showed that between 3-4 broods/yr were produced. Similar studies on the north Brittany coast have shown 2-3 broods/yr are produced (Michel Blanchard pers. comm.). The number of successful broods produced is thought to be a function of temperature regime with spawning occurring above 10°C and successful larval recruitment occurring above 15°C. Dredging for slipper limpets in June 2006 during this study showed a notably higher incidence of very small newly settled individuals in the upper estuary (near Grimes Bar) as compared to in the deeper cooler Carrick Roads section (on East Bank). This could suggest the warmer temperature regime in the upper estuary may allow a spawning earlier in the season and possibly therefore a greater number of spawnings/yr.

In summary, slipper limpets are likely to be able to reproductively out-compete bivalves once they are established.

A.3.2 Feeding Regime Although the slipper limpet is a gastropod complete with a grazing radula it is unusual in that it is well known as a sedentary filter feeder. However, unlike bivalves who are filter feeders throughout their life the newly settled slipper limpet is free to roam and graze in a manner similar to many gastropods. It is probable that only when forced to settle down by its adult needs for reproduction that the balance of food acquisition switches from grazing to filtering.

Studies have shown that the particle size range removed in the filtering process is comparable to oysters. This suggests direct trophic competition with bivalves. Indeed the IFREMER research station at Aarchion runs a major study programme to evaluate the degree of trophic competition within the Bay of Mont St Michel where major quantities of slipper limpets are found alongside mussels, Pacific oysters and flat oysters (Ref. 4).

Orton (Ref. 31) provides a comprehensive account of the filter feeding mechanism within the slipper limpet. The gill acts as the primary driver to the feeding mechanism by creating a cilia driven current allowing food particles to enter one side of the shell opening and with discharge of faeces and pseudo-faeces from the other. A mucus sheet is used to capture particles before being swept into a sausage like pellet of mucus and food which is then pushed down a groove towards the mouth where it is grazed. Orton describes how the slipper limpet can select other larger detritus which can also be grazed.

It therefore seems apparent that although the majority of its nutrition may be provided through

Section A – Slipper Limpet Population Status Andy FitzGerald Page 15 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study filter feeding the adult slipper limpet retains its ability to graze with its radula. It is possible that the gregarious nature of slipper limpets allows each animal to continue to graze its immediate substrate which, complete with mucus layer, would tend to form a good culture medium. In this way chains of slipper limpets could actually ‘watch the back’ of their neighbour and graze off other epiphytic growth that may interfere with the normal feeding process of the chain. Furthermore, anecdotal observations from the oystermen suggest that although slipper juveniles frequently settle upon oysters the converse is rarely true (Mike Parsons pers. comm.). This raises the suggestion of whether juvenile slipper limpets may graze over newly settled oysters, particularly in heavily infested areas, and therefore directly impact on the oyster fishery.

Another feeding aspect of interest is the capacity for filter feeders to consume both their own and competitors larvae. Pechenik and co-workers explored this aspect and showed that not only do adult oysters consume larval slipper limpets and adult slipper limpets consume larval oysters but adult slipper limpets also consume their own young (Ref. 32). Although this may sound a disadvantage it should be noted that in the presence of phytoplankton this consumption rate was reduced and in certain cases large slipper limpet larvae were actually rejected by the adults. It is possible that this strategy may allow slipper limpets to either re-absorb this biological resource if environmental conditions are limiting, or reduce the level of cannibalism if conditions are not.

In summary, slipper limpets are likely to be able to out-compete bivalves as they can adopt a number of feeding strategies.

A.3.3 Environmental Tolerance Slipper limpets can tolerate a wide range of salinities ranging from 18ppt to full salinity (Ref. 25). It can also thrive in both clean and muddy water environments (Ref. 25). The upper temperature limit for larvae is quoted as 30°C (Ref. 25). Lower temperature limits for adults are normally quoted as near freezing with extensive work by Ref. 29. Ref. 25 quotes a 25% mortality of the slipper limpet population following the exceptionally cold winter of 1962-63 where temperatures were 4-5°C on the south coast and 3-4°C on the east coast for a couple of months. The ability of slipper limpets to tolerate such a wide range of salinities, turbidity and temperatures allows them to extend throughout an estuary from headwaters to the mouth.

Depth requirements remain uncertain. Slipper limpets tend to be found in shallow sheltered coastal areas with the majority of high population growth areas in <30m depth. However, recent trials by French workers have shown that individuals are not adversely affected by depth or pressure (Michel Blanchard pers. comm.) Consideration of sea dumping in deep pits >80m depth was rejected in Marennes (Ref. 5). It was feared that redistribution of animals could spread infestation if animals were to remain alive unless the stock were capped with material to smother them. It is probably more likely that slipper limpets do not have a set depth requirement, other than shallow restricted coastal areas are warmer and have an extended residence time which would help recruitment and may provide greater food.

Slipper limpets do have certain weaknesses relative to bivalves: They cannot tolerate prolonged exposure effects (desiccation or freezing) and therefore are not found in inter-tidal zones. Heavy metals have a greater impact on slipper limpets than bivalves as demonstrated by the absence of slipper limpet infestation on oysters from Restronguet Creek. Another weakness is their

Section A – Slipper Limpet Population Status Andy FitzGerald Page 16 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study avoidance of high energy environments which may be a function of impaired feeding mechanism (Ref. 25) or to their inability to extract themselves if partially buried by mobile sediment.

A.3.4 Absence of Predators As the slipper limpet is adapted to a sedentary life, in its adult phase it shapes the growth margin of its shell to fit exactly the surface upon which it has settled. The advantage of this approach is that once the muscular foot is contracted it is extremely hard to break a slipper limpet off its substrate. The disadvantage is that if an individual in a chain is unfortunate enough to become separated it remains completely exposed with no ability to either reseal itself on another surface or even to seek a new refuge if it has an extended chain on its back. Dabs have been observed to contain slipper limpets within their stomachs although it is speculated that the animals consumed had been exposed individuals rather than actively predated.

Slipper limpets can be attacked by boring gastropods (tingles and drills) and starfish however these are both predators of bivalves. As the slipper limpet’s shell is so much thicker than oysters or mussels these predators can obtain an easier meal by attacking bivalves in preference. This was demonstrated by Ref. 33 which showed that both crabs and starfish would not prey on slipper limpets of a variety of sizes in the presence of mussels. It is however possible that newly settled juvenile slipper limpets with their thinner shells and roaming lifestyle could expose themselves to a higher level of predation than adult slipper limpets.

A.3.5 Distribution Strategies Considering that adult slipper limpets are sedentary they have been remarkably successful at extending their range (see Section A.4). The larval phase allows distribution in the water column and has been implicated in anthropogenic spread via ship ballast water (Ref. 34). In addition, adults have successfully spread by ‘piggy-backing’ on other species such as bivalves either in association with the relaying of infested shellfish or by marine fouling on ships hulls (Section 4.2).

As indicated in Section B2.1.2 fishing activities have been particularly attributed to the success of the species in terms of distribution and abundance. Fishing activities have been suggested as a reason for the heavy infestation of St Brieuc Bay (Michel Blanchard pers. comm.). Furthermore, the absence of bottom trawling has been suggested as a major factor for the low slipper limpet biomass (~150t) with low growth rates reported within Arcachon Bay (France) (Ref. 35).

A.4. EXTENSION OF RANGE

A.4.1 Natural Range and the US Crepidula fornicata is one of a number of Crepidula species that extend the length of the Atlantic seaboard of the US. Figure 5 shows the natural range of the slipper limpet on the East coast of the US from Ref. 28. Ref. 25 indicates this range extends to Mexico. Its southern range may be limited by reduced larval survival to 6 days at 35°C (Ref. 25).

This species has now become a non-indigenous invader to the west coast of the US with Puget Sound in Washington State recording infestation of the native Olympia oyster (Ref. 51). Other Crepidula species have penetrated down the west coast to California and even as far as Hawaii.

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Figure 5 – Slipper limpet natural range on US Atlantic Seaboard

Note: Ref. 28

A.4.2 UK and Europe Ref. 36 provides a good review of slipper limpet dispersion throughout Europe. The slipper limpet spread from the US to the UK and then to Europe where it now extends from the Mediterranean to southern Norway (Figure 6). This process is described in a number of reviews (Ref. 54 and Ref. 25). The first recorded invasive specimens were noted in 1872 at Liverpool and were thought to be associated with imports of the American oyster Crassostrea virginica.

Figure 6 – Slipper limpet range in Europe

Source: ICES 2005, Ref. 54

Stocks were well established off the Netherlands by the onset of WWII where large quantities of slipper limpets were consumed during the War (see Section D.2.1.1). The first record of slipper limpet extension in the Baltic was in 1940 in Kattegat and the Belt Sea (Ref. 37). However, the major extension into France did not occur until the Normandy invasion when large numbers of contaminated vessels and Mulberry Dock sections came to the area from infested UK estuaries. Ref. 5 tracks the time frame of the spread around the French coast since WWII as further waves of contamination occurred with the relaying of shellfish.

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Figure 7 – Slipper Limpet Distribution along French coastline

Note: Source Blanchard (1995). Population magnitude dictated by area of circle.

However, note that since 1995 certain populations have increased massively

(e.g. Bay of Brest: 1998 18,500t biomass 2005 120,000t biomass)

A second wave of invasion around the UK occurred following WWII as vessels were laid up in contaminated estuaries before being sent around the country for breaking. This method of dispersion was extensively considered by Cole in 1950 who ascribed this process for the contamination of Blyth, Milford Haven and Falmouth (Ref. 34). The slipper limpet now extends from Pembrokeshire to Yorkshire in the UK (Figure 8)

Figure 8 – Slipper limpet UK range

Note: Ref. 25

Population establishment must also be influenced by a number of factors beyond an initial seeding colony. Slipper limpets are still only present in low levels in the Plymouth Sound area (Ref. 25) yet a number of contaminated vessels must have passed through this major port following WWII. Furthermore, there have been records of unsuccessful colonisation which may be a result of temperature regime or other factors (e.g. Liverpool and Waddenzee).

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In the early 1970s, slipper limpets were discovered in the Mediterranean around Sicily and Calabria and by 1989 in the Languedoc lagoons on the coast of France.

Range limitation is thought to be strongly controlled by winter minimum temperatures as shown by work on the slipper limpet population which occurs on the German mussel beds in the Wadden Sea (Ref. 33) as discussed in Section A.5.1.4.

Range extension still continues today with the most recent report (1997) of a new sighting from the southern tip of Norway (Ref. 38).

A.4.3 The World Slipper limpet occurrence has also been reported from Uruguay and Japan (Ref. 54). Authorities in Ireland and Australia have identified the slipper limpet as a species with a high potential to invade their coastal waters.

Figure 9 – Slipper limpet range Worldwide

Source: ICES 2005, Ref. 54

A.5. COMPARATIVE ASSESSMENT

A.5.1 European Status The Brittany coast of France has long been recognised as one of the key areas of slipper limpet proliferation and superabundance within Europe. Although a number of estuaries and bays have been affected (Section A.4.2) the key seats of proliferation are considered to be:

Table 1 – Slipper limpet Tonnage in French ‘Hot-Spots’ Area Stocks of slipper limpets (wet weight) Bay of Brest 127,000t (2000) – Note 1 Bay of St Brieuc 450,000t – Note 2 Bay of Mont St Michel 150,000t – Note 3 Bay of Marennes-Oleron 5,000t (1998)

Note 1 - 18,500t (1998 population) – See Appendix B for 1994 population distribution

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Note 2 - 250,000t (1994 population) Note 3 - 100,000 (1997 population) – See Appendix B for 1997 population distribution

The rate of population growth is so significant in these areas that it is hard to place an accurate figure on the up to date tonnage. Some of these areas will be considered in a little more detail as they provide an interesting comparison with the Port of Truro fishery. The Bay of Brest and Mont St Michel Bay are provided as examples of areas where population levels have exploded, whereas the Arcachon Bay (France) and the Wadden Sea (Germany) provide examples of areas where the population has remained relatively low.

A.5.1.1 Bay of Brest The Bay of Brest is considered an interesting case study as the enclosed bay has many similar features to that of Carrick Roads and the Fal estuary system. Both areas are rias with deep water channels, riverine inputs, domestic waste water inputs, industrial port activities, shellfisheries and protected maerl beds. Critically, the temperature regime of the two areas are also very similar with ~8.5°C to ~17.5°C in the Bay of Brest for 2002 (Ref. 27) and 9.1°C to17.2°C for 2002 (Ref. 39).

Population growth in the Bay of Brest provides a stark illustration of how a slowly developing slipper limpet population can appear to reach a ‘tipping point’ beyond which population growth is rapid. Ref. 20 provides an illustration of this process with a review of the slipper limpet population estimates made over the years for the Bay of Brest. Figure 10 shows that in 1995 peak slipper limpet densities were ~400 ind/m2 in a few restricted upper estuary sites whilst the majority of area had <200ind/m2. Within the space of 5 years the extent of the agglomerations had spread with peak densities of >1,000’s ind/m2.

Figure 10 – Slipper limpet population growth Bay of Brest

Note: Ref. 5

1995 peak concentration ~400ind./m2

2000 peak concentration ~4000- 5000ind./m2

Ref. 27 provides a comprehensive account of the reproductive performance in the Bay of Brest following an extensive study from 2000-2003 which showed that 3-4 spawnings occurred each year. As the temperature regime is a major controller of this feature it is reasonable to assume a

Section A – Slipper Limpet Population Status Andy FitzGerald Page 21 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study similar frequency in Carrick Roads considering the similar temperature regime.

A.5.1.2 Mont St Michel Bay Mont St Michel Bay is provided as a case study comparison with Carrick Roads and the Port of Truro oyster fishery as this area too has a large well established flat oyster industry harvested by dredging.

Ref. 4 provides the most recent review of the slipper limpet population status in the Bay of Mont St Michel. This work reviews the population development in the area since the 1997 study (See Appendix B) and the progress with the ARVAL extraction programme (Section B.2.4). The 1995-1996 biomass was calculated as 100,000t within the bay. The population estimate for 2005 has increased to 150,000t. This increase in 8 years is despite extraction in 2001-2005 amounting to nearly 44,000t.

In addition to the stocks within the bay, significant tonnages exist in the Cotentin region off Granville (~29,000t) and to the north of the Mont St Michel Bay, in addition to large tonnages off the Channel Islands.

It should be noted that a significant proportion of the biomass is found in ‘hot-spot’ areas. Within the 129km2 sector of the Mont St Michel Bay area ~52% of the biomass may be found in ~11% of the area where densities are 70-100% sea bed coverage (2,000-12,000 ind/m2). Similarly in the 34km2 Cotentin area ~53% of the biomass may be found in ~14% of the area where densities are 40-70% seabed coverage (500-2,000 ind/m2).

Comparison of the 1997 and 2005 populations show the spread of the population ‘hot-spots’ with the extension of original peak areas and the formation of new aggregation centres. The spread of ‘ribbons’ of high density slipper limpets in the furrows between sand ripples can be picked up by side-scan sonar during the mapping exercises. The gyre circulation within the bay may also re- entrain released larvae to further aid recruitment.

Oystermen operating on the 12 designated beds or ‘Parcs’ close the season in April-May and actively manage the beds by removal of slipper limpets which are then dumped in two spoil grounds to the north of the harvest areas for subsequent collection (Section B.2.4). It is possible that the eastern dumping ground upstream of the ‘Parcs’ may become re-infested by the residual motion of the gyre currents (Michel Blanchard pers. comm.).

A.5.1.3 Arcachon Bay Arcachon Bay is located on the French Bay of Biscay coast to the south of the major Brittany populations. Consideration of the slipper limpet population in this area was provided by Ref. 35 which aimed to investigate why slipper limpets fail to dominate this area.

This area is provided as a comparative case study as it too has an oyster fishery (Crassostrea gigas production 15,000t/yr) and the temperature regime is similar to that of Carrick Roads (annual monthly average range of 9.5C° to 21.0°C with a salinity of 34-36ppt.)

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Ref. 35 describes how the slipper limpet first reached Arcachon Bay in 1969 and gave rise to a current stock estimation of 155t over 5% of the available area. This paper attributes the failure of the slipper limpet to dominate the bay to the limited area of suitable sub-tidal muddy sediments for settlement, the presence of large Zostera beds and the absence of bottom trawl fishing.

As a comparison with Carrick Roads it should be noted that although the oceanographic conditions appear at first glance to be very similar the limitations identified for the Bay of Arcachon do not apply to Carrick Roads. The Port of Truro fishery has extensive shelly muds for settlement, limited Zostera beds (by Trefusis point) and bottom dredging is undertaken. Already the slipper limpet biomass in Carrick Roads far exceeds the stock levels in the Bay of Arcachon.

A.5.1.4 German Wadden Sea The Wadden Sea is provided as a comparative case study as although slipper limpets first infested the area in 1934 (Ref. 40) densities only reach an average abundance on mussel beds of 141 ind/m2. This density and slow pattern of growth to date is similar to that experienced in Carrick Roads.

Ref. 13, conducted in 2000-2001, examined the main population controlling factors of predation, parasitism or life cycle restrictions and winter mortality. Experiences with crab and starfish showed negligible predation in the presence of mussels. Field observations showed no presence of parasites. Observation of larval occurrence over a number of years showed no problems in the production of larvae above 10°C in common with other study areas. The study did show that up to 97% mortality was experienced in extreme cold events which was attributed to prolonged periods of cold easterly winds in contrast to the 11-14% mortality for non-frost areas in southern Europe.

However, a direct correlation between the various mortality rates observed on different beds (26% to 97%) over the two years was not explained in terms of relative exposure. Ref. 40 indicates that the long term temperature range is 2.7C° to 18.1°C. This range is similar to that found in Essex (~2C° to 20°C) where slipper limpets are super-abundant (Section A.5.2.1) despite susceptibility to frosts. This comparison would suggest that winter minimum temperature is not the whole picture. Furthermore, Ref. 33 suggests that slipper limpets may take a number of years to recover from a particularly cold winter mortality event which directly contradicts the findings of Ref. 29 which showed a rapid recovery.

Ref. 33 does accept the possibility of other potential influences such as the shortage of potential settlement areas. Indeed this possibility would also fit in with the findings of Ref. 35 considered in the previous section.

It is possible that winter minimum temperature is an important factor in the establishment of an initial population. However, the proliferation beyond that to reach super-abundance appears to be more complex.

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A.5.2 UK Status The UK slipper limpet range extends from Pembrokeshire to Yorkshire with the main historic ‘hot-spots’ of concentration in the Solent and the Essex estuaries. However, it is not easy to establish the current impact on UK fisheries. Sea Fishery Committees around the coast were contacted from South Wales Sea Fishery to Sussex Sea Fishery in order to try and ascertain the perception of impact upon the fisheries and whether any formal management techniques are in place. Generally, there was little exact knowledge of the population status or whether specific fisheries were affected although a number of respondents were aware of certain areas where stocks had been spotted.

The Conchological Society of Great Britain and Ireland have initiated a new project reported on their website to try and map the extent of slipper limpet coverage (www.conchsoc.org). This society has provided data collected by their members into the NBN Gateway on the web which provides an on-line geographic data base from a number of sources. This data base has been compared with the early reported incidences of slipper limpet spread around the coast.

A.5.2.1 Essex The estuaries of Essex have long been considered the main seat of slipper limpet proliferation within the UK. A number of studies were conducted by MAFF workers from the Burnham-on- Crouch laboratory in the 1950’s when the population impact became apparent (Ref. 29 and Ref. 41). These comprehensive reports provide details on the slipper limpet density and population growth.

Ref. 29, although produced 50 years ago, still provides a valuable source of information on a variety of growth and environmental factors. This study showed that the majority of slipper limpets ceased to feed if temperatures dropped below 5°C. Field observations showed that the very cold winter with associated high levels of cold run-off in 1947 produced a high level of slipper limpet mortality. Walne measured the repopulation of the Crouch on the three successive years when monthly average temperatures mid-estuary for the Roach and the Crouch ranged from ~2°C to 20°C between 1948-1952. During this time population densities recovered from ~100ind. /50m dredge haul to ~1,000ind. /50m dredge haul.

It is notable that the Essex estuaries are colder than the temperatures obtained in Carrick Roads which would suggest less mortality in Carrick Roads. Conversely, the increased summer temperatures in the Essex estuaries may have allowed a high rate of spawning.

In terms of the population density and growth in the Essex estuaries some comparison can be drawn from the 1950 work and recent surveys although methodology has changed. Ref. 29 obtained peak slipper limpet densities of >1,000ind. /50m dredge. Assuming an area of 30.5m2 and a dredge efficiency of 16% this equates to (>205ind. /m2).

Recent quantitative data obtained for the Stour estuary as a result of survey data has been made available via the NBN Gateway. This data from a Unico-Marine survey for Harwich Haven Authority (1998-2000) shows that populations have possibly increased still further with a maximum count of 2,350ind. /m2 (averaged from two samples). Although this peak count is

Section A – Slipper Limpet Population Status Andy FitzGerald Page 24 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study comparable to the high levels found in the Bay of Brest the majority of sites had levels below 1,000ind. /m2.

Essex Sea Fishery confirmed that all of the estuaries in its area were heavily infested although there were no formal management techniques in place (Joss Wiggins pers. comm.)

Ref. 29 by Walne reviewed the density of slipper limpets in the US and comparative environmental conditions. This review showed that in Vineyard Sound on the east coast slipper limpets thrived with a temperature regime -1°C to 24°C and salinity regime 32 to 24ppt with densities recorded up to 1,258ind. /m2.

A.5.2.2 Solent The Solent has also long been recognised as a major seat of population within the UK. The primary reference work detailing chain densities was undertaken in 1973 (Ref. 42). This study showed that within the study area the major area of slipper limpets was located in the eastern approaches to the Solent whilst the deep channel with boulder field and high current velocity on the western approach was much less affected. The methodology for this survey was very similar to that employed in the CEFAS surveys in Carrick Roads using a 0.6m wide dredge with a similar mesh size. Slipper limpet abundance was also reported in terms of chains with most areas having <100 chains/50m haul (i.e. <333 chains/100m2) although some areas exceeded 200chains/50m haul (i.e. >666 chains/100m2). For comparative purposes such a dredge density could have equated to ~200 to 400ind. /m2 (assuming 16% dredge efficiency and x5-10 ind. /chain. This density was marginally higher than the current level for peak concentrations in Carrick Roads.

Data from the NBN Gateway available via the web shows some population data although insufficient coverage to allow a quantitative assessment of biomass in the area. More importantly the 1973 study showed that the major area of slipper limpets did not correspond to a major new find of oysters identified off Calshot and Stanswood to the west of Southampton. Since this time the oyster fishery has been developed although knowledge of the level of slipper infestation and its impact is limited (Ian Carrier pers. comm.). Despite this French merchants consider Solent oysters to be infested with slipper limpets (M. Jambon pers. comm.).

A.5.2.3 English Channel The Solent has formed the centre of slipper limpet population within the English Channel as described in the previous section. Abundance listings from the NBN Gateway show high populations to both the east and west of the Solent. High counts to the east were obtained off Hastings and Newhaven whilst to the west large numbers were also encountered off Bournemouth and Poole.

Poole Harbour has been subject to a massive level of population growth in recent years with a population estimate in 1984 indicating a biomass of ~32t (Ref. 43). Recently ~1,000t of slipper limpets were dredged off the oyster beds and removed as described in Section D.6.6 (Ian Davies pers. comm.).

Slipper limpets have been encountered in Portland harbour and off Weymouth which would

Section A – Slipper Limpet Population Status Andy FitzGerald Page 25 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study appear to be ideal areas for colonisation (Ref. 25).

The initial extension of slipper limpets into Lyme Bay was reported in 1950 (Ref. 31 1950). At the time individual specimens were obtained from a number of sites along the coast with ages estimated from growth curves placing initial settlement from 1946. Now slipper limpets are regularly found on scallops from the bay (Paul Fivian and Peter Tierney pers. comm.). These observations concur with the data available on the NBN Gateway which also show stocks off Beer, Exmouth and Brixham. The MARLIN database also records the presence of slipper limpets in the Salcombe Estuary as logged by the Marine Conservation Society survey (1977- 1982).

Data from the NBN Gateway show low counts of slipper limpets obtained in Plymouth Sound and the adjacent Yealm and Tamar estuaries. Observations by shellfishermen suggest a significant population in association with mussel beds on the Lynher estuary (Dave Hancock pers. comm.). As with Portland Harbour and the Salcombe estuary, Plymouth Sound would appear to be a prime area for future population growth. From personal observation mid-reaches of the Salcombe estuary already support a high number of chains visible at extreme low water springs.

A.5.2.4 South Wales The first report of x6 individual slipper limpets in Milford Haven was given in 1953 (Ref. 44). Now significant levels are found north of Neyland (Phil Coates pers. comm. & NBN Gateway).

A.5.3 Carrick Roads / Fal System Status

A.5.3.1 Historical Slipper Limpet Levels Slipper limpets were first reported in the Helford and Fal estuaries in 1952 (Ref. 34). Despite early attempts to manage the population with the payment of a bounty (see Section B2.2) the population became established. Early recorded populations were encountered at the mouth of the Helford rather than the current main areas of proliferation in the upper Carrick estuaries.

A number of oyster surveys have been performed in the area which also noted the incidence of slipper limpets. Appendix C provides some of the output from the recent CEFAS Slipper Limpet surveys (Ref. 7 and Ref. 8). As can be seen from Table 2, the catch rate remained stable from the 1970’s to the late 1980’s but has increased markedly since 2003. Although some of this increase may well be a function of differing methodology and the specific targeting of slipper limpets, the measured increase concurs with anecdotal observations from the oystermen who have also observed an increase in stock density.

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Table 2 – Carrick Roads Port of Truro Fishery Historical Slipper limpet ‘Chain Recovery’ Date Chains/100m haul 1970’s-1980’s 0-5 1980’s-1990’s 0-5 2002 0-5 2003 5-10 2004 35-40 2005 60-65 2006 70-75

A.5.3.2 Potential Reasons for Population Growth Why should the slipper limpet population suddenly take-off in Carrick Roads? There are a number of potential variables:

-Improving Water Quality. Slipper limpets are vulnerable to elevated heavy metal and TBT concentrations both of which have historically been high in this area. The Environment Agency has placed Integrated Pollution Controls upon the Port of Falmouth to limit TBT impact and treatment to reduce the load of heavy metals since the recent spills of contaminated groundwater from Wheel Jane in the Restronguet Creek. Further studies would need to be undertaken to establish whether a critical water quality boundary restricted population growth. -Biological Limitations. Although the reproductive strategy of the slipper limpet provides many advantages (Section A.3.1) the need for internal fertilisation does limit the chances of reproduction in low colonising densities. The rate of recruitment for larvae will be strongly influenced by flushing rates and resultant residence time within the water body. This would concur with the super-abundance in areas of restricted flushing or with a circulatory gyre. In essence, the greater the flushing, the lower the recruitment and the longer it will take to reach critical mass. A similar ‘tipping point’ in explosive population growth was observed in the barnacle Elminius modestus in Lough Hyne once a critical mass was obtained. Although environmental parameters were considered in this case the limitation of penis length is an obvious one (Keith Hiscock pers. comm.). -Increasing Temperatures. Slipper limpets are capable of multiple spawnings above 10°C with highly successful recruitment above 15°C. In addition winter minimum temperatures have been implicated as highly significant in terms of juvenile survival and therefore the overall level of mortality within the population (Ref. 33). It is interesting to note that the early introduction of slipper limpets to both the Waddenzee and Liverpool associated with shellfish movements both died out. Clearly increasing temperatures could allow increased success. Global warming has been attributed as a cause for population increase (Ref. 14). However, the super-abundance of slipper limpets in Essex estuaries at much lower temperature regimes suggested that this is not the primary consideration. No temperature analysis has yet been performed on the Carrick Roads temperature regime to test this hypothesis, although analysis of winter minimum temperature for Newlyn up to the early 1990’s showed no evidence of a change (Ref. 39).

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A.5.3.3 Population Density Population density can either be expressed as chains/100m2 (usually obtained by dredging) or as individuals/m2 (usually obtained by spot measurements such as with a grab). Each method has its relative advantages with dredges less susceptible to local density variation whilst grabs may be more quantitative as dredges ‘lose’ material. Catch rates from dredges can be crudely converted to population densities by dividing the area of the haul to provide output in chains/m2 and then factoring up to ind/m2 by the average number of ind/chain. The potential No. ind/m2 can then be factored from the assumed dredge efficiency (16%). Such manipulation can allow some cross comparison between areas which have used the two different approaches (i.e UK and France). This exercise has been performed for the mean and maximum catch from the 2006 survey as shown in Table 3.

Table 3 – Carrick Roads Slipper Limpet Density (2006) Parameter Mean Maximum No. chains/100m2 70.6 211 No. ind./m2 3.11 9.3 Potential No. ind./m2 19 58

In reality the peak slipper limpet counts in the ‘hot-spot’ areas are likely to exceed the maximum density depicted in the above table for the reasons considered in Section A.5.3.4 below. For example, the 2006 survey provided a lower peak density than the 2005 survey which is unlikely to be a result of dropping densities (the number of chains/100m2 increased) but may instead be a function of the greater number of sample points and the patchy distribution of high hot spots.

A.5.3.4 Carrick Road ‘Hot-Spots’ The distribution maps of slipper limpet chain catches from the CEFAS surveys (Ref. 6, Ref. 7 and Ref. 8) are re-presented in Appendix C with 2006 results presented in Figure 11.

Section A – Slipper Limpet Population Status Andy FitzGerald Page 28 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

Figure 11 – Slipper limpet 2006 survey of Carrick Roads

43000

Figure 2 TRURO OYSTER FISHERY 42000 Slipper limpet survey Note: March 2006 Chains per 100 m² Ref. 8

41000 Conversion of chains/100m 2 400 to ind./m provided 300 40000 in Table 3 200 100 0 39000

38000

37000

36000

35000

34000

33000 181000 182000 183000 184000 185000 186000

Although absolute chain no./haul did vary slightly between years the overall pattern of distribution is generally the same. East Bank (in the centre of the Outer Harbour area) remains one of the greatest population ‘hot spots’. Although for this and many of the Carrick Road beds population density can vary considerably over relatively short distances. In general, East Bank, Parsons Bank and Mylor Bank all have greater densities on the channel margins of the bed. Peak slipper limpet levels to the east of Mylor off Penarrow Point were not sampled in the 2006 survey as poor weather conditions limited the number of Outer Harbour stations visited. Riverine estuary sections also have hot-spots with the area around Grimes Bar (downstream of Malpas) appearing to be the worst affected.

One key feature is a general correlation between oyster levels and slipper limpet levels (see Ref. 8). There is however one major exception to this pattern with a high number of large oysters at Turnaware Bar and a low density of slipper limpets, making Turnaware Bar a favourable bed to work. It is possible that the high current velocities at the junction of the river and harbour sections are not favourable for slipper limpet development.

There is no data to indicate the presence of ‘hot spots’ to the south of the main oyster working area beyond the CEFAS sampling positions. In 2006 Southampton University performed a series of dives totalling ~4 hours in duration within the area over the St Mawes maerl beds. Only 6 chains were observed suggesting low densities of slipper limpets in this area (A. Jensen pers.

Section A – Slipper Limpet Population Status Andy FitzGerald Page 29 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study comm.). However, it is known that a significant coverage of scallops has become established in the outer reaches of Carrick Roads (Simon Toms pers. comm.) which could form a new population base for the slipper limpets.

It should be noted that the methodology to calculate densities outlined in Section A.5.3.3 uses the ‘average’ chain length obtained from the 2006 survey. Ref. 29 showed that the average chain length increased with proximity to the sea. This concurs with observations made by oystermen on the Carrick Roads fishery that smaller chains are found upstream (Frank Vinnicombe). If the same feature applies for Carrick Roads then the ‘average’ chain length should be assessed on a bed by bed basis. This would mean that in all probability the average chain length for the East Bank near the seaward limit of the fishery would be higher than the 2006 average. Densities would be accordingly higher.

It may be beneficial to recalculate the CEFAS stock assessment on a bed by bed basis. This will help target slipper limpet stock removal and monitor management effectiveness.

A.5.3.5 Population Growth Rates Table 2 provides a qualitative assessment of the population growth although it has been much harder to obtain a quantitative measurement. As indicated in Section A.5.3.1 differing methodology has complicated cross comparisons and even the most recent CEFAS population surveys in 2004, 2005 and 2006 are variable. Common stations used on all three occasions with average chain length and chain number have been used to calculate biomass as shown in Table 4.

The 2004 CEFAS survey estimated a slipper limpet biomass of 67t, which had increased to 164t by 2005, followed by an apparent decrease to 107t by 2006. This rate of population growth remains uncertain as biomass figures were obtained by factoring up the average number of individuals on a chain which had increased from <4 ind./chain in 2004 to nearly 6 ind./chain in 2005. There was therefore some doubt as to whether the 2005 survey may have biased sub- sampling of larger chains which would in turn have skewed the result upwards. The 2006 CEFAS survey results are much more accurately assessed with complete measurement of samples and nearly x3 more measurements than 2005 and are therefore considered more representative. Furthermore, the 2006 results had ~4 ind./chain in common with the 2004 results. Assuming 2004 and 2006 results are accurate a 26% population growth rate would define the values obtained and the estimate (in italics) for 2005.

Table 4 – Carrick Roads, Port of Truro Slipper Limpet Stock Biomass Year CEFAS Survey Potential (16% dredge efficiency) 2004 67t 420t 2005 164t (84.5t) 1025t (528t) 2006 107t 669t Note: 2005 (estimate in brackets) based on 26% population growth (see text).

The overall tonnage of slipper limpets, and the maximum density of slipper limpets in Carrick Roads, is x3 to x4 lower than that measured in the Essex estuaries in the 1950’s and the Solent in

Section A – Slipper Limpet Population Status Andy FitzGerald Page 30 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study the 1970’s (see Section A.5.2.1 and A.5.2.2 respectively). On this basis it could take 30-50 years for slipper limpet levels to get as bad as the super-abundance as seen today in these areas or France. However, it should be remembered that the temperature regime (and subsequent recruitment success) should be much higher in Carrick Roads than the Solent or Essex which may explain the much higher rate of increase, more closely allied to the scenario experienced in the Bay of Brest.

Ref. 26 reviews the dynamics of slipper limpet invasion which shows a low rate of initial growth, a rapid population explosion followed by a decreased rate of growth when an area approaches saturation. Clearly, the expected rate of growth for any slipper limpet population will vary according to the stage of the invasive process. St Brieuc Bay and Mont St Michel Bay have experienced growth rates of ~10%/yr in recent years whereas the Bay of Brest growth rate is probably closer to ~30%/yr. The CEFAS results suggest that the current 26% population growth in Carrick Roads is comparable to that experienced in the heavily infested areas of France. If this rate of population rise is maintained without check then it is possible that the current peak density of slipper limpets could reach super abundant levels (>1,000 ind./m2) in 10-15 years.

This study assumes a growth rate in biomass of 26%/yr and has been used in the targeting of management options. Growth rate and biomass will require periodical monitoring as considered in Section E.1.

A.6. SUMMARY

Slipper limpets are highly successful marine gastropods with a number of unusual features that give them an advantage over many commercial bivalve species. In low levels slipper limpets pose little threat to fisheries or the environment. However, if conditions are right the slipper limpet population can seem to explode after a ‘tipping point’ is reached. At high concentrations slipper limpets will impact upon commercial fisheries and alter the marine environment.

Slipper limpets originating from the east coast of the US have been successful invaders to many parts of the world and this process seems likely to continue.

Direct comparison with levels from other studies in the UK and overseas are not straight forward as methodology differs. Despite this some assumptions can be made to allow semi-quantitative observations to be made:

European comparisons to Carrick Roads and the Port of Truro fishery were made with two case studies of high population growth and two case studies of low population growth. It is considered that conditions in Carrick Roads are more closely allied to areas of high population growth.

UK comparisons to Carrick Roads are similarly diverse. Poole Harbour provides a stark example of population growth from ~32t biomass in 1984 to ~1,000t being removed in recent years. Measurements of slipper limpet densities in Lyme Bay have also increased significantly. Although officially recorded slipper limpet levels in Plymouth Sound and Salcombe estuaries are low, local observation by workers in the fishery show significant

Section A – Slipper Limpet Population Status Andy FitzGerald Page 31 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

levels effecting both mussels and scallop stocks. As with the European examples it would appear that population growth is likely to be linked to the presence of suitable habitat and spreading by man (i.e. trawling/dredging). Again this would suggest that the slipper limpet population in the Port of Truro fishery is likely to expand.

European slipper limpet densities in case study areas provide a potential indication of population growth rates of between 10-30%/yr. Worst case conditions in the Bay of Brest exhibited a growth from 18,500t in 1998 to 127,000t in 2005 with densities in ‘hot-spots’ increasing from ~200ind/m2 to >1,000ind/m2 in this short period of time.

In the UK, peak densities of slipper limpets in Carrick Roads (~60ind/m2) are still below peak levels of ~200ind/m2 which were found in the 1950’s for the Essex estuaries, and in the 1970’s within the Solent. Both of these original breeding grounds now have slipper limpet densities >1,000ind/m2 similar to those observed in ‘hot-spot’ areas in France despite a much lower temperature regime and likely lower recruitment rates.

It is concluded that Carrick Roads and the Port of Truro oyster fishery is under threat from the slipper limpet and remedial management practices should be adopted.

The level of slipper limpet removal needs to be scientifically based on the biomass of the population and the rate of growth. This study considers a 26%/yr biomass growth based on the Carrick Roads and Bay of Brest data.

There are a number of areas in the UK outside of the accepted Essex and Solent ‘hot-spots’ where slipper limpets have gained a foothold and could also become well established. There is great potential for explosive population growth to reach super-abundance in some of these areas. It is suggested that a national monitoring scheme should be adopted to better map the spread and densities reached in these areas. A study of the environmental parameters in these threatened areas could be compared with French ‘hot-spots’ in order to assess the degree of risk.

Section A – Slipper Limpet Population Status Andy FitzGerald Page 32 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

Section B - Management Options

B.1. OVERVIEW

B.1.1 Eradication Complete eradication remains impossible with the present techniques available under the current legislative framework. In 1952 Cole (Ref. 34) reported on the first incidences of slipper limpets in the Helford and Fal Estuaries and believed that it was quite possible to eradicate the species from the area at this early stage. At the time only low numbers of animals had been found, most of which were individuals and a bounty was available to the oystermen to remove the animals. Cole advocated careful and consistent working of the beds by the oystermen as the best means to remove viable chains. Even the use of mercuric chloride and copper sulphate dips were advocated as an extermination technique. Despite these efforts when the initial population was at its weakest, the slipper limpet became firmly established to the degree where the bounty was dropped and collection by oysterman ceased.

B.1.2 Control Population Removal of slipper limpets by either the commercial fishery or by the public authority remains the only viable option to try and maintain the ‘status quo’.

This is especially the case where oystermen would spend longer picking slipper limpets than oysters from dredges. The cost of population control can be viewed financially against the value of the fishery. Indeed mathematic models have been created to assess the impact of slipper limpets on the Bay of Brest and St Brieuc Bay scallop fisheries (Ref. 15 and Ref. 17).

B.1.3 Do Nothing As indicated in Section A.2 slipper limpets pose a threat to both the commercial fishery and the native ecology. Control measures will however impose time and costs on the fishery. This is a disincentive for individuals or authorities to address the longer term viability of the fishery. Public authorities can perceive the issue to be an industry problem and in their own best interest to resolve. The danger is that all bodies believe someone else should do something. However, one of the reasons why the slipper limpet manages to become so well established in certain areas is that it is not immediately perceived as a threat. Its impact is insidious and only becomes apparent when there is a very high level of seabed coverage.

In some areas (e.g. Solent and Essex estuaries) oystermen have learned to live with the slipper limpets. A high level of slipper limpet population on a sandy substrate can be tolerated when you have powered vessels and mechanical winches. This places a burden on the industry in terms of increased sorting time, potentially lower growth rates (increased trophic competition) and bed maintenance (intensive working needed to prevent the laying down of a cohesive muddy cohesive sediment). The cessation of the unique Port of Truro fishery with sailboat and punt would be a sad loss to local heritage and culture.

By the time the ‘do nothing’ option becomes unsustainable (i.e. the fishery on brink of closure or complete loss of habitat) the total cost of population control to the fishery and public bodies is vast and difficult to implement.

Section B – Management Options Andy FitzGerald Page 33 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

B.2. MANAGEMENT TECHNIQUES

B.2.1 Destruction by Chain Harrowing Chain harrowing is a technique used in order to remove soft sediment from the oyster beds then exposing the hard substrate for oyster spat settlement. The technique involves towing chains behind a powered vessel over the beds which resuspends the surface layer of sediment. It is a relatively ‘gentle’ technique and should not be confused with harrowing with a ‘toothed’ dredge that digs into the bed with the aim of bringing a maximum amount of shell and stone to the surface, (the chains in harrowing should also not be confused with the ‘chains’ of slipper limpets).

B.2.1.1 Theoretical Impact on Slipper Limpets Although the technique is intended primarily for oyster management purposes it has also been advocated as a method of keeping slipper limpets at bay. This was reiterated by oystermen from Essex who also believe that dredging to break up chains is beneficial (Joss Wiggins pers. comm.) Indeed in theory as adult slipper limpets can only effectively attach to their ‘home’ settlement surface, any breaking of a chain will ensure exposure of the individual and probable predation. Furthermore, the separation of a chain into a ‘female’ base and a ‘male’ top would potentially reduce sexual viability. Unfortunately, any beneficial aspects of breaking up slipper limpet chains are only likely to be apparent in the short term as discussed below.

B.2.1.2 Potential Risk of Technique There has been no quantitative monitoring of chain harrowing impact on slipper limpets yet French workers overwhelmingly believe that towed gear is one of the principal vectors for dispersion and slipper limpet success. When a chain is broken leaving one predominantly ‘female’ end and one inter-sex or ‘male’ end both short chains can return to viability within a season. The ‘female’ end cannot change sex back into a male (see Section A.3.1 on reproductive advantage) but can however simply recruit new juvenile males onto the chain. The ‘male’ end simply allows the bottom inter-sex or male individual to turn into a female. In essence, the breaking of the chain has in the longer term just created two viable chains with double the settlement potential.

B.2.2 Collection by Fishermen In low levels of infestation collection by the fishermen can be one of the most effective management techniques. This management practice was adopted in Carrick Roads during the early years of infestation with the payment of a 5 shillings bounty (Ref. 1).

Collection of slipper limpets by fishermen poses two key problems: capacity and cost.

Capacity for vessels in the Port of Truro Oyster fishery is considerably lower than the large scale options considered in Section B.2.4. If conducted during the oyster fishing season spare capacity

Section B – Management Options Andy FitzGerald Page 34 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study for slipper limpets would vary. Initially, landings may be limited to ~1bag/boat/day (i.e 25kg) yet as the season progresses more time may be available for sorting and this could increase to 5- 10bags/boat/day (125-250kg), (Tim Vinnicombe pers. comm.)

If oystermen were just to target slipper limpets there would be insufficient financial motivation at the French collection costs quoted in Section B.2.4.3 (~£0.01-0.07/kg). Removal as by-catch during oyster dredging operations may be possible although the spare capacity on board is limited particularly for the punts in the river section. Based on the assumption that a vessel lands 50kg/day the following bounty could be considered:

-Bounty to Oystermen – French Rates Payment at the rates cited for French studies for 50kg/day would equate to an income to the oystermen of £0.50-3.50/day. Oystermen are unlikely to be willing to participate at this level.

-Bounty to Oystermen – 100% subsidy of losses Collection of ~50kg slipper limpets/day would reduce sorting rates and was estimated to reduce oyster landings by ~½ bag of oysters due to reduced picking time (Frank Vinnicombe pers. comm.). At ~£1.60/kg and 25kg/bag this equates to a loss of £20/day.

When slipper limpets were last collected by the oystermen 4-5 years ago two vessels compared the impact of sorting slipper limpets on oyster landings over a 2 day period and calculated a bag of slipper limpets to cost ~£50/bag (Tim Vinnicombe pers. comm.) This level of payment would equate to £2/kg and would not be financially achievable.

-Bounty to Oystermen – 10% subsidy of losses Based on the example provided above and a 10% subsidy for losses a bounty of £0.20/kg could be paid providing a small income of £10/day for a landing of 50kg/boat/day.

Figure 12 – Sorting table for oysters with a haul of slipper limpets

Source: This study

However, even at this level there remain both financial hurdles to achieve this price and ethical objections from some parties who do not believe that the oystermen should be paid for improving their own industry. It has been remarked by some oystermen that removal of slipper limpets should be a mandatory activity for all oystermen on pain of exclusion from the fishery. Indeed Ref. 1 provides the suggestion of a bylaw to force fishermen to remove slipper limpets; however, the current Regulating Order does not provide these powers even if this approach were deemed

Section B – Management Options Andy FitzGerald Page 35 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study acceptable. However, Ref. 1 also highlights the potential that the Environment Act can be used as a mechanism for EA fishery bylaws for marine conservation.

A further suggestion may be to provide an incentive through the licence fee. This could consist of a fixed component payable by all vessels, and a variable component according to beneficial work performed on the fishery in the previous season (e.g. landing of slipper limpets).

B.2.3 Collection by Harbour Authority Unlike the oystermen’s sail boats or punts whose use is confined from October to March the Port Authority vessels could be used over a brief period following the closure of the oyster fishery but prior to the onset of spat settlement. Although the use of a powered vessel for bed maintenance is possible by the Harbour Authority outside of the oyster season, in practice such activities would need to fit in with other commitments. In consequence, some removal is likely to be undertaken in ‘quiet’ times during the winter season.

During this survey 40kg of slipper limpets were recovered in 2 hours by manually hauling. With the use of a winch and a wider dredge, recoveries of 50kg/hr should be possible allowing 1,000kg collection in 20hrs vessel time/week or 12.5t in half a season (~3day/wk for 3 months).

It is hoped that slipper limpet removal could be achieved as part of a wider maintenance of the oyster beds which could also include: chain harrowing, weed removal and the laying of cultch. All considerations for maintaining the oyster beds will require an ‘Appropriate Assessment’ for which negotiations are already underway with English Nature and the Environment Agency (see Section B.3.1).

Figure 13 – Small oyster dredge used for slipper limpet collection

Source: This study

Section B – Management Options Andy FitzGerald Page 36 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

B.2.4 Collection by Suction Dredge

B.2.4.1 The ARVAL Programme The French operate an ARVAL programme whereby ~30,000t/yr of slipper limpets are removed by suction dredge from St Brieuc Bay and Mont St Michel Bay. Slipper limpets are removed from the seabed via a modified 2m wide dredge head which removes the surface sediment. SECMA operate the aggregate extraction vessel Cotes D’Armour with an 800t capacity out of Portrieux in northern Brittany. Although this vessel is primarily employed to extract a variety of marine aggregates it is utilised for slipper limpet removal for a limited period each year.

As indicated in Section A.5.1.2 this programme has removed significant quantities of slipper limpets from the two operating areas over a number of years with 43,000t alone being taken from Mont St Michel Bay (Ref. 4)

B.2.4.2 Technique Limitations There are a number of limitations to the use of a suction dredge.

-Water quality impact. All fine sediment removed with the slipper limpets is screened on the vessel and returned to the sea. In areas of high dispersion this is not considered problematic. However, in restricted water bodies resuspension is of concern (Ref. 5). Furthermore, the nature of the sediment type will also greatly influence the potential degree of impact with the greatest risk posed by fine anoxic muddy sediments which could give rise to considerable dissolved oxygen sag, resuspension of ammonia and hydrogen sulphide.

Figure 14 – Slipper limpet removal using suction dredge

Note: Ref. 4 Slipper limpets suspended in a stream of seawater and screened on deck with dirty water returned to the sea.

-Substrate disturbance. On a level seabed with no obstacles less than 10cm of sediment will be removed with the surface layer of living slipper limpets. However, if bathymetry or boulder fields disrupt the wide suction head then the dredge can bite in deeper on one side.

Section B – Management Options Andy FitzGerald Page 37 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

Figure 15 – Diver Surveys of Suction Dredge Operation

Note: Ref. 4 Furrow created by 2m wide head of suction dredge creating clear path of extracted slipper limpets.

-Extraction efficiency in marginal areas. As the dredging operation is paid in terms of tonnage landed there is a disincentive to work both partially cleared areas and muddy areas which require greater purging to clean the shells. -Limited depth. The suction dredge can only operate in <20m depth as dictated by the length of the dredge pipe. -Limited vessel availability. In areas distant from the central processing plant a large amount of expensive vessel time is spent in steaming to and from sites. Such sites have operators who have expressed the desire to hire in another dredger for an extended period of intensive concerted work in their fishery to remove major quantities of slipper limpets (M. Jambon pers. comm.)

B.2.4.3 Extraction Costs Large scale industrial collection costs by suction dredge have been calculated for a 300t wet weight/day treatment system. Estimates in 1996 ranged from 40F/t (Ref. 2) to 60F/t (Ref. 2 Annex 4). This equates to ~£4.00-6.00/t or <£0.01/kg. More recent estimates for the same system in a more distant working area provide a rate 2 to 3 times higher (see below).

Collection costs have been estimated in the recent French review for the Bay of Brest (Ref. 5) for a variety of collection options to achieve removal rates of between 3,000-9,000t/year. A summary of the options and their respective cost were:

Table 5 – Slipper Limpet Collection Costs – French Experience (Ref. 5) Vessel Type Capacity/trip Cost/Yr (3,000t/yr) Cost/t Suction dredge 530t 54,000€/yr 18€/t Oyster Barge 50t 75,000€/yr 25€/t Goemoniers 5t 300,000€/yr 100€/t

As can be seen the cost/t is significantly affected by the vessel capacity. All these vessel options have a larger capacity than the vessels currently utilized in Carrick Roads.

Section B – Management Options Andy FitzGerald Page 38 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

One further possibility in order to utilise this option in Cornwall would exist if the French suction dredger were employed to remove previously collected slipper limpets through a separate contract for maintenance dredging in the area. The Cotes D’Armour vessel has a capacity of ~800t which is sufficient to remove all of the Carrick Road population in one go! This idea was discussed with the barge operators who were willing to consider such an approach if the extended travel distance could be justified by an external dredging contract requirement (Pierre Le Coz pers. comm.). Such a concept should be explored in the event that the Harbour Authority is considering major channel maintenance operations.

B.2.5 Stock Storage There is a need to consider temporary storage of slipper limpet stock between collection and treatment/utilisation. In some cases storage can actually be a method of killing slipper limpets and allowing flesh to rot before utilising the shells once they are clean. Ref. 5 considers a variety of storage options for processing between 3,000-9,000t/yr on an industrial scale. Options included: -On the seabed -On the land -On a barge

These options have been adopted and trialled to some degree by a number of workers in the past as considered below in greater detail.

B.2.5.1 On the Seabed. The seabed storage technique is currently practiced in the Bay of Mont-St Michel with two deployment areas to the north of the flat oyster beds (Ref. 4). Although this approach has the advantage of unlimited storage it does require specialised collection techniques such as the suction dredge operated as part of the ARVAL Programme.

B.2.5.2 On the Land. Land storage is considered problematic as stock quickly degrade and start to die. Walne (Ref. 56) cites that slipper limpets can be maintained alive in the air for several days. In practice the smaller animals die within a day and liquors are continuously released. Indeed slipper limpets are stored by CEMAR at the Pontrieux facility in a large holding bay for up to 48 hours prior to processing to allow a maximum draining of fluids before odour problems become too great (Pierre Le Coz pers. comm.)

The Bay of Brest proposal (Ref. 5) considered land storage at three potential sites following large scale stock removal with no need to maintain stock alive or in good quality. However, the potential odour problems were considered to be a major limitation to finding suitable sites for this approach.

B.2.5.3 On a Barge. The Bay of Brest proposal (Ref. 5) considered the use of a large scale barge from Holland

Section B – Management Options Andy FitzGerald Page 39 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study capable of storing up to 2,000t/load. This approach was considered a good solution as it allowed storage in close proximity to the collection zones which minimised transport times for the collection vessels. However, the hire of such a large capacity specialist barge was costed at an estimated 200,000€/yr and there was concern about maintaining the slipper limpets in good condition without rotting.

Modifications of this approach on a small scale could provide a good scheme for a management scheme in the Port of Truro fishery.

B.2.6 Stock Destruction In some cases the ‘storage’ option considered in the previous section can actually be a method of killing slipper limpets. This could then be the ultimate disposal site or could be used to allow the flesh to rot before utilising the shells once they are clean. The same options considered in the previous section as also used here:

B.2.6.1 On the Seabed. A number of schemes have used this approach for disposal with what appears to be a variety of environmental advice from the authorities. Both Ref. 3 and Ref. 5 cite a trial in 1995 near Fouras to the south of La Rochelle where a cooker was installed on the Island of Aix for the cooking of slipper limpets at 30t/hr which floated to the surface of the vat and were then discharged back to the sea. Observation of this trial indicated that that the technique was effective in both killing the slipper limpets, larvae and separating the flesh from the shell. However, there were some doubts as to the potential acceptability of a large quantity of organic matter being discharged on the seabed (Michel Blanchard pers. comm.). Ref. 5 also indicated that the technique was expensive.

Ref. 3 and Ref. 5 mention the use of slipper limpets to fill embankments to form hardened tracks for access to the oyster beds. This trial again in the La Rochelle area involved the dumping of slipper limpets in an inter-tidal area at HW before attempting to crush the shells at LW with a ‘Monster Truck.’ This attempt met with limited success as the caterpillar tracks just pushed a large quantity of the shells into the sand allowing some to survive and others to rot in-situ (Michel Blanchard pers. comm.) Ref. 3 and Ref. 5 both suggest the trial was not considered favourably due to the nauseous smell released as the flesh rotted.

Seabed disposal has been proposed for the Bay of Mont St Michel using a Dutch dredge to intensively remove slipper limpets from effected beds prior to dumping in a hole to allow the majority of buried animals to die allowing large scale cleaning of the whole fishery over a few months (M. Jambon pers. comm.) This is a similar approach to that which has been used in both Holland (Ref. 5) and Poole in the UK.

Oystermen in Poole had initially proposed to dredge and remove slipper limpets from within the harbour to be disposed of offshore in the spoil grounds of Swanage Bay (Ref. 45). The legal constraints of the responsible agencies forced the operator to place ~1,000t of slipper limpets within the fishery of origin (i.e. in a pile within Poole Harbour). Although buried stock died, surface animals survived (Ian Davies pers. comm.) The legal aspects of marine disposal or use

Section B – Management Options Andy FitzGerald Page 40 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study for cultch are considered in Section D.6.6.

B.2.6.2 On the Land. Land disposal was an easy option in the past with the placing of bags of slipper limpets above the HW mark on the foreshore to die. This approach is cited as a method for large scale disposal in the 1997 JNCC review of non-native species (Ref. 46) and has been used both in Carrick Roads (Colin Frost pers. comm.) and in France (M. Jambon pers. comm.). This method was recently proposed for Puget Sound on the west coast of the US as a means to ‘cure’ shells on the beach for around a month prior to use.

A small mass of slipper limpets (~5t/yr) continues to be cleaned from some of the muddy marginal beds by a limited number of oystermen before placing upon the foreshore away from urban areas in order to allow the shells to rot clean (Jon Bailey pers. comm.). Environmental considerations in France (M Jambon pers. comm.) will no longer allow this approach and are likely to be frowned upon in the UK (Simon Toms pers. comm.)

B.2.6.3 On a Barge. Unlike the storage option considered in the previous section this approach aims to kill slipper limpets by either brine immersion in a salt solution or smothering in a sealed bag. Once the shells had been picked clean by animals in the water they were fit to return to the bed as cultch. These approaches were adopted on a small scale in around 1997-1998 on the Carrick Roads fishery when a platform was operated at Mylor close to where many of the sail boats operate. Brine dipping has long been advocated as a quick small scale method for killing slipper limpets (Ref. 46).

There may be scope to modify this approach to an acceptable low cost technique if the methodology were designed with sufficient controls to ensure a minimal impact on the surrounding sediment and water column.

B.2.7 Removal by Pheromone Traps Pheromones are complex chemicals released by one individual with the aim of acting on another. Specific pheromones can be used for attraction either for reproduction or for settlement (e.g. oysters). Larval slipper limpets are known to be attracted by adult slipper limpet pheromones and this could therefore be a potential basis for a trap.

Pheromone traps have long been used as a means for successful control of nuisance insect species. This technique usually involves using a female sex pheromone to lure males to a trap where they can be sterilised before release to the wild where, once sterile they can compete against viable males.

Development of marine pheromone traps is less advanced with recent development in the US by the University of Michigan for controls for invasive species such as the lamprey in the St Lawrence seaway and the round goby. In the UK workers have recently worked with English Nature (EN) and the Environment Agency (EA) on development of a pheromone trap for the

Section B – Management Options Andy FitzGerald Page 41 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study alien signal crayfish which is out-competing the native European crayfish and widely regarded as a nuisance species (Ref. 47 and Ref. 48). This work was successful at providing a trap that could selectively target the nuisance species without capturing the native species.

However, in the case of the crayfish study the pheromone sex traps were not particularly more effective than normal food traps and this applied research programme came to an end (Gordon Watson pers. comm.) This approach although promising requires a long research period possibly as long as 9 years before specific pheromones can be isolated and artificial synthesis could be undertaken (Paul Stebbing pers. comm.). This observation concurs with the work on the sea hare (a sea slug) where research on mating agglomerations identified a pheromone termed ‘attractin,’ which in subsequent years ended up as a cocktail of pheromones – including other equally excitingly named compounds ‘seducin,’ ‘enticin’ and ‘temptin’!

Ref. 49 also considered the work of CEFAS Lowestoft on pheromones where finfish and crustacean pheromones have been successfully isolated and synthesized (Andy Moore pers. comm.). The UK has a high level of expertise in applied pheromone research with workers in both academic institutions (e.g. Portsmouth and Hull Universities) and agencies (CEFAS Weymouth and CEFAS Lowestoft). In addition, leaders in the slipper limpet field are also looking into pheromone techniques (Jan Pechenik pers. comm.)

In conclusion, the technique has great promise but cannot be considered a quick fix. It is suggested a national or even international funding programme is adopted. Initial enquires for such funding from EN and EA have proved unsuccessful (Roger Covey and Simon Toms pers. comm.)

B.3. INTEGRATED MANAGEMENT There is no ‘magic bullet’ for sorting out the slipper limpet problem. There are a number of potential means to manage the fishery some of which are strongly dependant on the economics of utilisation. In essence, a number of short term and long term measures will need to be addressed in order to solve this problem which will require integrated management.

B.3.1 Appropriate Assessment Techniques to manage or utilise slipper limpets within the area are likely to require an ‘Appropriate Assessment’ (AA). Potential activities of interest include disturbance of beds during collection, marine storage of stock, deposition of stock and the laying of slipper limpet shell for cultch. Furthermore, other related oyster management techniques such as chain harrowing and even oyster dredging are also likely to require assessment of whether they are deemed ‘significant’ in terms of their potential impact.

Under the Natural Habitats Directive (1994) fishery activities in European Marine Sites (EMS) are required to have an AA if activities are considered to have a significant impact on natural habitats. Since coming into force these regulations have placed a significant burden on industry with a degree of confusion for all parties. SEAFISH have been working to help industry address these needs (Ref. 50) and have an advisor to help in the AA process (Mark Gray pers. comm.). Ref. 50 shows that to date the majority of AA’s have involved seabed dredge activities, although these are not exclusively oysters (Mark Gray pers. comm.). A significant proportion of these

Section B – Management Options Andy FitzGerald Page 42 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study applications to date have taken over 12 months to process and have delayed implementation of new projects.

Carrick Roads has been designated as a Special Area of Conservation (SAC) and an AA may well be required for management activities. The need for an AA need not be a massive problem or burden to the industry. Examples of an oyster dredging AA include the study performed by SSFC in 2005 for the Solent which simply showed that the boats involved in the activity were operating outside of the key areas of concern and were not considered to be causing ‘significant’ damage to attributed features (Mark Gray pers. comm.).

Initial dialogue has been undertaken with both EN and the EA to identify the key areas of concern. In some cases the same activities are considered important for differing potential impacts. For example, chain harrowing to clean beds prior to oyster spat settlement is of interest to EN in terms of its potential impact upon the maerl beds (Roger Covey pers. comm.) whereas it is of interest to the EA in terms of its potential impact upon buried Alexandrium spores below 5cm depth in the sediment which if released could trigger toxic algal blooms (Simon Toms pers. comm.). Both agencies also have concerns regarding the potential re-suspension of potential harmful heavy metals and persistent organics such as TBT. In general, there is concern over all activities that give rise to re-suspension as demonstrated by the recent ban of scallop dredging in the outer Falmouth harbour (Simon Toms and Peter Tierney pers. comm.).

Owing to the inter-related aspects of many oyster management issues it has been proposed that slipper limpet aspects should be considered in conjunction with a wider AA for the whole fishery (Roger Covey pers. comm.). It is hoped that this approach will present a minimum of work, time and cost for all parties. In order to best facilitate the AA process with the minimum of delay and difficulties ‘Pre-Assessment’ consultations have already been undertaken between affected parties.

Generally, activities that have been conducted historically without impact (e.g. oyster dredging, limited laying of cultch and gentle chain harrowing) are considered ‘usual’ and will not require comprehensive assessment. Major changes to operations or the scale of operations, however could require greater study. Fortunately, once an initial baseline assessment is conducted ongoing annual activities should not require repeated additional studies. This approach has been adopted by Ports with respect to maintenance dredging activities and under the Natural Habitats Directive.

B.3.2 Slipper Limpet Removal Slipper limpet removal should be targeted at a rate equal to, or greater than the rate of population growth. At the moment this stands at a target removal rate of between 16-100t/yr (see Section A.5.3.5 for assumptions).

Consistent removal by all the fleet throughout the season could achieve this level of capture (assuming ~5t/vessel/yr). However, in reality under the current fishery operating regime it is unlikely that all vessels will participate and that some will be more effective than others. Removal from the fishery is also likely to be highly variable throughout the season with a low level of landings at the start of the season, when most boats will be actively targeting oysters,

Section B – Management Options Andy FitzGerald Page 43 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study increased landings mid-season, as oyster landings become reduced and sorting time is less pressured and low landings at the end of the season as the number of operating boats is reduced (Tim Vinnicombe pers. comm.)

Removal by powered vessel by the Port of Truro Harbour Authority is a vital aspect for heavily infested beds (e.g. East Bank) that have been abandoned by the fishery. Ref. 20 has shown that the invasive process is powered by aggregation of the most dense population centres. Therefore targeting of these bases must be a primary objective. Removal by the Harbour Authority need not be restricted to the current fishing season. This activity could be conducted in association with other oyster bed management activities as considered in the following section (e.g. chain harrowing, weed removal, laying of cultch). Progress in this area will require the completion and acceptance of an Appropriate Assessment (see Section B.3.1) and resources to undertake such activities. Unfortunately, the level of income from the fishery by licence fees alone is unlikely to provide sufficient income to warrant increased expenditure on such activities. Ironically, comprehensive management of the beds could encourage more licence uptake and income from the fishery to help fund these activities - a classic ‘chicken and egg’ scenario.

The payment of a bounty for slipper limpets to the oystermen arouses strong feelings from a number of parties. Some individuals believe that no bounty should be paid and that slipper limpet removal should be mandatory and enforced by regulations. Others believe that a bounty should be set at the level of lost earnings (see Section B.2.2). There is a spectrum in-between where there is scope for reasonable compromise whereby some recompense is granted for losses but the removal of slipper limpets does not become profitable enough to actively target the species. Perhaps a suitable ‘carrot and stick’ approach could be penalties to enforce a limited collection of slipper limpets coupled with a payment of a kilo rate on the basis that removal zones and quantities are noted. This will help track the effectiveness of population control. The concept is not without precedent - after all Japanese whalers are still allowed to hunt for ‘research’ purposes!

It is suggested that slipper limpet removal and storage will need to be conducted in a co-ordinated manner to ensure that materials are handled correctly and records maintained. In consequence, the collection and storage of slipper limpets removed by the oystermen will need to be undertaken by either the Harbour Authority of an intermediary acting on behalf of the Oyster Management Group. A system of bags possibly demarked by colour tags for each oyster boat will need to be established and administered along with a scheme of record keeping. Further potential duties of this support role to facilitate all stages of management and utilisation are outlined in Section E.2.2.2.

B.3.3 Targeted Chain Harrowing/Laying of Cultch Oyster spat require hard substrate to settle upon which can be provided by chain harrowing to clean stone and shell in-situ or by laying cultch (usually broken shell) into an area.

The use of crushed slipper limpet shells for cultch as a means of utilisation is considered more fully in Section D.4.3. Any cultch application will have to be considered in conjunction with the provision of cultch from the vast available scallop shell resources.

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Chain harrowing has historically been spasmodically performed in the estuary. This year work has been conducted off Maggotty Bank in the ‘River’ section and off Parsons Bank in the ‘Outer Harbour’ section.

Integrated management could aim to target specific beds in an agreed process of either returning neglected historical beds into productivity or to maintain and improve existing beds. The balance between chain harrowing and cultch laying will vary on a site specific basis and is likely to require differing levels of activity and duration according to the limits as specified in the AA. For example, gravelly beds close to the channel (such as the margins of East Bank) may be more suitable for chain harrowing than more muddy beds closer to Mylor which might present a greater environmental risk and could be better served by cultch. However, extensive chain harrowing on the East Bank should perhaps only be considered following intensive slipper limpet removal from this highly infested area. As the oystermen do not currently work this area due to the high levels of slipper limpets such removal may be more appropriately performed by a powered vessel which does not therefore limit this activity to the fishing season.

In this fashion the Port of Truro Oyster Fishery may plan to have a programme of activities covering a number of years with sequential efforts targeted at agreed priority beds.

B.3.4 Modeling of Fishery Value vs. Fishery Maintenance Costs The Bay of Brest case study and the impact of the slipper limpet on the scallop fishery (Section A.5.1.1) provide a good illustration for the Port of Truro oyster fishery management. Ref. 15 and Ref. 16 provide a financial modelling tool to assess the cost of different fishery management options, the impact of the invasive process and licence fee costs. It is suggested that once the trial season has been conducted and utilisation options have been more fully explored this approach should be considered as a management tool particularly if the licence fee cost is to be linked with the cost of maintaining the fishery.

B.3.5 Long Term Measures The use of pheromone traps as considered in Section B.2.7 is worthy of consideration on a National and International basis. During the course of this study experts in this technology have been identified both in the UK and the US with interest in participation also from France. The time-frame and cost of this development precludes the work being financed by the Port of Truro fishery alone. Indeed the next round of European Fisheries Funding (EFF) has a strong component to support sustainable fisheries and minimise environmental impact and as such the pheromone trap approach should be a good candidate for support.

A number of bodies have been approached including EN and EA to ascertain whether National funding may be available for this research.

B.4. SUMMARY Eradication of the slipper limpet problem is not currently possible. The ‘do nothing’ option cannot be adopted unless there is an acceptance that the current oyster fishery methods (i.e. dredging under sail and manual hauling) are put aside. Population control is possible with concerted effort now.

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An integrated management technique is therefore proposed that links fishing activities and bed maintenance to slipper limpet removal.

Short term options will include removal of incidental slipper limpet by-catch by oystermen and specific targeting of heavily infested un-worked beds (e.g. East Bank) by the Harbour Authority. These aims can be achieved in a proposed trial season.

Medium term actions will require ongoing monitoring of slipper limpet growth and the targeting of slipper limpet stocks to be removed on an annual basis. The cost of the management programme is hoped to be met primarily by the utilisation options. However, if this fails and public funds are not forthcoming scope exists to link management costs to the license fees. Scope may exist for a two phase license fee linked to beneficial fishery activities.

Long term potential removal options such as pheromone traps could be effective although the prohibitive costs of development will dictate a National or European approach to this management option.

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Section C – Extraction/Treatment Techniques

C.1. OVERVIEW A number of extraction/treatment techniques have been developed and trialled with varying success. The selection of methodology is dependant on the utilisation option selected and the scale of operation. Waste disposal options have not been considered in this report as it is unlikely that oystermen or the Harbour Authority will consider paying to remove slipper limpets to commercial disposal companies. If required a review of waste disposal options in the region to Animal By-Product regulation standards is provided in Ref. 49.

C.2. SEPARATION

C.2.1 Manual Shucking Manual shucking was clearly not appropriate to the industrial scale of processing required by the French operations (~300t/day) and therefore not considered in their proposal. However, removing the flesh by hand, although time consuming, remains the best approach to obtain a quality product if a high value application is required for the flesh. Shucking can be achieved by use of a winkle pin, blunt instrument or if quantity dictates even high pressure blowing.

In all cases the best results appear to be obtained when a whole chain is held in one hand and processed from the bottom upwards. This allows shucking one shell at a time in relatively quick succession dropping the clean flesh into one pot and the shell discard into another. This approach prevents exposure of the clean flesh to dirty shells. Care needs to be taken in the pre-treatment process to try and remove the smaller slipper limpets at the terminal position of the chain as these are not efficient to process and should be prevented from contaminating the flesh of shucked animals. Processing rates obtained in the study, flesh yields, wastage and projected costs are considered in Section D.5.1.

Pre-treatment of chains prior to shucking is a necessity as separation of the chains when alive is extremely hard and vastly adds to the time required for shucking.

C.2.1.1 Pre-treatment Blast Freezing. Freezing is an effective way of killing these animals allowing easy separation of chains during shucking. Unfortunately, this approach is dependant on access to suitable large scale facilities which would have implications for capital and operating costs. Ammodytes Ltd. in St Ives does have access to suitable freezers. However, their spare capacity is subject to fluctuations in the availability of other species (e.g. landings of mackerel). Investment and running of a large purpose built freezer unit for slipper limpets in the Falmouth area would be a poor use of resources as 80% of the animal is inert shell of low value. In contrast, blast freezing and storage of the final shucked flesh may be more cost effective.

C.2.1.2 Pre-treatment Brine Dipping. Soaking in a concentrated salt solution has been advocated as one method of killing slipper limpets (Ref. 29 and Ref. 46). Indeed the inability of slipper limpets to remain completely closed

Section C – Extraction/Treatment Options Andy FitzGerald Page 47 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study in such a hostile solution differs markedly from bivalves such as oysters. In consequence, the use of brine dipping is an effective way of killing and clearing slipper limpets off live oysters either during processing prior to dispatch to market or possibly even on board the oyster boats. The beauty of the method lies in that it is quick and does not expose the underlying oyster to risk of damage (unlike manual knocking off slipper limpets).

The use of brine dipping can be used on cleaned fresh slipper limpets before processing. Batches of stock can be prepared rapidly with death occurring in ~1 hour. A brief freshwater rinse can then be applied immediately prior to shucking. The advantage of this method is that processing is not tied to the availability of blast freezing facilities and can therefore be cheaply employed in the Falmouth area.

C.2.2 Ensilage Ensilage is the process whereby biochemical processes allow the breakdown of the flesh following the addition of suitable chemicals at an adjusted pH. Three main approaches used in different sectors are: -Acid ensilage -Fermentation -Alkaline Ensilage

All three methods were trialled upon slipper limpets by a French study in 1993-1994 (Ref. 2) and are reviewed for their suitability for the treatment of animal by-products in Ref. 49. These are outlined in the following sections.

C.2.2.1 Acid Ensilage This method relies on directly adding an acid to drop the pH below pH4 at which level enzymes allow the complex proteins to be broken down to their simple components. This method using formic acid is extensively used in the UK within the aquaculture industry for on site storage of fish farm mortalities (Ref. 52).

Unfortunately, this technique is not appropriate for whole shellfish as the acid just reacts with the shell to liberate carbon dioxide without dropping the pH (Ref. 2, Appendix 2).

C.2.2.2 Fermentation Ensilage This method also relies on an acid drop of pH although in this case the acid (usually lactic acid) is produced by bacteria through the fermentation of a sugar source. This method has been used in the aquaculture and agriculture sectors although its use in animal by-product applications in the UK is currently not favored.

This method was not particularly effective as the pH only dropped to ~6.4 to 6.8 (again as the solution will have been buffered by the shell). Although the method did manage to liquefy the flesh after 3 weeks, the liquor had a strong smell with high coliform and sulphate reducing bacterial levels.

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C.2.2.3 Alkaline Ensilage This method relies on the raising of the pH to around pH11 with the addition of an alkali. Unlike the acid methods outlined above which can take place with enzymes at room temperature alkaline techniques usually involve a heating stage. Ref. 2 proposes the use of sodium hydroxide at 80°C for 2 hours although a test at ambient temperatures also achieved a positive result after an extended period.

The effectiveness of this method was considered in Ref. 2, Appendix 2 which showed the technique was effective in eliminating bacteria and gave a positive result in removing the flesh. The scheme had little pricing information and the harsh operating conditions would dictate stringent Health and Safety precautions. The scale of stock present in the Port of Truro fishery is unlikely to warrant the high level of expenditure likely to be needed for this approach which was proposed for large scale input for trout or cat feed (Ref. 3).

C.2.3 Freezing and Knocking A trial was conducted during this study to try and produce a cost effective method for mass shucking of slipper limpets using freezing and knocking using existing equipment operated by a local oystermen. This project builds on a similar study undertaken by Cornwall College (David Smethurst pers. comm.) A table of results are provided in Appendix D with results of the flesh yield listed in Table 6.

In summary, the trial consisted of the following: -Pre-clean of shells prior to freezing. -Freezing. To kill slipper limpets and allow ‘chain’ separation. -Knocking. Frozen stock placed in cement mixer to break up ‘chains’ for separation. -Initial grading. Frozen stock placed through winkle sorter to separate small shells. -Knocking. Partially thawed graded stock placed in cement mixer to remove flesh . -Second grading. Partially thawed graded stock placed through winkle sorter to separate flesh.

The technique was effective in grading the shells although it was only partially successful in the separation of the flesh. Problems included: sticking of flesh onto conveyors and chutes, incomplete flesh separation, contamination of flesh from dirty shell, poor flesh quality as tissue was mashed by chains during the knocking stage. It was concluded that whilst rates of separation could perhaps be increased by lengthening the knocking period, the quality of the flesh would also suffer. It was also highly notable that a large quantity of very dirty water was generated by the winkle sorter. Current waste water disposal charges and potable water costs are high within the SW England area (Ref. 49) and would be likely to place a large financial burden if this technique were to be undertaken commercially.

C.2.4 Cooking and Knocking Cooking of the flesh provides an easy means of separation from the shell and has even been used as an effective means of killing and disposing of slipper limpets at sea (see Section B2.6). Ref. 3 provides details of a trial scheme in France to process slipper limpets and separate flesh from shell using cooking. The process can be summarised as:

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Stage 1 – Recovery from sea (industrial scale suction dredge or fishermen collection). Stage 2 – Cleaning and sorting (to remove stones and other shell types). Stage 3 – ‘Dehusking’ (shucking by breaking chains at 35C and cooking at 95C). Stage 4 – Sifting (sorted on a vibrating table allowing flesh to drop onto a conveyor below). Stage 5 – Drying. Stage 6 – Crushing of flesh to obtain a meal.

Product yields were estimated at 850kg of shell to 10kg of dried slipper limpet meal for every tonne of input material. A system was proposed to handle 75,000t/yr with a capital investment cost of 6-7 MF (~£60,000-£70,000). Operating costs were estimated at between 136-153F/t (~£14-15/t) of which around 60-70% was required for collection.

It is not clear how the proposed process would have prevented contamination of the flesh component with small shells which would have passed through the sifting stage. This technique was not taken forward to commercial exploitation. It should also be noted that the process was devised to provide the flesh as a powdered meal. The cooking of the flesh during processing would prevent its use for other applications such as human consumption.

C.3. WHOLE SHELL

C.3.1 Simple Crushing Unlike the industrial scale process where the organic flesh component is effectively ashed there are small scale crushing operations that directly use slipper limpets for agricultural purposes (Section D.3.2). Two operations exist in the Cancale area where ~1,000t/yr is processed using a variety of small scale crushers from which the operators earn a small income of around 15Euros/t. In one operation a triage conveyor system was operated whereby market size oysters were picked out, undersize oysters returned to the fishery and all other slippers and shell fragments were passed to the crusher before being conveyed into a trailer to be picked up by the farmer. Another operation had fabricated their own crusher from a road roller.

C.3.2 Crushing and Drying The French have conducted a comprehensive review of a variety of potential treatment options for industrial scale operations since 1995 (Ref. 2). The ARVAL programme incorporates the operation of a suction dredge (see Section B.2.4) to collect the slipper limpets before crushing and drying the material for use as a liming soil conditioner. A visit to the SECMA Plant at Pontrieux in Brittany during the course of this study identified the key processes and limitations of this application (Pierre Le Coz pers. comm.).

-Collection. Suction barge loads of ~700-800t are delivered via a restricted and tidal estuary. -Draining. A 1,000m3 tank allows drainage of the slipper limpets for 48 hours prior to processing. This operation can be problematic in terms of odour. -Crushing. Slipper limpets are washed and crushed which liberates a significant quantity of high load saline waste water. This requires treatment and also has a high potential to generate odours. -Drying. A rotary kiln drier operating at 20t/hr dries the crushed shell. At this point it is important that the mud content of the material has been minimised otherwise the air filters of the system can easily become clogged leading to expensive downtime.

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-Crushing. Once the flesh has been incinerated the shells are finely ground to ~150um. -Blending. As the calcium carbonate content of the material is not as high as pure lime it is sometimes necessary to blend the slipper limpets with chalk to increase the lime content. Again this is another reason to avoid mud content with the shells.

The capital cost of this 300t/day treatment system was estimated in 1995 at 6-8MF (Ref. 2) and a similar price for ~1M€ (Pierre Le Coz pers. comm). Financial assessments in Ref. 2 and Ref. 5 suggest an operating production cost of 80F/t (~£8/t) and that the cost of sales from the final product provide a slight profit.

-Cornish Facilities. Similar technology with a rotary kiln dryer and crusher on a smaller scale are currently operated by Western Waste based near Newlyn. This operation has a track record in processing crab and scallop by-products for ‘technical’ purposes and would be well placed to process slipper limpets. However, this service is provided as a waste disposal route and would cost ~£40-60/t (Ref. 49). Furthermore, material with high moisture content requires a greater level of pre-treatment which could further increase disposal costs. Distance from the disposal site and the small quantities of material to be removed on a weekly basis would further increase slipper limpet disposal costs.

Cornish Calcified Seaweed operated a drier, crusher and bagging unit out of Newham in the Port of Truro until 2005. This business would have been ideally placed to process the slipper limpets for soil conditioner and poultry feed type products. Sadly, the operation was closed when its licence to extract maerl from Carrick Roads was not renewed due to environmental restrictions (see Section D.6.4). The dryer and bagging unit still remain on the site which is now operated by Weston Blocks.

C.4. SUMMARY A number of different industrial scale extraction systems have been investigated by the French over the years. The quantity of slipper limpet material removed from the Port of Truro fishery (~25t/yr) would be insufficient to warrant the construction of a purpose built crushing and drying unit in the region when the French operate an industrial 30,000t/yr plant which still receives subsidies.

The low level of stock removal could however allow utilisation options that may warrant more labour intensive extraction techniques with low capital costs such as hand shucking following brine dipping. This approach as been advocated in the proposals Section E.3.1.1.

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Section D – Utilisation

D.1. ANIMAL CONSUMPTION

This section reviews some animal consumption applications before considering some of the limitations and proposals for the development of slipper limpets as animal food in the UK today.

D.1.1 Poultry Applications Walne (Ref. 29) reviews early attempts at utilisation of slipper limpets for poultry purposes. In WWI a small factory was established in West Mersea for the production of poultry grit whereby the flesh was allowed to rot out prior to crushing to various grades. From 1916 -1921 ~1,400t/yr of raw material was purchased from the fishermen at 10 shillings/t giving a production of 800t/yr of grit sold at £6/t. Although the scheme made a small profit the import of cheap oyster shell from the US as ballast dropped the price in 1922. The government withdrew funding and the scheme stopped. During WWII an investigation was performed on the use of mussels as a protein source for poultry meal but even the higher content of flesh in this species (dry weight at 7% of the original weight) was insufficient to be economical. In 1950 the officials considered a similar scheme for the use of slipper limpets. The experiment over several months showed that slipper limpets did provide a suitable source of protein for egg production. However, once again the low dry weight of the flesh (dry weight at 2.8% of the original weight) made the preparation cost uneconomical.

A later assessment of the economics in 2000 (Ref. 3) cited production costs at 136 - 153F/t (as slipper limpets) or 160 - 280F/t (as shell product) (or ~£16 -18/t) compared to a sale price of ~189F/t (as slipper limpets) or 220F/t (as product) (or £22/t). This result is comparable to a similar application considered for cattle (see following section). Both studies concur that on an industrial scale the application should just cover costs.

When the French studies are coupled with the earlier study of Walne it is suggested that the use of slipper limpet shells for poultry grit is economically marginal. Furthermore, slipper limpet shells would need to compete with the abundant scallop shell that already requires ‘disposal’ routes in the region.

As an interesting observation from this study the author’s ducks readily consumed the flesh (and shells) of the small slipper limpets unsuitable for shucking. The advantage of this approach is that no operational costs are needed to dry, crush and prepare a meal. It is possible that a small scale free range organic approach could allow the production of an added value poultry product. However, consumption of fresh meat off the shell would be difficult in a commercial setting (see limitations) and would need to be closely integrated in the overall slipper limpet utilisation project.

D.1.2 Cattle Applications In France the extensive studies performed over the years have included the study of cattle feeds for utilisation. Ref. 2 produced in 1996 considers slipper limpets both as a meal source and a mineral supplement. In contrast to the protein comparison of slipper limpet meal performed by Walne (Ref. 29) the Ref. 2 study suggests that a slipper limpet meal could be an important

Section D - Utilisation Andy FitzGerald Page 52 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study compliment to classic animal meals as it contains essential amino acids and other nutritionally beneficial components. In terms of the shell component this report lists the principal requirements necessary for the production as the efficient separation of flesh from shell, the absence of pathogens and the provision of a constant grain size between 2-4mm. This report suggests a production cost of 200-300F/t (~£20-30/t) as compared with a commercial price for chalk at 400F/t (~£40/t) or limestone at 150-200F/t (£15-20/t).

Legislative limitations (see Section D.6.2) would now restrict meal use for ruminants.

As with poultry grit (see previous Section) the economics of production as a calcareous feed additive in the context of the region are not likely to be viable.

D.1.3 Aquaculture Applications Trials have been performed using slipper limpets to culture trout and sea bream with a focus on assessing the nutritional quality of the flesh and the conversion ratios possible relative to standard proprietary feeds. As most finfish aquaculture diets are based upon fishmeal consideration has been given in these studies to using slipper limpets as an alternative source of meal. This section reviews the meal properties and performance of different aquaculture species.

Slipper Limpet Meal- The production of a meal from slipper limpets for use in aquaculture as a substitute for fishmeal has been considered in a number of reports. Walne (Ref. 29) compared fishmeal against slipper limpet meal in terms of protein content and potential economics. He observed that although slipper limpets could theoretically produce a 57% protein meal in practice 40-50% protein content was more probable. This would be lower than the 50-60% protein in fishmeal and as an inferior product would command a lower price and struggle to cover operating costs. Walne then concluded a possible solution would be to also utilise the shell as poultry grit separately in order to obtain maximum income for the majority of the raw material.

Fish meal production using fish processing by-product was considered for Newlyn in a project reported in 2004 for the Newlyn Fish Industry Forum (Ref. 49). This study concluded that small scale fish meal production in the region was not economically viable. In consequence, slipper limpet meal would face an even greater challenge as the volume of raw material is lower, fish waste ‘disposal’ revenue would not be created and the final product would have an uncertain market.

Trout- Ref. 2, Annex 3 provides a growth study of trout fed on slipper limpets compared with a control diet performed in 1995. The slipper limpet diet was prepared from an alkaline ensilage process (Section C.2.2.3). Duplicate test tanks were performed with an initial fish biomass of ~1,200kg which doubled in wet weight over a 12 week study period. Food conversion ratios for both test cases were just over 1 with only a marginal improvement in performance from the control diet. A number of specimens from both test conditions were processed and weighed to assess relative yields. There was only a 5-10% drop in weight between the slipper limpet and control diets.

Sea Bream- In 2000 Ref. 3 studied the performance of slipper limpet diets for sea bream culture. Three growth tests were performed comparing a standard extruded feed, a fresh slipper

Section D - Utilisation Andy FitzGerald Page 53 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study limpet feed and a composite preparation of 80% slipper limpets blended with additional components to supplement trace nutrients and vitamins in addition to gelatine to bind the diet together. Test fish were fed at a target 3% dry body weight/day and cultured over a 3-4 month period. By the end of the experiment the fish initially weighing 11g on average had grown to 55g based on a standard diet, and to 21g on a slipper limpet diet. Conversion ratios were ~1 and 3.65- 4.24 for the standard and slipper limpet diets respectively. Performance was slightly better with the slipper limpet based composite diet which produced conversion ratios of 1.6-2.13. However, the report concluded that the cost of composition of this diet was high and did not consider a specialised business based on the production of such a product would be viable.

D.1.4 Pet Food Applications Ref. 2, Annex 4 provides a taste test study of a slipper limpet product on cats. The study, conducted by the Veterinary School of Nantes, used eight test cats and compared consumption of a slipper limpet ensilage juice used to prepare or coat a food against a control diet. The results clearly showed that slipper limpets were not suitable for this application. However, the project raised the potential for future pet food applications if the use of aromas could be used to enhance the products.

D.1.5 Aquarium / Leisure Fishing Bait Applications As described in Section D.1.3 Ref. 3 conducted growth trials using fresh slipper limpets for sea bream. Although it was concluded that the use of fresh material was not the most suitable in an aquaculture setting its use for aquarium purposes was highlighted as a possibility.

Ref. 5 also mentions the use of slipper limpets as bait for sea bream fishing although it mentions that one project based in Cancale was not considered competitive due to the labour costs of shucking.

Contact with Blue Reef Aquarium in Newquay revealed that slipper limpets had already been successfully used. The manager expressed a preference for using slipper limpets if they could be provided at a comparable price to the clams and cockles normally provided by their supplier (Matt Slater pers. comm.) Blue Reef store their fresh feed in freezers and would prefer to purchase pre-frozen shucked animals owing to the bulk of whole animals in the shell.

The National Lobster Hatchery in Padstow also uses a small quantity of feed for its larger display animals and for the adult broodstock. The manager was happy to try slipper limpet samples as long as all material had been frozen to ensure biosecurity (Dom Boothroyd pers. comm.).

Ammodytes Ltd. based in St Ives is a major supplier of frozen fish products to the fishing bait and aquarium markets. Slipper limpets have been used by Ammodytes in the past with stocks obtained from both Penryn and the Solent. Stocks from the Solent are reputed to be larger, cleaner and can be obtained pre-shucked (Malcolm Gilbert pers. comm.). Although Ammodytes has preparation facilities, blast freezers and chilled transportation it does not consider that it is well placed to perform the shucking aspect of a slipper limpet operation. However, it would be willing to store, market and distribute pre-shucked frozen product to this market and participate in the trial season considered in the ‘Proposals’ Section E.3.2.1

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A possible local alternative for the provision of frozen angling bait via Ammodytes would be to provide fresh or frozen slipper limpets in the shell direct to local bait outlets. Although this would avoid the significant cost of shucking it would probably require a high service cost for a relatively small market and could undermine local suppliers (i.e. Ammodytes).

D.1.6 Commercial Fishing Bait Applications Fishing bait for potting applications (e.g. crab and whelk) is exempt within the Animal By- product Regulations. As one of the major costs for slipper limpet utilisation is shucking this application is a low return. Sale price for baits are generally low (~£0.50/kg, Ref. 49) however, the quality of the product does not need to meet human consumption standards. Indeed whelks are known to hunt carrion by smell so dead slipper limpet flesh may be quite effective.

One vessel targets green shore crab and velvet crab within Carrick Roads. If slipper limpets could be used as bait then slipper limpets could be utilised and crabs (oyster predators) could be removed from the system – a double benefit to the oyster fishery!

The proposed trial should seek to develop a close working relationship with local potting vessels in order to test slipper limpet use for bait applications. As shell applications (with clean material) provide a good potential source of income it may be possible to provide free slipper limpet bait in return for clean shell once the pots have been recovered. If this method is effective then it may be possible to support a dedicated local vessel. Such a synergy would be good for the local fishing industry and the environment.

D.2. HUMAN CONSUMPTION

This section reviews some previous and current human consumption applications before considering some of the limitations to development of slipper limpets as a food in the UK today. The assessment of the potential for developing slipper limpets for human consumption is based upon the possibilities of using the stock in the Carrick Roads / Fal estuary area.

D.2.1 Previous Applications

D.2.1.1 Early European Applications Walne (Ref. 29) reviews early attempts at utilisation of slipper limpets and many of the points he raised are still relevant over 50 years later. Walne observed that the British public are very conservative and that early attempts in 1926 by a large London shellfish merchant to sell slipper limpets at three shillings a bushel were unsuccessful. During the Second World War the Liebig company in Holland produced and successfully marketed a paste made from slipper limpets. Over the war 30,000t were processed for human consumption in this way however, the project was discontinued once the war was over. During this period of protein shortage slipper limpets were not commercially extracted in the UK for human consumption.

D.2.1.2 Current European Applications Since WWII France has experienced a massive increase in slipper limpet numbers and therefore

Section D - Utilisation Andy FitzGerald Page 55 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study in 1996 conducted comprehensive studies to look at ways to utilise both flesh and shell (Ref. 2). Despite these studies and the existing appetite for seafood in France, human consumption was not considered and only animal feed options were pursued on an industrial scale (see Section D.1). A later French study (Ref. 3) stated that although the flesh was edible it did not look attractive and was ‘elastique’. The most recent French review of utilisation options for the Bay of Brest (Ref. 5) stated that slipper limpets had been used in Spain and America as garnish on pizza although it also indicated that the separation of the flesh was not considered economical.

In order to overcome the extraction costs in France negotiations have taken place between French officials from the Cancale and St Malo areas with Spanish producers who intend to utilise slipper limpet within ragout dishes (M. Blanchard pers. comm.). Although this venture was reputed to consider a significant tonnage of slipper limpets, to date no details of this potential application have been verified. When questioned, local merchants have suggested that the final product cost will be unlikely to cover the transport (M. Jambon pers. comm.).

In Morocco slipper limpets are reported to have been marketed as ‘Rock Oysters’ and fed to tourists with uncertain success (Nigel Ellis pers. comm.).

D.2.2 Trial Preparations

D.2.2.1 SAGB Dinner Slipper limpets were featured in the starter course of the SAGB annual conference lunch in 2003. By all accounts the chowder dish, which was a blend with clams, was received well. However, even then the extreme time in shucking a significant quantity of slipper limpets was noted (Martin Laity pers. comm.).

D.2.2.2 Rick Stein / The Seafood Restaurant Rick Stein, the popular Westcountry TV chief, featured the Falmouth Oyster boats and was shown eating a raw slipper limpet ~1999/2000 (Matt Slater pers. comm.). Liaison with the Head Chef of The Seafood Restaurant revealed that they did attempt to put slipper limpets on the menu based around a starter dish of quick steamed limpets topped with capers. Unfortunately, the dish was not popular and was removed from the menu when it did not sell (Stephane Dellurne pers. comm.). When questioned The Seafood Restaurant were willing to try again using new recipes and were interested in testing the marinade ideas.

D.2.2.3 PESCA Trials Some recipe trials were prepared by the University of Plymouth (Seale Hayne College, Food Technology) at the request of PESCA. A number of dishes were produced and returned for the oystermen to taste and were again well received by those who tried them (Martin Laity pers. comm.).

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D.2.2.4 This Study Fresh Cooking Slipper limpets should not be prepared as bivalves and bear a closer relationship to other gastropod flesh (e.g. abalone) which must either be cooked quickly or over a long period at low heat.

Rapid cook - Shucked slipper limpet flesh flash fried in garlic butter for 30 seconds yielded a clean and good tasting dish. This short cooking method could possibly be restricted to appropriately safe slipper limpet sources as discussed in Section E.3.1.4.

Medium cook - Slipper limpets were initially cooked in the shell in the same way as mussels in garlic butter. Final product was rubbery and a little contaminated by dirt on the shell which could not be adequately cleaned from the shells when fresh.

Slow cook – A sweet chilli chowder was prepared covered and cooked at gas mark 1 for 5 hours. Although the dish did not taste particularly good the texture of the flesh was very soft confirming that slow cooking does produce a favourable texture. Rick Steins is enthusiastic in his recent book about a featured ormer (abalone) recipe with cinnamon and shiitake mushrooms that requires a long low cook. It would be interesting to perform a blind taste test between ormers and slipper limpets!

Smoking Cornish Cuisine based in Penryn specialises in smoking fish products and was willing to undertake a trial preparation of slipper limpets. A 1kg sample of shucked flesh was blanched in boiling water before being spread on a wire rack and placed in a smoking oven. The test sample was subjected to two treatments of ~1.5 hours before removal. Samples were vacuum sealed as shown below:

Figure 16 – Smoked slipper limpets in vacuum sealed pack

Source: This study

Samples when tasted had a good soft texture although the taste was overpoweringly smoky. Some fish types are pre-soaked in a concentrated brine solution which helps draw out moisture and so increases the product shelf life. This procedure was not conducted on the slipper limpet

Section D - Utilisation Andy FitzGerald Page 57 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study sample as the small volume of each piece allowed good penetration of smoke into the flesh. The shelf life of the product was estimated at 7 days (Nigel Ellis pers. comm.).

Marinades A number of preparations were made including: -Cider vinegar with smoked slipper limpets. This maintained the good texture of the smoking and reduced the harshness of the smoking process making a taste improvement. -Cider vinegar with sweet chilli and slipper limpets. -White malt vinegar with red seaweed (dulse) and slipper limpets. -White malt vinegar with ransom (wild garlic) and slipper limpets.

Finishes for these products were good although a great deal of effort was needed in the preparation.

Overseas Consumption Consumption of seafood in the Far East far outstrips that in the West partially due to consumers’ belief that fresh seafood consumption will allow better metabolism of alcohol (Clive Askew pers. comm.). There is a well established Korean market for whelks from the UK that could provide a similar product placement for slipper limpets using the established trade links. As whelks are also gastropods the flesh qualities may be similar to those of slipper limpets. Although no whelk processors remain in the SW (Clive Askew pers. comm.) Kildavanan Seafoods a major processor in Fleetwood still operates. Whelk processing at Fleetwood relies on chilled transport of product from around the country including the SW. The fresh whelks are pressure cooked, processed, graded and then frozen Individually Quick Frozen (IQF) within 24 hrs of capture (Ref. www.amseafoods.co.uk/whelks) – as shown below.

Figure 17 – Whelk Processing – Possible Model for slipper limpets?

Source: www.amseafoods.co.uk

Kildavanan Seafoods has offered to inspect a sample of slipper limpets and if the product is suitable will transfer it to Korea alongside a batch of whelks for testing by the Korean tasters. The traditional manner for consumption is with a little soy sauce (Sam Evan pers. comm.). It may be necessary to obtain a fresh slipper limpet sample for immediate direct transport for this

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D.3. SOIL AMENDMENT APPLICATIONS

D.3.1 Lime Soil Conditioner The ARVAL programme in France utilizes 30,000t/yr of slipper limpets which are removed by suction dredge (Section B.2.4) before processing at the SECMA plant in Pontrieux to form lime products. A description of the process is provided in Section C.3.2. Alternative uses as a specialist lime for niche market applications could be possible and have been proposed as the subject of a PhD study by the University of Bristol (Richard Ball pers. comm.).

As indicated the process to form lime products requires a significant capital outlay which will not be appropriate for the low level of production possible from the Port of Truro fishery.

D.3.2 Organic Fertiliser Although some small scale slipper limpet fertiliser operations do exist in France (Section C.3.1) odour considerations limit the extent of the operation and only ~250 hectares of land are suitable for use (M. Jambon pers. comm.).

At Vivier–Sur-Mer in France Ref. 5 cites an example of slipper limpets being used as fertiliser and lime conditioner to help vegetable crops although it states that there is no technical data on the performance of this approach.

The direct use of crushed slipper limpet shell as fertiliser in the region around Carrick Roads is unlikely to be considered acceptable in view of the high population density and tourist popularity of the area. The region is currently undertaking ‘in-vessel’ composting trials with fishery by- products although these applications would still present a net disposal cost (Ref. 49).

D.4. SHELL AGGREGATE APPLICATIONS

D.4.1 Bound Blocks and Surfaces Traditional block applications bind aggregates within a cement matrix. Truro Concrete Products (Weston Blocks) was contacted as a potential partner to generate shell product blocks using slipper limpet shells. This company situated by the dockside in Truro at the site of the old Cornish Calcified Seaweeds factory in Newham would be well placed to handle and utilise slipper limpet shells. Indeed the maerl drier and bagging unit is still available on site. However, after consideration the company was not currently interested in making slipper limpet blocks as this application was a little too specialised for their current wholesale markets (Mark Bolitho pers. comm.).

Another product presentation is to use a resin matrix to bind the aggregate. A range of applications including paths, tree surrounds and ornamental blocks, as shown in Figure 18, can be viewed on www.sureset.co.uk .

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Figure 18 – Resin Bonded Aggregate Surfaces

From: www.sureset.co.uk

This website provides application details and costs for DIY kits for resin bonded aggregates. These kits provide all of the equipment and materials needed in addition to the pre-weighted aggregate. At £70/pack for 25kg of aggregate this is an added value application that should be pursued.

The advantage of these attractive applications is that the surface is permeable to water. This is an advantage where plant watering is needed or surface run-off from hard surfaces is a concern.

These applications are becoming increasingly popular especially in view of current interest in limiting the impact of urban storm-water flows. Ref. 51 outlines plans to utilise the massive levels of slipper limpet shells in Puget Sound on the west coast of the US for porous pavements in the City of Olympia. Unfortunately, this ambitious scheme has not yet currently received funding (Scott Smith pers. comm.).

Cornwall Specialist Surfacing currently provides resin bonded paths and drives using a range of aggregates. The company based in St Austell received a slipper limpet sample and considered the potential suitability of the material as an aggregate. The initial assessment was that the material was unlikely to be suitable for driveway applications as the material was too coarse (Mike Nicholson pers. comm.). Block construction may still be possible but this was beyond the range of services offered by this company.

D.4.2 Loose Shell Uses Slipper limpet shells can be used as an aggregate for paths. Loose slipper limpet shells have been previously used as an aggregate for use on paths for a golf course (Martin Laity pers. comm.). Other wholesale aggregate applications could include attenuation gullies for storm water flows (Ref. 51).

Loose shells can be used in a similar fashion to bark as a decorative mulch covering for gardens. After a provision of a sample initial consideration by the trade was favourable if shells are suitably clean and priced. Contac Ltd. based in St Austell specialises in providing a variety of loose aggregates to the trade and the public for such purposes. This company has expressed a

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Ref. 52 indicates a price of £7-£20/25kg for bagged clean shell (£280-£800/t). A major Plymouth garden centre is retailing shell at £6.50/12.50kg (£520/t) (Ref. 49). This study has used a £400/t bagged shell price (Section F.7.). Wholesale bulk applications should be avoided as they provide a low return of £8-£9/t (ex-works) or ~£15/t delivered (Ref. 49).

D.4.3 Cultch for Oyster Settlement Cultch is the term given to a substrate used to enhance settlement of a commercial species. The best cultch not only provides a good initial settlement substrate but also is sufficiently small so as not to deform the shape and form of the developing bivalve. In this respect crushed mussel shell is often mooted as one of the best clutches for commercially acceptable shellfish. Mis-formed oysters on poor cultch are still of value to the fishery as they can be returned as broodstock and thus help to increase the spawning potential.

Slipper limpet shells have often been suggested as a source of cultch for oyster settlement. Indeed observations in the Solent show that slipper limpet shells can form settlement surfaces for oysters as shown in Figure 19 below (Lawrence Hawkins, Antony Jensen per. comm.). However, research on cultch, looking at immuno-competence and comparative shell types, suggests that slipper limpets are not the ideal choice.

Figure 19 – Oyster Settlement of slipper limpet shell

Photo: Antony Jensen

Consideration of waste shell by-product from the shellfish processing industry was undertaken as part of the Newlyn Fish Waste project (Ref. 49). This project identified the large stock of scallop shells in Falmouth as a potentially suitable source of cultch for the Port of Truro oyster fishery. The relative advantage of scallop shells over slipper limpet shells could be a limitation to the use of slipper limpet.

Shell used for cultch must be clean (or allowed time to self clean in the sea). In the case of scallop shell from shellfish processing the material is considered as an animal by-product and must be cleaned by an approved method before use in cultch applications, which is an accepted ‘technical’ purpose.

Ref. 53 produced in March 2006 sets out the requirements and prospective costs for the use of such shell for cultch purposes. This document provides a scenario for small scale cultch laying of 520t/yr with an illustration cost of £38.46/t to cover running costs or £51.28/t to cover set-up costs with a 3 year payback.

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A scheme to clean and crush slipper shells for cultch applications could also be considered for scallop shells which could be provided as a waste product by Ciamar. However, any shell cleaning plant to provide suitable cultch would present a cost to the shellfishery. It is likely that such a scheme would only be possible if part funded by a European Fisheries Fund project.

The potential to obtain payment via European funding for cultch should also be explored. The cost/benefit analysis of different potential shell applications is beyond the scope of this study and should be considered in concert with other shell types and on a regional basis.

D.5. LIMITATIONS

D.5.1 Flesh Yield Yield rates for slipper limpets are low and below the returns expected for commercial bivalve species. However, graded slipper limpets suitably sorted could be comparable to cockles where 10-20% yields can be expected (Clive Askew pers. com.). Rates quoted for slipper limpets in the literature are as follows:

Table 6 – Review of Slipper Limpet Flesh Yields Source % Flesh % Shell % Other Ref. 56 20% 80% Ref. 2 13.9% 74.2% 11.9% Ref. 3 15% 85% Ref. 5 29-37% 63-71% This study - 21-31% 79-69% fresh (fresh un-drained)

This study - 18% (drained) 73% 3% (small shell) frozen +6% (fluids) This study - 4% 41% 26% (large shell+flesh) automated 10% (small shell+flesh) +19% (lost shell+flesh)

As the different studies do not provide exact details of how these measurements are made direct comparisons are rarely possible. There are a number of factors that can affect yield:

Inclusion of body fluids- Significant quantities of fluid are released upon shucking. Measurements during this study, as shown above, indicated that body fluids accounted for around a quarter of the non-shell fraction (i.e. 18% yield when drained and ~24% yield un-drained). Fluids are also lost during the standing time before shucking due to the fact that slipper limpets do not tightly seal shut when removed from water. As such they are subject to a significant ongoing loss of fluids. This observation would tend to be confirmed by the wide range of moisture contents for the flesh quoted in the literature.

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Inclusion of the Visceral Mass- Some extraction trials for human consumption have only utilised the muscular foot and discarded the visceral mass which clearly vastly reduces the yield rate. Measurements during this study have shown that the visceral mass accounts for around half of the flesh mass which would on average drop the yield from 18% to ~9%.

Seasonal conditioning- Measurements during this study with animals obtained in April showed a high level of egg pouches brooded by the large females. It is probable that the flesh yield would be lower in animals immediately post-spawning or during the winter before animals can regain condition. Alternatively, processing of previously frozen animals gives rise to egg pouches that remain attached to the back of the lower slipper limpet and are therefore lost from the sample.

Sample Selection- The age and size of a chain will alter the shell : flesh ratio. Generally, older slipper limpets have much thicker shells and could therefore expect a lower proportional flesh yield. Inclusion of the dead empty slipper shell at the base of a chain will also affect calculations. A short chain of two live animals will include the weight of three shells which is proportionally more than a long chain of ten live animals which will include the weight of eleven shells. Finally, from an economic extraction perspective it is unlikely that workers manually shucking slipper limpets will bother with obtaining the flesh from the smaller limpets in a chain. If these un- harvested animals are placed in the ‘empty shell’ fraction then the yield will obviously be depressed. Values quoted suggest a loss of between 3-10% as small shells and flesh

Extraction Technique- Attempts at automated removal of flesh in this study (Section C.2.3) provided a low yield (~4%) as much of the visceral mass was mashed into the shell, some remained un-shucked and a significant proportion of the extracted flesh remained stuck to the machinery and was therefore lost.

D.5.2 Flesh Quality Attempts at automated removal of flesh (Section C.2.3) have provided an inferior quality product that would be unlikely to be acceptable for human consumption either from an aesthetic or hygiene perspective.

D.5.3 Processing Costs Only hand separation is likely to be a suitable extraction technique for human consumption purposes (Section C.2.1). Manual shucking has the added advantage of minimising the generation of large volumes of high load waste water and somewhat reduce the discharge cost.

Manual shucking and pre-treatment as specified in Section C.2.1 removes the need for massive capital investment. However, operating costs in terms of labour will be high. Estimates during this study indicated a processing rate of ~7.5kg/hr yielding ~1.5kg flesh. This places a price burden at minimum wage levels of £5.05/hr of £3.37/kg of flesh. Professional shuckers should be able to process slippers considerably faster and hence drop the processing cost/kg although a significant reduction will be required to meet the <£2/kg benchmark (Section F.5.) and still cover

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If slipper limpets are used for human consumption then under the Animal By-Products Regulations all shells and un-shucked flesh will need to be disposed of by approved methods. This would impose a major cost on a business with charges by Western Waste at ~£40-60/t imposing ~£0.24 to 0.36/kg on flesh processing costs. In reality production of small quantities of shell (e.g. 400kg/week) would create much larger disposal costs per tonne. As shells rapidly give off an unpleasant smell it would be necessary to either pick up, transport and dispose of waste more frequently or provide secure storage with odour control. It is suggested that shell is cleaned as specified in Section E.3.2.2 with the cost covered by the shell applications (Section F.7.)

D.5.4 Perception and Market Inertia Aesthetically slipper limpets in the shell are not the most appealing shellfish to consume. Alive, chains of slipper limpets tend to be slimy, muddy and smelly – not the most appetising combination. Unlike bivalves which cease faeces production once the shells are closed, slipper limpets remain partially open allowing oxygen exchange and continued faeces production. This means that even chains that have been cleaned have a high potential to become dirty once more unless immediately processed.

Shucked and washed slipper limpets are less off putting with a pleasant orange coloured foot and a darker coloured visceral mass. In a food preparation they appear at first glance little different from other shellfish although a closer inspection shows the small round foot becomes curved once cooked while the watery visceral mass disappears giving the whole animal the appearance of a small orange button. Options for addressing some of the market perception restrictions are considered in the proposals section.

Products for animal as well as human consumption would face difficulties in gaining access to the market in terms of product acceptance especially as the low level of production possible could not support wholesale agricultural markets.

Aquarium and bait markets should be possible to access so long as product placement is at the lower price range. Although the nutritional information for the slipper limpet suggests that it is a good protein source, with essential amino acids, lipids and vitamins it is unreasonable to initially expect customers to pay a premium price. In consequence, the trial outlined in Section E.3.2.1 will aim to provide free test samples before pitching the product as a clam equivalent. If customer response is positive and demand is sufficient then there may be scope to increase the sale price accordingly.

D.5.5 Unknown Product Availability As with other applications the management techniques considered for the slipper limpet are intended to reduce or eliminate this ‘pest’ species from the area. Although this is unlikely to be completely successful it is possible that continued removal of slipper limpets from the beds could reduce stock biomass to the level where product availability is low or intermittent. Even if slipper limpet supply were to remain constant there is a problem in making a business case for investment when the underlying principal is to eradicate your raw material!

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D.5.6 Access to Overseas Markets Export of slipper limpets from Falmouth to the limited overseas markets would face a number of challenges. The limited market has a massive level of natural supply of a low value product requiring high operating costs. It may be hard to provide competitive exports from the UK when French transport and labour costs are likely to be lower. Even if UK stocks could compete, slipper limpets could be provided at higher levels with more consistent supply from the more extensive stocks from other infested areas in the country.

D.5.7 Competition from Existing Established Products

D.5.7.1 Shellfish Products A variety of preparations for human consumption have been tested in this and previous studies. The use of marinades provides a good way of overcoming some of the negative perception of slipper limpets. However, the product would face a number of hurdles and would struggle to compete with other well established and locally available shellfish species such as cockles, clams, mussels and oysters. A trial season has been proposed to address the outstanding economic and market issues with the aim of providing a model business plan.

The use of slipper limpets for bait and aquarium purposes remains one of the major potential niche applications where the relatively low level of stock and inability to process on a large scale does not prejudice market access. However, slipper limpets would need to compete against established products and cheap imports. Ammodytes sell a clam from China already IQF and ‘freeflow’ with a low buy-in price of £2-3/kg. As Ammodytes would need to re-pack and freeze the product the financial bench mark for any slipper limpet product would need to be <£2/kg. This buy-in price is likely to be challenging (see Section F.6.).

D.5.7.2 Shell Products Ref. 49 reviews shell use applications in Cornwall in relation to the massive level of scallop shells generated in the region as a by-product of processing. Although the curved shell from the scallop does have a value for ornamental applications many thousands of tonnes of flat shells are dumped every year originating from Falmouth, Plymouth and Barnstaple.

Under the Animal By-product Regulations these shells are at present required to be disposed by designated approved means. Western Waste Ltd. based near Newlyn is currently equipped to process these shells by approved methods to provide shells for ‘Technical Purposes.’ In consequence, there is a much greater stock of crushed dry scallop shell available for applications. Furthermore, as Western Waste charges to process material, scallop shell products could be produced more cost effectively than slipper limpet shell products.

There could be scope to develop a range of regional shell products which with proper marketing and targeting could provide a better added value margin. This consideration is proposed in Section E.3.3.

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D.5.7.3 Fertiliser Products Cornwall County Council has been planning a regional green waste collection and compositing scheme in order to meet its recycling target commitments. This will provide a massive level of low grade compost to the market, (Ref. 49).

Fertiliser applications are not likely to be financially viable as the mass of material available for processing is too low to obtain the economies of scale for investing in the capital costs of ‘in- vessel’ composting technology that would probably be required for this application. Ref. 49 considered the costs of composting for fishery by-products with ~1,000t/yr of available material which still yielded a high disposal cost per ton. Although this application is technically possible, the low net value of fertiliser products will be unlikely to match the cost of production.

D.6. LEGISLATION There are legal considerations relating to both management and utilisation, which are themselves linked. Application of these regulations will therefore have a significant impact upon how slipper limpets are used or disposed of. There is an inherent conflict between the regulations such as the need to remove slipper limpets and other regulations that may hinder the development of any new application.

Regulations that promote the native oyster include the Habitats Directive and The Shellfish Act (1967) (Section 2) that places an obligation on the holder of the Regulating Order to maintain the shellfishery beds. In addition, the UK Biodiversity Action Plan lists the slipper limpet as a nuisance invasive species.

A number of regulations potentially restrict management/utilisation applications. As there has been a low level of precedence in this field, many legal considerations may require time and expense to resolve at a National level. It is proposed that the trial season should allow time for negotiations with local responsible agencies to help resolve these issues. It is probable that local trial solutions and resultant decisions may be ultimately considered on a National scale.

D.6.1 Shellfish Hygiene/Classification Slipper limpets are filter feeders and do have the potential to bioaccumulate microbiological pathogens and chemical toxins. Public health is protected by the Shellfish Hygiene Directive which places end-user concentration limits for the final product. In addition, under the Shellfish Waters Directive bivalves and gastropods require classification based upon the long term quality of production from the area where the shellfish are derived. According to this Directive, shellfish flesh quality is monitored throughout the year using the faecal coliform indicator E. coli. Areas are given a classification that dictates whether shellfish can be consumed and if so whether they require relaying or pre-treatment. In Carrick Roads and the Fal Estuary the oysters are obtained from a Class B area although the upper reaches of the Tresillian estuary are Class C. This means that all oysters require depuration within an approved system prior to placing in the market.

Discussions during the course of this study have lead to the issue human consumption of slipper limpets being referred by CEFAS to the Food Standards Agency (FSA). As slipper limpet rates of bioaccumulation and depuration are unknown by the FSA some testing has been required in concert with the Falmouth Port Health Authority who are responsible for testing shellfish quality

Section D - Utilisation Andy FitzGerald Page 66 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study in the area. After consideration it was decided to obtain slipper limpet samples from two diverse sites within the area adjacent to the standard oyster monitoring points. Dredging of slipper limpets samples was undertaken on the 14 June 2006 by the Port of Truro Harbour Authority in the River and Harbour Sections. Samples were placed on the Grimes Bar and East Bank monitoring points respectively. Sampling and testing has been performed by the Port Health Authority allowing an initial cross comparison of E. coli levels between the two species to crudely consider the relative levels of microbial bioaccumulation.

Table 7 Microbiological Quality of Slipper Limpets in Carrick Roads (E. coli counts/100g MPN)

Station 16 (East Bank) Station 5 (Grimes Bar) Date Slipper limpets Nat Oysters Slipper limpets Nat Oysters 27/06/2006 90 20 - - 25/07/2006 50 40 2200 - 21/08/2006 200 750 3500 3500 09/10/2006 220 220 1300 1300 Average 140 258 2333 2400

Sampling by Port of Falmouth Health Authority

The results obtained to date suggest that the filter feeding slipper limpets do tend to mirror similar microbial levels to those of Native oysters. So far the East Bank has achieved Class A whilst the Grimes Bar has achieved Class B quality. A set of at least x10 samples will be required to classify the shellfish waters and it is uncertain whether the Class A status not requiring depuration can be maintained. No protocol currently exists for the depuration of Class B slipper limpets thus preventing the sale of fresh stocks in the shell to the market.

It is still possible to consume shellfish obtained from a Class B area without depuration although material must be cooked to Torry Standards which dictate a core temperature of 90°C for at least 90 seconds. Unfortunately, this regime would prevent the short term cooking method as the flesh would be denatured to the rubbery form. Only long cooking methods would therefore currently be acceptable for slipper limpets from Class B waters.

CEFAS has also pursued discussions with their Spanish counterparts to consider what testing and controls they have put in place for consumption in their area. The official response from the Spanish is that slipper limpets are not used for human consumption (Andy Younger pers. comm.).

Further testing and research may be required in the UK before utilisation for human consumption is acceptable, particularly in Class B areas. It may be possible that consistent Class A quality results from the East Bank site may present fewer obstacles for human consumption.

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D.6.2 Animal By-Product Regulations If slipper limpets are obtained for human consumption then those components not utilised (i.e. small slipper limpets and dirty shell) could be deemed an ‘animal by-product’. Under EC Regulation No. 1774/2002 ‘Health rules concerning animal by-products not intended for human consumption’; This regulation consolidates much of the earlier legislation by providing a framework for the classification of material into three grades according to risk:

Category 1 High risk material (e.g. infected with known pathogens, or contaminants including excess levels of algal toxins). Category 2 Moderate risk material (e.g. fish farm mortalities and fish with residuals including other seafood such as shellfish from vivier systems). Category 3 Low risk material (e.g. fresh fish by-products).

In such circumstances slipper limpet by-products would be classed as Category 3 ‘low risk’ material and in common with other shell waste can be cleaned for use within ‘technical’ purposes outside of the human food chain.

EC Regulation No. 811/2003 ‘Intra-species recycling ban for fish’; prevents the feeding of a species back to the same species and allows feeding directly only to certain specified animals. In theory this approach could allow the consumption of any slipper limpet by-product by species outside the human food chain (e.g. green shore crab when used for bait). Furthermore, there is an exemption within the regulations that allows the use of Category 3 fish processing by-products as a bait within potting.

Some of the slipper limpet meal applications undertaken in the past would struggle to find acceptance now. Since the BSE crisis the use of animal derived meals for ruminants has been stopped even including the use of fish meal despite massive lobbying. It is unlikely that slipper limpet meal would be considered acceptable for use within cattle feed.

Ref. 52 provides a good review of the whole range of EU and UK regulations that apply to waste issues facing the fishing industry.

The Animal By-product Regulations are administered by DEFRA with enforcement and licensing undertaken by local authorities via the State Veterinary Officers. Mark Arrow is the responsible officer for the Cornwall region.

D.6.3 Animal Feed-Stuff Regulations The Feeding Stuffs Regulations 2000 (S.I. 2000 No. 2481) requires feeds to be "sound, genuine and of merchantable quality" whilst the Feeding Stuffs (Amendment) Regulations 2003 (S.I. 2003 No. 1503) sets out the maximum specified permitted levels for certain undesirable substances.

The trial season will need to undertake analysis of samples for List 1 substances such as heavy metals if there is a potential risk of contamination from certain areas. Guidance on such testing will need to be based on comparative results from historical oyster testing performed by Port of

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Falmouth Health Authority and CEFAS Weymouth. Potential concerns could include persistent organic compounds (e.g. TBT), toxic algae (e.g. PSP, DSP) in addition to heavy metals.

The Feeding Stuffs Regulations are administered by the Food Standards Agency (FSA).

D.6.4 Habitats Directive Natural Habitats Directive (1994) implemented via the Conservation (Natural Habitats) Regulations (1994) requires protection of specific identified features of biological importance within a defined European Marine Site (EMS). In the UK, JNCC and EN have defined a series of Special Areas of Conservation (SAC’s) of which Carrick Roads is one.

Carrick Roads has been designated as a SAC with a number of seabed features of conservation interest. Paramount in this area has been the preservation of the maerl beds. St Mawes Bank is one of the key maerl areas and within the designated bounds of the oyster fishery. At present this bed is little worked by the oystermen although the potential for increased regulation in this event remains (Ref. 1). Protection of these beds has played a key role in a number of schemes and marine related businesses over previous years including the placement of the new Falmouth waste water outfall, operation of seabed extraction by Cornwall Calcified Seaweed, and maintenance dredging in the area such as in the vicinity of Penryn marina.

One of the key implications of the Habitats Directive is that and ‘Appropriate Assessment’ may be required by EN as discussed in Section B.3.1.

General Ecosystem, Migratory Fish and Bass Nursery area designations also all apply to the Carrick Roads system. All of these designations will be drawn into the Water Framework Directive.

D.6.5 Water Framework Directive The Water Framework Directive (2002) sets out a comprehensive programme for catchment based improvements in water quality aimed to provide a ‘good’ status by 2015. At present this directive (administered by the EA) is still in the process of consultation and construction of operational programmes. In principal this Directive will pull in all the various needs of the other Directives impacting upon water quality as well as taking to account local user needs. In practice many vital aspects are still unclear. For example, it is uncertain how ‘non-indigenous’ species will be considered in the definition of ‘good’ quality status (Keith Hiscock pers. comm.). Resolution of these matters could have a significant impact to the legislative pressure to remove slipper limpets.

D.6.6 Waste Disposal The deposition of slipper limpets potentially falls under a number of different regulations dependent on where the material is to be deposited and in what form. Unfortunately, the regulatory authorities have little experience of dealing with slipper limpets and guidance is limited as legal definitions are uncertain.

Experience from Poole Harbour where 1,000t of slipper limpets were recently disposed of (Section A.5.2.3) suggests a complex legal situation. Initially the operator had intended to dispose of the material in the registered spoil ground offshore. The Marine Fisheries Agency

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(MFA) studied the legal position in respect to the Food and Environmental Protection Act 1985 (FEPA) and ruled that disposal of living slipper limpets in the spoil ground was not an exempt activity. Instead the mass was deposited within the area of the Several Order license holder (Alastair Mackenzie pers. comm.). Initial discussions with the Environment Agency (EA) indicated that an approach such as undertaken in Poole would not be considered acceptable in Carrick Roads (Simon Toms pers. comm.).

FEPA licenses for disposal at sea are rarely given if there is considered to be a practical land based alternative with the exception of dredging from ports and harbours. However, the Marine Consent Environment Unit (MCEU) website suggests that there is some scope for disposal of fishery by-products if supported by scientific data (Ref. www.mceu.gov.uk/mceu_local/fepa/FEPA-WASTE-DISPOSAL-MAIN.HTM). If a new license were required then a number of consultees would have to be contacted including the Crown Estates, Hydrographic Office, Department for Transport under the Coast Protection Act (1949). Such a process is unlikely to be quick.

Disposal within the controlled waters of an estuary falls within the remit of the EA. The Waste Management Licensing Regulations 1994 incorporate into UK law the provisions of the Waste Framework Directive 91/156. The use of slipper limpets for cultch within the fishery should be acceptable as the material has been derived from within the same controlled waters. However, there is a degree of uncertainty as to whether the material removed will be classed as ‘waste’ as strictly speaking any change to a material is considered as a ‘process’ (Gitty Ankers pers. comm.). This means that if slipper limpets are removed and deposited unchanged within the same area (such as at Poole) they are not waste. Yet if they are killed or have the flesh removed they are ‘changed’ and could be considered a ‘waste’ product. In practice the local EA office will judge each case on its own merits and if on balance no impact is deemed to occur a Waste Management Licence with a ‘Low Risk Permit’ could be granted.

It is proposed that the trial season is used to further negotiate local agency rulings. The use of a temporary process in a ‘trial’ scheme may be acceptable to the EA as adoption of such an approach will allow any potential impact to be monitored before any definitive judgement is made.

D.7. SUMMARY

Utilisation options are dictated by the scale of the slipper limpet stock available and the presence of suitable markets for potential products. Many large scale industrial applications considered by previous workers in France are not appropriate in this case.

Human consumption utilisation options exist for slipper limpets which are edible and can taste good if prepared in the right way. Although slipper limpets are consumed on a small scale elsewhere in the world the export potential is limited. There is scope to develop a small scale production of slipper limpet products for human consumption for niche markets although the business model would require careful investigation.

Slipper limpets can produce food for a variety of species with a number of studies already have

Section D - Utilisation Andy FitzGerald Page 70 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study looked at using them as a cheap protein or mineral sources for fish farming, pigs, cattle, poultry and cats. Assessment of the current limitations for these applications indicates that there is limited scope for the utilisation of slipper limpets for animal consumption in this region. However, a niche low volume, targeted market does offer limited scope in the aquarium and angling bait sectors which should be addressed in a ‘trial season’. The use of slipper limpets for whelk and green shore crab potting bait by local fishing vessels is also another application that could provide an income with a minimum of incurred costs.

Shell applications may exist in a variety of specialist aggregate applications which could possibly be linked with other regional initiatives to utilise shell from fishery processing.

The French authorities have invested heavily in investigating options for a number of years. The reality is that there is no simple answer for utilisation and limitations exist for all potential applications. It is intended that the proposed trial season will enable better identification of these limitations in the local setting thus enabling an assessment of economic viability to be made.

In the UK a number of legal regulations are likely to impact on some or even all of the proposed utilisation options. This will require ongoing negotiation with local responsible agencies throughout the proposed trial season.

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Section E - Proposals

E.1. FISHERY STATUS PROPOSALS

E.1.1 Ongoing Monitoring Any management of the slipper limpet problem will need to be reactive to changes within the fishery. This is necessary partially so that minimum target removal rates are set but also to monitor areas of growth or ‘hot spots.’

Monitoring can take two forms:

1) -a quantitative baseline obtained from a consistent scientifically based protocol using reproducible techniques and comparative sampling stations.

2) -a qualitative ongoing assessment by all operating within the fishery.

Both approaches have their own intrinsic value and should be kept in balance. Yearly scientific surveys such as those performed by CEFAS over recent years provide a good impartial assessment of the fishery on a ‘snapshot’ basis. However, unless they can be funded from external sources ongoing surveys could absorb resources that could be better targeted at actually addressing the problem. In the case of the Bay of Brest nearly 10 years have been spent in monitoring the growth and spread of slipper limpets before acting. Despite this even the most recent report highlights the need for more scientific knowledge (Ref. 5).

In essence, the current CEFAS surveys on one hand do not provide a definitive slipper limpet biomass, whilst on the other, are too expensive and time consuming to undertake each year. It is therefore proposed that quick, easy and cheap qualitative assessments are made on an annual basis, which are backed up by comprehensive quantitative assessments on a five or ten year basis.

E.1.2 Slipper Limpet Biomass Management of the slipper limpet problem can only be targeted efficiently on the basis of biomass assessment. This requires knowledge of the total level of stock within the fishery and the rate of growth. Without this knowledge there is no way (other than trial and error) of setting removal rates.

The CEFAS surveys conducted to date provide a great deal of data but with some high levels of uncertainty (e.g. disparity between 2005 and 2006 survey results). The use of dredge tows is good at levelling out small scale differences in seabed concentrations (Ref. 29). However, unlike the extensive survey methodology adopted in France to ‘ground truth’ the data there remains a high level of uncertainty due to the dredge efficiency. In consequence the biomass in the fishery could be ~100t or ~770t and the minimum removal target could therefore vary between 25t/yr to 200t/yr (Section A.5.3.5). Clearly the management programme and the utilisation options will need to be adjusted according to the amount of material actually requiring removal.

Annual assessments could be made by local authorities with a limited number of dredges at a few

Section E - Proposals Andy FitzGerald Page 72 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study key points with results recorded simply as kg/m2 requiring only weighing of the slipper limpets and the measuring of the length of the trawl. Bed specific biomasses can be further informed by the ongoing ‘collection monitoring’ considered in Section E.2.1.1.

Comprehensive assessments could use the 2006 CEFAS methodology (i.e. with complete counting of slipper limpet samples) but perhaps with some diver/grab ground truthing at a few key monitoring points to help range the dredge efficiency. There may also be scope to work in association with other scientific research in the area such as the summer oceanographic fieldwork undertaken by Southampton University.

This balanced approach should aim to provide a quantitative baseline for the annual qualitative monitoring.

A designated officer within the Harbour Authority should be responsible for consolidating all monitoring data from both scientific and fishery sources.

E.2. MANAGEMENT PROPOSALS There are a number of potential means to manage the fishery some of which are strongly dependant on the economics of utilisation. In essence, a number of short term and long term measures will need to be addressed which will require integrated management.

E.2.1 Combined Slipper Limpet Removal of 25t/yr The 25t/yr proposed removal rate from the fishery for the trial season is a target based upon 3 key criteria:

1) An achievable goal using existing vessel resources; There is limited capacity for handling slipper limpets within the sail boats and punts of the fishery. Many boats do not work throughout the season. Harbour Authority vessels are not designed to haul and store large quantities of stock.

2) Only a suitably small quantity of product is needed to supply a niche market; There is insufficient stock to consider large scale industrial applications. However, niche market applications tend to be small scale and must not be swamped with product which cannot be sold. The trial season must both stimulate the market and assess market potential.

3) Sufficient to keep slipper limpet population under control; Eradication is not an option with the techniques currently available. It is however, reasonable to assume that a programme can be put into place that will at least keep pace with growth and maybe even diminish the total population somewhat. Section A.5.3.5 indicates a growth rate of 26% on a biomass of 107t yielding an annual growth of 25-30t/yr. Unfortunately, there is a degree of uncertainly over the total biomass of the population due to limitations of the measurement techniques (Section E.1.). If the slipper limpet biomass in the fishery is higher then the landing rates will need to be increased accordingly (e.g. ~200t/yr if 16% dredge efficiency).

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E.2.1.1 Oysterman By-Catch Collection During Season (12.5t/yr) Section B.3.2 outlines the target slipper limpet removal rate from commonly fished beds throughout the season. It is assumed that 500kg of slipper limpets can be landed per week from October until March. This equates to ~25 weeks collection of ~12.5t. Therefore on average this would provide a weekly yield of ~100kg of clean flesh (assuming 20% yield) for sale and ~375kg of shell (assuming 75% clean shell).

This level of recovery is set low in order to be reasonable and assumes 50kg/boat/day and x2 boats working for 5 days per week. In practice, landings would not remain constant throughout the season as indicated in Section B.3.2.

E.2.1.2 Harbour Authority Collection Following Season (12.5t/yr) Section B2.3 outlines the target of slipper limpet removal from disused and heavily infested beds (e.g. East Bank). It is assumed that 1,000kg of slipper limpets are landed per week from April until June. This equates to ~12.5 weeks collection of ~12.5t.

E.2.2 Slipper Limpet Handling

E.2.2.1 Collection Monitoring A system of bags possibly demarked by colour tags for each oyster boat will need to be established and administered along with a scheme of record keeping. This approach is similar to that already undertaken by the merchants to identify oystermen’s landings.

Although merchants would be the logical ‘middle-men’ to administer the programme it is suggested that this activity might best be handled either by the Harbour Authority or an intermediary acting on behalf of the Oyster Management Group. Oyster merchants are incredibly busy especially in the height of the season with one primary objective - oysters. It is unlikely that merchants will be able to spare sufficient time to administer the handling and monitoring of slipper limpets as well. Slipper limpet handling and storage will need to be conducted in a co-ordinated manner to ensure that materials are handled correctly and monitoring records maintained. If the stock is not maintained in suitable condition then the potentially higher added value applications (e.g. human consumption) will not be possible.

E.2.2.2 Live Slipper Limpet Storage A system of stock storage will be required because input will be variable (i.e. according to oystermen landings) and output will fluctuate (i.e. according to Ciamar spare capacity). There is no suitable blast freezer in the vicinity and the value of the scheme is unlikely to fund a designated blaster freezer (and associated staff and premises). In consequence, it is suggested that offshore barge storage is proposed in a similar manner to that considered in the Bay of Brest (Section B.2.5.3).

A barge (such as a decommissioned fishing vessel) could provide a platform for unloading stock, holding material, cleaning and brine dipping material. If suitably positioned many of the sail

Section E - Proposals Andy FitzGerald Page 74 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study oystermen could directly drop their stock off on a daily basis. It is possible that the Harbour Authority (or an employed third party) could assist more distant vessels with the transfer of collected stock. The use of a recirculation pump or suitable low density holding cages would allow the storage of stock in good condition. Material could then be extracted for landing at Ciamar as required (without filling up their chiller). This would provide a buffer between the variable inputs and outputs.

The barge also allows a site to differentiate stock and therefore store stock in different cages according to the utilisation route. For example: -Higher quality stock with lower microbial counts obtained from East Bank may be preferred for a human consumption application. -Stock from Grimes Bar further upstream may be designated for aquarium applications. -Dead stock can be set-aside for collection as bait by potters (see Section F.4.). Surplus stock beyond Ciamar capacity could also be brine dipped on board in advance of offshore bait applications.

A capital allowance and revenue allowance has been made for the operation of the barge system (Section F.3.).

E.2.3 Business Model The proposed scheme relies on a number of partner organisations working together to undertake different aspects of the processing and utilisation. A successful scheme working with a number of private business partners will only be successful if all links in the supply chain obtain a suitable financial reward for their efforts. The weakness of this approach is that no-body has the overall responsibility to ensure the project all ties together or the overall aim of reducing slipper limpet impact. In the trial season it is proposed that the Port of Truro Oyster Management Group appoints a third party to be responsible for this function. At the end of this season the results will need to be reviewed with the objective of deciding a long term model for undertaking this activity on an annual basis.

Commercially, products with a high level of added value based on an unknown original product could present an unreasonable business risk. Impartial investors may prefer to manufacture the same preparations using a market accepted product. There is little financial incentive for a private business to take such a risk. In this scenario a body performing ‘social good’ such as a ‘Community Interest Company’ (CIC) may be a suitable approach. The trial season should assess the economic and logistic limitations of a co-operative approach between existing partners and assess whether a new connective role would be required.

E.3. UTILISATION PROPOSALS

E.3.1 Human Consumption Utilisation for human consumption could offer a limited outlet for slipper limpet flesh although a number of issues would need to be addressed.

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E.3.1.1 Economics of Shucking Low cost shucking of quality flesh remains the single most important factor for the success of this utilisation. The issue of manual shucking and the potential of local partnerships are explored in Section F.5. A trial season with a commercial shucking company such as Ciamar will be necessary to resolve this aspect.

E.3.1.2 Legislation Continued work will be required to address the concerns of the FSA in addressing the need for shellfish classification/hygiene testing (Section D.6.1). Ideally this should be performed prior to the trial winter season allowing immediate utilisation. Ongoing negotiations will also be required with the EA to consider waste licensing issues and EN to address ‘Appropriate Assessment’ needs for oyster management proposals (Section B.3.1).

E.3.1.3 Marketing Some clever marketing would be needed to attract the interest of the UK consumer. Discussions with Cornish Cuisine (based in Penryn) revealed that slipper limpets have been consumed in Morocco marketed as ‘Rock Oysters’. It is possible that promotion as a ‘Poor Man’s Oyster’ may have some potential although, as described above, the flesh qualities preclude cooking in a fashion similar to oysters. Further biologically deceptive name options for other species with a similar flesh quality could be ‘Slipper Abalone’ or ‘Button Squid’. Apart from the novelty aspect there is little business incentive to take on the uphill struggle of marketing a new species with a low margin when similar products could be produced from known accepted species. It is suggested that the best low risk option to develop this market would be to try and focus on careful product placement and slowly develop sales through existing local outlets. A marketing component should be included in the proposed trial season.

E.3.1.4 Fresh Food Market It is suggested that this sector would be hard to enter and the preparation of a highly perishable product for such an uncertain outlet would present a high risk. Trial promotional quantities of fresh stock could be provided at no charge to selected outlets to slowly try and develop this market once the legislation aspects have been agreed. However, the major potential outlet for this application could be via the whelk processors who supply overseas markets. It is proposed to provide a fresh test sample for this application ideally in advance of the trial programme.

E.3.1.5 Prepared Food Market Two product types could be produced each with a different target market with the aim of spreading risk:

1) A filler in another seafood product; Slipper limpets could be blended with other species in a seafood cocktail. This would have the advantage of ‘losing’ the slipper limpets but the disadvantage that a higher level of spend would be required to bring in other ingredients. One option would be to utilise other by-catch species obtained

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by the oystermen (e.g. queen scallops, mussels, whelks and crab). Such an approach would only be possible if there was close integration between all parties performing capture, collection and processing.

2) New novel products; Although this route could offer the potential to make a significant margin in a niche market there is a risk that success could quickly swamp the market. The emulation of products from other areas with massive levels of slipper limpets could out-compete Cornish production unless local placement remains the focus.

E.3.1.6 Production Facilities In the short term low level production should be encouraged through existing local businesses such as Cornish Cuisine where the infrastructure is already in place. Where possible it will be preferable to work with partner organisations to spread risk and not distort the existing local market. In the longer term it is uncertain whether a larger quantity of material could be handled by existing outlets and additional investment in new facilities may be appropriate. The trial season proposed should identify the potential level of market uptake and financial viability of this application.

E.3.1.7 Trial Season A number of existing businesses have expressed an interest in trials of slipper limpet shucking and production on a limited basis. It is proposed that systems are put in place to encourage the capture, collection and processing of slipper limpets for the winter season as detailed in Section F. Slipper limpet flesh will be utilised for aquarium, bait and human consumption purposes. The balance of product between these applications will partially be dictated by the suitability of the production area as the cleaner ‘Outer Harbour’ stocks may be better suited for human consumption whilst the ‘River’ stocks would still be acceptable for animal consumption purposes.

E.3.2 Animal Consumption

E.3.2.1 Processed Material A programme of collection, shucking, freezing, packing and distribution is proposed for a winter season (see Section F). As part of this project Ammodytes is willing to process stocks of clean shucked slipper limpets into 100g bags for the bait market and 500g bags for the aquarium market for trial. If free trial samples are sent out alongside existing orders it may be possible to stimulate market uptake. With over 40 aquarium customers around the country this could provide a significant level of exposure for the slipper limpet product.

E.3.2.2 Un-processed Material An unprocessed flesh application for potting bait also provides a fall-back utilisation option. Use of brine dipped stock for whelk and green shore crab potting by local vessels (Section F.4.) should be trialled in the coming season. This application route could prove to be one of the

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E.3.3 Shell Applications

As indicated in Section D.4. shell applications should not be considered in isolation from the wider shell applications for material generated by the local fish processors. Many of these issues were considered in the recent Newlyn Fish Waste Project (Ref. 49). The disposal of by-products from the fish processing sector has been identified by the SWRDA Fisheries Strategic Action Plan as a major hurdle to the industry.

It is proposed to try and further address these issues once more with the submission of a new project proposal beyond the scope of the slipper limpet trial season. It is hoped that slipper limpet shell applications can ‘piggy-back’ on such a project. However, to date a regional study looking at shell applications and a PhD to analyse shell properties in relation to specific applications that have been proposed to FIFG/SWRDA have not met with success.

E.3.3.1 Bound Shell Cornwall Specialist Surfacing based in St Austell would form a good partner organisation to develop this application in the region (Section D.4.1). There is also scope to consider bound applications such as pre-formed blocks, or DIY kits, which are currently beyond the range of this company.

E.3.3.2 Loose Shell Contac based in St Austell would form a good partner organisation to develop this application in the region (Section D.4.2.) However, the company currently does not host internet purchases which could help boost sales to a wider area.

E.3.3.3 Cultch In the absence of financial support it is unlikely that the oystermen will have sufficient resources to buy-back clean slipper limpet shell. It is uncertain at this stage whether the next round of European Funding (European Fisheries Fund, EFF) will consider purchase of cultch as an eligible activity for a project. One of the central axes of the forthcoming scheme is the sustainability of existing fisheries and it is hoped that the proposed project would score highly on the new schemes criteria.

E.4. SUMMARY

A schematic representation of a potential utilisation programme which includes the various applications is provided in Figure 20.

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Figure 20 – Schematic Diagram of Slipper Limpet Process Stages and Market Outlets

CRAB & FROZEN HUMAN NICHE BULK WHELK FEEDS & CONSUMPTION APPLICATIONS AGGREGATE BAIT BAIT

PROCESSING FOR FLESH PROCESSING SHELL CLEANING, ABR DISPOSAL COMMERCIAL BAIT & PACKAGING PROCESSING & (e.g. Western Waste) (new company?) (e.g. Ammodytes & PACKAGING Cornish Cuisine) (new company?)

MARINE STORAGE SHUCKING (new company?) (e.g. Ciamar)

DREDGED COLLECTION (e.g. oystermen & Harbour authority)

MARINE ‘TREATMENT’ CULTCH (subject to licence)

SLIPPER LIMPET SEABED STOCK

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E.4.1 Short Term Actions Prior to Trial -Obtain trial season funding.

-Supply fresh sample to Kaldavanan Seafoods for testing on Korean market.

-Progress with shellfish hygiene testing and negotiations.

-Follow up with shell application test samples.

-Obtain acceptance from English Nature of proposed management approach. This Draft Report would be used to inform an ‘Appropriate Assessment.’

-Prepare a short summary document of this report targeted at oystermen.

-Conduct public presentation to all oystermen to impress upon them the need to participate in the trial. Presentation should seek to demonstrate experience from other fisheries in both UK (e.g. Poole) and France (e.g. DVD from St Brieuc Bay).

-Prepare for trial by establishing collection/monitoring systems and constructing storage/cleaning barges.

-Re-present a shell applications proposal to FIFG/ SWRDA or via the forthcoming EFF.

E.4.2 Medium Term Actions During October-March Trial -Co-ordinate collection, storage, cleaning, shucking and supply of slipper limpets between oystermen, harbour authority, merchants, shucking company and end user companies. A summary of this process is provided in Figure 20.

-Ensure end user market feedback is obtained.

-Monitor seasonal biomass removed from specific beds within the fishery

-Obtain funding for 2007 stock survey (see below).

E.4.3 Long Term Actions Following Trial -Review season performance targets and obtain feedback from all parties (i.e. biomass removed, acceptance by oystermen and product suitability for different applications). -Undertake 2007 biomass survey. CEFAS dredged analysis to be supported by ground truthing. This will enable a firm setting for a future biomass removal target.

-Set target removal levels and market approach for following season and consider longer term funding measures and business plan.

-Participation and encouragement of National monitoring/treatment programmes (e.g. pheromone traps).

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Section F – Trial Season Financial Assessment

F.1. OVERVIEW This section considers outline costs for a trial season at a target production of 25t/yr. Although potential income levels are also considered it is proposed that this initial season is used to stimulate market and as such samples will be provided at a reduced cost.

This financial illustration is based on achieving a spread of utilisation applications with a variety of ‘added value’ levels. In this way the income projections provide both ‘best case’ and ‘worst case’ scenarios according to uptake of higher value utilisation. For ease, it has been assumed that the flesh yield is 20% and the shell yield is 80%.

Although it is hoped that all material could be processed provision has been made with an alternative set of illustrations assuming offshore bait applications for material not processed (Section F.4.).

F.2. COLLECTION AND MONITORING Collection costs are a function of slipper limpet density and the scale of vessel used for collection. Section B.2.5 reviews French collection rates from literature against probable rates for the Port of Truro fishery (Section B.2.3).

Table 8 – Trial Season - Collection Cost Oystermen Harbour Authority Total (Note 1) (Note 2) Cost/t £200 £900 - No. t/season 12.5 12.5 25 Season Period (wks) 25 12.5 37.5 Cost/season £2,500 £11,250 £13,750

Note 1 £0.20/kg cost from Section B.2.2. Note 2 20hr/wk staff time x2 men (@ £20/hr) = 250hr/season = £5,000 = £400/t 20hr/wk vessel time (@£25/hr) = 250hr/season = £6,250 = £500/t

As the collection cost of the harbour Authority far outstrips those of the oystermen theoretically the total cost could be reduced if the proportion gathered by the oystermen were increased (Table 13). In practice, if the Harbour Authority can utilise some of their staff and vessels on a part-time basis working around their other commitments then these costs may be absorbed under existing overheads and may even be eligible ‘in-kind’ project contributions.

The costs of collection within the scheme are pooled as an overhead cost and re-allocated to each utilisation application proportional to mass.

F.3. STORAGE / CLEANING AND HANDLING As with collection the Harbour Authority (or third party) costs for undertaking this activity form a major component of the scheme’s costs. However, this intermediate role is vital to the overall operation of the scheme.

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The cost to clean and handle slipper limpets has been estimated as shown in Table 9 below:

Table 9 – Trial Season – Handling and Cleaning Cost for 25t Extended Season (37.5 wks) Winter Season (25 wks) Staff Costs/t £150/t £100/t (Note 1) Vessel Costs/t £188/t £125/t (Note 2) Capital depreciation/t £40/t £40/t (Note 3) Total/t £378/t £265/t Total/season £9,438 £6,625

Note 1 Extended 37.5wks season: 5hr/wk staff time x1 man (@ £20/hr) = 187.5hr/season = £3,750 Winter 25wks season: 5hr/wk staff time x1 man (@ £20/hr) = 125hr/season = £2,500 Note 2 Extended 37.5wks season: 5hr/wk vessel time (@£25/hr) = 187.5hr/season = £4,688 Winter 25wks season: 5hr/wk vessel time (@£25/hr) = 125hr/season =£3,125 Note 3 Capital cost for barge storage £10,000 depreciated over 10 yrs = £1,000/yr or £40/t

The costs of handling within the scheme are pooled as an overhead cost and re-allocated to each utilisation application proportional to mass.

F.4. SHUCKING AND PROCESSING Manual shucking is well accepted as a major component of processing cost. The costs of shucking within the scheme are pooled as an overhead cost and re-allocated to each utilisation application proportional to mass (Table 10).

Table 10 – Trial Season – Slipper Limpet Processing Cost for 25t Cost/t (flesh) – Note 1 £2,020 Cost/t (whole) – Note 2 £404.00 No. t/season 25 Cost/season £10,100 Note 1: Staff time = £1.69/kg {as flesh} (50% improvement from £3.37/kg trial rate - Section D5.3.) Overhead of 20% = £0.34/kg. Staff time + overhead = £1.69 + £0.34 = £2.02 (or£2,020/t) Note 2: 20% flesh yield. Hence £2.02/5 = £0.40

F.5. UNPROCESSED FLESH APPLICATIONS In the event that processing costs are excessive or that sufficient market outlets cannot be found for the processed output a cheap and easy consumption option will be required (Table 11). Potting bait, as considered in Section D.1.6 can fetch ~£0.50/kg (£500/t), however, the brined unprocessed crushed slipper limpet may not command this return and has therefore been considered at both a full and reduced sale cost (Table 19).

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Table 11 – Trial Season – Bait Production for 25t Extended Season (37.5 wks) Winter Season (25 wks) Staff Costs/t £150/t £100/t (Note 1) Overhead Costs/t £75/t £50/t (Note 2) Capital depreciation/t £8/t £8/t (Note 3) Total/t £233/t £158/t Total/season £8325 £6450

Note 1 Extended 37.5wks season: 5hr/wk staff time x1 man (@ £20/hr) = 187.5hr/season = £3,750 Winter 25wks season: 5hr/wk staff time x1 man (@ £20/hr) = 125hr/season = £2,500 Note 2 Overheads to include room hire, power, salt and packaging. Extended 37.5wks season: Overheads (@£50/wk) = £1875 or Winter 25wks season: Overheads (@£50/wk) = £1250 or £50/t Note 3 Capital cost for chipper £2,000 depreciated over 10 yrs = £200/yr or £8/t

F.6. PROCESSED FLESH APPLICATIONS The processing cost for flesh (£2,020/t {flesh}: see Table 10), coupled with packaging/freezing costs shown in Table 12, would struggle to even meet the buy-in price for aquarium/bait applications. To justify this application either shucking efficiency will need to improve or a premium will need to be achieved on the market value for the product.

Section E.3. outlines the requirement for added value products within the trial. Although the margin may be greater for this type of product the capacity in this sector is likely to be low initially. Therefore additional low margin applications for the majority of the flesh will be required. A mix of the two market applications for 5t of flesh (20% of 25t) has been used in Tables 17 and 18.

Table 12 – Trial Season – Processed Flesh, Costs and Sales Animal – Aquarium/Bait Human Consumption Packaging/handling Cost/t (flesh) £700 (Note 1) £5,000 (Note 2) Income/t (flesh) £2,650 (Note 4) £10,000 (Note 3) Note 1: Assuming a buy-in price to Ammodytes of £1.95/kg and a £0.70/kg cost for handling Note 2: Costs assumed 50% product cost in packaging, other ingredients, staff time and overheads Note 3: Income: Marinade product assumed end point sale price of £1.00/100g (fresh). This price compares to ~£1.50/100g for cockle or mussels presented in a sweet spicy marinade 250g pot size with 100g drained weight of shellfish. £1.00/100g = £10,000/t Note 4 £2.65/kg aquarium by-in cost (Section D5.7.1)

F.7. SHELL APPLICATIONS

As with the flesh, only high value applications for the use of shell will cover the operating costs of the proposed scheme. Bulk aggregate applications have not been considered. It is also assumed that all 20t of shell (80% recovery on 25t) is utilised.

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Table 13 provides the costs and income for bagged (low added value) and resin bound (high added value) applications which are presented for Scenarios 1 and 2 in Tables 17 and 18 respectively.

Table 13 – Trial Season – Processed Shell, Costs and Sales Bagged Resin Bound Packaging/handling Cost/t (shell) £100 £400 (Note 2) Income/t (shell) £400 (Note 1) £2,000 (Note 3) Note 1: Income from bagged aggregate at £10/25kg bag Note 2: Cost for resin kits £10/25kg kit bag Note 3: Income from resin applications. £50/25kg bag

F.8. SUMMARY

F.8.1 Baseline Overheads Production scenarios include collection, handling and shucking costs (Tables 8-10) which are lumped together as a general overhead cost. Packaging and sales costs (Tables 11 and 12) are included proportionate to the degree of added value utilisation in the ‘low,’ ‘moderate’ or ‘high’ projections.

The financial summaries for Scenarios 1 to 3 (Tables 17, 18 and 19) are all provided for the ‘winter’ season which has a lower baseline cost than the ‘extended’ season. However, this could reduce the high value utilisation of flesh as material would not be available in the summer unless expensive blast freezing is used.

The proposed trial season can go ahead with a minimum of capital investment. £10,000 has been accounted for the provision of a barge to form the focus for slipper limpet storage, handling and cleaning. A depreciation cost for this component has been added to Table 9.

F.8.2 Scenario 1 –Processed, High Utilisation, Full Costs A variety of utilisation options for both flesh and shell are required to maximise profits as no one application provides sufficient income to cover the scheme overheads. The disadvantage of this scenario is the higher level of operating costs relative to scenario 2.

Table 14–Processing Cost under Full Utilisation and Cost Basis Cost Scenario Season Collection Handling Shucking (total) Cost (total) (Note 1) (Note 2) (£/season) (£/season) (£/season) (£/season) (Note 3) (£/t) 1A - All costs included 37.5wks 13750 9438 10100 33288 1332

1B - All costs included 25wks 13750 6625 10100 30475 1219

Note 1: Harbour Authority = HA Note 2: 25wks (Oct-Mar, Fishing season). 37.5 wks (Oct-Jun, Fishing season+3 additional months) Note 3: 25t/yr

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Seasonal cost and income analysis has been calculated for a range of illustrations according to the degree of added value applications as shown in Table 17.

F.8.3 Scenario 2 –Processed, High Utilisation, Limited Costs Overall scheme profitability is vastly improved if Harbour Authority activities are not charged to the scheme. A variety of cost illustrations are summarised in Table 15 with differing levels of charging. A financial summary of this scenario is presented in Table 18.

Table 15 – Processing Cost under Full Utilisation and Limited Cost Basis Cost Season Collection Handling Shucking Cost (total) Scenario (total) (Note 1) (Note 2) (£/season) (£/season) (£/season) (£/season) (Note 3) (£/t) 2A - No HA collection costs 37.5wks 2500 9438 10100 22038 882

2B - No HA collection costs 25wks 2500 6625 10100 19225 769

2C - No HA 37.5wks 2500 0 10100 12600 504 Collection + handling or 25wks costs Note 1: Harbour Authority = HA Note 2: 25wks (Oct-Mar, Fishing season). 37.5 wks (Oct-Jun, Fishing season+3 additional months) Note 3: 25t/yr

F.8.4 Scenario 3 – Unprocessed, Low Utilisation, Limited Costs This low value scenario assumes all 25t are unprocessed and that the oystermen undertake all slipper limpet collection (i.e. no Harbour Authority collection costs) as shown in Table 16. Profit can only be achieved if a bait price of >£250/t is obtained.

Table 16 – Low Value Utilisation with Limited Costs Cost Season Collection Handling Shucking Cost (total) Scenario (total) (Note 1) (Note 2) (£/season) (£/season) (£/season) (£/season) (Note 3) (£/t) 3 - No HA Collection costs + 25wks 2500 3950 0 6450 258 Processing costs Note 1: Harbour Authority = HA Note 2: 25wks (Oct-Mar, Fishing season). Note 3: 25t/yr

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Table 17 – Trial Season – Scenario 1, Financial Summary for Complete Processing Low Proportion of Added Value (20:80) Cost/t Cost/t Product Application Quantity (general) (applications) Cost/t (total) Cost Income/t Income Profit Profit Margin t (£/t) (£/t) (£/t) (£) (£/t) (£) (£/t) (£) (%) Flesh Animal consumption 4 1219 700 1919 7676 2650 10600 731 2924 38% Flesh Human consumption 1 1219 5000 6219 6219 10000 10000 3781 3781 61% Shell Loose bagged 16 1219 100 1319 21104 400 6400 -919 -14704 -70% Shell Resin bound 4 1219 400 1619 6476 2000 8000 381 1524 24% TOTAL 25 41475 35000 -6475 -16%

Moderate Proportion of Added Value (50:50) Cost/t Cost/t Product Application Quantity (general) (applications) Cost/t (total) Cost Income/t Income Profit Profit Margin t (£/t) (£/t) (£/t) (£) (£/t) (£) (£/t) (£) (%) Flesh Animal consumption 2.5 1219 700 1919 4797.5 2650 6625 731 1827.5 38% Flesh Human consumption 2.5 1219 5000 6219 15547.5 10000 25000 3781 9452.5 61% Shell Loose bagged 10 1219 100 1319 13190 400 4000 -919 -9190 -70% Shell Resin bound 10 1219 400 1619 16190 2000 20000 381 3810 24% TOTAL 25 49725 55625 5900 12%

High Proportion of Added Value (80:20) Cost/t Cost/t Product Application Quantity (general) (applications) Cost/t (total) Cost Income/t Income Profit Profit Margin t (£/t) (£/t) (£/t) (£) (£/t) (£) (£/t) (£) (%) Flesh Animal consumption 1 1219 700 1919 1919 2650 2650 731 731 38% Flesh Human consumption 4 1219 5000 6219 24876 10000 40000 3781 15124 61% Shell Loose bagged 4 1219 100 1319 5276 400 1600 -919 -3676 -70% Shell Resin bound 16 1219 400 1619 25904 2000 32000 381 6096 24% TOTAL 25 57975 76250 18275 32% Notes: All material shucked Flesh yield 20%, shell yield 80% 25t/yr harvest over ‘winter’ 25wk season Cost breakdown in Table 14

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Table 18 – Trial Season – Scenario 2, Financial Summary for Complete Processing and Limited Cost Basis Low Proportion of Added Value (20:80) Cost/t Cost/t Product Application Quantity (general) (applications) Cost/t (total) Cost Income/t Income Profit Profit Margin t (£/t) (£/t) (£/t) (£) (£/t) (£) (£/t) (£) (%) Flesh Animal consumption 4 769 700 1469 5876 2650 10600 1181 4724 80% Flesh Human consumption 1 769 5000 5769 5769 10000 10000 4231 4231 73% Shell Loose bagged 16 769 100 869 13904 400 6400 -469 -7504 -54% Shell Resin bound 4 769 400 1169 4676 2000 8000 831 3324 71% TOTAL 25 30225 35000 4775 16%

Moderate Proportion of Added Value (50:50) Cost/t Cost/t Product Application Quantity (general) (applications) Cost/t (total) Cost Income/t Income Profit Profit Margin t (£/t) (£/t) (£/t) (£) (£/t) (£) (£/t) (£) (%) Flesh Animal consumption 2.5 769 700 1469 3672.5 2650 6625 1181 2952.5 80% Flesh Human consumption 2.5 769 5000 5769 14422.5 10000 25000 4231 10577.5 73% Shell Loose bagged 10 769 100 869 8690 400 4000 -469 -4690 -54% Shell Resin bound 10 769 400 1169 11690 2000 20000 831 8310 71% TOTAL 25 38475 55625 17150 45%

High Proportion of Added Value (80:20) Cost/t Cost/t Product Application Quantity (general) (applications) Cost/t (total) Cost Income/t Income Profit Profit Margin t (£/t) (£/t) (£/t) (£) (£/t) (£) (£/t) (£) (%) Flesh Animal consumption 1 769 700 1469 1469 2650 2650 1181 1181 80% Flesh Human consumption 4 769 5000 5769 23076 10000 40000 4231 16924 73% Shell Loose bagged 4 769 100 869 3476 400 1600 -469 -1876 -54% Shell Resin bound 16 769 400 1169 18704 2000 32000 831 13296 71% TOTAL 25 46725 76250 29525 63% Notes: All material shucked Flesh yield 20%, shell yield 80% 25t/yr harvest over ‘winter’ 25wk season Cost breakdown in Table 15

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Table 19 – Trial Season – Scenario 3, Financial Summary for Low Value Utilisation with Limited Costs Low Bait Market Price Cost/t Cost/t Product Application Quantity (general) (applications) Cost/t (total) Cost Income/t Income Profit Profit Margin t (£/t) (£/t) (£/t) (£) (£/t) (£) (£/t) (£) (%) Mixed Bait 25 258 0 258 6450 250 6250 -8 -200 -3% TOTAL 25 6450 6250 -200 -3%

High Bait Market Price Cost/t Cost/t Product Application Quantity (general) (applications) Cost/t (total) Cost Income/t Income Profit Profit Margin t (£/t) (£/t) (£/t) (£) (£/t) (£) (£/t) (£) (%) Mixed Bait 25 258 0 258 6450 500 12500 242 6050 94% TOTAL 25 6450 12500 6050 94%

Notes: No material shucked All mixed crushed product 25t/yr harvest over ‘winter’ 25wk season Cost breakdown in Table 16

Section F – Financial Assessment Andy FitzGerald Page 88 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

Section G - Conclusions

Status The Port of Truro oyster fishery in Carrick Roads and the Fal estuary has a slipper limpet problem that appears to have increased in recent years. Despite this, the level of infestation, although significant, is still low relative to other major ‘hot spots’ in the UK and Europe.

Similar patterns of growth with ‘tipping points’ have been experienced elsewhere. Failure to act quickly (within 10yrs) could have a major impact on both the fishery and the marine environment in this important SAC area. Future management in a potentially highly infested area would be difficult, expensive and would require adverse/harsh removal techniques.

Slipper limpet stock assessment data has been used to set a target removal rate of 25t/yr to keep pace with growth.

Management There is currently no easy way to eliminate slipper limpet stocks. One must either learn to live with them and adapt fishing techniques accordingly or try to manage population growth.

Industrial extraction techniques such as suction dredging are inappropriate for the fishery at this stage. Small scale removal via the oystermen and Harbour Authority vessels is still the most cost effective technique of removal. Removal and collection will need to be largely funded by suitable utilisation options.

Scope exists to develop new elimination techniques such as pheromone traps although these will take time and funding for R&D perhaps through National or International projects.

Extraction of Flesh Industrial scale extraction is not a current option. Small scale automated techniques using existing equipment have been attempted in this trial but yielded a poor quality product with low yield. Manual shucking remains the only effective albeit expensive extraction option.

Utilisation There is no quick and easy answer to utilise slipper limpets cost effectively. The French authorities have been expending a large amount of money in research and trials on this topic since the early 1990’s and are still struggling with the problem.

Slipper limpet flesh can be utilised in small scale niche applications for aquarium/bait markets and potentially for human consumption although legislative constraints still restrict development of this market. These potential applications are economically marginal as the former would have a low profit margin whilst the second would have a high risk. Use as a local bait for whelks and crab could provide a low value application with no legislative boundaries or processing costs.

Slipper limpet shell utilised as a specialist aggregate requires product development and marketing to achieve maximum returns. Cultch applications are unlikely to provide a high level of income and could only be considered as part of a funded project.

Section G - Conclusions Andy FitzGerald Page 89 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

Large scale industrial applications such as the agricultural use or meal preparations are not appropriate to the area.

Proposals Any management and utilisation options will need to be agreed with the responsible agencies through the development of an ‘Appropriate Assessment’ (AA) as techniques could have a significant impact in this SAC. It has been suggested that any AA should encompass all inter- related aspects of the oyster management and not just slipper limpets.

A target removal rate of 25t/yr has been proposed for the fishery with collection via the oystermen and the Harbour Authority. An integrated management approach has been proposed whereby removal and ongoing monitoring are adopted. A designated Harbour Authority officer, or appointed third party, should be responsible for co-ordination of monitoring, management and utilisation programmes as all aspects are linked.

A trial over the season could allow better evaluation of costs and income with which to inform future participation. The proposed business partnership between local businesses could yield a small income to all parties involved in the supply chain. However, margins would be low with a high degree of risk. Oystermen and Harbour Authority can attempt removal and collection and Ciamar (based in Falmouth) undertake shucking. A number of partner companies are well placed to develop different potential complimentary applications: -Cornish Cuisine (based in Penryn) to develop/market human consumption products. -Kaldavanan Seafood (based in Fleetwood) for overseas consumption. -Ammodytes (based in St Ives) develops the aquarium/bait market. -Contac (based in St Austell) for loose bagged shell applications.

Financial Utilisation for a variety of niche market added value applications may be able to provide a financially viable project. Profitability will depend on a number of features which must be explored within the trial season. Key parameters include: -Recharge of Harbour Authority costs. -Processing costs for the shucking of flesh. -Market uptake of added value applications.

The low tonnage of removal envisaged would require a minimal capital investment for equipment if partners can employ existing plant and vessels.

Full processing and utilisation with complete cost recharge could cost between £41K - £58K. Profitability is dependant on the utilisation of most material for high added value applications.

Partial utilisation for bait purposes without processing could reduce operating costs to £6K - £7K although profitability would be minimal.

Failure to provide a viable private business case may require a different operational model with access to some public funding probably required in future years.

Section G - Conclusions Andy FitzGerald Page 90 of 101 Port of Truro Oyster Management Group Slipper Limpet Utilisation / Management Study

Appendix A – References Ref 1. SW PESCA, March 2002. Management Plan for the Port of Truro Oyster Fishery.

Ref. 2 Comite D’Expansion Economique Des Cotes D’Armor. January 1996. “La Valorisation Industrielle, Des Crepidules En Bretagne.” Report for Comite Regional Des Peches Maritimes De Bretagne. Annex 1. LDA22 (Laboratoire De Developpement Et D’Analyses). September 1993. “Recherche Sur Les Possibilites De Valorisation Des Crepidules.” Annex 2. LDA22 (Laboratoire De Developpement Et D’Analyses). November 1993-January 1994. “Etude De La Faisabilite Technique D’Un Ensilage De Crepidules”. Annex 3. Ecole Nationale Veterinaire De Nantes. February 1995. “Etude D’Appetence Chez Le Chat” Annex 4. AGROVAL. “Faisabilite Technico-Economique De La Valorisation Des Crepidules A Raison De 300 Tonnes/Jour.”

Ref. 3 Dessein, A. and Gondouin, E., 2001. “Valorisation De La Chair De Crepidula Fornicata.” DESS Exploitation Des Ressources Vivantes Cotieres, Universite De Caen.

Ref. 4 Blanchard, M. Clabaut, P., and Chantal A., March 2006. “Cartographie et Evaluation du stock de crepidules en baie du Mont St Michel, en 2004.” IFREMER report DYNECO/EB /06-01.

Ref. 5 CREOCEAN, March 2006. “Projet D’Extraction Et De Transformation De La Crepidule en Rade De Brest”. Report for Brest Metropole Oceane.

Ref. 6 CEFAS, 2004. Distribution of the Slipper Limpet Crepidula fornicata within the limits of the Truro Oyster Fishery Order, 2-4 March 2004. Report C2157.

Ref. 7 CEFAS, 2005. Distribution of the Slipper Limpet Crepidula fornicata within the limits of the Truro Oyster Fishery Order, 1-3 March 2005. Shellfish Resource Team Report No. 61.

Ref. 8 CEFAS, 2006. Oyster and Slipper Limpet Survey, 7-9 March 2006. DEFRA/MFA Reference: FEP 736.

Ref. 9 INVABIO, 2002-2006. French National Programme for Coastal Environment: The Bay of Mont-St Michel Project. Report in progress. (www.ifremer.fr/delec-en/projects/Crepidule/chantier.htm)

Ref. 10 Hawkins, L. Evaluation of Factors Affecting Native Oyster Stock Regeneration, DEFRA Project FC 0926.

Ref. 11 de Montaudouin, X., C. Audemard, and P.J. Labourg, 1999. Does the slipper limpet (Crepidula fornicata, L.) impair oyster growth and zoobenthos biodiversity? A revisited hypothesis. Journal of Experimental Marine Biology and Ecology 235, 105-124.

Ref. 12 Thieltges, D.W., 2005. Impact of an invader: epizootic American slipper limpet Crepidula fornicata reduces survival and growth in European mussels. Marine Ecology Progress Series 286, 13-19.

Ref. 13 Thieltges, D.W., 2005. Benefit from an invader: American slipper limpet Crepidula fornicata reduces star fish predation on European mussels. Hydrobiologia 541, 241-244.

Ref. 14 Nehls, G., Diederick, S. and. Thieltges, D.W. (2006) Wadden Sea Mussel Beds Invaded by Oyster and Slipper limpets: Competition or Climate Control? Helgoland Marine Research 60, 135-143.

Ref. 15 Fresard, M. and Boncoeur, J., 2004. ‘Cost-Benefit Analysis of a Project Concerning the Management of an Invasive Species in a Coastal Fishery: The Case of Crepidula fornicata in the Bay of Brest (France). IIFET Japan Proceedings.

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Ref. 16 Fresard, M., Boncoeur, J. and Carval, J.P., October 2005. ‘Managing the Spread of an invasive Species in a Coastal Shellfishery under Ecosystemic Uncertainty: Cost-Benefit with Reference to the Bay of Brest (France)’. 8th International Conference of Shellfish Restoration.

Ref. 17 Fresard, M. and Boncoeur, J., 2005. ‘Biological Invasion of a Commercial Fishery by a Space Competitor: a Bioeconomic Analysis of the Bay of St Brieuc Scallop Fishery.’ NAREA Workshop on Invasive Species, Maryland June 2005.

Ref. 18 Le Pap, O., Guerault, D. and Deraunay, Y., 2004. Effect of an invasive Mollusc, American Slipper Limpet Crepidula fornicata on Habitat Suitability for Juvenile Common Sole Solea solea in the Bay of Biscay. Marine Ecology Progress Series 277, 107-115.

Ref. 19 de Montaudouin, X. & Sauriau, P.G., 1999. The proliferating Gastropoda Crepidula fornicata may stimulate macrozoobenthic diversity. Journal of the Marine Biological Association of the United Kingdom, 79, 1069-1077.

Ref. 20 Guerin, L., Guarini, J.M. and Thouzeau, G., October 2005. ‘Impact of the Current Proliferation of the Alien Crepidula fornicata on Shellfish Habitat and Resources in the Bay of Brest (France).’ 8th International Conference of Shellfish Restoration.

Ref. 21 Grall, J. & Hall-Spencer, J.M., 2003. Problems facing maerl conservation in Brittany. Aquatic Conservation, Marine and Freshwater Ecosystems, 13, 55-64.

Ref. 22 ‘Biological Invasions (INVABIO)’ LEMAR, University of Brest. (http://www.univ-brest.fr/IUEM/UMR6539/prog_scientif/INVABIO/invabio1_uk.htm)

Ref. 23 Martin, S. et al., October 2005. ‘Respiration, Calcification and Excretion of an Invasive Species Crepidula fornicata: Implication for C and N Fluxes in Impacted Area.’ 8th International Conference of Shellfish Restoration.

Ref. 24 Thouseau, J. et al., October 2005. ‘Impacts of the Feeding Activities of the Invasive Slipper Limpet, Crepidula fornicate on Silicon Cycle in the Bay of Brest.’ 8th International Conference of Shellfish Restoration.

Ref. 25 Rayment, W.J., 2001. Crepidula fornicata and Aphelochaeta marioni in variable salinity infralittoral mixed sediment. Marine Life Information Network: Biology and Sensitivity Key Information Sub- programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 04/05/2006]. Available from:

Ref. 26 Dupont L., 2004. Invasion des côtes françaises par le mollusque exotique Crepidula fornicata : contribution de la dispersion larvaire et du système de reproduction au succès de la colonisation. Thèse de Doctorat, Ecole Doctorale Diversité du Vivant, Université Pierre et Marie Curie, 124 pages. Dir. F. Viard.

Ref. 27 Richard, J., Huet, M., Thouzeau, G. and Paulet, Y.M., October 2005. Reproduction of the Invasive Slipper Limpet, Crepidula fornicata in the Bay of Brest, France. Marine Biology (in press).

Ref. 28 Collin, R., 2001. ‘The effects of mode of development on phylogeography and population structure of North Atlantic Crepidula (Gastropoda: Calyptraeidae)’ Molecular Ecology 10, 2249–2262.

Ref. 29 Walne, P.R., 1956. The biology and distributions of the slipper limpet Crepidula fornicata in Essex Rivers. With notes on the distribution of the larger epi-benthic invertebrates. Ministry of Agriculture, Fisheries and Food, Fishery Investigations, Series 2, 20, 1-50.

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Ref. 30 Viard, F., Ellien, C. and Dupont, L., 2006. Dispersal ability and invasion success of Crepidula fornicata in a single gulf: insights from genetic markers and larval-dispersal model. Helgoland Marine Research, 60, 144–152.

Ref. 31 Orton, J.H., June 1914. On Ciliary Mechanisms In Brachiopods And Some Polychaetes, With A Comparison Of The Ciliary Mechanisms On The Gills Of Molluscs, Protochordata, Brachiopods, And Cryptocephalous Polychaetes, And An Account Of The Endostyle Of Crepidula And Its Allies. Journal of the Marine Biological Association of the United Kingdom, 10, Number 2, 283-311.

Ref. 32 Pechenik, J.A., Blanchard M. and Rotjan R., 2004. Susceptibility of larval Crepidula fornicata to predation by suspension-feeding adults. Journal of Experimental Marine Biology and Ecology 306, 75- 94.

Ref. 33 Thieltges, D.W., Strasser, M., Van Beusekom, J.E.E., Reise, K., 2004. ‘Too cold to prosper - winter mortality prevents population increase of the introduced American slipper limpet Crepidula fornicate in northern Europe.’ Journal of Experimental Marine Biology and Ecology, 311, 375-391.

Ref. 34 Cole, H.A., 1952. The American slipper limpet (Crepidula fornicata L.) on Cornish oyster beds. Ministry of Agriculture Fisheries and Food. Fisheries Investigation Series 2 17 (7), 1–21.

Ref. 35 de Montaudouin, X., Labarraque, D., Giraud, K. & Bachelet, G., 2001. Why does the introduced gastropod Crepidula fornicata fail to invade Arcachon Bay (France)? Journal of the Marine Biological Association of the United Kingdom, 81, 97-104.

Ref. 36 Blanchard, M., 1997. Spread of the slipper limpet Crepidula fornicata (L. 1758) in Europe. Current state and consequences. Scientia Marina. 61(SUPPL. 2), 109-118.

Ref. 37 Zaiko A., 2005. Crepidula fornicata. In: Baltic Sea Alien Species Database. S. Olenin, E. Leppakoski and D. Daunys (eds.). (http://www.ku.lt/nemo/mainnemo.html)

Ref. 38 Sjotun, 1997. A new observation of Crepidula fornicata (Prosobranchia, Calyptraeidae) in western Norway. Sarsiam, 82(3), 275-276.

Ref. 39 FitzGerald, A., September 2003. ‘Demonstration Growth and Mortality Trials to Establish the Suitability of the European Abalone (or Ormer) for Culture in Cornish Coastal Waters.’ A FIFG Project on behalf of Cornwall Sea Fisheries.

Ref. 40 Thieltges, D.W., Strasser, M., Reise, K., 2003. The American slipper-limpet Crepidula fornicata (L.) in the Northern Wadden Sea 70 years after its introduction. Helgoland Marine Research 57, 27-33.

Ref. 41 Mistakidis, M.N., 1951. Quantitative Studies of the Bottom Fauna of Essex Oyster Grounds. Ministry of Agriculture, Fisheries and Food, Fishery Investigations Series 2, 17, 1-47.

Ref. 42 Barnes, R.S.K., Coughlan, J. & Holmes, N.J., 1973. A preliminary survey of the macro-scopic bottom fauna of the Solent, with particular reference to Crepidula fornicata and Ostrea edulis. Proc. Malac. Soc. Lond., 40, 253.

Ref. 43 Dyrynda, P.E.J., 2001. Distributions and ecological impacts of non-native species within natural estuarine channels (Poole Harbour, UK). In Abstracts: Second International Conference on Marine Bioinvasions, March 9-11, 2001. New Orleans, LA.

Ref. 44 Cole, H.A. and Baird, R.H., 1953. The American Slipper Limpet (Crepidula fornicata) in Milford Haven. Nature, London, 172, 678.

Ref. 45 Laing, I., Walker, P. and Areal, F., February 2005. ‘Native Oyster Stock Regeneration - A Review of Biological, Technical and Economic Feasibility A feasibility study of native oyster (Ostrea edulis)

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stock regeneration in the United Kingdom.’ CARD Project FC1016. (http://www.seafish.org/upload/file/main/Oyster%20Feasibility%20Study.pdf)

Ref. 46 Eno, C.N., Clark, R.A., Sanderson, W.G., 1997. Non-native marine species in British waters: a review and directory. Joint Nature Conservation Committee (JNCC), Peterborough.

Ref. 47 Stebbing P.D., Watson, G.J., Bentley, M.G., Fraser, D., Jennings, R., Rushton, S.P., Sibley, P.J., 2004. Evaluation of the capacity of pheromones for control of invasive non-native crayfish- Part 1 of 2. English Nature Research Reports No. 578, English Nature, Peterborough, UK. (http://www.english-nature.org.uk/pubs/publication/PDF/578.pdf)

Ref. 48 Stebbing P.D., Watson, G.J., Bentley, M.G., Fraser, D., Jennings, R., Sibley, P.J., 2005. Evaluation of the capacity of pheromones for control of invasive non-native crayfish- Part 2of 2. English Nature Research Reports No. 633, English Nature, Peterborough, UK. (http://www.english-nature.org.uk/pubs/publication/PDF/633.pdf)

Ref. 49 Newlyn Fish Industry Forum, December 2004. ‘Newlyn Fish Waste Biotreatment Scheme Cost/Benefit Assessment of Options.’

Ref. 50 Sea Fish Industry Authority, Lake, N., March 2006. ‘"European Marine Sites and the Current Impact of Environmental Appropriate Assessments on the Management and Operation of Commercial Fishing and Aquaculture Activities". http://www.seafish.org/upload/file/about_us/Final%20AA%20Report%20Complete%20PDF.pdf

Ref. 51 Walker, C., April 12, 2005. How One City May Put an Alien Species to Good Work. National Geographic News. http://news.nationalgeographic.com/news/2005/04/0412_050412_snails.html

Ref. 52 Sea Fish Industry Authority Report SR537. November 2000. ‘Fish Waste Production in the UK – The Quantities Produced and Opportunities for Better Utilisation.’

Ref. 53 Sea Fish Industry Authority Web Update, March 2006. ‘Disposal of seafood waste at sea’ (http://www.seafish.org/upload/file/about_us/Disposal%20of%20Seafood%20waste%20at%20sea%20 28_3_06.pdf)

Ref. 54 ICES, 2005. Report of the Working Group on Introductions and Transfers of Marine Organ-isms (WGITMO), By Correspondence, ICES CM 2005/ACME: 05, 173 p.

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Appendix B – French Case Study Plots Bay of Mont St Michael – (Courtesy of M. Blanchard)

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Bay of St Brieuc in 1994 – (Courtesy of M. Blanchard)

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Appendix C - CEFAS Survey Results for the Port of Truro Fishery

From Ref. 7

From Ref. 8

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Appendix D – Automated Extraction Trial Output

Extraction trial undertaken on 19/4/6 using ’freeze-knocking’ technique (see Section C.2.3.)

Methodology Stage 1 -Pre-clean of shells prior to freezing. Stage 2 -Freezing. Stage 3 -Knocking. Stage 4 -Initial grading. Stage 5 -Knocking. Stage 6 -Second grading.

Courtesy of Ammodytes for use of blast freezer and Martin Laity for use of winkle sorter.

Results Shell Size After Freezing After Extraction whole Shell Flesh Shell+flesh Total Loss kg % kg kg Kg kg kg Grade 1 - 10mm 1.23 6% 0.23 0.76 - Grade 2 - 13mm 0.85 4% 0.45 0.04 0.04 Grade 3 - 15mm 18 90% 7.57 0.08 5.13 Total 20.08 8.25 0.88 5.17 14.3 5.78 % of original 100% 41.1% 4.4% 25.7% 71.2% 28.8%

Evaluation A poor percentage recovery rate was obtained after extraction. A large amount of mixed shell and flesh remained un-separated. Increased time in stage 5 may have increased extraction although this would have reduced flesh quality (more mashed up) and increased the level of loss. The loss from the system was observed throughout the process with solid flesh material sticking to equipment (conveyor + winkle grader) and liquid dripping from process to be washed away by water from spray bars. It should be noted that the winkle sorter spray bars were needed to remove material stuck on the low gradient inclines of the winkle sorter. A large quantity of very concentrated effluent was generated that would be expensive to discharge in a commercial setting.

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Appendix E – Contact Listing

Fishery Related Groups / Individuals Mr J. Bailey Port of Truro Oyster fisherman Mr C. Bates Port of Falmouth Health Authority Cpt. A. Brigden Port of Truro Harbour Authority Mr I. Carrier Southern Sea Fishery Mr P. Coates South Wales Sea Fishery Mr G. Cooper Port of Falmouth Health Authority Mr I. Davies Formerly of Oakwood Oysters (Poole) Mr P. Favian Lyme Bay Scallop diver Mr P. Ferris Port of Truro Harbour Authority Mr C. Frost Port of Truro Oyster fisherman Mr D. Hancock Fowey Sea Farms Mr M. Laity Port of Truro Oyster fisherman+merchant Mr K. Oatman Salcombe Estuary scallop dredger Mr M. Parsons Port of Truro Oyster fisherman Mr F. Vinnicombe Port of Truro Oyster fisherman Mr T. Vinnicombe Port of Truro Oyster fisherman Mr J. Wiggins Essex Sea Fishery

Private Company Contacts Mr M. Bolitho Truro Concrete products Mr D. Boothroyd National Lobster Hatchery (Padstow) Mr S. Dellurne The Seafood Restaurant (Padstow) Mr N. Ellis Cornish Cuisine (Penryn) Mr S. Evans Kaldavanan Seafood (Fleetwood) Mr R. Furse Contac Mr M. Gilbert Ammodytes (St Ives) Mr M. Nicholson Cornwall Specialist Surfaces (St Austell) Mr M. Slater Blue Reef Aquarium (Newquay) Mr P. Tierney Ciamar (Falmouth)

French Oystermen / Fishery Related Groups and International Experts Mr M. Blanchard IFREMER Dr L. Dupont Roscoff Marine Biological Station / MBA Dr M. Fresard University of Brest / LEMAR Mr Jambon Bay of Concale Oyster fisherman+merchant Mr P. Le Coz CEMAR Director, Portrieux Mr F. Le Boat TradOcean (Cancale shellfish merchant) Dr J. Pechenik Tuffs University (US) Dr S. Riou CREOCEAN Dr S. Smith Washington Department of Fish and Wildlife Mr M. Soulas CAD22 / Cotes d’Armor Developpement

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UK Agencies / Authorities Ms Gitty Ankers Environment Agency – Waste Division Dr C. Askew Shellfish Association of Great Britain Dr R. Ball Interface Analysis Centre, Uni. Of Bristol Mr R. Covey English Nature Dr E. Edwards OBE Shellfish expert and former MAFF scientist Dr K. Hiscock Marine Biological Association Dr L. Hawkins Southampton Oceanography Centre Mr M. Gray SEAFISH A.A. Advisor Dr A. Jensen Southampton Oceanography Centre Dr I. Laing CEFAS Weymouth Dr J. Light Conch. Society of Great Britain and Ireland Mr A. Mackenzie Marine Fisheries Agency Dr A. Moore CEFAS Lowestoft Mr D. Smethurst Formerly of Cornwall College Dr P. Stebbing CEFAS Weymouth Mr M. Syvret SEAFISH Inshore Group Mr S. Toms Environment Agency Mr P. Walker CEFAS Lowestoft Dr G. Watson Portsmouth University Dr A. Younger CEFAS Weymouth

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