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Review of National Cockle Mortality Issues and Options for Fishery Management in Kent and Essex IFCA

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Review of National Cockle Mortality Issues and Options for Fishery Management in Kent and Essex IFCA Appendix A to Agenda item B3 Review of National Cockle Mortality Issues and Options for Fishery Management in Kent and Essex IFCA Dr Andrew Woolmer March 2013 Cockle Mortality and Biosecurity Management Review Contents 1. Introduction ................................................................................................................................ 3 1.1. The Thames cockle fishing industry ..................................................................................... 3 1.2. Management of the cockle stocks ....................................................................................... 3 1.3. KEIFA response to mortalities in cockle stocks ................................................................... 4 1.4. Overview of mass mortality in cockles ................................................................................ 4 1.4.1. Physical Environmental factors ........................................................................................ 7 1.4.2. Anthropogenic Factors ..................................................................................................... 8 1.4.3. Pathogens and disease .................................................................................................... 9 2. Case Studies of Recent UK Mortality Events ............................................................................ 12 2.1. Burry Inlet, South Wales .................................................................................................... 12 2.2. The Three Rivers Estuary, South Wales ............................................................................. 19 2.3. Dee Estuary ........................................................................................................................ 22 2.4. Traeth Lafan (Lavan Sands) ................................................................................................ 22 2.5. Dyfi (Dovey) Estuary .......................................................................................................... 23 2.6. Angle Bay ........................................................................................................................... 23 2.7. The Wash, Norfolk ............................................................................................................. 24 2.8. Horseshoe Point, Lincolnshire ........................................................................................... 28 2.9. Budle Bay, Northumberland .............................................................................................. 29 2.10. Camel Estuary, North Coast Cornwall ............................................................................ 29 2.11. Helford and Ruan (Fal) Creeks, South Coast Cornwall ................................................... 29 2.12. Exmouth, South Coast Devon ........................................................................................ 32 3. Analysis ..................................................................................................................................... 33 3.1. Comparative table ............................................................................................................. 33 3.2. Trends in Historical Cockle Classification Status – England and Wales ............................. 37 3.3. Sex ratios in Cockles from affected sites ........................................................................... 40 4. Discussion.................................................................................................................................. 42 References ....................................................................................................................................... 46 Appendix 1. “Atypical” Mortality: Potential Risks and Mitigation Options ..................................... 51 2 | P a g e Cockle Mortality and Biosecurity Management Review 1. Introduction 1.1. The Thames cockle fishing industry Up until the late 1960s all cockles were collected by hand raking. Following a decline in the hand- raking fishery the hydraulic cockle dredge was developed by the White Fish Authority. This proved successful although damage rates to cockles were initially high. The development of new harvesting systems saw the introduction of the solids handling pump in the early 1990s, this combined with other modifications to dredge design has meant that catch smash rates of around 20% in the 1970s have now mostly been reduced to below 5%. As the industry modernised, new vessels were built with even greater catching capacity, which in turn triggered the need for improved monitoring and management of the fishery. In 1991 new European Shellfish Hygiene legislation came into operation, which proceeded to open up the fishery and put increased pressure upon stocks, to a level that could be detrimental to its sustainable long term production. To counteract this KESFC worked with the local cockle industry to develop the present day level of fishery management. 1.2. Management of the cockle stocks To help develop and protect the cockles within the district a series of byelaws were passed which laid down the conditions by which people could remove cockles in a way that was deemed sustainable. To this end there are byelaws limiting: • maximum vessel size • engine power • dredge size • minimum cockle size • maximum damage rate • closure of beds/closed season • fishing times and quantities landed • additional fishing permit requirements The Thames Estuary Cockle Fishery Regulating Order came into operation in 1994 and covers the major section of the fishery, only 14 vessels are licensed to fish for cockles within this area. An important part of management has been policy that closes beds to commercial exploitation once stock levels drop below set limits. In addition to local vessels, traditionally up to 20 visiting vessels from the Wash and West coast ports have worked the outer areas not covered by the Regulating Order. Skippers are required to return catch data showing area fished, quantity taken and fishing time. Generally cockle beds outside the regulating order have been opened for 1-4 weeks, with the decision to close based on catch rates dropping below 1 tonne an hour. Although the fishing duration can be less than a month the value of the cockles harvested from these sites has been up to £1.5M at first point of sale. 3 | P a g e Cockle Mortality and Biosecurity Management Review 1.3. KEIFA response to mortalities in cockle stocks In 2008 the Wash cockle fishery started to suffer significant cockle mortalities with losses reported to be as high as 14,000 tonnes. In 2009 the Wash cockle fishery continued to show significant mortalities (estimated to be 6,000 tonnes) and although the hand rake fishery remained open, the lack of available stock meant that the dredge fishery was closed (this management regime continued for 2010, 2011 and 2012). In 2010 the KESFC decided to take a precautionary approach on the possibility of spreading the cause of high cockle mortality in the Wash area by maintaining the closure of cockle beds outside the area of the Regulating Order. This decision has been reviewed each year by the KESFC/KEIFCA since then and the Authority has decided to maintain its precautionary approach and keep the beds closed to all cockle fishing vessels. Aims of this report: This report aims to provide KEIFCA with an objective information from which management decisions can be evidenced. This report focuses on the following aspect: Review UK and European cases of recent mass cockle mortalities Identify commonalities between mortality events and identify possible causative factors Review management actions for managers faced with mortality events including preventative measures 1.4. Overview of mass mortality in cockles Cockle populations, like other bivalve species, suffer from periodic mass mortalities with resulting population crashes. These events are not uncommon, having been reported for decades, and have been associated with a variety of factors including disease, predation, pollution, recruitment failures, over-fishing and most recently climate change (Ducrotoy et al., 1989). A number of environmental factors have been implicated with cockle mortalities including algal blooms, deterioration in water quality, eutrophication, temperature, salinity, and weather events such as storms. These events have been reported with an increasing frequency and intensity in bivalve species in the last 50 years (Walter et al., 2007; Hayes et al., 2001). See Table 1 for a synthesis. What have become termed as ‘Atypical’ cockle mortalities have been reported in the UK since 2002. In order to provide clarity it is useful to provide a comparison of ‘typical’ and ‘atypical’ mortalities: Characteristics of typical mortalities: These are commonly episodic mortality events punctuating extended periods of recovery and persistence of the population. These are often associated with a clear causative agent. These may manifest as a sudden catastrophic mass mortality or a prolonged event occurring over a single season. 4 | P a g e Cockle Mortality and Biosecurity Management Review Post-event the population either recovers to pre-mortality state of multiple year classes and spatial distribution, or, in some instances, may be locally extinct for a period until environmental conditions are suitable. Characteristics of atypical mortalities: These are chronic and persistent mortality events that repeat over a number of years. May begin with
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