Cockle, cockles

Cerastoderma edule

Method of production — Caught at sea
Capture method — Suction dredge
Capture area — North East Atlantic (FAO 27)
Stock area — England
Stock detail

Kent & Essex IFCA district (within the TECFO area only)


Sustainability rating three info

Sustainability overview

The Thames Estuary cockle fishery is managed by the Kent and Essex Inshore Fisheries & Conservation Authority (KEIFCA). KEIFCA has conducted annual cockle surveys in the Thames Estuary since 1988, to determine the distribution, density and population of cockles in the district. This information in turn informs the management strategy of the cockle fishery. This rating covers two different areas, the area within the Thames Estuary Cockle Fishery Order (TECFO) and area outside the TECFO. Recruitment into cockle populations is highly variable. Hand gathering is not allowed so this rating only covers suction dredge fisheries. Suction dredge gear used to harvest cockles are associated with relatively low levels of bycatch, however, can cause some habitat damage. The IFCA mitigate this by conducting habitat assessments to reduce the level of cockle dredging occurring in sensitive habitats. The common cockle is an abundant mollusk species found in tidal flats in bays and estuaries in Europe. Cockles are a major food source of crustaceans, fish, and wading birds. Cockles are found buried up to 5 cm in sand, muddy sands and muddy gravel; on middle to lower intertidal and sub-tidal sediments. The Thames fishery is one of the largest cockle fisheries.

Biology

The common cockle is a bivalve mollusc found buried in mud and sand in estuaries and on beaches. Cockles have distinctive rounded shells that are slightly heart shaped. It is a bivalve (two identical shells) belonging to the family Cardidae meaning heart-shaped. An organ called a siphon allows the animal to feed and breathe whilst buried in the sand. They can jump by bending and straightening the foot - the end bit- which is often coloured red and called the red nosea. The shell size is up to 5cm long, although average sizes tend to be around 3-4cm. Maturity occurs at a shell length of around 2cm. Cockles spawn from March to August, although exact times will vary from region to region.

Stock information

Criterion score: 0.5 info

Stock Area

England

Stock information

The stock status of cockles in this area is unknown and there are conflicting indicators for biomass (very high numbers of adult cockles, however, there are very poor growth rates).

The most recent stock assessment suggests that there is a good outlook for the fishery in the next two years, provided that the cockles which were left on the grounds at the end of the fishery survive the winter and experience good growth rates in spring 2018, therefore, there is no concern for biomass.

There is no information to determine if fishing mortality is sufficient for the stock and therefore, there is concern for fishing mortality.

Cockles are considered a higha resilience species.

Management

Criterion score: 0.5 info

The KEIFCA manages cockles through management areas: there are 14 grounds within the area covered by the TECFO (1994) and eight grounds outside the area covered by the TECFO. The majority of the fishery is managed under the TECFO.

The main management measures covered by the harvest control strategy include the minimum size, seasons, closed areas, fishery closures, permits and Total Allowable Catches (TACs). TACs are divided between licence holders (for areas inside the TECFO area) or permit holders (for areas outside the TECFO area). TACs vary depending on the results of the stock assessments. The minimum landing is 16 mm and only 10% of the catch is allowed to be below this size. Within the TECFO, no licence holder is allowed to carry on board or land more than 13.6 cubic metres of cockles within any fishing trip. The minimum size may be reduced to 14mm if permitted by the Permitted Cockle Fishery Management Plan.

Surveys suggest that the management plan has resulted in a sustainable, commercially viable cockle stock.

Sustainable management of cockles is also required to ensure sufficient food for wading birds and marine species and comply with habitat regulations to reduce damage to features of the Essex Estuaries SAC and Mid Essex Coast SPA sites.

Monitoring

Annual cockle stock surveys have been conducted since 1988 in the Thames Estuary. Stock surveys determine the distribution, density and age structure of cockles to estimate their population size. Cockle recruitment events and increased winter survivability is also monitored since weather events such a high levels of winter storms can have a major impact on their populations. Regular surveys are used to set a TAC.

Each licence holder must return detailed catch logs.Vessel Monitoring System is used to monitor and enforce the fishery. These are also used to ensure compliance with Habitat Regulations Assessments.

Enforcement
There is a high level of surveillance and enforcement inside and outside the TECFO area. Since hand gathering is banned within the TECFO area, surveillance and enforcement is targeted towards the 14 licenced vessels in the TECFO and on visiting vessels (outside the TECO) when open.

Capture Information

Criterion score: 0.5 info

Bycatch
Suction dredge displaces cockles from sediment using water jets. They are then lifted on-board using a lift pump, where they are riddled (where the small cockles are isolated and can be discarded). Bycatch may include invertebrates such as shore crabs. The level of endangered protected or threatened species catch is considered to be low, unless the fishery is occurring near sea grass beds. Additionally, much of the fishery area occurs on highly dynamic intertidal sands where the majority of the catch is cockles and therefore bycatch is lower.

Habitat
Much of the fishery area occurs on highly dynamic intertidal sands or in the shallow subtidal zone which are subject to frequent natural disturbance. However, the majority of the cockle fishery occurs on a European Marine Site (EMS) Special Area of Conservation or Special Protection Areas for birds under the EU Habitats (European Council directive 92/43) and Birds (European Council directive 147/43). Protected features include sandbanks that are covered at low water and intertidal mud and sand where cockle dredging is carried: these areas are likely to be less vulnerable than the surrounding saltmarshes and sea grass beds. Since the majority of the fishery lies within a Special Area of Conservation, IFCAs use VMS data to ensure that the risk to sensitive habitats are reduced. Additionally, KEIFCA have implemented a byelaw prohibiting the use of bottom towed fishing gear over the seagrass feature.

Habitat protection: Intertidal muds appear to be relatively-well protected from suction dredging to the north of the River Blackwater, but less to the south. A recent Habitat Regulations Assessment suggests that dredging could present “a significant effect on the intertidal sand, mud, muddy sand or mixed sediment features of Essex Estuaries SAC and bird features of Benfleet and Southend Marshes SPA, Thames Estuary and Marshes SPA, Foulness SPA and Outer Thames SPA if it was not managed. However, Natural England suggests that there are sufficient management has been implemented to mitigate these effects. However, it is debated whether these thin strips of protection are effective at protecting the intertidal seagrass.

The higher proportion of fishing occurs on intertidal muds, intertidal sand, muddy sand and course sediment, yet muddy sands are particularly intolerant to towed demersal fishing gear such as trawling or dredging impacts. There is minimal protection for these habitats in the areas of the highest fishing pressure. Therefore, it is unknown if management is sufficient to protect the ecosystem.

References

Heywood, J.L., Webster, P. and Bailey, D. 2017. Thames Estuary Cockle Survey Report 2016. Kent and Essex Inshore Fisheries and Conservation Authority. 46 pp.

Kent and Essex Inshore Fisheries Conservation Authority. 2018. Fisheries in EMS Habitats Regulations Assessment for the 2018 Thames Estuary Cockle Fishery Order Area Fishery. KEIFCA/EE/TECFO18. Version 1.2. Available at: https://www.kentandessex-ifca.gov.uk/wp-content/uploads/2018/05/Appendix-C-to-Agenda-item-B5.pdf

Kent and Essex Inshore Fisheries Conservation Authority. 2017. 2017 Cockle Fishery Management. Agenda Item No. B3. Available at: https://www.kentandessex-ifca.gov.uk/wp-content/uploads/2017/11/Agenda-item-B3.pdf

Kent & Essex Inshore Fisheries and Conservation Authority. 2017. KEIFCA Meeting minutes 30th November 2017. Available at: https://www.kentandessex-ifca.gov.uk/wp-content/uploads/2018/01/2017-11-30-KEIFCA-meeting-minutes.pdf

Worrall, J. Highs and lows in east coast cockles. 4th July 2017. Fishing News. Available at: https://fishingnews.co.uk/features/highs-and-lows-in-east-coast-cockles/

Kent and Essex Inshore Fisheries Conservation Authority. 2017. Cockle Fishery update. Agenda Item B2. Available at: https://www.kentandessex-ifca.gov.uk/wp-content/uploads/2017/09/Agenda-item-B2.pdf

Kent & Essex Inshore Fisheries and Conservation Authority. 2018. The Thames estuary cockle fishery order 1994 regulations. Available at: https://www.kentandessex-ifca.gov.uk/i-want-to-find-out-about/regulations/tecfo/