Clam, Razor, clams

Solen spp.

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

North West IFCA district only


Picture of Clam, Razor, clams

Sustainability rating five info

Sustainability overview

There are currently no permitted razor clam fisheries in English waters. Until the Northwest Inshore Fisheries Conservation Authority (IFCA) authority has determined the state of the stock and the impact of fishing for razor clams on the environment, the fishery will not proceed.

The stock status of razor clams in England is unknown and the only management currently in place is a minimum conservation reference size of 100mm.

Generally, dredging is the most popular methods to harvest razor clams as it is a highly efficient. However, dredging can be destructive to both bycatch and benthic habitats. Conversely, hand gathering methods (which have received minor interest) is much less efficient but is a highly selective method, presenting much fewer negative environmental impacts and a higher quality product.

Market demand for razor clams has been rapidly growing market for South East Asia (predominantly China). The UK market is limited to mostly restaurants. Three native species of the genus Ensis are currently commercially exploited in Scotland and Eire: E. ensis, E. siliqua and E. arcuatus. The market prefers the larger E. siliqua.

Biology

Razor clams are bivalve molluscs. There are 6 species found in British intertidal waters. 2 are of commercial importance, namely Ensis siliqua and E arcuatus. E directus was introduced to European waters probably in 1978 through tanker ballast water. Spawning occurs in summer. Fertilised eggs develop into mobile larvae hours after fertilisation. The larval phase includes several stages and lasts for about 3-4 weeks, during which time they drift with the current. The larval phase ends when larvae settle, attaching themselves to sand or shell by byssal threads. At around 0.5cm length juveniles burrow into sand. Relative to other commercially important bivalves Ensis are long-lived, slow growing, and attain sexual maturity late in life. They may survive to 10-15 years and an average adult can reach a size of 12.5cm, although growth will cease by age 10. E.siliqua and E.arcuatus can live in excess of 20 years. E. arcuatus reaches sexual maturity between 73 and 130 mm and E. siliqua mature between 118 - 140 mm in Scotland. They are filter feeders and normally lie vertically in the sediment with 2 small siphons, through which they feed, visible on the surface. Razor clams burrow into the sediment around the extreme low water mark and in the shallow subtidal and are capable of rapid burrowing if disturbed.

Stock information

Criterion score: 1 info

Stock Area

England

Stock information

The stock status of razor clams is unknown. Previous studies have been authorized but few have been conducted: the 2006 CEFAS Eastern Irish Sea bivalve survey found that overall numbers recorded were low. The north Irish Sea stocks are the most exploited (Tully, 2017), at high levels and intel suggests there has been a risk of illegal fishing.

The Liverpool Bay Razor Clam (Ensis spp.) survey suggested that abundance of razor clam was very variable dependent on location.” This differs for species found in the NWIFCA District where populations of different species inhabit similar locations and have been reported to move around. Previous work by CEFAS in 2013 - 14 to carry out experimental electro-fishing for razor clams in the District was abandoned, after two attempts resulted in no catch from areas where Ensis spp. were previously reported.

Razor clam are a relatively slow-growing and long-lived species. They also have intermittent recruitment which increases their susceptibility to over-exploitation.

Management

Criterion score: 1 info

The only management measures for razor clams are the minimum landing size if 100mm. Age of maturity is estimated to be at least three or four years (which is around the minimum landing size). However some sources suggest that maturity may not occur until greater lengths (i.e. 120 mm).

There is currently no legal fishery for razor clam but there have been multiple requests and demand to fish for razor clams and there is intelligence suggesting that there is a risk of illegal fishing. To mitigate this, NWIFCA has enacted a Use of a Dredge Byelaw 2017 to prevent illegal uses of dredges (where dredges are being used to fish for razor clams).

A previous CEFAS study in the area recommended management measures should include making gear more selective to reduce shell damage and increase the minimum landing size.

Capture Information

Criterion score: 1 info

Summary
Dredging occurs in muddy sand/sandy mud seabed substrate, and bycatch in the region is unknown but likely to be high.

Justification
There is currently no permitted razor clam fisheries in English waters but some dredge studies have been trialled in these waters. Though no endangered, protected or threatened species were recorded in previous studies, dredging has been associated with a high level of bycatch in other areas: bycatch levels vary between 30% and 70% of the total catch. Previous dredge studies in the NWIFCA found that main bycatch included Echincocardium cordatum (Heart urchin) and additional clam species. Damage to bycatch ranged from 10 to 28% of individuals. More research is needed to determine the overlap of target and non-target species in the NWIFCA District.

Generally, dredge fishing is reported to cause significant impacts to be seabed and change community composition. In deep sandy habitat, immediate impacts of hydraulic dredging caused furrows, causing a dramatic change to seabed topography, still detectable a year later. However, in exposed shallow sandy subtidal environments, impacts were no longer visible after eleven weeks. Impacts of hydraulic dredging for bivalves on benthic sediments in the intertidal zone were not significant. The hydraulic dredge is very efficient (90%) at razor clams extraction and also removes undersized immature individuals compared to non-hydraulic dredges (fishing for clams, scallops and oysters where efficiency has been recorded at 10-35%).

There is some protection afforded to sheltered areas, to protect sensitive habitats, as part of the Inshore Fishing (Scotland) Act 1984. Dredges also interact and impact algae and other epifauna and infauna, which are either not brought aboard or are discarded either alive or dead.

References

Aitken, A., and Knott, M. 2018. Razor Clams in the North Western IFCA District: is there potential for a sustainable fishery?. Report for NWIFCA. Available at: https://www.nw-ifca.gov.uk/app/uploads/Agenda-Item-7-Annex-B-Razor-Clams-in-the-NWIFCA-District.pdf.

Gaspar M.B., Chcharo L.M. (2007) Modifying Dredges to Reduce By-catch and Impacts on the Benthos. In: Kennelly S.J. (eds) By-catch Reduction in the Worldas Fisheries. Reviews: Methods and Technologies in Fish Biology and Fisheries, vol 7. Springer, Dordrecht

NWIFCA. 2018. Minimum Sizes. [Accessed 17/05/18]. Available at: https://www.nw-ifca.gov.uk/minimum-sizes/

NWIFCA Technical, Science and Byelaw Committee 6th February 2018. RAZOR CLAM REPORT. Available at: https://www.nw-ifca.gov.uk/app/uploads/Agenda-Item-7-Razor-Clam-Report-TSB-Feb-2018.pdf

Cappell, R., J. Hambrey, J. Addison (2017). DFA Dutch North Sea Ensis Public Comment Draft Report. Acoura Marine. MSC Sustainable Fisheries Certification. Accessed online at: https://fisheries.msc.org/en/fisheries/dfa-dutch-north-sea-ensis/@@assessments Accessed on: 20/11/17.