Development and application of a novel approach to assessing razor clam (Ensis sp.) stocks.


Describe the impacts resulting from your research

Research leading to the provision of science advice on the abundance of razor clams (Ensis spp.) in inshore beds. Support to MArine Scotland in establishing a managed fishery for these species.

Who or what is affected by your research?

Inshore razor clam fisheries; Marine Scotland; Marine Scotland Science.

How did your research contribute or influence these changes?

Landings of razor clams in Scotland have been as high as 900 tonnes with a value of £3,000,000 but have since fallen back to around 3-400 tonnes (£1,500,000). Razor clams are found in shallow sandy sediments and can be extracted using dredges or collected by hand after adding salt to the burrows. They are quite slow-growing so over-exploitation of stocks has always been a concern. Over the last decade or so electrofishing has emerged as a dominant extraction technique which is also highly efficient. Whilst illegal under EU rules it has undoubtedly been taking place on a large-scale and much of the peak of razor landings probably has its origins from this harvesting technique. Recently the Scottish government has initiated moves to clamp down on illegal electrofishing with the intention of moving the fishery to a properly managed basis with licenced vessels and controlled fishing areas. SAMS have been working with Marine Scotland and Marine Scotland science to develop improved methods of assessing the stocks of Ensis as a first step towards establishing a regulated sustainable fishery. The stocks of razor clams have not been properly surveyed since the 1970s so current knowledge of the state of the stocks is weak.

SAMS have developed a towed video camera array which can be deployed behind electrofishing rigs in order to collect data on the abundance and sizes of razor clams in the beds. The video data are processed with computer imaging software in Matlab to correct for camera lens distortions allowing accurate measurements and counts of the razor clams to be made. The technique has recently been applied in initial surveys in the Sound of Harris and in the Clyde. The data are presently being analysed but will be used by Marine Scotland to inform their establishment of controlled fishing areas. We anticipate that further work will continue over the next few years, both to establish present stock levels at different sites but also to monitor the impacts of the fishery. the value of the impact will likely be between £1-3 million per year.
Impact statusIn preparation
Impact date20162020