To Develop the Methodology to Undertake Stock Assessments on Razor Fish Using Combinations of Video Monitoring and Electrofishing Gear

Data Type: 
Marine Scotland Data Portal

Scottish Marine and Freshwater Science Vol 8 No 6

Fisheries for razor clams (Ensis siliqua and Ensis arcuatus) have gone through a series of expansions in Scotland associated with changes in markets and the introduction of new harvesting techniques. Electrofishing has been recently introduced as an efficient method of forcing clams to the surface of the seabed where they can be collected by divers. Although electrofishing is illegal under European legislation the available evidence suggests that the method could be less impacting on the benthic habitat than alternate techniques, such as mechanical and hydraulic dredges. Electrofishing is also much more efficient than forcing the clams to emerge by pouring high concentration brine into the burrows (a technique known as ‘salting’). Concerns over the use of electrofishing therefore relate mainly to its efficiency and the health and safety risks of using the equipment itself (potential H&S risks are not dealt with in this report). Electrofishing therefore, has the potential to lead to over-harvesting and depletion of razor clam beds, especially considering the slow growth rates of razor clams. A further concern is that there have been very limited surveys of the stock status of Ensis beds around Scotland so that the impacts of harvesting would be difficult to assess. Historical stock assessments in Ireland and Scotland have mainly used dredges or salting followed by divers counting the emergent clams within quadrats . As mentioned previously dredges cause damage to the habitat, as well as to the clams themselves, whilst counting using divers is slow, expensive and samples relatively small areas. The present project was designed to evaluate whether combining an electrofishing rig with a towed video-camera array could be used to assess the razor clam resources in a bed in an efficient manner.