Report on razor clam surveys on Tarbert Bank

Introduction

The aim of this survey was to use a combination of electrofishing with towed video to assess the quantities and sizes of razor clams (Ensis spp.) on Tarbert Bank. This is one of a series of surveys in areas where razor clam harvesting is permitted under the Scottish Government’s scientific trial on electrofishing (Scottish Government, 2017, 2019). Areas where commercial shellfish harvesting is permitted are also limited by hygiene regulations and waters are classified for this purpose by Food Standards Scotland (https://www.foodstandards.gov.scot/business-and-industry/industry-specific-advice/shellfish).

In addition, commercial razor clam harvesting is not permitted in some locations for nature conservation reasons, based on advice from NatureScot. Evidence from previous field surveys, and monitoring of the fishery, shows that even within the larger permitted fishing areas, the distribution of Ensis is patchy. Razor clams only occur in commercial densities in certain locations and fishers recognise specific areas or beds where fishing is worthwhile. Predetermined randomised surveys covering the whole of the production area are therefore unlikely to yield particularly useful information because much of the area is not suitable habitat. The present survey thus made extensive use of local fisher knowledge, as well as fishing location data collected by Marine Directorate (formerly Marine Scotland), to target the parts of the production area which have been regularly fished during the trial. For Tarbert Bank the latitude 56ºN divides the area into a northern part where electrofishing is permitted, and a southern part where it is prohibited. Additional tows were therefore conducted in the southern area for comparison purposes.