Shocks, Shells & Stocks

: Impacts of trial electrofishing for razor clams in Scottish shallow coastal habitats

Abstract

Referred to colloquially in Scotland as ‘spoots’, razor clams belonging to the genus Ensis are the subject of lucrative fisheries. Burrowed within sandy substrates, they are found patchily distributed throughout Scotland’s shallow coastal seas. Where conditions are particularly favourable, razor clams can form dense aggregations, or ‘beds’, which offer the opportunity for commercial harvest. Landings of these common bivalves by Scottish vessels have increased substantially since the mid-1990s and the fishery is now extracting around 650-750 tonnes of razor clams each year, valued at approximately £6 million per annum. Harvest techniques include artisanal hand-picking, as well as more intensive mechanical and hydraulic dredging. Most fishers, however, favour electrofishing because it is efficient, appears environmentally benign, and produces a high-quality product. Yet, despite these potential benefits, electrofishing is prohibited under EU law. Although the UK has retained the EU’s prohibition of electrofishing post-Brexit, in February 2018, the Scottish Government commenced a trial of electrofishing for razor clams under scientific derogation. The trial imposes strict controls with an operating framework specifically designed to address long-standing knowledge gaps. The overall objective of the trial is to evaluate whether this electrofishery can operate sustainably and be integrated within Scotland’s inshore fisheries management processes. Yet, uncertainties remain regarding sustainability at full commercial scale. The work conducted in this PhD contributes several areas of supporting knowledge required by the Scottish Government to evaluate the trial.
From an ecological standpoint, there is concern that exposure to the applied electric field may have lasting effects on non-target species, with potential adverse implications for the wider benthic community. The common shore crab (Carcinus maenas) and the common starfish (Asterias rubens), both important components of Scottish razor clam habitats, were exposed to experimental electrical fields in tank-based experiments to investigate the physiological effects on these non-target invertebrates. A variety of physiological and behavioural markers were monitored immediately before exposure, and then for 10 days afterwards. The stress related metabolite L-lactate became elevated in the haemolymph of shore crabs but returned to baseline levels ~24 hours following exposure, suggesting a short-lived stress response. No significant effects were discerned in starfish when evaluated using time taken for self-righting behaviour and coelomocyte viability. These findings corroborate previous observational findings which suggest that electrofishing for razor clams causes only minor adverse effects in non-target organisms of the fishery.

Datum der Bewilligung	23 Juni 2026
Originalsprache	English
Gradverleihende Hochschule	University of the Highlands and Islands
Betreuer/-in	Clive Fox (Supervisor)