Organism and ecological impacts of electrofishing in Scottish shallow coastal habitats

We are seeking applicants with strong interests in marine organism physiology and/or benthic ecology to take part in an exciting new PhD project in collaboration with Marine Scotland and Marine Scotland Science.

Over the last decade, electrofishing has developed in shallow marine coastal sites around Scotland. The principal targets are two species of razor clam (Ensis siliqua and Ensis magnus). These shellfish command high prices in the Far East which has driven a fishery that has increased substantially since the mid-1990s reaching a value of around £3 million per annum and extracting 400-500 tonnes of razors per annum. Electrofishing is preferred by the fishers because it produces a cleaner and hence more valuable product compared with other harvest techniques, such as dredging. It is also claimed that electrofishing is more benign from an environmental view but there is limited scientific evidence to support this. Some research has been conducted on the short-term impacts of electrofishing on razor clams and other non-target benthic organisms. These studies suggested that impacts are limited with razor clams being observed to rebury a few minutes after the electrical field has passed. Non-target organisms such as juvenile flatfish, starfish and crabs were either temporarily stunned or apparently unaffected. On the other hand there is anecdotal evidence that electrofished razor clams do not ‘depurate’^a as well as those harvested using other techniques. This suggests that electrofishing may affect the physiology of the clams in the short and possibly medium-term.

Although previously illegal under the EU Common Fisheries Policy, the Scottish Government has established a tightly controlled research-scale trial electrofishery for razor clams in a number of locations around Scotland. The impacts of the trial fisheries on the Ensis stocks are being monitored by Marine Scotland Science. However, concerns remain about potential longer-term impacts on both smaller and under-sized razor clams that are not collected, and on the wider benthic ecosystem, especially with industry pressure to open out wider areas to electrofishing.

The aims of the project will be to conduct laboratory and field-studies to address these issues. The project may include a variety of laboratory and field based approaches including:-

1. Aquarium based experiments comparing the growth, filtration and other physiological performance indicators of razor clams and other non-target organisms collected using electrofishing with samples which have been collected by alternate means. Organisms will be marked using suitable tags (visible elastomer for flatfish, starfish etc.), external marking of the shell for bivalves and maintained in mixed groups so that compared subjects experience the same environmental conditions.

2. Comparing physiological performance of organisms exposed to electrical fields with control organisms - growth, filtration clearance rates for filtration feeding organisms (razor clams and other non-target bivalves), swimming activity rates assessed using SAMS video observation facility (flatfish and decapods), oxygen uptake rates using respirometry, muscle energy metabolites and protein profiles.

3. Field sampling within and adjacent to the Scottish experimental electrofishing areas to investigate whether there are any detectable impacts on the wider benthic communities from electrofishing activity.

4. The student will also have the opportunity to work with Marine Scotland Science’s Assessment team in terms of analysing background data on the trial fisheries. Such data include fishing intensity, catch records and information on sizes of shellfish being landed.

5. Marine Scotland Science are also collecting shells from the experimental fisheries and are interested in the student applying methods of age determination to establish age-length relationships, and growth characteristics for razor clams in the different fishing areas. These data could be used in stock production models and potentially age-based stock assessment methods.

^a Depuration (purification) is a process by which shellfish are held in tanks of clean seawater under conditions that maximize the natural filtering activity. This results in purging of intestinal contents including microbial contaminants such as E. coli thus reducing chances of contamination of the shellfish when eaten.