Electrofishing for razor clams trial: update - February 2021 to January 2022

7. Marine Directorate Science

MD Science continues to collect a range of biological and fisheries data under the trial and are still focussed on the biological and ecological goals:

• to gather local level information on razor clam populations and stocks, including accurate data gathered by trial participants to supplement stock survey work;
• to ensure sustainable harvesting levels; and,
• to gather further information about the impacts of the electrofishing method on target and non-target species.

From August 2018, samples of live razor clams have been sent to MD Science on an approximately monthly basis. At the start of the trial, MD Science requested monthly samples of approximately 200 animals from each trial area. These are dissected and a sub-sample undergo further histological examination. Sampling was suspended from April 2020 to March 2021 due to COVID-19 pandemic but resumed on a reduced basis from April 2021. Restrictions at the Marine Laboratory regarding staff access and safe work practices meant that sampling was reduced to focus on four trial areas (Firth of Clyde, Firth of Forth, Gigha and Broad Bay) and the number of live razor clams reduced from 200 to 30 individuals, the maximum processing capacity of the laboratory under the controls in place at the time. New laboratory space was sourced and sampling conducted by one scientist to accommodate physical distancing guidelines in place. A total of 5,616 live razor clams have been sampled from August 2018 to January 2022 (Table 1), with 807 razor clams further examined by histology for maturity staging and spawning activity.

*August-December only

**January only

Trial participants also provide length measurements of a sample of the razor clams landed from each trial area. Between August 2018 and January 2022, a total of 32,461 razor clams were measured by fishers (and processors) and data collated by MD Science (Table 2). For two trial areas (Firth of Forth and Firth of Clyde) for which sufficient sample data are available, length frequency data obtained from self-sampling were combined with official landings data to provide a raised annual landings-at-length distribution. These data were averaged over a four-year period (2018 – 2021) and aggregated for use in Length Cohort Analysis (LCA). A detailed assessment of progress towards the biological and ecological objectives of the trial is in the course of completion. This will include an assessment whether these data indicate trial controls ensure harvesting at sustainable.

*August-December only

**January only

In addition, MD Science analysed REM data to study the spatial distribution of catches and combine fishing effort and landings data to monitor landings per unit effort. Analyses of REM data have been developed further through the Scottish Government Data Science Accelerator Programme (DSAP) which allowed MD Science analysts to learn new data science skills. This program incorporated the use of analytical tools required to work with the new sources of fisheries data generated by tracking and monitoring technologies.