Scottish Marine and Freshwater Science Vol 12 No 10

This report describes a survey carried out in Largo Bay, Firth of Forth in 2020. The original work plan was interrupted due to Covid-19 but a survey of the area currently being fished was completed prior to lock-down. A combination of a commercial electrofishing rig and towed video was deployed using the fishing vessel ‘Maxine’. The video recordings were subsequently analysed for the number and sizes of razor clams observed on the surface of the seabed following passage of the electrofishing equipment. These count data were converted to area densities (numbers of razor clams m-2) based on estimates of the swept area from tow start and end positions recorded from the vessel chart plotter.

The use of towed video combined with electrofishing appeared to work well in Largo Bay. The lowest number of tows completed in any one day was four but this was due to worsening weather conditions and under good conditions up to 11 tows were completed each day. The video recorded was generally of sufficient quality to allow identification of objects on the seabed with only a few tows having parts of the field of view obscured by sediment kicked up by the camera sled. Although the efficiency of the electrofishing equipment is assumed to be high, this has not been formally confirmed by comparison with other methods such as dredging (Hauton et al., 2007). The estimates of E. siliqua densities provided in this report therefore represent a minimum for the razor clam stock in Largo Bay in 2020.