- Nearshore areas provide critical habitat for a range of fish species targeted by commercial and recreational fisheries, both of which make an important contribution to local economies in rural areas. However, established trawl survey methods are not suited to many nearshore areas, owing to shallow depths, obstructions on the sea bed or vulnerable habitats, so there is a lack of information on fish abundance in these areas.
- The aim of the present project was to develop and test survey methods applicable to Scottish inshore waters, focussing on baited underwater cameras, fish traps, systematic rod-and-line surveys and observations of fish bycatch in crustacean trap fisheries, and to carry out associated studies of fish movements.
- A lightweight baited underwater camera system was developed that could be deployed by two persons from inshore fishing vessels and small boats. The system consisted of a digital camera and strobes in underwater housings, mounted on a frame of aluminium alloy tubing, suspended above the seabed by sub-surface floats on one leg of a J-shaped mooring. The camera was baited with oily fish and a standardized 1 hour deployment period was used, to minimize variability in results due to changing tidal currents and bait degradation. Photographs were taken at 30 second intervals throughout the deployment period. On retrieval, the photographs were examined to derive indices of fish abundance, such as the time to first arrival of particular species (TFA) and the maximum number of individuals seen in the field of view at any time during the deployment (MaxN).
- The BUC system was developed and tested in the Firth of Clyde and then deployed at a range of other locations in Lamlash Bay, Arran, the Firth of Lorn, the Sound of Mull, Loch Sunart, Loch Etive, around Skye, Galloway and in Orkney.
- The BUC system was successfully deployed from a range of types of vessel in depths down to 40 m. Over thirty species of fish were recorded in total, including species of commercial interest, with lesser spotted dogfish, Scyliorhinus canicula, being the most commonly recorded. The number of species and indices of abundance were highest at sites on the Galloway peninsula.
- When compared within a single area, BUC detected more species than angling or fish traps, but less than in visual transects by SCUBA divers. BUC shows great potential as a cost-effective survey method, able to show relative differences in abundance between areas. It is likely that it would also be effective in detecting temporal trends, though this was outside the scope of the present project.
- A Norwegian design of collapsible cod trap, Roscoff traps designed for common prawns and Norway lobster creels were investigated as fish traps. There were differences in catch rates and species composition related to the trap design. Roscoff traps appeared to be suitable for sampling juvenile cod (Gadus morhua) in complex habitat in shallow water, whereas collapsible cod traps are suitable for larger fish, but need to be fished in greater numbers to obtain sufficient data.
- Creel fisheries were surveyed by questionnaire and by on-board catch sampling. A range of fish species is taken as bycatch in creels, with some obvious differences in species composition between crab fishing and Norway lobster fishing in relation to the depths and ground types fished. The present results suggest that the catch rates of commercial fish species may be too low for creeling to be a useful way of monitoring fish stocks, but sampling throughout the year in different areas would be desirable to assess this more fully.
- A small-scale pilot study in Galloway indicated some potential for rod-and-line surveys to generate useful information on the abundance of certain fishes. The Scottish Sea Angling Conservation Network and the Scottish Shark Tagging Project already collect information on catches of angling target species and on tagging and recaptures of tagged fish. This would be augmented by encouraging anglers to submit returns with an indication of fishing duration even when they have not caught anything. However, we were unsuccessful in recruiting volunteers to participate in a randomized angling survey. Further work is required to develop statistically robust angling surveys in which volunteer anglers would be willing to participate. Experience indicates that payment of expenses would be required for volunteers to agree to fish according to a survey protocol.
- To study movements of a species of interest to recreational sea anglers, spurdog (Squalus acanthias), ten specimens in Loch Etive were tagged with data storage tags designed to record water temperature and depth. To date, one tag has been recovered and the downloaded data shows an interesting pattern of nocturnal movements into shallow water. More information should become available when more of the tagged spurdog are recaptured.
- The following recommendations arise from the present study:
- To improve our understanding of baited methods of surveying fish and to develop improved estimates of abundance, modelling studies of bait odour dispersal and fish responses are required, building on previous work in this area.
- Further trials of baited underwater cameras at different sites and under different conditions are required to assess the degree of variability in the different types of abundance index that can be derived.
- Further work to compare different survey methods is required at sites with greater fish abundance, e.g. at sites around the Galloway peninsula.
- A BUC system with greater depth limit (e.g. 200 m) should be developed to extend the range of habitats in which it can be used to include other species of interest.
- Further work is required to assess the size and species selectivity of different designs of fish trap.
- An intensive pilot survey of an area of interest, such as an actual or proposed marine protected area, by BUC and fish traps would provide a good test of the ability of these methods to generate data of use to inshore fishery managers and conservation interests.
- Seasonal sampling of fish bycatch in Norway lobster and crab creel fisheries is desirable to further assess the potential for creel fisheries to be used to monitor fish populations.
- Ongoing analysis of recreational sea-angling catch and tagging records should be encouraged and supported by Marine Scotland.
- There should be continued engagement between recreational sea-anglers and fishery scientists in Marine Scotland and universities.
Scottish Industry Science Partnership Report
SISP project 005/09
Philip Smith, Ian Burrett, David Bailey, Francis Neat, David Donnan, Katherine Dunlop, James Thorburn, Rosanna Milligan, Steve Bastiman, and Jane Dodd. 2010. Development and Evaluation of Methods for Surveying Fish Populations in Nearshore Waters .Scottish Industry Science Partnership Report : i-iv, 1 -50. https://nsuworks.nova.edu/occ_facreports/103.