Scottish Marine and Freshwater Science Vol 6 No 16
The objective of the project was to determine spatial turnover rates of scallops at two spatial scales: (i) at the scale of individual fishing patches (tens to hundreds of metres), determining immigration rates following fishing; and (ii) at the local fishery scale (1-10 km and greater), determining potential sources of immigration to fishing patches from more distant areas. This report addresses the first of these spatial scales, using depletion fishing experiments coupled with tagging to estimate size-specific population size and site-fidelity to small experimental areas.
Data and Resources
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Orkney Islands, Scotland
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2013-01-01 to 2014-12-31
UK Open Government Licence (OGL)
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Depletion fishing experiments were undertaken to estimate the density and size-composition of scallop populations at a local scale. Depletion fishing involves repeated removal of catch on a defined sample plot, measuring the rate at which the catch rate declines as the total catch accumulates. Fifteen depletion experiments were conducted in Orkney waters during 2013 and 2014, comprising five fishing occasions at a location to the south of Wyre, five in Scapa Bay and five close to Fara (Figure 1). The results of the Wyre experiments are reported here, undertaken on board the fishing vessel Three Boys (K905, skipper Emlyn Grieve) at a location to the south of the island (59°6.48’N, 2°57.93W). The survey line was marked out by a heavy sinking rope, left in situ between fishing occasions. Fishing covered a strip of 2 m either side of the rope, and the length of rope covered (and marked for future reference) was 178 m, determined by the coverage of the first bout of fishing. The survey area was thus 712 m2. Fishing was undertaken by a team of four divers employing their usual hand-gathering technique but collecting all sizes of scallops encountered. All scallops captured on each bout of fishing were counted and measured (shell height and width). All scallops not retained for landing were returned to the survey area, distributed along the line by a diver placing scallops on the sea bed. Three fishing bouts were completed on each occasion, limited by dive time and diminishing catch rates. The five depletion fishing occasions were 25 June, 8 August, 7 October and 18 November 2013, and 13 June 2014. Other than the depletion experiments, no fishing activity is thought to have occurred on the Wyre grounds over the duration of the survey series.
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Marine Scotland Science
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