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Assessment of size selectivity in hydraulic clam dredge fisheries
- Sala, Antonello, Brčić, Jure, Herrmann, Bent, Lucchetti, Alessandro, Virgili, Massimo
- Canadian journal of fisheries and aquatic sciences 2016 v.74 no.3 pp. 339-348
- clams, fisheries, fisheries management, models
- In hydraulic dredge clam fisheries, the onboard mechanical sorting can be considered as the main catch selection process. The catch is mechanically sorted by a sieve made up of a series of successive grids with holes of decreasing diameter. The effect of the grid hole diameter and sorting speed of the vibrating sieve of a hydraulic dredger was investigated in a field study to determine its clam selection properties and to formulate proposals aimed at improving fishery management. Data analysis demonstrates that it is technically impossible to achieve a knife-edge selection and that there is scope for improving the size selection process, for instance by increasing grid hole diameter, which, however, can be accompanied by a reduced catch of both undersized and commercial-sized individuals. An increase in the hole diameter to 21.71 mm, while ensuring less than 5% retention of undersized individuals, would entail a retention of 67% of the commercial sizes. The modelling approach applied can be extended to investigations of other dredge gear types and nonmobile benthic species.