Assessment of size selectivity in hydraulic clam dredge fisheries

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 undersize individuals and commercial sizes. An increase in the hole diameter to 21.71 mm, while ensuring less than 5 % retention of undersize individuals would entail in retention of 67 % of the commercial sizes. The modelling approach applied can be extended to investigations of other dredge gear types and non-mobile benthic species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author