The impact of hydraulic dredging on ocean quahog populations

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In the present study three experiments were carried out out to measure the overall efficiency of a commercial hydraulic dredge used to surway ocean quahog in Icelandic waters. Direct effects of hydraulic dredging activity on ocean quahog populations by estimating size selectivity of the dredge and rate of shell breakage were evaluated. The mean dredge efficiency was variable, estimated between 20 and 86 %. The dredge was highly selective towards clams greater than 70 mm in shell length as 70-85% of the clams caught had the shell length between 70-90 mm. The rate of the shell breakage of ocean quahog in the catch was 25-37% and of those left behind in the dredge track 11-32%. Ocean quahog was the only species visible on underwater photographs and almost no bycatch was observed from the dredge.