A comparison of direct macrofaunal mortality using three types of clam dredges

Published source details Gaspar M.B., Leitão F., Santos M.N., Chícharo L., Dias M.D., Chícharo A. & Monteiro C.C. (2003) A comparison of direct macrofaunal mortality using three types of clam dredges. ICES Journal of Marine Science, 60, 733-742.
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This study is summarised as evidence for the following.

	Action	Category
	Modify the design of dredges Action Link

Modify the design of dredges

A replicated, controlled study in 2001 in one area of sandy seabed in the North Atlantic Ocean, off southwestern Portugal (Gaspar et al. 2003) found that a new dredge design with a shorter mouth did not reduce the proportion of damaged or dead invertebrates caught with the dredge, compared to two traditional dredge designs, but damaged and killed lower proportions of invertebrates left in the tracks following dredging. The proportions of individuals that entered the dredge and were damaged or dead were similar using the new design (damaged: 5%, dead: 5%), a traditional design with a long mouth (damaged: 3%, dead: 3%) and another traditional design with a short mouth (damaged: 7%, dead: 6%). However, the proportion of invertebrates left in the tracks following dredging were lower using the new design (damaged: 17%, dead: 17%), compared to the long-mouthed traditional design (damaged: 42 %, dead: 29%) or the short-mouth traditional design (damaged: 26%, dead: 18%). Three dredge designs were compared: a new design with a shorter mouth and metallic grid instead of a net bag to retain the catch, a traditional design with a long mouth and more teeth, and a traditional design with a short mouth (“north dredge”). A total of 12 tows (4/design; 5 min/tow) were undertaken in June at 8–10 m depth. A net bag was fitted to the end of each dredge to retain the caught organisms that would otherwise escape through the dredge mesh. Divers also sampled the sediment in the dredge tracks after each tow to assess the proportion of invertebrates not caught but left damaged or dead due to dredging (54 quadrats/tow; extracted using a 5 mm mesh sieve). All invertebrates were identified, counted, weighed and given a damage score (1= in good condition, 4= crushed/dead).

(Summarised by: Anaëlle Lemasson & Laura Pettit)