Referenced paper Narvarte M., González R., Medina A. Apart from mussels, sea urchins and brittle stars dominated all samples. Average proportions of mussels and unwanted catch (mostly invertebrates) were estimated for each sample.
All species were sorted (mussels unwanted catch), counted, weighed and identified. Four 40 kg commercial bags of catch hand-harvested by divers in the same area were obtained for comparison. Nineteen tows (5 min duration) were conducted in May 2007 on the mussel bed at 14–20 m depth with a standard artisanal dredge (1.6 m mouth width, 80 mm net bag mesh size). More commercially targeted mussels were caught by hand-harvesting (76%) than the dredge (57% of total catch). The percentages of unwanted sea urchins Arbacia dufresnei and brittle stars Ophioploccus januarii caught (% by numbers of total catch) were lower by hand-harvesting (sea urchins: 2% brittle stars: 32%) than dredging (sea urchins: 9%, brittle stars: 68%). In total, hand-harvesting caught 27 species of unwanted catch, while dredging caught 47. 2012) found that hand-harvesting mussels caught fewer unwanted species including fewer unwanted sea urchins and brittle stars than with standard artisanal dredges. 2011 - same experimental set-up as Navarte et al. Supporting evidence from individual studiesĪ replicated, controlled study in 2007 on a mussel bed in the San Matías Gulf, South Atlantic Ocean, Argentina (Navarte et al. Commercial catch abundance (1 study): One replicated, controlled study in San Matías Gulf found that more commercially targeted mussels were caught by hand harvesting than by using a dredge.Unwanted catch condition (1 study): One replicated, controlled study in San Matías Gulf found that, when harvesting mussels, the damage caused to unwanted sea urchins and brittle stars was similar by hand harvesting and by using a dredge.Unwanted catch abundance (1 study): One replicated, controlled study in San Matías Gulf found that, when harvesting mussels, hand harvesting caught fewer unwanted sea urchins and brittle stars compared to using a dredge.Unwanted catch richness/diversity (1 study): One replicated, controlled study in San Matías Gulf found that, when harvesting mussels, hand harvesting caught fewer species of unwanted catch compared to using a dredge.Unwanted catch community composition (1 study): One replicated, controlled study in San Matías Gulf found that, when harvesting mussels, the community composition of the unwanted catch was similar by hand harvesting and by using a dredge.Both were in San Matías Gulf, South Atlantic Ocean (Argentina). Two studies examined the effects of hand harvesting instead of using a dredge on subtidal benthic invertebrate populations.(2011) Artisanal dredges as efficient and rationale harvesting gears in a Patagonian mussel fishery. (2007) Immediate effect of intertidal non-mechanised cockle harvesting on macrobenthic communities: a comparative study.
Marine Ecology Progress Series, 134, 131–150. (1996) Effects of scallop dredging on a soft sediment community: a large-scale experimental study. (2005) Effects of harvesting methods on sustainability of a bay scallop fishery: dredging uproots seagrass and displaces recruits. 2011).īishop M., Peterson C.H., Summerson H.C. 2005 Leitão & Gaspar 2007 Narvarte et al.
#Hand dredge manual
Hand harvesting, (for instance using hand-pushed rakes, hand-dredge, dip nets, harvesting-knife, or direct manual harvesting) instead of dredging can have fewer negative impacts on subtidal benthic invertebrates and the surrounding seabed (Bishop et al. Dredging, for instance for bivalves, normally involves towing a heavy steel frame along the seabed, which negatively impacts subtidal benthic invertebrates due to direct physical damage, and changes to the seabed structure and topography (Currie & Parry 1996).
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