Chapter 14 - Quantifying and Managing the Ecosystem Effects of Scallop Dredge Fisheries

Bryce Donald Stewart, Leigh Michael Howarth

Research output: Chapter in Book/Report/Conference proceedingChapter


Global landings of scallops have grown dramatically in recent decades and these fisheries are now among the most lucrative in several countries around the world. Despite this apparent success story, concerns have arisen about the wider ecosystem effects of scallop fisheries. This is particularly the case for the most common type of fisheries which use dredges to rake scallops off the seafloor. Here the evidence for negative effects arising from this practice are reviewed and suggestions offered as to ways in which scallop fisheries might be better managed. In general, dredging causes loss of biodiversity and reduces the complexity of benthic habitats by flattening substrates and removing structurally complex species such as hydroids, bryozoans, and seaweeds. This is significant because such habitats are key nursery and feeding areas for a wide range of species, including commercially important fish and shellfish. Scallop dredging also catches a variety of more mobile species such as crustaceans, echinoderms, fishes, and in certain areas, sea turtles, which is clearly of concern. Despite these general rules, the magnitude of effects varies considerably in different habitats. The most severe are in biogenic reefs such as formed by maerl and mussels, so there is a strong argument for fully protecting such areas. Reef and cobble habitats also appear relatively susceptible, but soft sediments such as sand, mud and gravel (which are the focus of most scallop fisheries) appear more resilient, particularly in areas adapted to high levels of natural disturbance. Determining the full effects of dredging remains difficult, however, because most fishing grounds have been exploited for decades, long before scientific study began. Long-term protected areas are beginning to provide insights into the recovery and composition of benthic communities in the absence of dredging. Continued study of these areas will be key to gaining a better understanding in the future. In terms of reducing the ecosystem effects of dredging, an approach that combines effort control, gear modifications, and spatial management is suggested. Spatial management is showing great promise where it has been applied as it can offer a win-win scenario which protects vulnerable habitats while boosting scallop stocks by providing breeding and nursery refuges; however, spatial management must be carefully planned to maximise biological benefits while accounting for socio-economic factors. Scallop fisheries must also be managed in unison with other fisheries in order to restore diversity and resilience to oceans facing an uncertain future of climate change and growing anthropogenic pressure.
Original languageEnglish
Title of host publicationDevelopments in Aquaculture and Fisheries Science
Subtitle of host publicationScallops: Biology, Ecology, Aquaculture, and Fisheries
EditorsSandra E. Shumway, G. Jay Parsons
Place of PublicationOxford
Number of pages26
ISBN (Electronic)9780444627193
ISBN (Print)9780444627100
Publication statusPublished - 8 Jun 2016


  • Fishing effects
  • by-catch
  • Essential Fish Habitat
  • Biogenic reefs
  • Fisheries management
  • Ecosystem Approach

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