Patterns and impacts of fish bycatch in a scallop dredge fishery


Correspondence to: B. D. Stewart, Environment Department, University of York, Heslington, York, YO10 5DD, England. E-mail:


  1. Dredging for marine bivalves can cause considerable damage to benthic invertebrates and habitats. However, it is largely unknown how dredging affects fish communities. In this study patterns and impacts of fish bycatch in scallop dredges around the Isle of Man, in the north Irish Sea, were investigated by analysing data from fisheries-independent surveys conducted between 1992 and 2005.
  2. Almost all (97.6%) tows of the survey gear generated fish bycatch, with a total of approximately 50 species recorded. Cuckoo ray (Leucoraja naevus) and monkfish (Lophius piscatorius) dominated the bycatch, accounting for 46.82% of the total. Three other species of particular commercial or ecological interest; lemon sole (Microstomus kitt), plaice (Pleuronectes platessa) and lesser spotted dogfish (Scyliorhinus caniculus), were also abundant. Most of the cuckoo ray, monkfish and plaice captured were juveniles, whereas lesser spotted dogfish and lemon sole were a mixture of juveniles and adults.
  3. In general, rates of fish bycatch appeared low, but this may be at least partly because background fish densities around the Isle of Man were also low. There was considerable spatial, temporal, and species-specific variation in fish bycatch, and the finer meshed dredges traditionally used to catch queen scallops (Aequipecten opercularis), caught significantly more fish than the great scallop (Pecten maximus) dredges.
  4. The density of lesser spotted dogfish bycatch increased significantly over the 14 years of the study whereas the density of monkfish decreased significantly. These patterns appear to reflect differences in the susceptibility of the two species to capture and damage by scallop dredging, and/or have been caused by regional trends in stock levels. An assessment of the impact of the local great scallop dredge fishery indicated that it may be catching substantial numbers of monkfish.
  5. Given the recent expansion of scallop dredging around the UK, such effects should be factored into ecosystem-based management plans.

Copyright © 2012 John Wiley & Sons, Ltd.