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Providing evidence to improve practice

Action: Use an otter trawl instead of a dredge Subtidal Benthic Invertebrate Conservation

Key messages

Read our guidance on Key messages before continuing

  • One study examined the effects of using an otter trawl instead of a dredge on subtidal benthic invertebrates. The study was in the Irish Sea (Isle of Man).

 

COMMUNITY RESPONSE (1 STUDY)

  • Unwanted catch overall composition (1 study): One replicated, controlled, study in the Irish Sea found that an otter trawl caught a different species composition of unwanted invertebrate and fish species (combined) compared to two scallop dredges.

POPULATION RESPONSE (1 STUDY)

  • Overall abundance (1 study): One replicated, controlled, study in the Irish Sea found no difference in total invertebrate abundance and biomass living in or on the sediment of the trawl tracks following fishing with either an otter trawl or two scallop dredges.
  • Unwanted catch overall abundance (1 study): One replicated, controlled, study in the Irish Sea found that an otter trawl caught fewer unwanted invertebrates and fish (combined) compared to two scallop dredges.

OTHER (1 STUDY)

  • Commercial catch abundance (1 study): One replicated, controlled, study in the Irish Sea found that an otter trawl caught similar number of commercially targeted queen scallops compared to two scallop dredges.

Supporting evidence from individual studies

1 

A replicated, controlled, study (date of study not reported) in a sandy area in the north Irish Sea, Isle of Man (Hinz et al. 2012) found that an otter trawl caught fewer unwanted invertebrates and fish (combined), and a different unwanted catch species composition, compared to two dredge designs. The otter trawls caught fewer unwanted invertebrates and fish (4 individuals/1,000 m2) than the two dredge types (23–59 individuals/1,000 m2). In addition, overall unwanted catch species composition was different between the otter trawl and the two dredges (species composition data presented as graphical analyses). Unwanted otter trawl catch was reported to be dominated by fish, whereas unwanted dredge catch was dominated by invertebrates. Following fishing with either gear, there were no changes in total invertebrate abundance and biomass living in or on the sediments (raw data not presented). The otter trawl caught similar amount of commercially targeted queen scallops Aequipecten opercularis (45 scallops/1,000 m2) compared to the dredges (15–48 scallops/1,000 m2). Three queen scallop fishing gears were compared: an otter trawl, a new dredge design, and a traditional Newhaven dredge. The study site was subdivided into 12 trawling lanes (40 m wide, 1 nm long) in 20–23 m water depth. Each fishing lane was allocated to one gear design (4 lanes/design). Commercial and unwanted catches were sorted, identified, counted and weighed. Before, and seven days after fishing trials, invertebrates (size unspecified) were sampled in each lane using a 2-m beam trawl (5-min tow; 6 tows/lane) and a sediment grab (0.1 m2; 6 grabs/lane).

Referenced papers

Please cite as:

Lemasson, A.J., Pettit, L.R., Smith, R.K., and Sutherland, W.J. (2019) Subtidal Benthic Invertebrate Conservation: Global Evidence for the Effects of Interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.