Use an otter trawl instead of a beam trawl

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

50%
Certainty

34%
Harms

10%

Calculating overall effectiveness category

Background information and definitions

Trawling is a method of fishing that involves pulling a fishing net (trawl) through the water behind one or more boats. A beam trawl is a type of trawl where the mouth of the net is held open by a wooden or metal beam, which can be up to 14 m long. Beam trawls can negatively impact subtidal benthic invertebrates through direct physical damage, bycatch, and alterations to the seabed (Bergman & Van Santbrink 2000). Other types of fishing methods may be less damaging to the seabed and its invertebrates. Otter trawls, for instance, have a pair of boards or metal plates (otter boards) which attach to the sides of the net and keep the net open as it is pulled through the water (Schwinghamer et al. 1998). Otter trawls are alternative fishing methods which may potentially cause less damage to the seabed and benthic invertebrates (Broadhurst et al. 2012).

Evidence for other interventions related to otter trawl is summarised under “Threat: Biological resource use – Use more than one net on otter trawls”, and “Use an otter trawl instead of a dredge”. Evidence for other interventions related to using different fishing gear is summarised under “Threat: Biological resource use”.

_{Bergman M.J.N. & Van Santbrink J.W. (2000) Mortality in megafaunal benthic populations caused by trawl fisheries on the Dutch continental shelf in the North Sea in 1994. ICES Journal of Marine Science, 57, 1321–1331.}

_{Broadhurst M.K., Sterling D.J. & Cullis B.R. (2012) Effects of otter boards on catches of an Australian penaeid trawl. Fisheries Research, 131–133, 67–75.}

_{Schwinghamer P., Gordon Jr D.C., Rowell T.W., Prena J., McKeown D.L., Sonnichsen G. & Guigné J.Y. (1998) Effects of experimental otter trawling on surficial sediment properties of a sandy‐bottom ecosystem on the Grand Banks of Newfoundland. Conservation Biology, 12, 1215–1222.}

Study locations

Key messages

One study examined the effects of using an otter trawl instead of a beam trawl on subtidal benthic invertebrates. The study was in the North Sea (Germany and Netherlands).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Overall abundance (1 study): One replicated, paired, controlled study in the North Sea found that otter trawls caused similar mortality of invertebrates in the trawl tracks compared to beam trawls in sandy areas but lower mortality in silty areas.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, paired, controlled study in 1992–1995 in four areas of sandy or silty seabed in the south-eastern North Sea, Netherlands and Germany (Bergman & Van Santbrink 2000) found that the effects of otter trawls compared to beam trawls on invertebrate mortality varied with the sediment type. Otter trawls caused similar mortality of invertebrates in the trawl tracks compared to beam trawls in sandy areas (otter: 0–41%: beam: 1–53%) but lower mortality in silty areas (otter: 1–65%: beam: 2–82%). In spring-summer 1992–1995 parallel strips (2,000 x 60 m, 300 m apart, number unspecified) in one sandy location and three silty locations were fished with either a commercially used beam trawl with tickler chains or an otter trawl. Prior to trawling, mega-invertebrates (>1 cm) and macro-invertebrates (> 1 mm) were counted from samples taken in each strip using a dredge and a sediment grab. After 24–48 h following trawling, all strips were sampled again using the same methods. Mortality (from trawling) of invertebrates present in the trawl tracks was calculated using the difference between the before and after-trawling abundances (assuming all animals killed by trawling had been eaten by predators).
Study and other actions tested
Referenced paper
Bergman M. & Van Santbrink J.W. (2000) Mortality in megafaunal benthic populations caused by trawl fisheries on the Dutch continental shelf in the North Sea in 1994. ICES Journal of Marine Science, 57, 1321-1331.

Please cite as:

Lemasson, A.J., Pettit, L.R., Smith, R.K. & Sutherland, W.J. (2020) Subtidal Benthic Invertebrate Conservation. Pages 635-732 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Subtidal Benthic Invertebrate Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Fit a funnel (such as a sievenet) or other escape devices on shrimp/prawn trawl nets Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Fit one or more mesh escape panels/windows on pots and traps Action Link	No evidence found (no assessment)	0	Synopsis Link
Use more than one net on otter trawls Action Link	No evidence found (no assessment)	0	Synopsis Link