Deploy fishing gear at different depths

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • One study evaluated the effects on marine mammals of deploying fishing gear at different depths. The study was in the Arafura Sea (Australia).





  • Reduction in entanglements/unwanted catch (1 study): One controlled study in the Arafura Sea found that fishing nets deployed 4.5 m below the water surface had fewer entanglements of dolphins than surface nets.

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

  1. A controlled study in 1986 of pelagic sites in the Arafura Sea, northern Australia (Hembree & Harwood 1987) found that fishing nets deployed 4.5 m below the water surface had fewer entanglements of dolphins than surface nets. Entanglement rates of dolphins (including common bottlenose dolphins Tursiops truncatus and spinner dolphins Stenella longirostris) were lower in nets deployed 4.5 m below the water surface (0.2 dolphins/deployment) than in nets deployed at the water surface (0.4 dolphins/deployment). For target species, average catch rates were lower for mackerel in nets deployed 4.5 m below the surface (0.9 fish/deployment) than in surface nets (4 fish/deployment), but did not differ significantly for sharks, tuna or billfish (see original paper for data). A commercial vessel carried out 37 deployments of two fishing nets: one deployed at a depth of 4.5 m; one deployed at the water surface. Both nets were 4.9 km long x 15 m deep with a mesh size of 140–150 mm. Dolphin entanglements and target fish catches were recorded for each of the 37 deployments in February–March 1986.

    Study and other actions tested
Please cite as:

Berthinussen, A., Smith, R.K. and Sutherland, W.J. (2021) Marine and Freshwater Mammal Conservation: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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Marine and Freshwater Mammal Conservation

This Action forms part of the Action Synopsis:

Marine and Freshwater Mammal Conservation
Marine and Freshwater Mammal Conservation

Marine and Freshwater Mammal Conservation - Published 2021

Marine and Freshwater Mammal Synopsis

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