Deploy fishing gear at different depths

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

Effectiveness

50%
Certainty

35%
Harms

15%

Calculating overall effectiveness category

Background information and definitions

Deploying fishing gear at different depths may reduce interactions with marine and freshwater mammals, and subsequent entanglements and unwanted catch (‘bycatch’) of mammals. However, the feasibility of this intervention will depend on the type of fishery and the ecology of the target species.

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).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (0 STUDIES)

BEHAVIOUR (0 STUDIES)

OTHER (1 STUDY)

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

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
Referenced paper
Hembree D. & Harwood M.B. (1987) Pelagic gillnet modification trials in northern Australian seas. International Whaling Commission report, 37.

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

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Marine and Freshwater Mammal Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Use an electric current to deter mammals from fishing gear Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Introduce fishing gear exchange programmes to encourage fishers to use gear that reduces unwanted catch of mammals Action Link	No evidence found (no assessment)	0	Synopsis Link
Use passive listening devices to detect mammals and prompt fishing vessels to move away Action Link	No evidence found (no assessment)	0	Synopsis Link