Deploy fishing gear at different depths
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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.
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