Pelagic gillnet modification trials in northern Australian seas

Published source details Hembree D. & Harwood M.B. (1987) Pelagic gillnet modification trials in northern Australian seas. International Whaling Commission report, 37.
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This study is summarised as evidence for the following.

	Action	Category
	Attach acoustically reflective objects to fishing gear Action Link
	Deploy fishing gear at different depths Action Link

Attach acoustically reflective objects to fishing gear

A replicated, controlled study in 1984–1985 of two pelagic areas in the Timor Sea and Arafura Sea, Australia (Hembree & Harwood 1987) found that attaching metallic bead chains to fishing nets did not reduce dolphin entanglements. In both years of the study, dolphin entanglement rates did not differ significantly between nets with bead chains (rates not reported; total entanglements: 1984 = 3 dolphins, 1985 = 29 dolphins) and conventional nets (total entanglements: 1984 = 21 dolphins, 1985 = 17 dolphins). Three dolphin species were entangled: common bottlenose Tursiops truncatus, spinner Stenella longirostris and pantropical spotted dolphins Stenella attenuata (see original paper for data). In 1984, a commercial vessel fished two types of gill net: one with 4-mm bead chains (8 or 16-m vertical chains attached at 8 m intervals; fished for 450 h); and one conventional net (fished for 354 h). Both net types (approximately 5 km long x 16 m deep, mesh size 150 mm) were deployed 3 m below the water surface. In 1985, a commercial vessel fished gill nets (10.5 km long; 39 deployments in total) with alternating 1-km sections with and without 4-mm bead chains (woven into the net in diagonal rows). Nets (15 m deep, mesh size 140–150 mm) were deployed at the water surface. Fishers recorded dolphins entangled in the nets in September–October 1984 and September–November 1985.

(Summarised by: Anna Berthinussen)
Deploy fishing gear at different depths

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.

(Summarised by: Anna Berthinussen)