In situ examination of the behaviour of fish in response to demersal trawl nets in an Australian trawl fishery

Abstract

In situ examination of the behaviour of fish was undertaken with underwater cameras positioned on demersal trawl gear used by Australia’s South East Trawl Fishery. Blue grenadier (Macruronus novaezelandiae), pink ling (Genypterus blacodes) and whiptails (Coelorinchus spp.) swam in an anguilliform mode whereas other species displayed a carangiform swimming mode. Tiger flathead (Neoplatycephalus richardsoni) and ocean perch (Heliocolenus spp.) were active in response to the approaching trawl net compared with the generally passive activity of whiptails, New Zealand dory (Cyttus novaezelandiae), and jackass morwong (Nemadactylus macropterus). However, when in the body of the trawl, gemfish were active while ocean perch, whiptails and New Zealand dory were generally passive. Some blue grenadier, ocean perch and whiptails escaped capture by passing through open meshes in the trawl mouth, whereas tiger flathead passed under the ground gear. In the trawl body, small numbers of blue grenadier passed through open meshes in the top panel whereas numerous spotted warehou swam faster than the towing speed, presumably escaping capture by swimming forwards and out of the trawl. Interspecific behavioural variation in escape response could be utilised to design more efficient trawl gears.