ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.

Seals ain't turtles: Will trawl exclusion devices work with Australian fur seals?

Richard Tilzey

Bureau Of Rural Sciences, KINGSTON, AUSTRALIA

THEME: ASFB

A major component of the South East Fishery is the winter (June- August) trawl fishery for spawning blue grenadier off west Tasmania. Seal bycatch became a major conservation issue in this fishery in 1999, when 87 seals were killed by 3 freezer-trawlers. Seals have become habituated to feeding around such vessels and fur seal populations in Australia are increasing. During the 2000 season, industry funded Seal Exclusion Device (SED) trials on freezer-trawlers. The FRDC funded similar trials in 2001 and 2002. The basic design of SEDs is similar to Turtle Exclusion Devices used in prawn fisheries. Blue grenadier loss via the SED grid and escape hatch was a major problem in initial trials. SED use in 2000 and 2001 improved the survival of captured seals. However, comparison between SED and non-SED trawls found that the incidence of seal bycatch in SED shots was about twice that for non-SED shots in both years. Whereas a SED prevents seals from entering the codend where most mortality occurs, its structure provides additional access to the net and also creates a seal 'feeding-chamber'. Seals are more intelligent and mobile than turtles and underwater video footage has recorded seals entering SEDs via the escape hatch. Although SED effectiveness remains in question, seal avoidance tactics used by freezer-trawlers when shooting/hauling nets appear to be very successful. Total seal captures by these vessels have fallen from 89 in 1999 to 53 in 2000 and 26 in 2001, with fishing effort remaining constant.