Interactions between longline vessels and seabirds in Kerguelen waters and a method to reduce seabird mortality

In recent years, a new longline fishery for the fish Dissostichus eleginoides has developped in the vicinity of South Georgia and Kerguelen islands, two internationally important breeding areas for procellariiform birds. Attractiveness of this fishery for seabirds, together with the incidental capture of birds and a method to reduce mortality were investigated during 13 days of fishing activity in Kerguelen waters in February 1994. Between 100 and 600 seabirds were always observed behind the longline vessel. The main ship-following species were the white-chinned petrel (67% of the counts), the giant petrels (8%) and three species of albatrosses, the wandering (11%), black-browed (6%) and grey-headed (2%) albatrosses. All these species are attracted by sinking hooked baits during line settings, more attempts to feed on baits being made by skilled divers such as the white-chinned petrel (87% of the total number of tries), the black-browed (7%) and the grey-headed (6%) albatrosses, than by species never observed submerged such as the wandering albatross (<1%). Consequently, seabird bycatch included only species being able to dive, i.e. the white-chinned petrel (n = 36) and the grey-headed albatross (n = 2). Marked differences in the mortality rate were observed between day and night (1.00 versus 0.38 birds per 1000 hooks), and, at night, when the decklights were on or off (0.59 versus 0.15 birds per 1000 hooks). Importantly, dumping of homogenized offal during line settings greatly reduced incidental capture of seabirds (only 1 white-chinned petrel killed on 41 longlines), mainly because birds were more attracted by offal than by hooked baits. On average, 10-fold higher mass of offal (crushed head, gut and tail of D. eleginoides) than that of bait was thrown overboard during line settings. Moreover, offal sank slower than hooked baits, being thus available in larger amounts and during a longer time for seabirds. We therefore proposed to include the dumping of offal during line settings in the regulations of the longline fishery for D. eleginoides in order to minimize seabird mortality.