Construction and evaluation of an underwater setting device to prevent accidental capture of seabirds on tuna longliners
Parks and Wildlife Service Tasmania
Population declines have been identified for six albatross species, and fisheries related mortality has been implicated in these declines.From the fishers perspective, each time a bait is removed by a seabird, or a seabird is caught on a hook, the chance of catching a fish is reduced.Accidental capture of seabirds is a deleterious event from both the seabird and the fishers perspective and it is in every body’s interest to find more effective solutions to this problem
1. To redesign and construct an improved capsule setting device which is capable of achieving a 5 second cycle setting time at a setting depth of 3m, and is safe for crew to use in all conditions.
2. To determine the effectiveness of the capsule setting device in preventing seabirds from taking bait during setting.
3. To evaluate the impact of the capsule setting device on catch of target species
4. To define optimum installation configuration and deployment strategy of capsule setting device in relation to the influence of propeller and hull turbulence.
Longline fishing is one of the world's major methods of catching fish (Lokkeborg 1999). Some seabirds, particularly albatrosses and petrels have learnt to take bait from longlines while the lines are being set and when doing so put themselves at risk. If they either swallow the hook or become entangled in it, they are subsequently pulled underwater by the weight of the mainline, and drowned. Longline fishing is currently believed to be the most serious threat to the survival of albatross populations worldwide (Robertison and Gales 1998).
Many longlining countries are now requiring their fishers to take steps to minimise the accidental capture of seabirds on longlines. The Food and Agricultural Organisation (FAO) recently endorsed the preparation of National Plans of Action, to address this issue.
The Australian Threat Abatement Plan (TAP) for the Incidental Catch (or bycatch) of Seabirds aims to significantly reduce the bycatch of seabirds during longline operations by setting a maximum catch rate, and requiring use of various mitigation measures. Fishers that can demonstrate a technique of setting and hauling longlines which does not make the baited hooks available to seabirds can be issued with a permit to operate without any of the restrictions outlined in the TAP, such as night setting or weighting lines. Setting lines underwater, out of sight or reach of seabirds has the potential to be such a technique.
Keywords: seabirds, accidental mortality, underwater setting