Publications
Prepared by
Biodiversity Group Environment Australia in consultation with the Threat Abatement Team
Environment Australia, 1998
ISBN 0 642 21420 4
Oceanic longline fishing is a technique used to target pelagic and demersal finfish and shark species. A longline consists of a main line with numerous baited hooks attached on branchlines. The configuration of the longline can vary considerably depending on the target species, fishing area and the size of the fishing vessel. The line can be set parallel to the surface on floats or anchored vertically. The number and type of hooks and the length of the branchlines also depend on the target species (Chapman 1990). Longlines targeting pelagic species can be up to 100km long and carry 600 – 3500 barbed steel hooks on 40m long branchlines (Brothers 1991; AFMA observer data). Demersal longlines have up to 10 000 hooks on 1m branchlines (Chapman 1990, Brothers 1995). Generally, Australian demersal longline operators set around 1000 hooks.
Longline fishing in the southern oceans is undertaken by fleets operating on the High Seas and in the territorial waters of Australia, New Zealand and southern African and American countries. In Australian waters, longlining is used by domestic vessels and Japanese vessels operating under access agreements with the Australian Government.
Longline by-catch is one of the greatest threats to seabirds (Birdlife International 1995). By-catch during longline fishing occurs when seabirds are attracted to fishing vessels by discards and baits and ingest baited hooks during the setting or, less commonly, hauling of the longline. The hooked birds are subsequently pulled under the water by the weight of the line and drown.
Longline fishing commenced in the southern oceans in the 1950's. By-catch of seabirds by longlines was first reported from band returns by Morant (1983). Subsequently, Weimerskirch and Jouventin (1987) documented a dramatic decline in Wandering Albatross Diomedea exulans populations on the Crozet Islands, and implied that longline and trawl fisheries may have been the cause. However, the magnitude of the problem was not fully realised until 1988 when Nigel Brothers (1991) calculated the number of albatrosses killed annually on Japanese longlines in southern oceans.
Studies by Brothers (1991) and Murray et al. (1993) based on direct observation of by-catch rates aboard Japanese pelagic longline vessels targeting southern bluefin tuna Thunnus maccoyii in Australian and New Zealand waters, respectively, confirmed the threat to seabirds from longline fishing operations.
The Australian Government recognised the threat and listed the incidental catch (or by-catch) of seabirds during oceanic longline fishing operations as a key threatening process on Schedule 3 of the Endangered Species Protection Act 1992 on 24 July 1995.
The current worldwide albatross by-catch rate on pelagic longlines is, on average, approximately 0·4 birds observed caught per thousand hooks set (Alexander et al. 1997). The actual catch rate varies between fishing areas and seasons. When combined with the millions of hooks set each year, longlining is a significant threat to a number of albatross species.
The impact of increases in mortality above natural levels is particularly significant in albatrosses. Albatross species are very long lived. If successful, pairs produce a single chick every one or two years (depending on the species) and the chicks can take as long as 11 months to fledge. Breeding does not occur until 5 -12 years of age. This reproductive strategy results in low levels of recruitment. Even slight additional mortality affecting young or adult birds may significantly reduce the viability of most seabird species. For example, the demographic characteristics of most seabird species make them unusually sensitive to increases in mortality rates (Weimerskirch and Jouventin 1987).
In most cases, the level of additional mortality that any seabird species can sustain is difficult to determine because each of the affected seabird species has at least one population which is vulnerable or has unknown status. There is insufficient information on the origin of the seabirds killed on longlines and hence the impact of longline by-catch on individual breeding populations.
This plan therefore takes the approach of prescribing an overall reduction in seabird by-catch and concentrates on mitigating the threatening process which can be measured, and not on seabird population status which cannot be adequately measured within the life of this Plan due to logistic, biological and resource constraints. Further research on monitoring of endangered seabird populations will be addressed in relevant recovery plans.
It is encouraging to note that some members of the fishing industry are already implementing practices to minimise seabird interactions. A number of modifications to fishing equipment or practices have been developed to reduce the by-catch of seabirds on longlines. Many of these mitigation measures prevent birds accessing baits during the line setting process. During line setting baits are available to seabirds from the point at which they are cast from the fishing vessel until they have sunk out of diving range of the birds (Brothers 1991). Precisely how fast a bait needs to sink so that birds cannot take it is governed by three factors: whether additional bait protection (such as a bird scaring line) is being used, the vessels' line setting speed and the diving capabilities of the seabirds present. For example, a vessel setting at 3 knots provides a baited hook with protection for longer than does one setting at 10 knots. Depending on bait type, weather and sea conditions, pelagic longline baits might be vulnerable to bird attack for up to 20 seconds after deployment.
This plan focuses on implementing a range of mitigation measures as a key action in reducing seabird by-catch to an acceptable level.
The impacts of demersal longline fishing operations in Australian waters on seabirds has not been determined and will be investigated in the early stages of this Plan's implementation.