Publications
Prepared by
Biodiversity Group Environment Australia in consultation with the Threat Abatement Team
Environment Australia, 1998
ISBN 0 642 21420 4
This section of the Plan describes the fisheries affected by the actions outlined under the Plan and the seabird species which are threatened by longline fishing by-catch.
Longline fishing involves setting a single line (mainline) containing many individual hooks on branch lines or snoods. The mainline can either be anchored or drifting. It can be oriented vertically or horizontally and vary considerably in length and number of hooks.
Longlining methods can be divided into two groups:
They are described by Alexander et al. (1997) as follows:
Mid water set longlining involves a single longline up to 130km in length holding between 600 and 3000 branch lines, each about 35m in length terminating in a baited hook. Hooks are usually suspended 50 – 150m below the surface of the water from lines suspended by floats (AFMA observer data). This method is mainly used to target various species of tuna and broadbill, and is used by Japan, Korea, Taiwan, Indonesia, Australia and New Zealand. The principal market for longline caught tuna is the lucrative Japanese sashimi market. In the AFZ pelagic longlining is used by domestic operators and Japanese vessels operating under a Bilateral Access Agreement. The two fisheries differ in scale and methods of operation.
The domestic pelagic longline fishery is centred on the East Coast of Australia. Only two Australian vessels currently longline in the rest of the AFZ and this fishing effort is largely in north-western Australia, an area with a low probability of seabird by-catch, although there is little data to confirm this view. It is expected there will be a gradual increase in longline activity off the west coast and in external territories in future years. The Australian fleet is comprised of around 65 active vessels, each typically 18 – 25m in length, although there is considerable variability within the fleet. The fleet operates largely within 100 nautical miles of shore and is opportunistic depending on weather conditions. The longlines used by Australian vessels have 800 – 1400 hooks (Brian Jeffriess, pers. comm). There is currently no formal observer program in this fishery.
Japanese longline fishing vessels have access to Australian tuna and billfish stocks under an annual Bilateral Access Agreement between the governments of Australia and Japan. Japan pays an access fee which funds an observer program and contributes to research on tuna and ecologically related species, including seabirds. Japanese effort has declined in the AFZ in recent years as the Japanese vessels have been excluded from areas of the AFZ. In 1996 the Japanese pelagic longline fishery consisted of a fleet of about 60 vessels. Eight of these fished in the Tasmanian sector of the AFZ where seabird by-catch is highest. Japanese vessels are typically larger than Australian vessels (40 - 60m) and fish further offshore and on the High Seas. The longlines set by the Japanese vessels are up to 135km long and have up to 3500 hooks. It appears that in 1998 there will be no bilateral agreement to allow Japanese pelagic longline fishing vessels to fish inside the Australian Fishing Zone.
Bottom-set longlines are principally used to target ling Genypterus sp., and school Galeorhinus galeus and gummy shark Mustelos antarcticus in the AFZ. Bottom-set longlines may be set in water depths ranging from 100 – 2500m. This method of fishing is also used extensively in Antarctic waters to target toothfish Dissostichus sp., although there is currently no Dissostichus fishing occurring in the AFZ. There are three methods: Dropline, Demersal Longline and Trotline.
A dropline comprises a series of baited hooks attached by (generally) short snoods to a main line. A buoy is attached at one end of the mainline and a weight is attached to the other end. The mainline extends from the water surface (buoy end of line) to the sea bed (weighted end of line), and because most target species of Australian dropline operations commonly aggregate within 100 metres of the seabed, the hooks are usually attached to the bottom 100 metres of the line (the weighted end), approximately 1 metre apart. This can be varied for other target species with different behavioural characteristics.
Demersal longlines comprise a series of baited hooks that are attached by (generally) short snoods to a rope mainline which is anchored to the ocean floor at each end. This method is most often used by fishers to target shark or ling. Other scale fish species are also caught, but usually as commercial by-catch of their shark fishing operations. A buoy and dahn pole carrying a flag are attached by way of a buoy-line to the main-line at each of its ends, for retrieval of the gear. The main-line is hauled by a line hauler from one end of the main-line, usually over a roller mounted on the vessel gunnels in the mid-section of the boat. Within the southern shark fishery there is a limit of 2000 hooks for a single operation.
A trotline usually comprises two main-lines, suspended from the water surface (buoy end) to the sea bed (weighted end). These are joined by a rope fastened at each end, at a predetermined depth, to one of the main-lines. Sets of 'droppers' suspend from the cross-rope, each of which may have up to 20 - 30 baited hooks attached to it by short snoods. To counter the weight of these droppers, the cross-rope usually has a certain number of floats attached to it at regular intervals.