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Antarctic Marine Living Resources (AMLR)

Seabird mortality in longline fisheries

What are longline fisheries?

Longlining is one of the main methods used to catch
fish and longline fisheries occur in most oceans and
seas in the world.

While there are many variations of what constitutes a
longline fishery, in general there are two types -
pelagic longline fisheries and demersal longline fisheries.

eing hauled
Patagonian Toothfish being hauled
aboard a fishing vessel

Pelagic longline fisheries target tunas (eg. blue fin tuna, yellow fin tuna, big eye tuna, albacore tuna) and swordfishes. These species are caught from 50-300 metres deep in the water on longlines suspended by floats.

Operations vary from small boats that fish close to the coast to vessels that fish on the high seas.

Vessels that fish on the high seas might have freezers of 200-300 tonnes capacity and can stay at sea for several months.

Pelagic longliners might deploy longlines up to 130 km long with 3,000 hook-bearing branch lines. Branch lines are usually 30-40 metres in length and 50 metres apart on the longline, and are light enough to bob up and down in the water column in order to attract fish. Longlines are set and hauled back in on every day of the fishing operation.

Demersal longline fisheries are also called ground fisheries because they target fishes that live at-or-near the seabed. Species targeted include hake, ling, cod, sablefish, halibut and Patagonian toothfish.
Demersal species are often caught in very deep water – for instance the Patagonian toothfish can be caught from 500-2,500 metres deep.

Demersal longlines differ from pelagic longlines in that the branch lines (holds the hook) on demersal lines are only 0.4 m long and are spaced 1.4 m apart. This means that even reasonably short longlines might carry a very large number of hooks: demersal longline vessels might set and haul up to 40,000 hook/day.

Seabird mortality in longline fisheries

What seabirds are affected and how do they get killed?

The main species of seabirds killed in longline fisheries are albatrosses and other species of petrel.
The main mortality occurs in the southern oceans south of 30S, and in the northern oceans north of 30N.

In the northern hemisphere the commonest species killed are the Arctic fulmar, black-footed albatross, laysan albatross and various species of shearwater, while in the Southern Hemisphere examples of species killed include the
black-browed albatross, grey-headed
albatross, wandering albatross, shy
albatross, white-chinned petrel and
grey petrel. It should be noted, however,
that any species of seabird in the petrel
family that is aggressive and good at
seizing prey (or baited hooks) at the
waters’ surface, or is a proficient diver,
will be vulnerable to longline fishing.

Black Browed Albatross killed by a longline fishing hook

Seabirds get caught when baited hooks are payed out from vessels during line setting operations.
When longlines are deployed they flounder near the surface which provides visual cues for seabirds.
Seabirds take baits by surface-seizure or by diving for them. They bite the baits, become hooked and when longlines sink to target depths the birds get pulled underwater and drown.

Seabird mortality in longline fisheries

How serious is the problem?

Seabirds are affected by many things that occur in their environments. They suffer from predation by man, erosion of habitat, pesticide contamination of eggs, depletion of prey by fisheries and changes to the oceans and wind patterns due to global warming. However, none of these issues is thought to affect seabirds as much as longline fishing. For example, in the Patagonian toothfish longline fishery in the Southern Ocean, and in the tuna longline fisheries in the Indian Ocean, it is likely that tens-of-thousands of seabirds, principally albatrosses, giant petrels and white-chinned petrels, are killed annually. The problem is most severe in the illegal longline fishery for Patagonian toothfish because the fishery occurs in defiance of the law and international agreements designed to protect fish stocks and bycatch species like seabirds, and it is unlikely that efforts would be made by fishermen to safeguard seabirds from becoming hooked on gear.

Seabirds like albatrosses are unable to cope with unnatural levels of mortality because they mature fairly late in life and they only have one young each year or every second year. As well, partners mate for life and if one partner is lost to longline fishing then it may take many years for the surviving partner to find a new mate and re-commence breeding. Longline fishing is generally accepted as being the reason why many populations of albatrosses and petrels have decreased in number (some populations by as much as 40%) and why many albatross species are listed as being either endangered with extinction or of unfavourable conservation status.

Seabird mortality in longline fisheries

How can seabird mortality in longline fisheries be reduced?

Practices by fishing vessels
Fortunately a range of mitigation measures exist to reduce seabird kills in longline fisheries. During line setting operations lines of streamers trailed behind vessels over the area where hooks enter the water are very effective as is setting lines in total darkness. The combination of night setting and streamer lines can reduce mortality of most seabird species by up to 90%. Mortality can also be reduced by adding weight to longlines to expedite sink rates, and by setting longlines deep underwater through a tube. The latter method is relatively new and is still in the formative stages of development, but promises to be the best option to date, because underwater setting eliminates the visual cues that seabirds rely on to take bait. Dyeing baits blue (to disguise them against the water) is also effective.