Seabird mortality in longline fisheries

What are longline fisheries?

Longlining is one of the main methods used to catch fish and occurs in most oceans and seas in the world. While there are many differences in what makes up a longine fishery, there are two main types

• pelagic – open ocean
• demersal – sea bed

Pelagic longline fisheries

Target tunas (eg. blue fin, yellow fin, big eye, albacore) 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 set out 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.

Patagonian Toothfish being hauled aboard a fishing vessel. Photograph: Graham Robertson

Demersal longline fisheries

These 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 a depth of 500-2,500 metres. 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.