Seabird bycatch

Many different species of seabird are affected by fishing, with main groups for concern being albatrosses, petrels, shearwaters and penguins. The impact of longlining, both demersal and pelagic, has received greatest scrutiny. During longline setting, seabirds take bait from hooks that are floating on or near the surface. Seabirds can actually remove up to 70% of the bait from longlines, which can be very costly to the industry. Some of the seabirds taking bait will be caught on the hooks and are likely to drown. Seabird bycatch has been identified as a significant source of mortality for some species, particularly albatrosses, where population declines have been linked directly to longlining mortalities. Seabirds have also been caught in trawls, driftnets, gillnets and by recreational fishers

Ghost fishing trammel net off Wales. Tangled gadoid
probably lured the shag into the net. © Blaise Bullimore/CCW

Commercial longlining began in the 1950s, targeting tuna and tuna-like species, and rapidly expanded through the 60s and 70s in both the southern and northern hemispheres. Dermersal longlining began in the 80s, targeting species such as the Patagonian toothfish (Dissostichus eleginoides) and further developed in the 1990s targeting ling and hake. For pelagic longlines, there are about 3000 baited hooks per set, on mainlines that may be over 100km in length. In contrast, the demersal longlines deploy up to 20,000 hooks per set on a mainline that is approximately 15km in length. It should be noted, however, that some fisheries placing large numbers of hooks in the water, actually have a smaller seabird bycatch than other fisheries deploying less effort. Factors such as type of gear used, time of day for setting, and the season and area fished all affect the level of bycatch.

Much of the work examining seabird bycatch in longline fisheries has focused on the southern hemisphere and the Southern Ocean in particular. However, this method of fishing is expanding in European waters and rates of seabird bycatch (0.16 to 0.69 birds per 1000 hooks set) are comparable to those observed elsewhere. Longliners in European waters have caught gannets (Sula bassana), fulmers (Fulmarus glacialis), Manx shearwaters (Puffinus yelkouan), Cory's shearwaters (Calonectris diomedea), Balearic shearwaters (P. mauretanicus), Audouin's gulls (Larus audouinni) and yellow legged gulls (L. cachinnas).

Bycatch tends to be highest in the vicinity of major breeding colonies, decreasing rapidly with distance from such sites. It has been estimated that the Japanese drift net of the North Pacific kills between 214500 and 76300 seabirds annually. However, in recent years the industry has undergone major changes with the increased use of mitigation measures. Mitigation measures include:

Night setting, which will reduce the bycatch of diurnal species such as albatrosses. However, species that forage at night, e.g. white-chinned petrels (Procellaria aequinoctialis), will still be at risk.
Discarding offal during line setting to lure birds away from the baited hooks. This has been successful in some areas, but where setting occurs over extended periods of several hours it becomes impractical.
Weighting lines to increase sink rate. This is suitable for manual longlining only. When fishing in deep waters or poor weather, however, the lines are often broken if weighted.
Line shooters, which set lines with slack (i.e. no tension), thereby increasing sink rate. This method has been found to half the seabird bycatch.
Dying the bait to make it less visible has reduced albatross contact with baits by 90%. However, this is only feasible for those fisheries using artificial baits.
Underwater setting funnel or chute, which guides lines down to a certain depth, significantly reduces seabird bycatch.
Bird scaring devices, such as a line with suspended streamers mounted on a pole at the vessel stern. Considered the most effective in the North Atlantic fisheries.

However, it should be noted that in the late 1990s, increased regulation, the high market price for tuna, billfish and toothfish, and the introduction of quotas, has lead to an expansion of illegal, unreported and unregulated (IUU) pelagic longline fishing. These fishermen are highly unlikely to be using mitigation devices. IUU fishing for Patagonian toothfish was estimated to have taken between 36300 and 90100 seabirds between 2000 and 2001.

Seabird bycatch

Further Reading: