Trawl fisheries are a cause of significant levels of seabird bycatch when birds (primarily larger bodied albatrosses and petrels) collide with warp cables at the back of boats, and become entangled in nets during the later stages of hauling. Up to 40 species are thought to be affected, with 10’s of thousands estimated to be dying each year.
While seabird bycatch in long-line fishing has been known since the 1980s, the threat posed by trawl fisheries has also become apparent in recent years (Bartle 1991, Weimerskirch et al. 2000, Sullivan et al. 2006). No global review of the impact of trawl fishing on seabirds has been undertaken, but there are a number of regional and national levels studies that highlight the significance of the problem (Wilson et al. 2004).
In Argentina, studies (Gonzalez-Zevallos et al. 2007, Yorio et al. 2010) on Magellanic Penguin Spheniscus magellanicus and Imperial Shag Phalacrocorax atriceps breeding at a newly designated marine park in Golfo San Jorge, assessed the potential spatial conflict between these seabirds and commercial hake and shrimp trawl fisheries. The observed foraging patterns suggest a high probability of spatial conflict and incidental mortality was regularly recorded in both fisheries, at rates that varied between 0.02 and 0.34 individuals per haul depending on species and fishery (Yorio et al. 2010).
In New Zealand, Bartle (1991) recorded an average bycatch catch rate of 0.263 birds/haul in a squid trawl fishery. 83% were recovered from the net sonde cable, with the remainder entangled in various parts of the net.
At Kerguelen, Weimerskirch et al. (2000) recorded a mean mortality rate of 0.48 birds/day on trawl vessels targeting toothfish Dissostichus eliginoides or mackerel icefish Champsocephalus gunnari. Higher rates were observed on vessels using net sonde cable and targeting the smaller icefish. Approximately 1/3 of mortality was caused by net sonde cable.
In Alaska, Zador et al. (2008) highlighted the potential year-round overlap of Short-tailed Albatross Phoebastria albatrus distribution and fishing areas of the vast Alaska groundfish trawl fishery, in which the catch of one of the target species, walleye pollock Theregra chalcogramma, is the second largest in tons among all fisheries.
In the Falklands/Malvinas, Sullivan et al. (2006) estimated that >1500 seabirds, predominantly Black-browed Albatross Thalassarche melanophris, were killed by demersal (bottom) finfish trawlers in 2002/2003.
Historically the Bengula Current (covering the Exclusive Economic Zones of South Africa, Namibia and Angola, and adjacent international waters) has had high levels of seabird bycatch in trawl fisheries (Petersen et al. 2007, 2008). In 2005/06 it was estimated that 18,000 seabirds were killed in the South African hake trawl fishery, one of the first trawl fisheries in which this problem was identified (Watkins et al. 2008). In South Africa, it was estimated that 85% of birds were killed by the powerful warp cables that attach the trawl net to the fishing vessel, entangling particularly the long-winged albatrosses and dragging them under the water. The remaining 15% died entangled in nets during shooting and hauling (Watkins et al. 2008). Of the birds killed, 70% were Shy T. cauta and Black-browed Albatross T. melanophrys, 14% were Cape Gannet Morus capensis and 9% White-chinned Petrel Procellaria aequinoctialis. All of these species are globally threatened or near-threatened. BirdLife’s Albatross Task Force has been working with the trawl fleet in South Africa since 2006 to reduce this bycatch, and began work in Namibia in 2008. This work has succeeded in significantly reducing the scale of the problem in these areas.
Related Case Studies in other sections
Compiled 2008, updated 2013
BirdLife International (2013) Trawl fisheries cause significant mortality to albatrosses . Presented as part of the BirdLife State of the world's birds website. Available from: http://birdlife.org/datazone/sowb/casestudy/167. Checked: 29/09/2016