Impacts of fishing techniques on the Patagonian toothfish fishery in the Southern Ocean
- Trawling for Patagonian toothfish from the research vessel RSV Aurora Australis. (Photo: © C. Materia-Rowland)
- Wandering albatross hooked and drowned on a longline. (Photo: © G. Robertson)
Fishers use various techniques to harvest marine species in the Southern Ocean. Fishing for Patagonian toothfish is conducted by trawling and longlining, although some pot fishing has been tried.
Trawling
There are principally two types of trawling – bottom and midwater trawling. Until the late 1980s Patagonian toothfish fishing was entirely a bottom trawl fishery. However, bottom trawling indiscriminately harvests non-target species or bycatch including Humped rockcod (Gobionotothen gibberifrons), various icefish species and skates (Raja Georgiana and Bathyraja spp.). Trawling also causes environment impact by scraping and ploughing the seabed, which resuspends sediment and destroys benthos (or the marine fauna living in and on the bottom of the ocean).
Longlining
Longline fishing involves setting a mainline (also called a groundline or motherline) with many individual baited hooks on branchlines (also called a snood, secondary line, gangion or gangline) (Ashford 2001; Preston et al. 1998). Some longliners set lines of over 100 kilometres with more than 20 000 hooks attached, although they vary considerably in length and number of hooks (Birdlife International 2001).
Longlines can be deployed demersally, pelagically or semi-pelagically. The Patagonian toothfish fishery currently uses three types of demersal longline gear (Ashford 2001), including the Spanish and autolining/Mustad methods (Kock 2001; Alexander et al. 1997; Bjordal and Løkkeborg 1996), and a third method that takes the best features from the Spanish and autolining/Mustad systems (ISOFISH 2002). According to ISOFISH (2002), approximately 80 per cent of illegal fishing vessels use the Spanish longlining method, as opposed to the autolining/Mustad method that requires more expensive equipment. Refer to Fallon and Stratford (2003) for more details on demersal longline fishing.
Demersal (bottom set) longlining is also called ‘ground fishing’ because it targets fish that live at, or near, the seabed (Bjordal and Løkkeborg 1996). This technique was introduced to the Patagonian toothfish fishery in 1985/86, it was in full commercial operation at South Georgia by 1988/89 and around the Kerguelen Islands by 1991/92 (Kock 1994), and it led to a rapid increase in exploitation during the 1990s (Fallon and Kriwoken submitted). In this fishery, lines longer than 5000 m and armed with up to 5000 baited hooks that are set at depths ranging from 500-2500 m (AAD 2001). Vessels can set and haul up to 40 000 hooks per day.
Although longlining is an effective fishing technique, it is not highly selective and is one of the greatest threats to seabirds and non-target marine species including finfish, skates and rays. In particular, longlining attracts seabirds by providing food (bait and discarded bycatch and offal). Seabirds are usually caught on baited hooks during the setting procedure and are drowned as the line sinks below the water surface. Every longline hook has the potential to hook incidental catch (or bycatch) and it is estimated that between one and 10 billion longline hooks are set globally each year (Birdlife International 2001).
According to Kock (2001:46), the "main unresolved problem of fisheries management in the Southern Ocean (…) is the bycatch of albatrosses and large petrels in longline fisheries". Southern Ocean wandering albatross, black-browed albatrosses and white-chinned petrels appear to have the greatest interaction with fisheries (Croxall and Gales 1998), although other species including grey-headed albatrosses and yellow-nosed albatrosses have been taken (Ryan and Watkins 2000). The ad hoc CCAMLR Working Group on Incidental Mortality Arising from Fishing (WG-IMAG) estimates that seabird bycatch due to IUU fishing in the CCAMLR Area since 1996 is between 278 400 to 700 200 birds (WG-IMAG 2002) (Table 3).
Table 3: Estimated total potential seabird bycatch associated with IUU fishing for Patagonian toothfish in the CCAMLR Area.
Lost and broken lines (from longlines and trawl nets) can also entangle fish, marine mammals, birds and vessels, and discarded bands from bait boxes ‘collar’ marine mammals. In addition, discharged fish offal can potentially cause population increases in some seabird populations and dependency on this food source.
References:
AAD (2001). Seabird mortality on longline fisheries: What are longline fisheries? Australian Antarctic Division, Hobart, Australia, Accessed 18 December 2001.
Alexander, K., Robertson, G. and Gales, R. (1997). The incidental mortality of albatrosses in longline fisheries. A report on the workshop from the First International Conference on the Biology and Conservation of Albatrosses, Australian Antarctic Division, September 1995, Hobart, Australia.
Ashford, J.A. (2001). In support of a rationally managed fishery: Age and growth in Patagonian toothfish (Dissostichus eleginoides). Unpublished Doctoral Dissertation, Old Dominion University, Durham, UK.
Birdlife International (2001). Longlining statistics. The global seabird conservation program. Birdlife International, Accessed 10 July 2002.
Bjordal, Å. and Løkkeborg, S. (1996). Longlining. Fishing New Books, Cambridge University Press, Cambridge, UK.
Croxall, J.P. and Gales, R. (1998). An assessment of the conservation status of albatrosses. In Robertson, G. and Gales, R. (eds), The albatross: Their biology and conservation. Surrey Beatty and Sons, Chipping Norton, Australia. 46-65.
Fallon, L.D. and Kriwoken, L.K. (submitted). International influence of an Australian non-governmental organisation in the protection of Patagonian toothfish. University of Tasmania, Hobart, Australia.
Fallon, L.D. and Stratford, E. (2003). Issues of sustainability in the Southern Ocean fisheries: The case of the Patagonian toothfish. Report for the Lighthouse Foundation, School of Geography and Environmental Studies, University of Tasmania, Hobart, Australia.
ISOFISH (2002). Background longline fishing techniques: Patagonian toothfish profile. International Southern Oceans Longline Fisheries Information Clearing House (ISOFISH), Hobart, Australia, Accessed 22 February 2002.
Kock, K-H. (1994). Fishing and conservation in southern waters. Polar Record, 30(172), 3-22.
Kock, K-H. (2001). The direct influence of fishing and fishery-related activities on non-target species in the Southern Ocean with particular emphasis on longline fishing and its impact on albatrosses and petrels: A review. Reviews in Fish Biology and Fisheries, 11, 31-56.
Preston, G.L., Chapman, L.B. and Watt, P.G. (1998). Vertical longlining and other methods of fishing around fish aggregating devices (FADs): A manual for fishermen. Secretariat of the Pacific Community, Noumea, New Caledonia.
Ryan, P.G. and Watkins, B.P. (2000). Seabird bycatch in the Patagonian toothfish longline fishery at the prince Edward Islands: 1999-2000. Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), Hobart, Australia, WG-FSA-00/30, p. 13.
WG-IMAG (2002). Incidental mortality of seabirds during unregulated longline fishing in the Convention Area: Working Group on Incidental Mortality Arising from Fishing. In the report of the Twenty-first meeting of the Commission. Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), Hobart, Australia.