Catches of this species were first reported in the Convention area in the mid 1970s, though there has been evidence of some take by the Soviet fishery near the end of the 1960’s (Kock, 1992). The longline fishery for toothfish was introduced at South Georgia and Kerguelan near the end of the 1980s, at which time the yields increased considerably. Currently, toothfish is fished primarily using longline gear, although in limited areas trawl gear has been employed, as well as some limited attempts at using pots. Since the mid 1990s, reported catches in the Convention area from all gear types have been on the order of 12,000 to13,000 metric tones, with a high of 16,394 during the 1999/2000 fishing season (CCAMLR 2003a) . Catches since the late 1990s have been taken primarily around South Georgia in the Atlantic Sector, Kerguelen, and McDonald and Heard Islands in the Indian sector, with lesser amounts taken around Crozet and Prince Edward and Marion Islands.
A primary threat to Patagonian toothfish in the CCAMLR Convention area Dissositchus eleginoides is illegal, unreported, and unregulated fishing and trade in this species. Despite conservation measures imposed CCAMLR, a considerable proportion of catches taken in CCAMLR waters and sold in international markets since 1996 has been the result of illegal exploitation. For example, the estimated unreported catch of Patagonian toothfish in CCAMLR waters during the 2002/03 fishing season was around 10,070 metric tones, about 39% of the total Dissostichus spp. catch (CCAMLR 2003b). During the previous year, about 44% of the total take in the convention area was illegal. With the annual value of the illegal catch in the hundreds of millions of U.S. dollars, there continues to be an incentive to illegally harvest this species.
Current management and conservation measures for Patagonian toothfish include precautionary total allowable catch limits by each statistical area or division, area and season closures, a catch documentation scheme, mandatory coverage by satellite-based vessel monitoring systems, prohibition of directed fishing except in accordance with specific conservation measures, a scheme that requires members to prohibit landings from non-party vessels that have been sighted in CCAMLR waters without proof that fish were transshipped or caught outside CCAMLR waters, an agreement to assess the potential viability of trade restrictive measures against nations whose vessels violate CCAMLR conservation measures, and vessel identification and marking requirements. The seriousness of illegal fishing for Patagonian toothfish, as well as the threat to undermining the CCAMLR management measures, is well understood.
A major component of the management of this species is based on the incidental mortality of seabirds. Declines in seabird populations in the Southern Ocean have been linked to longlining operations (Prince et al. 1997; Weimerskirch et al. 1997; Ashford and Croxall, 1998). Seabirds in jeopardy include several species of endangered albatross. Thus, CCAMLR has imposed a number of required seabird mitigation measures for the Patagonian toothfish fishery. Recent evidence suggests that these measures, when fully implemented, have considerably reduced seabird bycatch in the legal fishery. Nevertheless it is likely that seabird mitigation measures are not employed by illegal fishers. Thus, the illegal catch of Dissositchus spp. has may substantially disturb the Southern Ocean ecosystem.
Toothfish distribution, biology and ecology
The geographic distribution of the Patagonian toothfish is circumpolar, occurring along slope waters in the Pacific off Chile from 30∞S to Cape Horn (Fischer and Hureau, 1985), in the southern Atlantic along the coast and slope waters of southern Patagonia and Argentina, the islands and banks in sub-Antarctic waters including South Georgia, Malvinas/Falkland Islands, Shag Rocks, and the islands of the Scotia Arc (Gon and Heemstra, 1990), to south of South Africa and south of New Zealand including the sub-Antarctic waters of the Indian Ocean and Macquarie Island on the Indo-Pacific boundary of the Southern Ocean (Lloris and Rucabado, 1991). Southernmost records of the species occur near the Antarctic Peninsula (Fischer and Hureau, 1985). The bathymetric range extends to 2,500 to 3,000 m. A species similar in many regards to D. eleginoides is the Antarctic toothfish, Dissositchus mawsoni. While superficially similar to D. eleginoides, D. mawsoni has a more high Antarctic coastal distribution while D. eleginoides is more likely to be encountered on seamounts associated with sub-Antarctic archipelagos near or outside the Antarctic convergence. There is evidence that the two species ranges may overlap in certain places.
There are several characteristics of the life history of Patagonian toothfish that make the species vulnerable to overexploitation though non-optimal harvesting practices. The production of large yolky eggs (Everson, 1984) implies that fecundity of Patagonian toothfish is comparatively low, with potential fecundity ranging from 238,000 to 546,000 eggs (Kock 1992). In addition, Dissositchus eleginoides matures at a relatively late age, with age at first spawning from 8-10 years of age (Kock, 1992). Patagonian toothfish likely spawns on the slopes of South Georgia and the Kerguelan Islands (Kellerman and Kock, 1988; Kellerman, 1990; Koubbi et al. 1990). The species, along with most Antarctic Nototheniid fish, mature at about half of their maximum length (Kock and Everson, 1998), although there remains uncertainty over size at sexual maturity.
The species is relatively slow growing and long lived. Estimates of age and growth have been made based on samples taken in the southwest Atlantic (Zakharov and Frolkina, 1976), the Kerguelen Islands (Hureau and Ozuf-Costaz, 1980), and regions in the Indo-Pacific boundary of the Southern Ocean (Horn, 1998). Due to the longevity and slow growth of the species, aging of otoliths and scales is imprecise. Zakharov and Frolkina (1976) estimated a 20-25 year longevity, though it is widely believed that these fish likely live to be 40-50 year old, or older. Estimates of natural mortality for all stocks of Patagonian toothfish are currently very poorly understood. At South Georgia and Heard Island, natural morality is approximated as half of the current best estimate of the growth parameter K. There is a considerable need to conduct further research toward better estimates of this important population parameter, and the processes that influence it.
The Patagonian toothfish is an opportunistic carnivore that mainly feeds on fish, cephalopods and crustaceans. However, it has been observed that the dietary habits are influenced by biogeographical differences, local availability of food items, depth and predator size (Goldsworthy et al. 2002, Pilling et al. 2001). This species is preyed upon by a variety bird and marine mammal species, including albatrosses (Cherel et al. 2002) and seals (Green et al. 1998).
Assessment Methods and Management Strategy for Pategonian Toothfish
The current assessment methodology adopted by CCAMLR used as the basis for setting total allowable catches is the based on an estimate of long term annual yield (Constable and de la Mare 1996, Constable et al. 2002). This estimate factors in life history characteristics, recruitment projections from recruitment trawl surveys, changes in the fishing patterns of the commercial fleet, and in the case of South Georgia, an adjustment using standardized catch rates. The long term approach evaluates different levels of projected catch that satisfy adopted decision rules pertaining to the estimated median spawning stock biomass over the lifetime of the cohort. Because Patagonian toothfish is a long lived species, this projection has been carried out to 55 years in recent assessments.
There are two decision rules adopted by CCAMLR to evaluate a long term precautionary yield for Patagonian toothfish. These are a) the probability that the spawning stock biomass during the projection period falls below 20% is 0.1, and/or b) the ratio of the median spawning biomass to the median pre-exploitation spawning biomass is 50%. The estimate of precautionary long term yield is that which first triggers either of these decision rules. The then serves as a basis for mangers to set total allowable catches for each statistical management area or division within CCAMLR waters.
This approach to setting long term yields does not directly take other components of the Antarctic ecosystem into account, with the exception of decision rule b), which allows escapement of biomass that can potentially be used towards maintenance of the ecosystem. However, conservation measures for this fishery other than long term annual yield provide considerable safeguards to other components of the ecosystem. These include measures that shut the fishery down or move it to a different location if incidental bycatch of skates or rattails exceeds a prescribed level, line weighting requirements and other required seabird mitigation measures, and area or seasonal closures to protect seabirds during their breeding season.
Although the management regime for Patagonian toothfish is not based on directly factoring in elements of the Antarctic ecosystem, the multifaceted approach employed by CCAMLR for this species appears to be ecologically suitable based on several factors. The prey species of Pategonian toothfish are not harvested commercially, none of the predator species are exploited (with the indirect exception of incidental mortality by vessels not using seabird mitigation measures), and the species is long lived and less impacted by short term changes in the ecosystem that may impact krill and mackerel icefish. Nevertheless, the high worldwide demand and considerable economic value continues to foster illegal fishing practices which challenge the successful sustainable management of this species.
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