Patagonian toothfish
(also known as Bacalao and Bacalao de profundidad in Chile; Merluza negra in Argentina and Uruguay; Légine australe in France; Marlonga-negra in Portugal; and Tandnoting in Sweden)

Dissostichus  eleginoides  (Smitt, 1898)
(previously classified as Dissostichus amissus (Gill & Townsend, 1901) and Macrias amissus (Gill & Townsend, 1901))


 


 
Areas where Patagonian toothfish have been found


Map from AquaMaps


 
A history of the Patagonian toothfish fishery

Today the Patagonian toothfish (Dissostichus eleginoides) is the most valuable fishery in Antarctic or sub Antarctic waters. Commercially and in restaurants it is sold as Chilean Sea Bass. Prices can exceed $US10 per kilo for headed, gutted and tailed fish in the main markets in Japan and the United States. Unlike nearly all other Antarctic fish, the toothfish can grow to a large size (just over 2 m long and 100 kg in weight) and this, together with its high quality white flesh and few bones, make it highly sought after - particularly given the growing scarcity of other premium-quality species from around the world.

This has led in the last few years to a large-scale illegal fishery, which attempts to poach fish from the major areas of distribution of the toothfish around the sub Antarctic islands and other submarine ridges in the Atlantic and Indian Ocean sectors of the Southern Ocean. Large numbers of vessels fishing illegally were first noticed in 1996 in the western part of the Indian Ocean, but they soon spread eastwards towards Kerguelen and Heard Islands where they were seen by Australian and French licensed vessels in 1997. Although difficult to estimate reliably, it is thought that illegal catches were very high in these first couple of years - possibly two to three times the legal catch of this species from all sources - and probably caused a significant depletion of the fish stock in some localities. As a result of surveillance and arrests by some countries, including Australia, illegal fishing has declined. It still however remains a serious problem, with illegal catches being similar to the level of legal catches in the 1999-2000 season.

Since the start of fishing activity in sub Antarctic waters in the early 1970s, toothfish had been a minor bycatch species in the trawl fisheries for marbled rock cod and grey rock cod, particularly around South Georgia and the Kerguelen Islands. It was only in 1985 that commercial quantities of toothfish were discovered at Kerguelen. There had, however, been a substantial fishery off the Chilean coast since the mid-1970s, so markets were already established for this species. Since then, the fishery for this species developed rapidly and expanded to other areas, including South Georgia, Marion and Prince Edward Islands, and Crozet Islands. In 1994 an Australian trawl fishery began at Macquarie Island, followed by Heard Island in 1997. Although started as a trawl fishery, most toothfish is now caught by longline, except for the Australian fishery and part of the French fishery at Kerguelen. In the 1999-2000 season, approximately 14,500 tons were caught in the sub Antarctic waters managed by CCAMLR and a further 11,500 tons were taken outside CCAMLR waters off Chile, Argentina and the Falkland Islands.

Patagonian toothfish is now known to occur throughout the southern hemisphere in cool temperate and sub Antarctic waters, from the east and west coasts of South America eastwards through all of the sub Antarctic islands, submarine plateaus and seamounts to the Campbell Plateau south of New Zealand in waters from 300 m to over 2000 m depth. It probably also occurs in the Pacific sector, but little exploration has been done there. It is replaced in the high latitudes close to the coast of Antarctica by its close relation, the Antarctic toothfish (Dissostichus mawsoni), for which a fishery is currently being developed.

Patagonian toothfish are caught close to the sea bed and most fishing occurs between 400 m and 1500 m depth. They are large, active, predatory fish that feed mostly in the water column on squid and fish, but they have a very varied diet that can include bottom-living organisms such as crabs and prawns. Studies on their age and growth are not yet conclusive, but it appears that they can live at least 45 years, with males maturing at about 10 years and females at about 12 years. Spawning is thought to take place in winter (June-July) in depths of at least 1500 m. Young stages spend some months at least in surface waters before moving to the sea bed where they appear to move deeper as they grow. Tagging experiments suggest, surprisingly for such an apparently active large species, that fish generally do not move more than a few tens of miles over a period of several years. Recently, however, there have been two instances of tagged fish recaptured at different islands several hundred miles from their tagging position, so the extent to which fish interchange between different fishing grounds is not yet resolved.

Dick Williams
Antarctic Marine Living Resources Program, AAD


 

The Patagonian toothfish (Dissostichus eleginoides) is a large pelagic predator, belonging to the family Nototheniidae. It occurs on the shelf and shelf-slope off islands and banks in the Southern Atlantic, Indian and Pacific Oceans, notably within the influence of the Antarctic Circumpolar Current. In the South Atlantic, it occurs as far south as the South Sandwich Islands; the closely related species, Dissostichus mawsoni, occurs further south. D. eleginoides also occurs off the South American coast from Peru to Cape Horn and north off Argentine Patagonia.

Fishing began in the 1970s off northern Chile and in the South Atlantic and South Indian Oceans. To start with, fishermen used bottom trawling over continental shelves and caught few toothfish, mostly incidentally while fishing for other species. Long-lining for toothfish was developed in northern Chile during the 1980s; and probably first used at South Georgia in 1986 and off the Kerguelen and Crozet Islands in the southern Indian Ocean in 1992. Longlining gave access to deeper waters along the shelf-break and better returns. Toothfish catches grew rapidly, with new fisheries developed off southern Chile, Argentina and the Falkland Islands; and off Heard, Macquarie and the Prince Edward Islands. Chile and Russia have been the main catching nations historically; more recently Argentina and Norway have become important, but vessels registered in diverse countries such as Panama and Vanuatu are involved in the fishery. The toothfish is highly prized in Japan, selling at US$6.00/kg in mid-1995, and is sold in the United States under the name of Chilean sea bass – a prized choice on the restaurant tables of Washington D.C. and New York. CCAMLR fisheries managers estimated the total catch in 1995 around South Georgia and the adjacent Rhine and North Banks alone at 6171.1 tons. In 1997, they estimated the catch for the CCAMLR area at 107,000-115,000 tons, of which 70% was caught illegally.

Patagonian toothfish grow to over 2m long, and live upwards of 20 years. Absolute fecundity is low at between 48,000 - 528,900 eggs/individual over the life history, although relatively high for a notothenid. Spawning is annual, occurring between June and August (SC-CCAMLR XI). Size of first spawning is ca. 80 cm for males and ca. 100 cm for females. Little is known of their early life history: eggs are considered to be pelagic and have been found occasionally in the water column. Larvae and post-larvae have been found only infrequently, and generally within the upper 50 m of the water column. Juveniles are found on the continental shelf at ca.500 m, with increasingly large individuals along the continental slope in deeper waters. Maximum depth at which fish have been caught is ca. 2900 m.

Patagonian toothfish display considerable flexibility in feeding patterns. Diet varies between regions and with life stage and depth. Juveniles largely eat krill (Euphausia superba) in Antarctic regions, while adults feed on cephalopods and other fish (e.g. Champsocephalus gunnari) feeding on krill, suggesting an ability to move large distances from the continental shelf. This evidence is corroborated by their occurrence in sperm whale stomachs in pelagic waters of the Southern Ocean. Diet off Chile is almost exclusively of fish, while off South Georgia benthic crustaceans are present in a large proportion of full stomachs from fish taken in water deeper than 1000m. The digestive tract is adapted for ingesting large items. The proportion of full stomachs varies between regions and with depth.


 
What we need to know to manage the fishery

Little is known of population structure. Yet most techniques for assessing fish stocks rely on identifying isolated populations with no immigration from outside or migration out. To use these techniques, we therefore need to know how toothfish move in time and space. Variations in published growth parameters suggest there is a population boundary between the southern South America - Scotia Arc region and the islands of the Southern Indian Ocean. This evidence is supported by increasing levels of a disease causing degeneration of protein (jelly meat) off southern Chile, which has also appeared off South Georgia but has not been recorded in fish from the Indian Ocean or northern Chile. Parasite loadings indicate some isolation between fish populations found along the north and south coasts of Chile but also between the Patagonian shelf and South Georgia.

But this evidence may be related more to differences in the environment encountered by older life stages than to different sources of population recruitment. The Southern Ocean is circumpolar, connecting the southern Atlantic, Indian and Pacific Oceans. It is a major site of production of several water masses, including Antarctic Surface Water, Antarctic Intermediate Water and Antarctic Bottom Water, which spread out of the Antarctic regions to lower latitudes. Mixing with North Atlantic Deep Water creates Circumpolar Deep Water, which may form the source of the Common Water of the Indian and Pacific Oceans. Thus, the Southern Ocean is not one homogeneous body of water ; it is marked by considerable change in water masses both vertically and horizontally and, so close to their origin, the differences between water masses is very pronounced. These differences can affect how fast fish grow and the food they have available – the differences can also affect their predators. But most importantly, the water structure may affect how toothfish move.

Within the Southern Ocean, the Antarctic Circumpolar Current (ACC) moves eastward around the Antarctic continent. After the ACC passes through the Drake Passage, the current moves north along the Patagonian shelf to meet the Brazil Current, after which it travels eastward across the Atlantic. In the Indian Ocean, the current passes along the Crozet and Kerguelen Island groups, to meet the Macquarie Ridge before splitting into two off the Campbell Plateau south of New Zealand. Extensive mixing with Pacific Waters occurs until the current returns to the Drake Passage. Much of the water transport occurs within three fronts (polar, Antarctic and continental) which mark large changes in temperature and salinity. The fast currents at these fronts may also act as conveyers for transporting toothfish to move around the Southern Ocean.


 
Summary of Work So Far

Sampling longlines for toothfish

Biologists at CQFE have developed a multi-stage randomized design to sample fish caught by commercial longline. Results from trials indicate that variation at a scale of c500 m accounted for 76% of all variance in the abundance of the captured population, while variation between fishing days accounted for 24%. Most variation in length composition was captured at scales less than 500 m (79%). Sampling 16 10-coil lengths of line/day on 36 days of a voyage of 60 days hauling was the optimal sampling strategy.

Population structure and growth of toothfish

Stock structure, critical to good fisheries management, can be inferred from growth differences between areas – if fish do not move between areas, differences in temperature and food availability between the areas will lead to differences in growth rate. However, if fish move between these areas, the differences in growth will be homogenized. So we can test between rival hypotheses of 1) movement between two areas and 2) no movement between these areas, by seeing if there are differences in growth – unless of course the temperature and food regimes between the areas are so similar that no growth differences are generated.


Click to enlarge

Example of age count from transverse section
of otolith of
Dissostichus elegenoides

Using the age estimation developed at CQFE, we obtained age data from toothfish taken from the Falkland Islands and South Georgia in the South Atlantic, and the Kerguelen Islands and Heard Island in the southern Indian Ocean. We estimated von Bertalanffy growth parameters for each area, and constructed models to describe the rival hypotheses of stock mixing and separation between areas. We then selected between the models using normal likelihood methods. The growth data supported the hypothesis of stock separation between the Falkland Islands and South Georgia, but not between South Georgia and Kerguelen.


 

Stock Assessment



Click to enlarge

Demersal longline equipment in the fishery Patagonian Toothfish
A: The Spanish Manual System
B: The Japanese Manual System
C: The Norwegien Automated System

The development of longlining techniques for fishing Patagonian toothfish (Dissostichus eleginoides) led to a rapid increase in exploitation rate during the early 1990s, which progressively affected fisheries around southern South America and the Southern Ocean. The level of illegal fishing was high yet the fish were considered to be long-lived and slow-growing, indicators of vulnerability to rapid over-exploitation. But lack of knowledge of the basic biology of toothfish precluded the use of an array of powerful population dynamical techniques commonly used by fisheries managers.

Rigorous analyses of growth, mortality and population age structure depend on accurate age data. With age-based information, the effect of management choices can be simulated using dynamic pool and age-structured assessment (ASA) models. Age-structured models can be used to examine the effect of age-specific vital rates, allowing managers to ascertain which stages of the life history cycle are vulnerable to over-exploitation under a particular set of conditions. Moreover, age-based data can aid modeling of community interactions, allowing impacts on other species to be assessed as part of an ecosystem approach to fisheries management.

But these methods all rely on accurate and representative information on age and a single, closed population with no emigration or immigration. Scientists at CQFE have been working on techniques to obtain these data and determine the rates of movement of toothfish.


 
Age - Length Relationships



Click to enlarge


 
Acknowledgments

Funding for this research has come from:

United States National Science Foundation
(
Grant No. OPP-9614756)
British Antarctic Survey

The work described on this website was part of a collaboration between research groups from several nations belonging to the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR).  Collaborating institutions include:

British Antarctic Survey
 
Museum National d’Histoire Naturel, France
Universidad Austral de Chile
Instituto de Fomento Pesquero
, Chile
Australian Antarctic Division
Marine and Coastal Management, South Africa
Bundesforschungsanstalt fhr Fischerei, Germany
New Zealand National Institute of Water and Atmospheric Research
Falkland Islands Fisheries Department