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Antarctic toothfish, Antarctic cod
Antarctic toothfish (D. mawsoni) in McMurdo Sound
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Suborder:	Notothenioidei
Family:	Nototheniidae
Genus:	Dissostichus Smitt, 1898
Type species
Dissostichus eleginoides Smitt, 1898
Synonyms
Macrias T. N. Gill & C. H. Townsend, 1901

Dissostichus, the toothfish, is a genus of notothen found in the Southern Hemisphere. Both species are marketed in the United States as Chilean sea bass (or Chilean seabass) or less frequently as white cod. "Chilean sea bass" is a marketing name, coined in 1977 by Lee Lantz, a fish wholesaler who wanted a more attractive name for selling the Patagonian toothfish to Americans. In 1994, the U.S. Food and Drug Administration (FDA) accepted "Chilean sea bass" as an "alternative market name" for Patagonian

toothfish. The toothfish was remarkably successful in the United States, Europe and Asia, and earned the nickname “white gold” within the market.

Toothfishes are vital to the ecological structure of numerous Southern Ocean ecosystems. For this reason, on 4 September a national day is dedicated to the toothfish in South Georgia.

Species

Two species in this genus are recognized:

• Dissostichus eleginoides Smitt, 1898 (Patagonian toothfish)
• Dissostichus mawsoni Norman, 1937 (Antarctic toothfish)

Distribution

The Patagonian toothfish is distributed circumpolarly near the Antarctic Convergence, spanning the Atlantic, Pacific and Indian sectors of the Southern Ocean, with a few populations near the Antarctic Peninsula as well as the coasts of Chile and Argentina (reviewed in Garcia de la Rosa, 1997). The Antarctic toothfish is distributed around the Antarctic continental shelf and in the Ross Sea, generally south of 60°S (Arana and Vega, 1999).

Both species are benthopelagic as adults: The Patagonian toothfish has been found between 600 and 1500 m, and the Antarctic toothfish tends to be found at even greater depths, between 1300 and 1900 m (Petrov, 2011). The Patagonian and Antarctic toothfish populations overlap geographically in the southern Indian Ocean, north of the Ross Sea and several south Atlantic islands (reviewed in Roberts et al., 2011). The Southern Ocean has not yet been fully sampled, so both species may extend further throughout the region (Collins et al., 2010).

Morphology and body size

The Patagonian toothfish and the Antarctic toothfish are markedly similar in appearance, but can be identified via several morphological features. The Patagonian toothfish has a characteristic scaleless patch between the eyes and a longer visible lateral line (Fischer and Hureau, 1985).

Both species are long-lived and relatively slow-growing. The Patagonian toothfish can live up to at least 50 years of age and the Antarctic toothfish can live to at least 35 years of age. Both species show the fastest growth in the first 10 years of life, and reach maximum body size around 20 years of age (Horn, 2002). The Patagonian toothfish grows at a documented average rate of 2.0 cm and 1 kg per year (Ainley et al., 2013). Toothfishes are large in size, with both species reaching maximum sizes exceeding 100 kg (reviewed in Eastman and DeVries, 2000). This trait distinguishes the toothfishes from other notothenioids.

History

The Patagonian toothfish was initially captured in the 1970s as bycatch via cod trawl fishing vessels around South Georgia Island and off the coast of South America. Most of the individuals caught using this method were juveniles. In 1987, The Patagonian toothfish was caught as bycatch via long-line fishing, a technique that captured the larger adults (reviewed in Constable et al., 2000). The fish, marketed as “Chilean Sea Bass,” became widely successful in restaurants due to its large size and white, oily flesh, which can by cooked in a nearly limitless number of ways.

Fish were collected in massive numbers, first in Chile and later in Argentina after the Chilean population declined abruptly in 1994 (reviewed in Knecht, 2006). Exploratory fisheries for the Antarctic toothfish were established in the Ross Sea in 1996/1997 (Hanchet, 2010). The fisheries for the two toothfish species are intended to be distinct; however, there is some concern that the species are indistinguishable to non-experts on fishing vessels (Willock, 2002). In 2013, the United States Food and Drug Administration (FDA) eliminated market distinctions between the species, meaning that the Antarctic toothfish, like its congener, could also be marketed as Chilean Sea Bass. Previously, the Antarctic toothfish was sold under the name “toothfish” (Fda.gov).

Commercial fisheries

All fisheries south of the Antarctic Convergence are regulated by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which is a subset of the international Antarctic treaty system designed to prevent exploitation of the region’s natural resources. CCAMLR currently oversees thirteen licensed toothfish fisheries, including seven exploratory fisheries and one research fishery. The five established licensed fisheries target the Patagonian toothfish exclusively, and the exploratory fisheries, mostly concentrated in the Ross Sea, target the Antarctic toothfish primarily. The research fishert targets both species.

The Patagonian toothfish, which has been collected and sold since 1977, is currently being removed legally from the Southern Ocean at an estimated rate of 12,000 to 17,000 tons per year. The Antarctic toothfish, which has been collected and sold since 1988, is currently being removed legally from the Southern Ocean at an estimated rate of 4,000 tons per year (Ccamlr.org, Toothfish fisheries). All known Antarctic toothfish and most Patagonian toothfish populations fall within the CCAMLR Convention Area. More northern The Patagonian toothfish populations are managed by the nations that control the respective regions in which the populations reside; however, these nations are still required to adhere to CCAMLR regulations (Lack and Sant, 2001).

Illegal, unreported and unregulated fishing

CCAMLR is currently allowing fisheries to remove the Antarctic toothfish at rates that would reduce the population to 50 percent biomass. However, some scientists are concerned that current estimations of the toothfish biomass may be inaccurate due to a number of factors, including illegal, unregulated and unregulated (IUU) fishing activities (Abrams, 2014).

IUU activities can be challenging to prevent and prove (discussed in Knecht, 2006). However, centralized international collaborative efforts (between Australia, New Zealand, the United Kingdom and France) to mitigate IUU activities have been reported as successful. Current measures include CCAMLR’s catch-documentation scheme along with on-sea, satellite and aerial surveillance. Current reports indicate that implementation of these measures has reduced IUU activity by an estimated 90 percent (Osterblom and Bodin, 2012). However, others have criticized that these numbers may be inaccurate, as IUU fishing in the Southern Ocean is difficult to prove (Abrams, 2014).

Diet and ecological importance

Both species occupy similar feeding niches. They are piscivorous at all life stages (McKenna, 1991). Juveniles mostly prey on small notothenioids, krill, squid and pelagic fishes. Prey range increases with maturity (reviewed in Roberts et al., 2011). As adults, both species consume a variety of fishes, cephalopods and crustaceans (Roberts et al., 2011).The Patagonian toothfish is opportunistic, and sometimes scavenges penguin and fish remains that sink from the epipelagic zone (Stevens, 2004). The toothfishes may compete with Adélie penguins for prey such as silverfish and krill.

In addition, toothfish are important prey for large mammals. Patagonian toothfish predators include elephant seals, sperm whales, and killer whales (Collins et al., 2010). Antarctic toothfish predators include Weddell seals and whales, especially killer whales (reviewed in Ainley and Siniff, 2009). Some data suggests that the overfishing of toothfish may stress whale populations. Hucke-Gaete et al. (2004) observed that when toothfish were removed from via longline capture, killer whales were more likely to prey on nearby sperm whales.

Migration and reproductive cycle

Much remains unknown regarding the life cycles of both toothfish species, particularly the Antarctic toothfish. Much of the existing data has been collected by reports from commercial fishing vessels. Current research suggests that both the Patagonian and Antarctic toothfishes tend to form discontinuous populations, meaning that little gene flow exists between populations (Kuhn and Gaffney, 2008) (Smith and McVeagh, 2000).

Both species migrate during spawning season. However, the specific duration and distance of these migrations have not been fully characterized. Tag and release experiments on the Patagonian toothfish have demonstrated that most individuals migrate an average of 15 miles from their habitat, and that any migratory movement generally occurs after the fishes reach maturity (Williams et al., 2002). However, some anecdotal evidence demonstrates that the Patagonian toothfish may be capable of migrating between the northern and southern poles, likely by submerging beneath tropical and temperate waters (Moller et al., 2003).

Patagonian toothfish

The Patagonian toothfish spawns in deep waters during the austral winter and early spring, between June and September. Discontinuous oogenesis development patterns suggest that Patagonian toothfish do not spawn annually (reviewed in Collins et al., 2010). Individuals migrate to spawn in shallower waters (800-1000 m), although migration patterns can vary widely between different geographic populations (Laptikhovsky et al., 2006). Some data suggest that spawning yields decrease at higher latitudes (Arana, 2009).

Egg development occurs over a period of approximately three months, with hatching occurring in October or November (Evseenko et al., 1995).  After hatching, the planktonic larvae drift for a period of time, likely until February. Around this time, the fish reach a critical size and become bathypelagic. They gradually inhabit deeper waters as they grow, migrating down the continental slope. Adult fish are generally found at depths greater than 500 m (reviewed in Collins et al., 2010).

Antarctic toothfish

The life cycle of the Antarctic toothfish is less well understood. Researchers and fisheries are limited to collecting this species during the austral summer and autumn (December to May) due to harsh polar conditions during the austral winter (June to August). Scientists have not yet collected any juvenile or larvae Antarctic toothfish (discussed in Young, 2012), and have not yet verified the location, season or frequency of spawning activity.

Hanchet et al. (2008) used all previously collected data from 1996 to 2008 to generate an updated model for the life cycle of the Antarctic toothfish within the Ross Sea fishery, although the authors note that much of this model is based on speculation and much of the data has not yet been collected fully. They estimated that the Antarctic toothfish adults spawn between June and November, and that spawning likely occurs north of 70°S, beyond the Ross continental shelf and slope.

Eggs likely have a development period of four to five months and hatch between November and February, developing more slowly than their Patagonian toothfish counterparts. Current data suggests that spawning requires a large amount of reproductive tissue, and may not occur annually. Planktonic larvae likely undergo larval drift for a period of several months, likely into late summer or early autumn. Some larvae drift likely eastward of the Ross Sea, while other larvae may drift westward. Researchers predict that the Antarctic toothfish inhabit benthic regions after reaching 15 cm. Sub-adult individuals develop within the Ross Sea and gradually inhabit deeper waters over a period of two to three years. Hanchet et al. (2003)

Conservation efforts

The Marine Stewardship Council has currently certified six toothfish fisheries, including the Ross Sea, as sustainable (Msc.org, 2014). Many environmental advocates have opposed the certifications, appealing for protection of the Southern Ocean’s exceptionally unique nature. In June 2010, 500 scientists formed the Antarctic and Southern Ocean Coalition (ASOC), advocating to CCAMLR for special protection of the entire Ross Sea (Asoc.org, 2010).

Chilean Sea Bass has been placed on the Red Lists of Greenpeace International and the One World One Ocean Campaign (Greenpeace, 2010; Bedolfe, 2012). As a result, a number of restaurant and grocery owners have publicly opted to not prepare or sell Chilean Sea Bass (Trenor, 2010). Furthermore, advocacy projects have been undertaken to increase the scope of public awareness. The New Zealand documentary The Last Ocean was released to communicate the issue of toothfish fisheries, conveying the need to protect the Southern Ocean’s native biodiversity. (Young, 2012).

In October 2016, a 1.55 million km2 area portion of the Ross Sea was designed as a marine protected area, meaning that most fishing is banned in the area. The area will remain protected until 2052.

References

1. Smitt, F.A. 1898 Poisson de l'expédition scientifique à la Terre de Feu.
2. Johanna P. Pierre, JPEC Ltd (August 6, 2013) . "Chilean Seabass" (PDF). Monterey Bay Aquarium Seafood Watch. Monterey Bay Aquarium Foundation. Archived from the original (PDF) on 21 February 2014. Retrieved 12 February 2014. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
3. "The Invention of the Chilean Sea Bass". Priceonomics. Retrieved on 16th May 2015.
4. "John Weller's "The Last Ocean: Antarctica's Ross Sea Project: Saving the Most Pristine Ecosystem on Earth"". Radio Times with Marty Moss-Coane. WHYY. February 12, 2014. Retrieved 12 February 2014.
5. ^ G. Bruce Knecht, Hooked: Pirates, Poaching, And the Perfect Fish", 2006. ISBN 1-59486-110-2. p. 9
6. http://en.mercopress.com/2015/09/04/toothfish-day-celebration-in-south-georgia-and-south-sandwich-islands
7. https://www.youtube.com/watch?v=GlnegoEzeL0
8. Froese, Rainer; Pauly, Daniel (eds.). "Species in genus Dissostichus". FishBase. February 2014 version.

• "Dissostichus Smitt, 1898". Integrated Taxonomic Information System.

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