There are only a few types of Antarctic fish, all well-adapted to the cold.
The mackerel icefish (Champsocephalus gunnari) is one of a group of species exclusively found in the Southern Ocean known as 'white-blooded' fishes. These fishes survive without the red oxygen carrying pigment haemoglobin in their blood cells that other fishes have. This means their blood is colourless.
Mackerel icefish grow to 44 cm long at the Heard and McDonald Islands and are thought to live 4-5 years.
This species is found mainly around the Heard and McDonald Islands, Îles Kerguelen and island in the south Atlantic such as South Georgia.
Mackerel icefish was once the most abundant species found near shore in waters less than 400 m. Declines in population sizes in the 1970s and 1980s linked to overfishing have resulted in less icefish being available for fishing.
Icefish form schools and migrate each 24 hours from near the seafloor during the day to feed on plankton and small fish (including juvenile icefish) in midwater during the night.
They are an important food for many seabirds and seals, and also other large fish.
Antarctic toothfish and Patagonian toothfish
There are two species of toothfish: the Antarctic toothfish (Dissostichus mawsoni) and the Patagonian toothfish (Dissostichus eleginoides).
They are very similar in appearance and habits but the Antarctic toothfish is found in the high latitude region close to the Antarctic continent whereas the Patagonian toothfish is found in subantarctic waters on shelves around islands and submarine banks.
Distribution and abundance
Toothfish are bottom-living, in depths of 100 m to 3000 m, but move off the bottom on occasion to feed.
The Antarctic toothfish has antifreeze proteins in its tissues and blood because the seawater is below the normal freezing point of tissue. The Patagonian toothfish does not have these proteins because it lives in warmer water.
Commercial fishing of the Patagonian toothfish is managed by CCAMLR (the Commission for the Conservation of Antarctic and Marine Living Resources) around most of the subantarctic Islands, but not off the southern coast of South America. Long-lining is the most common fishing method. Fishing by trawling tends to catch fish in the smaller size range. In some circumstances trawls can damage the seabed.
Illegal fishing of the Patagonian toothfish was a very serious problem in the late 1990s and early 2000s. In 1997/98 about 11000 tonnes were caught legally in the CCAMLR area, but the illegal catch was estimated to be 32000 tonnes. In some areas the illegal activities have reduced the stocks of toothfish markedly. Several nations have arrested a number of boats fishing illegally.
Through increased controls on harvesting and trade by CCAMLR and significant enforcement efforts by Australia and France, illegal unreported and unregulated (IUU) fishing for toothfish has declined to near-zero levels in waters under national jurisdiction. Some IUU fishing persists elsewhere in the CCAMLR Area and was estimated at about 1300 tonnes in 2010.
Toothfish reach sexual maturity (can produce eggs and sperm) when they are between 70 cm and 95 cm long. At this size the fish are between 8 and 10 years old.
Toothfish eggs and larvae are pelagic (free swimming/floating near the sea surface) and the larvae feed on zooplankton.
Toothfish can grow up to 2 m long and weigh 100 kg when fully grown. They can live up to 45 years.
Diet and predation
Toothfish eat small fish and squid in midwater and a range of fish, crabs and prawns on the bottom.
Few species have been recorded as having toothfish as a large part of their diet. However, some known toothfish predators are:
- Black browed albatross (Diomedea melanophrys) which forage for juveniles around Îles Kerguelen
- Southern elephant seals (Mirounga leonina) and Antarctic seals (Arctocephalus gazella) at Heard Island that occasionally eat toothfish
- Some sperm whales (Physeter macrocephalus) captured near Antarctica during the 1970's that had large toothfish in their stomachs
- Killer whales (Orcinus orca) that have been filmed eating toothfish when they are caught on longlines around Île Crozet.
Toothfish are often regarded as the most important Antarctic fish, due to the extent of their commercial exploitation. Commercial fisheries catch these fish by trawling, the setting of longlines, and the use of baited pots. Careful regulation and monitoring of commercial fisheries and significant enforcement activities by countries such as Australia and France has seen illegal, unreported and unregulated (IUU) fishing for toothfish fall to near-zero levels in waters under national jurisdiction; elsewhere in the CCAMLR Area IUU fishing still persists.
The Coalition of Legal Toothfish Operators (COLTO) is an organisation of legal industry members who work with conservation groups, national governments and CCAMLR to improve fisheries resources management and eliminate IUU fishing for toothfish.
Antarctic cods (Notothenia)
One of the most abundant groups are the Notothenioids, also referred to Antarctic cods (although they are not true cods). These fish have an antifreeze in their blood which prevents it from freezing despite their proximity to ice.