Toothfish fishing

Toothfish are important to the commercial fishing industry, as they are valued as a table fish in the United States and Europe for their white, flaky, oily flesh. There are two species of toothfish which are found in the cold waters of the subantarctic and Antarctic oceans. The Patagonian toothfish lives in subantarctic waters while the Antarctic toothfish is found further south.

Toothfish are caught by midwater trawling and by longlining. The midwater trawling started in the late 1980s. In the 1990s longliners started to target toothfish at depths of greater than 600 metres.

The illegal toothfish fishery has had a severe impact on the environment in the southern Atlantic and Indian Ocean sectors of the Antarctic Ocean It has been estimated that more than 50 per cent of toothfish traded is illegally caught, and includes juveniles vital to the ongoing toothfish population.

Juvenile toothfish aggregate on seamounts and banks, in nearshore areas, and in shallow areas around islands. This behaviour makes the juveniles easier to target by trawl vessels than the adults. As a result, juvenile fishing mortality is high in these areas. Juveniles are also taken as by-catch in the krill fishery. 

However, many management measures are in place to ensure minimal effects of the toothfish fishery on the environment in the Ross Sea. This is in line with the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) policy of taking an ecosystem approach to managing fisheries. Management includes close monitoring of vessels in the area to prevent illegal fishing, catch limits for toothfish and by-catch species (fish caught incidentally to the ‘target’ species), seabird and fish by-catch mitigation measures, and zero discard of any waste or offal.

Longline fishing

Longline fishing uses hundreds, or even thousands of baited
hooks hanging from a single line. Longlines can be set to hang near the surface (pelagic longline) or along the sea floor (demersal longline). Toothfish are caught on demersal longlines, which may be set on the sea floor at depths exceeding 1000 metres.

The San Aspiring fishing vessel was longlining for toothfish in the Ross Sea when it caught the colossal squid. Each longline has about 8,000 hooks, and four longlines are set at one time. The hooks are usually baited with arrow squid or jack mackerel, using an automatic baiting machine. It takes about two hours to set one line.

Unlike bottom trawling, longlines rarely become entangled with benthic corals and have little impact on benthic organisms or habitat. By-catch species when fishing for toothfish are closely monitored by CCAMLR. Initially there was no explicit regard for by-catch. However, since 1999 catch limits have been imposed on all by-catch species to ensure that the levels of catch do not exceed biological or ecologically sustainable levels. Longline fishing methods catch small amounts of skates and rattail fishes (grenadiers), and vessels must stop fishing if they exceed the allowable catch of these species.

Pot fishing for toothfish has been tried around South Georgia. However, pots were found to take crabs as by-catch, and the technique is regarded as of concern in relation to crab populations.

Further references
Images
Image 01
Sanford Limited New Zealand's vessel San Aspiring in the Southern Ocean.

Courtesy of John Bennett
Image 02
Crew members of the San Aspiring bring up a toothfish (Dissostichus mawsoni) on a longline.

Photograph by John Bennett
Courtesy of John Bennett
Image 03
Longlining for toothfish in the Ross Sea, Antarctica.

Photograph by John Bennett
Courtesy of John Bennett
Image 04
Skipper John Bennett and Sue Bennett with a toothfish on board the San Aspiring.

Courtesy of John Bennett
Image 05
A crew member of the San Aspiring checking the longline hooks, ready for toothfishing in the Ross Sea.

Photograph by John Bennett
Courtesy of John Bennett
Image 06
Captain John Bennett, skipper of the fishing vessel San Aspiring.

Courtesy of John Bennett
Image 07
Map of Antarctica showing the Southern Ocean and the Ross Sea, where the colossal squid was caught.

Courtesy of Antartica New Zealand
Videos
Video 01
Demand for the toothfish puts pressure on the fishery, requiring careful management by CCAMLR.

Courtesy of Graeme Sinclair, Frontier Television (NZ) Ltd
Video 02
Preparing for the toothfish fishing season in the Ross Sea.

Courtesy of Graeme Sinclair, Frontier Television (NZ) Ltd
Video 03
Fishing for toothfish on longlines.

Courtesy of Graeme Sinclair, Frontier Television (NZ) Ltd
Video 04
Fishing for toothfish on longlines.

Courtesy of Graeme Sinclair, Frontier Television (NZ) Ltd
Video 05
The San Aspiring in the Ross Sea, more than 1,900 kilometres from home, ready to start fishing.

Courtesy of Graeme Sinclair, Frontier Television (NZ) Ltd