The Southern Ocean
The Southern Ocean surrounds Antarctica and represents approximately 15 percent of the world’s ocean area. It extends from the coast of the continent northwards to the Antarctic Polar Front, a physically and biologically distinct frontal zone where the cold water of the Southern Ocean encounters, and flows under, the warmer and more saline sub-Antarctic water of the Atlantic, Indian and Pacific Oceans.
The position of the Antarctic Polar Front varies seasonally and geographically, but is generally located near 50°S in the Atlantic and Indian sectors of the Southern Ocean and 60°S in the Pacific sector.
The Southern Ocean has three distinct ecological zones:
- an ice-free zone to the north
- an extensive seasonal pack-ice zone between approximately 55–60° and 70–75°S
- a permanent pack-ice zone adjacent to the continent.
Harvesting marine resources
The living marine resources of the Southern Ocean have been harvested since 1790 when sealers first hunted fur seals for their pelts. By 1825, some populations of fur seal were hunted close to extinction, and sealers began hunting elephant seals and some species of penguins for their oil.
Whaling in this area began in 1904 and all seven species of whales found in the Southern Ocean were extensively exploited.
Antarctic finfish, crabs, squid and krill, a keystone component of the Antarctic ecosystem, have also been exploited at various levels since the early 1960s.
Although seal harvesting continued on a small scale into the 20th century seal populations were reduced to the extent that most commercial harvesting was in decline by the mid-1820s. There has been no commercial sealing in Antarctica since the 1950s. A Convention for the Conservation of Antarctic Seals was established to avoid future over-exploitation of seal populations.
The Convention established permissible catch limits for species such as crabeater, leopard and Weddell seals. Annual catch limits were set at 175 000 individuals for crabeater seals, 12 000 individuals for leopard seals and 5 000 individuals for Weddell seals. A zoning system was established with closed hunting seasons. Total protection was given for the rare Ross seal and southern elephant seal and certain species of fur seal.
Of the major whale groups only the minke whale escaped severe depletion due to commercial fishing. Exploitation on this species (the smallest of the large whales) only began in the early 1970s. Although several hundred thousand Antarctic minke whales exist and the species is not considered to be endangered there was an appreciable decline in the estimated abundance of minke whale between 1982/83–1988/89 and 1991/92–2003/04. Present estimates of total Antarctic abundance range from around 460 000–690 000 individuals. Several hundred minke whales are taken annually in this area by Japan for research sanctioned by the International Whaling Commission.
A moratorium on commercial whaling was introduced in 1987. Whale sanctuaries were established in the Indian Ocean in 1979 and Southern Ocean in 1994.
Management of whales in the Antarctic (and elsewhere) is the responsibility of the International Whaling Commission and they are evaluating the recovery of whale stocks and the effectiveness of the moratorium and sanctuaries. There are indications that some species of whale are recovering, but the low abundance of some of the largest species has made total numbers difficult to estimate from sightings data.
Large-scale fishing for fin fish did not begin until the late 1960s, and important species included lanternfish (myctophids), mackerel icefish (Champsocephalus gunnari), marbled rockcod (Notothenia rossii) and Patagonian rockcod (Patagonotothen guntheri). By the late 1970s, certain species of finfish had been severely overfished in some areas.
Overall trends in fishery catches have varied widely, reflecting intense fishing during the 1960s and 1970s prior to the establishment of CCAMLR. Such fishing led to the overexploitation of stocks of marbled rockcod, and large and possibly ecosystem-related peaks in catches of mackerel icefish in the mid 1970s and 1980s.
There were also large but variable catches of krill from around 1978 until the early 1980s when the Soviet fleet was disbanded following the break-up of the former USSR. By the mid-1980s, CCAMLR had implemented a long-term prohibition of directed fishing on finfish in Subareas 48.1 and 48.3, and on marbled rockcod in Subarea 48.3. Since that time, further prohibitions on directed fishing have been implemented, notably for toothfish.
In the 1980s and 1990s, fishing focused on krill, Patagonian toothfish (Dissostichus eleginoides), mackerel icefish and, to a limited extent, squid and crab. The development of new harvesting technology and markets in recent years has created growing interest in exploratory fisheries targeting Antarctic toothfish (Dissostichus mawsoni) adjacent to the continent, and renewed interest in krill fishing. Catches from the Southern Ocean are dominated by those from the Southern Atlantic but remain around one third of catches taken in 1980s and 1990s.
When considered by major statistical area, the overall catch of the South Atlantic (Area 48) has shown a steadily increasing trend from a low in 1993 of 64 000 tonnes to 131 700 tonnes in 2009.
In the Indian Ocean zone (Area 58), following the highly variable catches that occurred from 1970 to 1990, landings stabilised at a small fraction of this period’s maximum, though with a slightly increasing trend.
In the Pacific sector of the Southern Ocean, following a period of highly variable catches from 1977 to 1992, and then no reported landings until 1998, landings showed a generally increasing trend with a peak of 3 730 tonnes in 2005.
These figures reflect the reported catch. During the 1990s and early 2000s illegal, unregulated and unreported (IUU) fishing took large unreported quantities of toothfish that may have exceeded the reported catch by five to six times.