Habitat and Biology
Climatic zone: Polar. Vertical distribution: Pelagic; Demersal/Benthic.
Water Area Overview
The Southern Ocean surrounds Antarctica and represents about 15 percent of the world’s ocean area. It extends from the coast of the continent north to the Antarctic Convergence. This is 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 Southern Ocean is characterized by an eastward-flowing Antarctic Circumpolar Current and a series of clockwise-rotating gyres that contribute to a westward-flowing East Wind Drift along the Antarctic coast. The Southern Ocean has three distinct ecological zones: an icefree zone to the north; an extensive seasonal pack-ice zone between about 55–60°S and 70–75°S; and a permanent pack-ice zone adjacent to the continent.
The Antarctic Convergence front encircles Antarctica and is formed by cold, northward-flowing Antarctic waters sinking beneath the relatively warmer waters of the sub-Antarctic. Associated zones of mixing and upwelling create high biological productivity, especially of Antarctic krill. The convergence separates two hydrological regions with distinctive marine life and climate. The position of the Antarctic Convergence varies seasonally and geographically, but is generally located near 50°S in the Atlantic and Indian sectors of the Southern Ocean and near 60°S in the Pacific sector. The Southern Ocean (Figure B16.1) is divided for statistical purposes into: Area 48 (Antarctic Atlantic), between 70°W and 30°E; Area 58 (Antarctic Indian Ocean), between 30°E and 150°E; and Area 88 (Antarctic Pacific) between 150°E and 70°W.
Antarctic krill (Euphausia superba) is a keystone circumpolar species of the Southern Ocean. It is abundant in the seasonal packice zone, where it provides the staple food for many species of whales, seals, penguins and other seabirds, and fish that inhabit the region. This is particularly so in the Antarctic Atlantic region, and this area is where krill fishing is focused. E. superba is also dominant in Area 58, while another species Euphausia crystallorophias is abundant in Area 88, but these populations are not currently fished.
|Figure B16.1 The Southern Ocean (Area 48, 58 and 88) |
Considered a single stock: No
PROFILE OF CATCHES
The marine living 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 had been hunted close to extinction. Sealers then began hunting elephant seals and some species of penguins for their oil. Whaling in Areas 48, 58 and 88 began in 1904, and all seven species of whales found in the Southern Ocean were extensively exploited. Large-scale fishing did not begin until the late 1960s. Important species fished 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 regions.The marine living 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 had been hunted close to extinction. Sealers then began hunting elephant seals and some species of penguins for their oil. Whaling in Areas 48, 58 and 88 began in 1904, and all seven species of whales found in the Southern Ocean were extensively exploited. Large-scale fishing did not begin until the late 1960s. Important species fished 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 regions.
Overall trends in fishery catches have varied widely, reflecting intense fishing in the 1960s and 1970s. Such fishing led to the overexploitation of stocks of marbled rockcod and large fluctuations in catches of mackerel icefish in the mid-1970s and 1980s. These fluctuations were possibly related to large variations in recruitment (Kock and Everson, 1997). There were also large but variable catches of krill from about 1978 until the early 1990s when the Soviet fleet was disbanded following the breakup of the former Soviet Union.
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 seen growing interest in exploratory fisheries targeting Antarctic toothfish (Dissostichus mawsoni) adjacent to the continent, and renewed interest in krill fishing. At its peak in 1982, the krill fishery contributed about 13 percent of the global annual catches of crustaceans.
Catches from the Southern Ocean are dominated by those from the Antarctic Atlantic. As a consequence, the total catch from Area 48 has traditionally dominated reported landings from the Southern Ocean with relatively minor landings from the other two regions. In 2009, catches recorded from this region were 90 percent of the total recorded catches from the Southern Ocean. However, recent catches remain about one-third of the general period of the 1980s and 1990s (Figure 16.2).
When considered by major statistical area,7 the overall catch of the Antarctic 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 Antarctic Indian Ocean (Area 58), there were highly variable catches from 1970 to 1990. After that time, landings stabilized at a small fraction of this period’s maximum, although with a slightly increasing trend. In the Pacific sector of the Southern Ocean, catches were also highly variable from 1977 to 1992. No landings were reported after that until 1998. Then, reported landings showed a generally increasing trend with a peak of 3 730 tonnes in 2005 (Table D8, Table D11 and Table D18). In the 1990s and early 2000s, IUU fishing took large unreported quantities of toothfish. These unreported catches may have exceeded the reported catch by five to six times (e.g. SC-CCAMLR, 2010, Annex 8, Table 5).
|Figure B16.2 Annual nominal catches in Areas 48, 58 and 88 |
Antarctic Atlantic (Area 48)
|Figure B16.3 CCAMLR boundaries of statistical reporting areas in the Southern Ocean |
The krill fishery is the dominant fishery in the Antarctic Atlantic. Historically, peak catches were taken in early and late 1980s with catches of 374 000 tonnes in 1982 and 400 000 in 1987. These large catches were made prior to the breakup of the then Soviet Union and the disbanding of the Soviet fishing fleet. Krill catches have been between 100 000 tonnes and 150 000 tonnes in the last decade (Figure B16.4). These lower catches reflect a decrease in fishing effort rather than overfishing. The fishery has operated predominantly in Area 48, around the South Shetland Islands (Subarea 48.1) and South Orkney Islands (Subarea 48.2). It generally occurs in summer when pack-ice is at its minimum extent and adjacent to South Georgia (Subarea 48.3) in winter. In 2008–09, 126 000 tonnes of krill was reported from Subareas 48.1, 48.2 and 48.3. In 2009–2010, 211 984 tonnes of krill was harvested from the same subareas. As a result, the krill fishery in Subarea 48.1 was closed following the highest recorded catch. This was the first time that a subarea had been closed because catches had reached the threshold amount (155 000 tonnes). Intentions to catch 410 000 tonnes in 2010–11 had been indicated by the main fleets in this fishery from Norway and the Republic of Korea. A change in the fishing pattern for krill had been reported, with the catches coming mostly from Subarea 48.2 in 2008–09 and from around Bransfield Strait in Subarea 48.1 in 2009–10. The fishery concentrated in Subarea 48.1 in 2009–2010. Moreover, the krill fishery was able to operate in Subarea 48.1 in winter because of the low level of pack-ice.
The former Soviet fleet fished intensively on rockcods (Nototheniidae) in the decade starting in 1966, and catches peaked at almost 400 000 tonnes in 1970. The CCAMLR implemented long-term prohibitions on the directed fishing on rockcods and other finfish species in Subarea 48.1 and 48.2, and on marbled rockcod in Subarea 48.3 between 1984 and 1986. The results of repeated scientific surveys to investigate recovery from this intense period of fishing have been inconclusive (Kock, Belchier and Jones, 2004). The collapse of the marbled rockcod fishery was followed by the expansion of a fishery for mackerel icefish (Champsocephalus gunnari), which peaked at about 190 000 tonnes in 1983. This fishery also was soon depleted by a combination of regional overfishing and highly variable annual recruitment. The icefish fishery is now managed by the CCAMLR, and fishing is permitted in Subarea 48.3 at a relatively minor level – just under 2 000 tonnes in 2009.
In 2009, krill dominated landings (95.7 percent), followed by Patagonian toothfish (Dissostichus eleginoides) (2.6 percent). The toothfish catch represented 59.5 percent of non-krill landings, followed by mackerel icefish (Champsocephalus gunnari) (31.4 percent of non-krill landings) (Figure B16.4). Of these, Patagonian toothfish is the most valuable species. It is the dominant species of toothfish in Subarea 48.3. Antarctic toothfish (Dissostichus mawsoni) dominates the catch in the Subareas 48.4 and 48.6. The increased landings of krill have attracted considerable international attention because of the important role of krill as a prey species in regional ecosystems.
Antarctic Indian Ocean (58)
|Figure B16.4 Annual nominal catches of selected species in Area 48 |
In the Antarctic Indian Ocean, catches from vessels targeting toothfish now dominate the fishery – 9 000 tonnes in 2009 (Figure B16.5). Catches are down from their peak of about 12 000 tonnes in 2000 and have been essentially stable since 2002. Patagonian toothfish dominates the catches in Divisions 58.5.1 and 58.5.2 and Subareas 58.6 and 58.7, while Antarctic toothfish (Dissostichus mawsoni) dominates the catches in Divisions 58.4.1, 58.4.2, 58.4.3a and 58.4.3b. Ridgescaled rattail (Macrourus carinatus) is taken as bycatch in the fisheries for toothfish, and form a byproduct in the fisheries operating in the French EEZs. The once-important fisheries for mackerel icefish (54 187 tonnes in 1977) and grey rockcod (Notothenia squamifrons) (52 912 tonnes in 1972) continue to show no sign of recovery, and fishing on these species is prohibited.
Antarctic Pacific (Area 88)
|Figure B16.5 Annual nominal catches of selected species in Area 58 |
The fishery in the Antarctic Pacific is relatively small, and it is dominated by catches of Antarctic toothfish (Dissostichus mawsoni) with a total of 2 917 tonnes taken in 2009 (91 percent of reported landings from Area 88) (Figure B16.6). This species is taken in exploratory fisheries in Subarea 88.1 and 88.2 that were initiated in 1987. Catches have been stable since around 2004. The bycatch in Area 88 is largely Macrourus spp.
|Figure B16.6 Annual nominal catches of selected species in Area 88 |
Management unit: No
The management of marine living resources in the Southern Ocean is the mandate of several international organizations. The International Whaling Commission (IWC), established in 1946, is responsible for management and conservation of whales. The Convention for the Conservation of Antarctic Seals, ratified in 1978, reports to the Scientific Committee on Antarctic Research, which undertakes the tasks requested of it in the convention. The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), established in 1982, is responsible for the conservation of marine species including seabirds and the management of fisheries in the Southern Ocean. It purposely has a wide mandate that encompasses all ecological aspects of the area for which it has competence. Under this mandate, the CCAMLR pioneered the implementation of the precautionary principle and the ecosystem-based approach to fisheries management. The CCAMLR meets annually and the extensive reports of its Scientific Committee and those of the Commission are available on its Web site (www.ccamlr.org).CCAMLR
In 1982, parties to the Antarctic Treaty established the CCAMLR under an international convention. Its purpose was to apply an ecosystem approach to the conservation of marine living resources in the Southern Ocean. Conservation was defined to also include rational use. The conservation principles set down in the convention require that exploited populations must not be allowed to fall below an abundance close to that which ensures their greatest net annual increase. Depleted populations must be restored to such abundance, and the risks of changes to the marine ecosystem that are not potentially reversible in two or three decades must be minimized. Importantly, ecological relationships between harvested, dependent and related species must be maintained.Whales, Southern Ocean
These stringent principles embody an ecosystem approach to the management of living resources. It sets the CCAMLR convention apart from other regional marine resource management regimes. Management of fishing must not only aim to conserve the targeted species (status shown in Table D8, Table D11 and Table D18), but take into account the impact of fishing on those animals that prey on, and compete with, the targeted species. In its broadest interpretation, the convention requires that management action should take into account the impact of activities on all living organisms in the Antarctic ecosystem or subsystems.
The status and management of the marine ecosystem of the Southern Ocean is reviewed annually by all member countries of the CCAMLR. These assessments are based on information gathered from the commercial fisheries and fishery surveys, the Scheme of International Scientific Observation aboard fishing vessels, and CCAMLR’s Ecosystem Monitoring Program. Fishery resources are reassessed and decisions are agreed by consensus. The management regime applied is defined by conservation measures that regulate all fisheries, and fishing for research purposes within the CCAMLR convention area (Areas 48, 58 and 88). The CCAMLR’s unified framework for fisheries includes new and exploratory fisheries and assessed fisheries, as well as lapsed and closed fisheries.
Complementary management measures are also in force in territorial waters adjacent to Prince Edward and Marion Islands (South Africa), Crozet Islands and Kerguelen Islands (France) and Heard and McDonald Islands (Australia) in Area 58. Of particular interest has been the recent creation of the world’s largest fully protected marine reserve in the Australian sub-Antarctic. The Heard and McDonald Islands Marine Reserve (65 000 km2; see www.environment.gov.au/coasts/mpa/heard/) should ensure that this pristine ecosystem remains intact. It surrounds the uninhabited Heard and McDonald Islands and includes two large zones of the Southern Ocean. The Heard Island reserve is intended to protect the habitat and food sources of seals, penguins, albatrosses and other marine life.
The CCAMLR has also declared the first high seas marine protected area (MPA) to the south of the South Orkney Islands in Area 48 (94 000 km2). This MPA is the first component of a Southern Ocean MPA network. Fishing activities are prohibited along with the discharge and disposal of refuse from fishing vessels. This area also provides an opportunity to improve monitoring of the effects of human activities and climate change on the Southern Ocean.
Whaling in the Southern Ocean began with the introduction of industrial harvesting methods in the early twentieth century. It has a complex, although well-documented, history. Of the major whale groups, only the minke whale escaped severe depletion. Commercial exploitation on this species (the smallest of the large whales) only began in the early 1970s. Several hundred thousand Antarctic minke whales exist and the species is not considered to be endangered. However, 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 minke whale abundance range from about 460 000 to 690 000 individuals. Several hundred minke whales are taken annually in Areas 48, 58 and 88 by Japan for research that is endorsed by the IWC. Recovery of the southern whale stocks proceeds slowly depending on species.A moratorium on commercial whaling was introduced in 1987. The Southern Ocean Whale Sanctuary surrounds the Antarctic continent and is bounded by the 40°S parallel in the Antarctic Atlantic, the 55°S parallel in the Antarctic Indian Ocean and the 60°S parallel in the Antarctic Pacific Ocean. 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 IWC. It evaluates 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.Seals, Southern Ocean
Early hunting had almost decimated populations of seals in many locations in the Southern Ocean by 1830. This led to a decline in the sealing industry, although it continued on a small scale into the twentieth century. However, there has been no commercial sealing in Antarctica since the 1950s. The Convention for the Conservation of Antarctic Seals was established to avoid future overexploitation of seal populations. It established permissible catch limits for species such as crab-eater, leopard and Weddell seals. Annual catch limits were set at 175 000 individuals for crab-eater 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.Krill, Southern Ocean
Krill is central to the food chain in the Southern Ocean, and its circumpolar standing stock is generally estimated at about 500 million tonnes. There remains much uncertainty over the accuracy of these production estimates for krill. The decline in krill catches in 1992 (Figure B16.7) was attributed to a combination of factors. These included economic factors, a shift in fishing effort from krill fisheries to finfish fisheries, and the breakup of the Soviet Union, which until then had dominated the fishery. There was no evidence that the decline of the fishery was not due to overfishing.
The CCAMLR Scientific Committee has noted that “Interest in krill fishing continues to grow and catches exceeded 200 000 tonnes in 2009/10.” Following an extensive four-vessel acoustic survey in Area 48, the CCAMLR set a new precautionary catch limit of 5.61 million tonnes for krill in Subareas 48.1–48.4. Precautionary limits are implemented in each subarea. A further small-scale subdivision of these catch limits will be required before the fishery is allowed to expand above a trigger level of 620 000 tonnes. This trigger level is not linked to an assessment of virgin biomass (B0). The CCAMLR Scientific Committee also expressed concern over krill escape mortality and the impact of krill fishing on fish larvae and krill predators. For these reasons, krill fisheries are closely monitored because vessels target krill aggregations on the shelf or at the shelf break. In many cases, these aggregations are close to the breeding sites of land-based krill predators such as penguins. The interaction between krill fisheries and land-based krill predators is being researched under the CCAMLR’s Ecosystem Monitoring Program. The potential impact of climate change upon the extent of ice-sheet coverage in the Antarctic has also been of concern. This is because of its possible affect upon krill life history and recruitment variability. The CCAMLR is cognizant of the need to consider the influence of recruitment variability on the calculation of sustainable yields.
Toothfish, Southern Ocean
|Figure B16.7 Annual nominal catches of selected species in Areas 48, 58 and 88 |
Toothfish is harvested under exploratory and assessed fisheries in Areas 48, 58 and 88. Two species are taken: Patagonian toothfish (Dissostichus eleginoides), representing 70.3 percent by weight in 2009; and Antarctic toothfish (Dissostichus mawsoni), representing 29.7 percent (figure B16.7). Patagonian toothfish occur mostly near the sub-Antarctic islands and to the north of the CCAMLR convention area. Antarctic toothfish occur predominantly along the continental coastline of Antarctica. Annual landings within the CCAMLR convention area have been stable at just below 16 000 tonnes since 2002.Mackerel icefish, Southern Ocean
Catches of toothfish from both inside and outside the CCAMLR convention area are reported using the CCAMLR’s Catch Documentation Scheme (CDS). In addition to total landings of 15 784 tonnes of toothfish in 2009 from Areas 48, 58 and 88, 9 952 tonnes of Dissostichus spp. were taken outside the CCAMLR convention area in 2009–2010 (to October 2010). This compares with 12 806 tonnes in 2008–09, which was mostly taken in Areas 41 and 87.
Since May 2000, the CCAMLR has operated its CDS for Dissostichus spp. This scheme was established under Conservation Measure 10–05 to assist in the management and conservation of toothfish. The CDS is designed to track the landings and trade of toothfish caught inside the CCAMLR convention area. It has also been extended to toothfish fisheries in adjacent waters. The scheme provides the CCAMLR with the information necessary to identify the origins of toothfish entering the markets of contracting parties. It allows the CCAMLR to determine if it was harvested in the CCAMLR convention area in a manner consistent with its conservation measures. This process is facilitated by the use of an electronic system for recording toothfish landings and product movements. The landing or transfer of toothfish from a vessel is certified by the port State where it is landed. Any export, import or re-export is tracked by the CDS, and documentation must accompany each consignment of fish.
Fishing for icefish is now concentrated in the vicinity of South Georgia (Subarea 48.3) and about Heard Island (Division 58.5.2). In the 2009–2010, season the catch limit set for C. gunnari in Subarea 48.3 was 1 548 tonnes, and only 12 tonnes had been caught by October 2010. The catch limit for C. gunnari was recommended to be 2 305 tonnes in 2010–11 and 1 535 tonnes in 2011–12. For Heard Island (Division 58.5.2), the catch limit for the 2009–2010 season was 1 658 tonnes and the catch reported for this division was, at October 2010, only 365 tonnes. The CCAMLR manages both fisheries using a short-term assessment method based on the results of pre-recruit surveys (SC–CCAMLR, 2010, Annex 8). It is recognized that additional work remains outstanding on the assessment method for icefish. The method always predicts a precautionary yield and the question remains as to whether a rebuilding strategy needs to be undertaken for such stocks when they have small biomasses. The catch limit for C. gunnari in 2010–11 was to be set at 78 tonnes. As an additional precaution, directed fishing on finfish along the Antarctic Peninsula (Subarea 48.1) and around the South Orkney Islands (Subarea 48.2) is prohibited.Crab resources, Southern Ocean
An exploratory fishery for crabs in Subarea 48.2 was undertaken for the first time in 2009–2010. Fishing effort consisted of 79 140 pot hours and 17 sets. However, only three Paralomis formosa males were captured. No member of the CCAMLR indicated that they intended to fish for crabs in Subarea 48.2 in the 2010–11 season. There was also no new information available on the stock status of crabs or the conduct of the fishery in Subarea 48.3.Elasmobranchs, Southern Ocean
Rajid rays are the dominant elasmobranch group caught as bycatch in the Southern Ocean fisheries. Some species of sharks are also taken (e.g. Somniosus antarcticus), but they represented less than 0.2 percent of the elasmobranchs catch in 2009. Of the ray species identified, Bathyraja eatonii is the most common (53.4 percent). The CCAMLR had undertaken initiatives in the “Year of the Skate” to collect biological data on skates and implement a tag-recapture programme. On all vessels, all skates must be brought on board or alongside the hauler to be scanned for tags and for their condition to be assessed.
Source of information
Marine and Inland Fisheries Service, Fisheries and Aquaculture Resources Use and Conservation Division. FAO Fisheries and Aquaculture Department “Review of the state of world marine fishery resources” FAO FISHERIES AND AQUACULTURE TECHNICAL PAPER.
No. 569. Rome, FAO. 2011.
The bibliographic references are available through the hyperlink displayed in "Source of Information".