FAO Fisheries Circular No. 920 FIRM/C920
REVIEW OF THE STATE OF WORLD FISHERY RESOURCES: MARINE FISHERIES
Marine Resources Service,
Fishery Resources Division,
FAO, Rome, Italy
17. SOUTHERN OCEANS
FAO Statistical Areas 48, 58 and 88
The Southern Ocean is bounded to the south by the Antarctic continent and to the north by the Antarctic Convergence; as such it is the only water mass to stretch completely around a continent. The Antarctic Convergence is the region where the cold Antarctic surface waters meet, and sink below, the warmer sub-Antarctic surface waters of the southern Atlantic, Indian and Pacific Oceans, and occurs between the 50th and 60th degree parallels. The environment of Antarctic fish is characterized by marked seasonality in primary and secondary production, high oxygen concentrations and low but stable temperatures. A major physiological feature of fishes of the region is adaptation against freezing. The Southern Ocean ecosystem is dominated by krill, Euphausia superba, whose biomass may reach 1 000 million t. Krill form dense swarms that may be several hundreds of metres in extent and contain densities of several kilos per cubic metre.
The great historical importance of the Southern Oceans was for whale fishing and, with the demise of this fisheries in the 1960s, it was anticipated that fisheries would shift to the whale's food - krill. Although commercial fisheries have been targeting this species since the late 1960s, the catch can be best described as incidental. This has not been the case for the larger demersal fish which are found in Southern Ocean waters; these stocks have been heavily fished, mainly by longline, and often in an unregulated manner as the species of the area are readily accepted on international markets. A major concern regarding the marine ecosystem of this area has been the consequences of thinning and disappearance of the ozone layer, a meteorological phenomenon which is most pronounced in polar areas. This has the effect of decreasing the amount of ultra-violet radiation which is filtered by the atmosphere, and there is evidence that this may affect plankton. Another consequence on global warming is the retreat of the ice front. This is resulting in new areas of the seafloor being exposed to direct sunlight and the creation of possible new fish habitats. Large sections of the ice cover have broken away and this will have uncertain affects on the ecosystems of the area.
PROFILE OF CATCHES
Greatest reported landings from the Antarctic area were in 1982 (607 700 t) and coincided with the peak landings of krill (528 201 t) (Figure B17.1, Table XVI). Krill landings (Figure B17.2) started to increase rapidly from 1977 on, fell in 1983, then reached another peak in 1986 before the fishery collapsed because of lack of profitability and market demand. A fishery, important in the past, that has failed completely for market reasons was that for the myctophid, Electrona carlsbergi. Landings went from 78 488 t in 1991 to zero in 1993 and subsequent years.
|Figure B17.2||Figure B17.3|
RESOURCE STATUS AND MANAGEMENT
While Antarctic krill have a circumpolar distribution, being found south of the Polar Front and north of the ice edge, the assumed centres of high krill concentration are areas 48.1, 48.2 and 48.3 (i.e. the area around South Georgia and the Antarctic Peninsula). In the past there has been a seasonal shift in the fishery from South Georgia (48.3) in winter to South Orkneys (48.2) and South Shetlands (48.1) in the summer.
Krill biomass is currently estimated at 35 400 000 t in Area 48 and 3 900 000 t in Division 58.4.2. Based on an assumption that 'precautionary' harvests of krill should not exceed 11.6% of the biomass, precautionary catch limits of 4 100 000 t for Area 48 while for Division 58.4.2 a precautionary catch limit of 450 000 t have been proposed. In reality, catches in 1994-95 have been far below these limits as follows: Japan 60 304 t, Poland 6 287 t and Ukraine 51 325 t, for a total of 117 916 t (i.e. an increase of 32.8% over catches in the 1993-94 season). No catches were reported by Chile and Russia, which had reported krill catches in the previous season.
The Patagonian toothfish has a widespread distribution in the sub-Antarctic zone, and knowledge concerning the distribution of this species is considered to be still incomplete. Catches of 11 705 t in 1995 were reported for this species from the convention area, but CCAMLR noted that reported landings in Subarea 48.3 under-represented the true level of landings (official records were only 40% of those believed to have occurred). Official landings were up ~100% over 1994. However, a TAC of 4 000 t was set for Subarea 48.3 in 1996, compared to estimated landings of 6 171 t in 1995. Reports of illegal fishing for this species by re-flagged vessels appear to be a persistent theme from this fishery.
Landings of icefish of 3 936 t in Division 58.5.1 (Kerguelen Islands) were reported for 1995, a fishery which in the past had reached 25 852 t. This fishery is essentially closed, with no re-opening of the fishery to occur without a pre-recruit survey. There has been no resumption of the fishery for Electrona carlsbergi in Area 48.3 in which the last landings (46 960 t) were reported in 1992.
With their long periods to sexual maturity and low fecundity rates, it will be a long time before any recovery of the large whales is possible. Of these, the blue whale has been the most affected, followed by the humpback and sei whales. Minke whale numbers have increased, as have crabeater and fur seals. The numbers of the other major whales have decreased. A harvest of 400 minke whales per season is taken for scientific purposes in the Southern Oceans through the Japanese scientific programme, although this fishery is the subject of controversy.
The Southern Oceans area, containing the marine interface with the Antarctic ice cap as well as the Polar Front, is an area sensitive to the effects of global warming. In 1995 an enormous area of the ice cap broke away turning a surface area into sea for the first time in recorded history. These ice shelves, 200-500 m thick, occupy about one third of the Antarctic coastline and have an area exceeding 10 000 km2. Primary production beneath these shelves was considered to be impossible. Thus a reduction in this ice cover could have large ecological implications. Also of concern has been the possible effect of increased ultra-violet radiation on photosynthesis by phytoplankton, a consequence of the reduction of the ozone concentration in the upper atmosphere.
There is little doubt that the management of marine resources by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has resulted in conventional practices that are unusual in other international organisations responsible for management of fisheries elsewhere, mainly because CCAMLR has a constitutional requirement to undertake an ecologically integrated approach to management of fisheries. This is manifested in a number of ways: (1) ecological relationships between harvested, dependent and related populations should be maintained and (2) any changes that are not reversible within 20-30 years should be prevented or minimised.
CCAMLR has also responded to the requirements to explicitly consider 'uncertainty' in its approach to management. A general yield model has been developed that uses a standard application of differential equations to examine different patterns of growth, mortality, spawning and fishing on estimates of yield per recruit. The model is used to evaluate the performance of stocks under different yield regimes, either as a proportion (K) of the unfished biomass or as a specified catch. A decision rule is used in setting quotas such that the probability, during the projection period, of the spawning stock biomass falling below 20% of its initial level should not exceed 10%. The value of 20% as a minimum spawning biomass is used on the basis that recruitment overfishing occurs more frequently below this level.
CCAMLR has also instituted strict rules governing the way fisheries are undertaken, to assist in data gathering for assessment purposes. For example, in the toothfish fishery in Area 48.3, fishing effort must be distributed in a manner, both in area and in time, that ensures that the catch-per-unit-effort data can be used as an effective measure for fisheries management. In the now closed fishery for icefish in the same area, fishing is not to resume without 100% vessel coverage by scientific observers, haul-by-haul reporting of catch and position data and, further, vessels must undertake a resource survey following a specified design. Similar conditions are imposed on other new fisheries in the convention area.
The other areas of concern have been minimising incidental mortality to seabirds during longlining operations. To achieve this, a wide range of operational measures must be adopted, (e.g. use of thawed bait to ensure bait sinks as quickly as possible; setting the gear at night with a minimum of vessel lighting and dumping of offal far from the gear when the gear is being set or hauled). Where by-catch must be reduced, vessels are required to move by at least 5 miles if by-catch of species under quota protection exceeds 5% of the catch and may not return before 5 days.