Australian Antarctic Territory, Territory of Heard Island and McDonald Islands, and observations on Macquarie Island Tasmania
Theme commentary
Australian National Committee on Antarctic Research
prepared for the 2006 Australian State of the Environment Committee, 2006
Marine ecosystems
The elevated biological productivity of parts of the Southern Ocean region, such as the sea-ice zone, supports a high biomass and considerable biological diversity.
The ecosystems of the Southern Ocean have been subjected to considerable human-induced pressure for over 200 years. Sealing, whaling and fishing have had significant effects on the stocks of marine species and, more recently, human-induced climate change may be changing the physical environment of the oceans.
Some seal populations have yet to show signs of recovery from the exploitation of the 19th century. Whales were severely over-harvested in the early and mid-20th century, and although some species (for example humpbacks) are making a slow recovery, the status of others (for example blue whales) is uncertain. Minke whales have been harvested less than other species but there is still debate over their numbers, highlighting a need to improve the methods of estimating the abundance of large marine mammals.
Fish have been harvested on a commercial scale in the Southern Ocean since the 1960s and many stocks have never recovered from the initial phase of over-exploitation. Current finfish fisheries are low in tonnage but high in value so have suffered greatly from illegal, unregulated and unreported fishing. The krill fishery remains one of the world’s last under-exploited marine stocks with a catch limit some 40 times the current catch. Concerns in Southern Ocean fisheries management include: the problem of bycatch (seabirds, fish and invertebrates); the definition of ecological units for management for all harvested stocks; illegal, unregulated and unreported fishing; stock assessment; and the effects of a changing environment on management approaches.
Climate change is the main environmental concern for marine ecosystems. The current warming trend is expected to affect the rate of nutrient upwelling, and the melting rate of the pack ice in spring. Increased levels of carbon dioxide will affect the acidity of the upper layers of the ocean which will have effects on the health and normal function of marine organisms.
Plankton and microbes
Plankton are sensitive to environmental change and are proven indicators of ocean health, with higher fidelity than direct physical measurement due to their amplified responses to changes in their environment (Hunt and Hosie 2003, 2005).
Planktonic and microbial communities in the Southern Ocean are very complex and diverse, with over 500 species recently documented (Scott and Marchant 2005), covering a size range from 0.7 µm to 4 mm. They constitute by far the major component of the region’s biomass, and have comparatively rapid generation times, with a succession of species dominating during the season. Since 1991 zooplankton has been routinely and repeatedly surveyed (Hosie et al 2003). Major changes in the North Atlantic and in the North Pacific are well-documented and it is believed that similar changes are occurring in the southern hemisphere.
Time series analysis of plankton of the permanent open ocean zone has shown relatively stable associations between each summer for the typical dominant zooplankton. These permanent open ocean zone zooplankton maintained a consistent association with each other from spring to autumn. However, the sea-ice zone showed a marked change in species composition around 2000. In the 1990s, krill were dominant, and overall zooplankton abundance was very low. In 2000, 2002, 2003 and 2004, overall abundances were higher and the smaller copepod crustaceans dominated—a group more typical of the permanent open ocean zone. It is too early yet to determine if this is a permanent regime shift or part of a cyclic pattern.
The permanent open ocean zone north of the sea-ice zone has a higher abundance and diversity of plankton than previously thought (Hosie et al 2003). The open ocean is typically dominated by small zooplankton such as smaller copepod crustaceans, krill species and appendicularians (a free-swimming relative of the sessile sea-squirt), all typical and prominent grazers of phytoplankton. Large single-celled animals, protists, are also common and abundant. The sea-ice zone, by contrast, is characterised by larger copepod crustaceans, and larger species of krill such as the Antarctic krill (Euphausia superba), the coastal crystal krill (Euphausia cystallorophias) and the smaller big-eye krill (Thysanoessa macrura) (Hosie et al 2003).
Fisheries
Fishing is the only large-scale commercial resource harvest currently undertaken in Australia’s Antarctic Territory. However, from 2005 about 1000 minke whales will be taken yearly from the Southern Ocean by Japan under its scientific whaling programme. Fish of the Antarctic region have long been exploited, often with lasting effects on species and whole ecosystems. A number of species have become threatened by over-harvesting or illegal fishing. While fisheries in the Antarctic region today are focused on Patagonian toothfish, icefish and, to a lesser extent, krill, there is some potential for new fisheries to emerge. Australia has commercial fisheries in the vicinity of Heard and the McDonald Islands and around Macquarie Island, and in the waters off Australia’s Antarctic Territory.
The Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) was signed in 1981 to address concerns that an increase in krill catches in the Southern Ocean could have a serious effect on populations of krill and other marine life, particularly on birds, seals and fish, which mainly depend on krill for food. CCAMLR aims to conserve the marine life of the Southern Ocean, while not excluding harvesting carried out in a rational manner. The CCAMLR Commission meets annually at its headquarters in Hobart.
Patagonian toothfish have been harvested recently at a number of locations in the sub-Antarctic, and a closely related species is harvested in Antarctic waters. The fishery has attracted unauthorised operators from several countries that are working outside the regulatory framework. Such illegal, unregulated and unreported fishing is of concern because it undermines attempts to manage stocks sustainably. The high value of Patagonian toothfish means that this species has been targeted by both legal and illegal fishing operations, and in some areas the stocks have been negatively affected. Most operations for Patagonian toothfish have utilised long-line fishing techniques, which take much bycatch , particularly seabirds. Seabird mitigation measures in the legal toothfish fishery have been extremely successful but there still remains a substantial problem with the illegal fishery.
There is continuing interest in fishing for toothfish and other fish species off Australia’s Antarctic Territory. This may result in a slight rise in catches for this region but substantial rises in catches are unlikely. Squid fisheries remain a possibility but fishable stocks of commercial species have not been found. Krill remains the only large Southern Ocean stock which has a current harvest level far below that which is believed to be sustainable. It is likely that the next decade will see an expansion in the krill fishery, driven largely by demands for aquaculture feed.
There has been a decline in estimated illegal, unregulated and unreported catches over the last three years, although estimates for 2005 are at similar levels to 2004. Pressure from surveillance operations in traditional fishing areas within the Convention Area appears to have forced illegal, unregulated and unreported fishing on to high seas areas within the Convention Area.
Further development of finfish fisheries is unlikely because most known fish stocks are either close to maximum levels of exploitation or are in a depleted state. There were 4–6 notifications (covering 6–11 vessels) for new and exploratory finfish fisheries in 2005–06 in Divisions 58.4.1, 58.4.2, 58.4.3a and 58.4.3b (IMAF 2005). Depending on the size of the precautionary catch limits, this implies that if all vessels operated simultaneously, the available catch per vessel could be lower than that required for economic viability, especially for those vessels operating in high latitudes where fishing faces considerable operational difficulties.
Between 1980 and 1996 (and in the years before CCAMLR) there were considerable catches of krill in Divisions 58.4.1 and 58.4.2, peaking at over 100 000 tonnes per year in 1981 and 1982. There is evidence of increasing interest in the krill fishery, which might result in a spreading out of fishing effort from the South Atlantic where it is currently concentrated, but there are currently no formal proposals for harvesting krill off East Antarctica. Because precautionary catch limits have been set for Divisions 58.4.1 and 58.4.2 and there are no regulations requiring notification of intent to commence krill fishing, a fishery in these divisions could occur at any time.
The total krill catch limit off east Antarctica is currently 890 000 tonnes per year, based on Australian surveys conducted in 1982 and 1996. The Australian Government Antarctic Division will update the earlier results following a survey of Division 58.4.2 in 2006.
Cetaceans
Baleen and toothed cetaceans occur in the marine waters adjacent to the Australian Antarctic Territory and around Heard and the McDonald Islands and Macquarie Island. The baleen whales—blue, fin, sei, humpback, southern right and minke—are the species which were subject to commercial whaling. Toothed whale fauna is more diverse and includes the once commercially hunted sperm whales (primarily males, which feed in the higher latitudes) and bottlenose whales, along with killer whales, a number of dolphin species, the spectacled porpoise, pilot whales and the poorly understood beaked whale species.
Over the past few decades, populations of southern hemisphere humpback whales and southern right whales have been increasing annually. Some populations of humpback whales are estimated to return to pre-exploitation abundance estimates within the next ten years. Much less is known about the recovery of the baleen whales, which do not migrate near land masses.
No estimates exist for fin, sei or sperm whales. Blue whales are estimated to be increasing, but still to be at less than one per cent of their pre-exploitation abundance. Ship-based surveys to estimate the abundance of minke whales have been conducted for the past 30 years, but the methodology and analysis is complex and an understanding of potential bias is incomplete. Estimates of about 760 000 minke whales around Antarctica were agreed at the International Whaling Commission (IWC) in 1989 for the preceding decade, but there are no currently agreed estimates.
New acoustic techniques are being developed, with the potential to yield relative abundance estimates for vocal species. These techniques are best developed for blue and fin whales, but are likely to be applicable to other baleen whales and some toothed whales.
New techniques are being developed in Australia to track large whales with satellite tags, and to determine from small biopsy samples critical elements of their life history. This will improve greatly the understanding of population structure and survey design for cetaceans.
The only direct take of cetaceans in Australia’s Antarctic Territory is that of Japan’s scientific whaling. This greatly expanded program has the potential to expand further in the future and may be at levels that affect the targeted populations. Efforts by pro-whaling countries in the IWC may also see a resumption of commercial whaling in the Southern Ocean.
Southern Ocean cetaceans do not seem to be subject to other direct takes such as bycatch. However, indirect effects, such as the potential ecological consequences of global climate change, may have potent effects on the cetacean assemblages.
Seals
Historically, the main threat to seal populations has been through direct exploitation. Land-breeding seals have been more susceptible and vulnerable to harvesting than ice-breeding seals because they form dense aggregations on land when breeding. The land-breeding seals were exploited heavily throughout the 19th century and populations at most breeding locations declined to very low levels, rendering continued exploitation increasingly uneconomic, although it continued at decreasing levels well into the 20th century.
An indirect threat to seal populations is the exploitation of their prey (krill and fish) through fishing. CCAMLR currently needs improved estimates of predator abundance, including seal abundance, to take into account the food requirements of predators when setting catch limits for krill and fish. Other impacts, such as global climate change, may affect seal populations through changes in primary and secondary production and water circulation.
Populations of land-breeding seals have increased from low levels after heavy exploitation at Heard and the McDonald Islands and Macquarie Island in the 19th century and into the early 20th century. A decline in pupping rates on Heard Island and in pup growth rates on Macquarie Island coincides with an increase in sea surface temperatures north of the islands over the last 15 years.
Fur seal populations continue to increase at both Heard Island and Macquarie Island. Southern elephant seal populations, after recovering very substantially since early exploitation, have declined by about half between the 1950s and the 1980s, but numbers are currently stable. The cause of their earlier decline is not certain but seems associated with wide-scale changes in the Southern Ocean beginning in the middle 1960s. A recovery plan that has been prepared for sub-Antarctic fur seals and southern elephant seals calls for continued population monitoring of those species. Other land-breeding seals have very substantially recovered from the low post-exploitation levels and are no longer considered to be endangered.
Data on the status and trends of ice-breeding seals are far less certain. Recent surveys in Australia’s Antarctic Territory in 1999–2000 have provided uncertain estimates of the current status for this group of species, and it is therefore difficult to assess trends.
The 1999–2000 Australian Antarctic Pack Ice Seals Survey estimated the crabeater seal population between 60 °E and 150 °E at around 950 000, although there is considerable uncertainty in the 95 per cent confidence limits despite the extensive survey using the most sophisticated methods available. Ross seals were estimated to be around 60 000. No estimates for leopard or Weddell seals are yet available. It will be difficult to make inferences about population trends from early and recent survey data because of differences in survey and analytical methods, and inherent uncertainty in population estimation.
Flighted sea birds
Numerous species of flighted seabirds occur in great numbers in the Australian Antarctic Territory and on the Australian sub-Antarctic islands. While many of those are visitors only, some species do breed in Australia’s Antarctic Territory and associated areas, in colonies typically comprising thousands to tens of thousands of breeding pairs. Due to the overlap of commercial fishing areas with the foraging ranges of seabirds, the two interact directly. It is believed to be here that most of the mortality among seabirds occurs, particularly among various species of albatross and medium-sized petrels, as birds drown either by swallowing baited hooks or by being entangled in fishing gear.
The most immediate effects of climate change in the Southern Ocean include changes to sea-ice extent and acidification. Both of these factors are likely to influence the lower trophic levels of the food web—the prey of seabirds.
Seventy-two species of birds have been recorded at Macquarie Island, 34 species of seabird at Heard Island (of which 15 are recorded as breeding on the islands), and six flighted seabirds are known to breed in the ice-free areas of Australia’s Antarctic Territory. Two endemic terrestrial birds at Macquarie Island—the banded rail (Rallus philippensis macquariensis)and the red-fronted parakeet (Cyanoramphus novaezelandia erythrotis)—became extinct in the 19th century. The Heard Island cormorant (Phalacrocorax nivalis) breeds on Heard Island, and is the only endemic marine bird species in Heard and the McDonald Islands. The only non-marine endemic bird species on Heard Island is the black-faced sheathbill (Chionis minor).
Heard Island cormorants are listed as vulnerable, and breed in four small colonies. The population estimate has increased from about 200 pairs (Green 1997) to about 1100 pairs, with the recent discovery of a new colony (Woehler 2006).
Macquarie Island shags (Phalacrocorax purpurascens) are listed as vulnerable, and breed mainly on hard-to-access offshore stacks or islets (Brothers 1985); their current population status is not known but 11 colonies appeared to have 472 breeding pairs in October 2003 (M Schulz and J Lynn unpublished data).
Albatrosses and petrels are probably the most threatened birds worldwide, and both breed at Macquarie Island. While albatross populations are affected by commercial longline fishing activities globally, the breeding populations of Black-browed (Thalassarche melanophyrys) and Grey-headed (Diomedea chrysostoma) albatrosses at Macquarie Island appear to have remained relatively stable (Terauds et al 2005). However, both populations are small and any change in, for example, adult survival can significantly reduce the number of potential recruits to the colonies.
With fewer than 15 pairs breeding annually the Wandering albatross (Diomedea exulans) is the most critical of the seabird populations at Macquarie Island. However, access to major breeding areas on the island has been restricted, with the result that the population is now three times larger than in the 1980s (Gales et al 2004).
The number of Southern giant petrels (Macronectes giganteus) at Macquarie Island has doubled since the 1970s and appears to be stable. However, giant petrels are known followers of fishing vessels, and continuous monitoring of the population is required (Gales et al 2004). In Australia’s Antarctic Territory, giant petrel (Macronectes species) populations appear to have declined since their discovery some 40 years ago (Woehler et al 2003).
The Macquarie Island population of Subantarctic or Brown skuas (Stercorarius antarcticus) comprised some 550 breeding pairs in the mid-1980s. No recent island-wide counts have been made (Schulz and Gales 2004).
For the smaller petrels breeding on Macquarie Island, introduced species, such as house cats (Felis catus) and black rats (Rattus rattus), have been a threat as these predators attack the birds in their burrows and destroy eggs and chicks. The recent eradication of cats from the island has led to the return of some burrowing petrels that had not been seen on the island for many years. However, the populations of rats and house mice need urgent attention as they continue to threaten the small petrels directly, and indirectly through the destruction of habitat, such as for example the tussock grass (Poa cookii) beneath which the critically endangered blue petrel (Halobaena caerulea) breeds in burrows.
Many of the seabird colonies are in remote areas and their status is largely unknown. However, even in the vicinity of stations, regional data on seabird populations are rare and long-term trends cannot be determined (see, for example, Croxall et al 1995).
Penguins
Seven species of penguin are known to breed regularly in, or occasionally visit, the ice-free areas of Australia’s Antarctic Territory, Heard Island and Macquarie Island, and to feed in the oceans surrounding these areas.
A recent review, which assessed penguin population trends at sites where data were available for a minimum of five repeated annual counts over a ten-year period, could analyse data for only two species at three sites in Australia’s Antarctic Territory, Heard Island and Macquarie Island.
Gentoo penguin breeding populations at Heard Island have been estimated at 10 000 pairs in the 1950s and 16 600 pairs in 1987. The breeding population at Macquarie Island was estimated at 3800 pairs in 2002.
Breeding populations of king penguins are difficult to estimate because not all the breeding population is present at breeding sites at any one time. At Heard Island, data collected between 1963 and 1993 suggest the population is doubling every five years (Woehler 2006). The most recent estimate of the breeding population is 15 000 pairs. At Macquarie Island the population of 150 000–170 000 pairs in 2000 is believed to be continuing to increase, following a rapid recovery from commercial harvesting early last century.
The macaroni penguin is the most abundant penguin species at Heard Island, with breeding populations estimated at 1 000 000 pairs at each of Heard and McDonald islands, although no seabird data are available for the McDonald Islands since 1980. There is no information on trends in macaroni penguins. Rockhopper penguins are very difficult to assess because of the broken and difficult terrain they inhabit, but breeding populations have been tentatively estimated at 10 000 pairs at Heard Island, 100 pairs at the McDonald Islands, and possibly up to 100 000 pairs at Macquarie Island. Declines in rockhopper populations of up to 80 per cent have been reported at several locations elsewhere in the sub-Antarctic, but it has not been possible to determine whether similar declines have occurred in Australia’s region.
Royal penguins have been estimated at approximately 850 000 breeding pairs at Macquarie Island, but no information on trends is available. Chinstrap penguins have occasionally been observed visiting Heard Island but do not breed there. The status of penguin populations at the McDonald Islands is uncertain. The habitable area of the McDonald Islands has increased greatly since eruption began in 1992, and it is likely that populations of many species have grown significantly.
Adélie penguins breed at numerous ice-free sites across the entire Australian Antarctic Territory and non-breeding birds are occasionally seen at Heard Island. The estimated total breeding population of 662 000 Adelie pairs has been derived from data collected at all sites over the 32-year period 1956–88. Data from the CCAMLR Ecosystem Monitoring Program (CEMP) indicate no trend in the breeding population of Adelie penguins at Béchervaise Island (near Mawson) over the past 15 years, but counts prior to the CEMP suggest a sudden increase in the local breeding population just before the commencement of CEMP. Estimates of the Adelie breeding population have increased steadily at Whitney Point (near Casey) from 1960 to the present, with current estimates about 6 times greater than in 1960.
Emperor penguins breed at several sites across Australia’s Antarctic Territory, and non-breeding birds are occasionally seen at Heard Island. An estimate of the Emperor penguin breeding population in Australia’s Antarctic Territory of 59 000 pairs has been derived from data collected over the 27-year period 1958–85. Counts of breeding populations have been one-off or intermittent at all sites except one, Taylor Glacier, where regular counts have been undertaken since 1988. The Taylor Glacier counts indicate a slight but steady decrease in numbers from 1988 to the present, with an average population of about 2900 breeding pairs.