Australia State of the Environment Report 2001 (Theme Report)
Australian State of the Environment Committee, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06751 5
Australia's marine mammals comprise a rich and varied fauna of some 43 species of cetaceans (whales, dolphins and porpoises), 10 species of seals, and the Dugong.
Many of the cetaceans found in Australian waters are inhabitants of the deep oceans and come to notice infrequently, usually when stranded on shore, e.g. the Pygmy Sperm Whale (Kogia breviceps). Several dolphin species habitually or occasionally frequent coastal waters, including the widely distributed Bottlenose and Common Dolphins, and the less common and elusive Indo-Pacific Humpbacked Dolphin (Sousa chinensis), and Irrawaddy Dolphin (Orcaella brevirostris), both of which are tropical species.
The so-called ' great whales' - Blue Whale (Balaenoptera musculus), Fin Whale (B. physalus), Sei Whale (B. borealis), Bryde's Whale (B.edeni), Minke Whale (B. acutorostrata), Humpback Whale (Megaptera novaeangliae), Southern Right Whale (Eubalaena australis), and Sperm Whale (Physeter macrocephalus) - were once hunted commercially in Australian waters and in adjacent parts of the Southern Ocean and their numbers were greatly depleted. All these species, with the exception of Bryde's Whale, undergo extensive annual migrations between summer feeding grounds in the Southern Ocean and warmer waters in lower latitudes where calving and mating occur during winter.
A national assessment of cetaceans in Australian waters (Bannister et al. 1996) concluded that the Blue Whale is endangered because numbers remain critically low.
In contrast, the numbers of Southern Right, Humpback and Fin Whales are now increasing, although their populations are still well below pre-exploitation levels. They are still categorised as vulnerable under the EPBC Act. Australia's populations of the Sei Whale have declined by 5% in the past 40 years alone, and there are estimated to be only 25 000 individuals remaining.
As the current status of the Sperm Whale and the Indo-Pacific Humpbacked Dolphin, Irrawaddy Dolphin and Spinner Dolphin (Stenella longirostris) is uncertain, they are provisionally categorised as insufficiently known. Even less information is available for the other species, because they normally occur far offshore.
The trend for numbers of Humpback Whales migrating along the east coast is increasing.
Figure 14: Estimated number of Humpback Whales migrating up the East Coast.
Source: EPA (1999)
Whale-watching is a developing industry based upon the desire by people to see and interact with whales and dolphins, ranging from simply watching whales from the shore to organised boat tours and ' swim with whales' activities. In Victoria, the whale-watching industry is valued at $17 million per year.
However, the activity can be a pressure to the whales. For example, vessels may create noise (and vibration), pollution and may physically injure a whale. Cetaceans have particularly sensitive hearing that plays an important role in communication, navigation and prey location.
Figure 15: Distribution of threatened cetaceans.
Source: Environment Australia
Since the 1980s, Australia has pursued a conservation-oriented policy on whales, via membership of international bodies, including the International Whaling Commission (IWC).
In July 2000 Australia and New Zealand presented the South Pacific Whale Sanctuary proposal at the annual meeting of the IWC. Most members of the commission supported the sanctuary, but it failed to obtain the required three-quarters majority. The proposal will be put to the IWC again.
The Government is putting into effect a draft recovery plan for Blue Whales in Australian waters, and a recovery plan for the Southern Right Whale is being drafted. The listing of the Sei and Fin Whales by the Commonwealth in 1998 means that recovery plans will be developed for both species.
Conservation efforts saw Humpback Whale numbers recover to such an extent that the whale was moved from endangered to vulnerable in 1998.
Humpback Whales are very acrobatic.
Source: M Simmons, Great Barrier Reef Marine Park Authority
Whale-watching is mostly conducted in inshore waters subject to State controls. National guidelines for whale-watching have been developed (ANZECC 2000) with the aims of minimising harmful impacts on cetaceans and allowing people to enjoy and learn about the animals. These guidelines apply to all whales, dolphins and porpoises.
Australia's sea lions and fur seals were hunted extensively by sealers during the 19th century, mainly for their pelts. Recovery has generally been slow, but in recent years some fur seal breeding colonies have expanded significantly, several new colonies have been established, and numbers have also increased at several traditional resting sites within the wider feeding ranges of the two species. The Australian Sea Lion remains widespread but is nowhere common.
Ten species of seals occur regularly in the Australian region. Five belong to the family Otariidae or eared seals, of which three breed on islands adjacent to the mainland and two on sub-Antarctic islands. Five species belong to the family Phocidae or true seals, of which one breeds on Heard and Macquarie Islands. Others breed around the Antarctic including off the Australian Antarctic Territory. Antarctic Fur Seal breeding colonies at Heard, McDonald and Macquarie Islands are small, but numbers appear to be increasing at all sites. Sub-Antarctic Fur Seals have colonised Macquarie Island in recent times, but numbers are still low.
Pressures on general feeders such as sea lions and fur seals arise from their attraction to fishing activity and they become habituated to taking netted or discarded fish and offal. Adult sea lions and fur seals in mainland and Tasmanian waters are vulnerable to capture in shark nets and trawl nets, and their young risk drowning when raiding rock lobster pots for the bait. The level of incidental bycatch in these fisheries is not well documented.
As a requirement of Marine Stewardship Council certification, the Western Rock Lobster Fishery is developing a detailed monitoring program to document the bycatch and any other interactions with sea lions (and other important species). If the level of bycatch or interaction is unacceptably high, the fishery can take further measures to reduce effects on these species.
Significant numbers of seals entangled in fishing gear have been seen at colonies in southern Australia and Tasmania, but losses in population terms are unknown because many seals entangled in lost or discarded nets or large pieces of debris probably die at sea. About 2% of seals at haul out or resting sites in Tasmania are entangled in net fragments and other plastic litter at any time (Commonwealth of Australia 2001b). Even in remote regions like Heard and Macquarie Islands Fur Seals have been found entangled in plastic strapping. The fishing industry has initiated measures to reduce the problem of entanglement.
In the sub-Antarctic, critical areas for the breeding of seals (and sub-Antarctic birds) have been recognised by inscription of Heard and Macquarie Islands onto the World Heritage list and through the proclamation of a marine park to the east of Macquarie Island.
Figure 16: Distribution of seals and sea lions.
Source: Environment Australia (2000)
In the sub-Antarctic, the Southern Elephant Seal (Mirounga leonina) and the Australian Fur Seal (Arctocephalus pusillus) formed the basis of two large sealing industries in the 19th century. Hunting had ceased by early in the 20th century and soon afterwards the elephant seals are thought to have regained their original levels.
Since the 1950s the population trends for the two groups of seals have shown markedly different characteristics. The population of Elephant Seals at Macquarie Island had decreased dramatically by 1999 to approximately 40% of that in 1959. Linear extrapolation of the population trend suggests that Elephant Seals might become extinct on the island by 2050.
In contrast, the numbers of fur seals have increased significantly at both Macquarie and Heard Islands. These populations have been re-established from species breeding elsewhere in the sub-Antarctic.
The reason for the changing populations of the seals is uncertain at present. Competition for food between Australian Fur Seals, Elephant Seals and King Penguins (which are also rapidly becoming more numerous at Heard and Macquarie Islands) may have advantaged Fur Seals and penguins to the detriment of Elephant Seals. Changes in the Southern Ocean environment have also been implicated, including the rapid decline in the area of sea ice that occurred between 1950 and 1973. Elephant seals are known to enter the pack ice zone to feed.
Annual census of Elephant Seals on Macquarie Island.
Source: Antarctic Division (2000)
The Dugong is the only strictly marine herbivorous mammal, the sole living representative of the Family Dugongidae. Australian Dugongs (Dugong dugon) constitute a significant percentage of the world population. They occur in the Australian tropics and subtropics, from Shark Bay in Western Australia to Moreton Bay in Queensland.
Some populations of Australian Dugongs have declined dramatically since European settlement, largely as a result of human activities, but others do not appear to be currently threatened. Their specialist requirement for seagrass habitat makes them vulnerable to human influence. Important populations of Dugongs are given in Marsh et al. (1999).
Figure 17: Distribution of Dugong around the Australian coastline.
Source: Environment Australia (2000)
Dugongs are vulnerable to large sharks, estuarine crocodiles and Killer Whales. They are also at risk from stranding in cyclonic storm surges. Sources of human mortality include: boat strikes, fishing and beach protection nets. Important seagrass habitats may be obliterated by loss of light caused by sedimentation associated with floods and cyclonic storms.
Dugongs are a fishery under the Torres Strait Treaty and Torres Strait Fisheries Act. It is estimated that the harvest of Dugongs in the Torres Strait during the 1990s was in the order of 1000 per year (Marsh et al. 1999). It should be noted that if the estimate of Torres Strait Dugong population at about 28 000 is correct, this harvest is greater than the estimated sustainable yield of 2% of the current female population, and may be unsustainable if other pressures such as incidental catch and habitat loss are not dramatically reduced. A recent survey (Marsh & Lawler 2001) indicates that Dugong numbers in the southern Great Barrier Reef region have increased from an estimated 1682 in 1994 to an estimated 3993 in 1999. However, the 1999 numbers are not significantly different from those obtained in 1986-87 surveys. The increase in numbers between 1994 and 1999 is thought to be due to factors other than just natural increase.
Dugongs are protected under State and Northern Territory Acts. Dugong Protection Areas were declared in the southern and central Great Barrier Reef region in 1997 by the Great Barrier Reef Ministerial Council, particularly to protect Dugongs from certain netting practices. Areas of inshore seagrass habitat in the Gulf of Carpentaria and the Great Barrier Reef region have been permanently closed to trawling. A moratorium on Dugong hunting has been agreed with several Indigenous communities and Indigenous hunting is not permitted in the Great Barrier Reef region, south of Cooktown.