Overall, biodiversity in Australia’s marine regions is in good condition. However, biodiversity is very poor in some coastal places and areas on the continental shelf and upper slope, as a result of human activities. A number of iconic species have failed to recover or continue to decline from earlier impacts of excessive hunting and fishing. These include Australian sea lions, which are endemic to temperate southern Australian waters and are showing no substantial signs of population recovery from the hunting of previous centuries; the whale shark, only smaller specimens of which appear to be visiting Western Australian waters; and southern bluefin tuna, formerly a major predator in our regional seas that has been fished to the edge of population survival and is continuing to be fished. In addition, there are many more habitat and species issues in smaller local areas. As for all species, more detailed national assessment of marine biodiversity is required to clarify the nature, extent and significance of the biodiversity condition.
In the Antarctic region, some populations of seals and penguins that were slaughtered in huge numbers in the late 19th and early 20th centuries have recovered. Other populations, especially among the seabirds, suffer great losses as bycatch in commercial fishing operations. Most whale species that visit the Southern Ocean are still on the list of endangered species. Many subantarctic islands harbour alien plant species that often thrive and outcompete endemic species, and these threats are increasing as the climate warms. Changes in the ocean due to climate change, such as rising sea surface temperatures and ocean acidification, are also bringing about change as northern species start to move south, and key biological processes such as shell calcification are disrupted for existing endemic species.
Further substantiation of this summary and more details of the state of, and trends in, marine species and ecosystems can be found in Chapter 6: Marine environment and Chapter 7: Antarctic environment.