Biodiversity

Biodiversity – the variability among living organisms, including within species, between species and of ecosystems – is essential to the natural environment, and to human survival, wellbeing and economic prosperity (Convention on Biological Diversity Article 2).

Our continent and surrounding seas support 600,000–700,000 native species, and a very high proportion of these are found nowhere else in the world. For example, about 85% of Australia’s plant species are endemic to the continent, and Australia is home to half of the world’s marsupial species. The rate of discovery and formal description of new species has slowed considerably over the past decade, even though, in many species groups, there are many more species that are unknown than known. The best estimate is that 70% (or 400,000) of all Australian species of plants, animals, fungi and other organisms have yet to be discovered, documented, named and classified (Cassis et al. 2017). Although some ‘unnamed’ species can be conserved effectively through conservation of habitats, this is not always the case, and they may be rare or threatened and therefore at threat of extinction before they can be recognised. Taxonomists are continually discovering and describing new Australian species.

In 2020, 763 new species were named, including 297 insects, 166 fungi, 77 plants, 57 spiders and 21 vertebrates (Taxonomy Australia 2021). However, this is significantly fewer than in previous years. The significant reduction in the annual rate of naming of new species is likely due to reduced investment in taxonomy in many parts of Australia. Although citizen science is rapidly improving our ability to collect information on our wildlife (see Citizen science), being unable to correctly determine all our species is a massive impediment to best-practice conservation (see Research funding).

Indigenous Australians attribute tremendous knowledge, spiritual, cultural and symbolic value to our plants and animals, as well as to the broader environment. Many species are spiritually or culturally important, including as totems, sources of food or medicine, materials for tools or implements, and indicators of health of Country. Culturally significant species feature prominently in Indigenous knowledge, including language, ceremonies, stories, lore, identity and narratives.

Wildlife species that are highly visible (and attractive to humans) tend to be better understood. In general, species that are prominently visible (e.g. vertebrates, flowering plants) are well known, and groups that are rarely noticed (e.g. most invertebrates, fungi) are poorly known. This can lead to biases in our overall understanding of diversity, and whether species and groups are threatened. Birds, which are both visible and attractive, make up the single largest proportion of identified threatened fauna species in all areas except the Northern Territory (where mammals make up the largest proportion).

Assessment Biodiversity
2021
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, and the situation is deteriorating.

Assessments of state range from very poor to good
Assessments of trend range from deteriorating to unclear

Assessment Threatened species
2021
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, and the situation is deteriorating.

Threatened plants and animals are generally in a poor and deteriorating state due to increased land clearing, urban expansion and invasive species. The positive exceptions are crocodiles, and some marine mammals and fish in northern and central Australia.
Assessments of state range from very poor to poor
Assessments of trend range from deteriorating to improving
Related to United Nations Sustainable Development Goal targets 14.4, 14.5, 15.1, 15.2, 15.4, 15.5

Assessment Threatened ecological communities
2021
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, and the situation is deteriorating.

The number of nationally listed threatened ecological communities has been increasing. Approximately half are Critically Endangered, and most of the new listings since 2016 are Critically Endangered.
Assessments of state range from very poor to poor
Assessments of trend are deteriorating
Related to United Nations Sustainable Development Goal targets 13.1, 14.2, 14.5, 15.1, 15.5

Assessment Migratory species
2021
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, and the situation is deteriorating.

Populations of many migratory species, including most migratory shorebirds, have been declining for several decades, with a complex range of pressures affecting them both within Australia and in other parts of the world. Most migratory shorebirds are threatened. Seabirds and marine mammals are assumed to be in good condition, with some known improvements in focal species, but population data are unavailable for many species.
Assessments of state range from poor to good
Assessments of trend range from deteriorating to unclear
Related to United Nations Sustainable Development Goal targets 14.2, 14.5, 15.1, 15.5

Species decline

Over the past 2 centuries, Australia has lost more mammal species than any other continent and continues to have one of the highest rates of species decline among countries in the Organisation for Economic Co-operation and Development. For some species, it is too late, with more than 100 Australian species listed as Extinct or Extinct in the Wild under Australian national, state or territory legislation. The true number of extinctions is likely to be significantly higher, since many species are poorly surveyed or poorly described, or both.

The 2 pressures that have caused the most extinction of Australian terrestrial species since the beginning of colonisation are introduced species (causing the loss of 64 species), and habitat loss and clearing (62 species). In an analysis of all nationally listed threatened terrestrial and aquatic plants and animals in Australia as of July 2018, the same 2 threats were most frequently listed: habitat loss, fragmentation and degradation (1,210 taxa); and invasive species and disease (966 taxa) (Ward et al. 2021). In more recent times, known extinctions have been associated with introduced disease, sea level rise, and introduced reptiles and fish (Woinarski et al. 2019).

More than 1,900 Australian species and ecological communities are known to be threatened or at risk of extinction. In 2021, more species are listed as threatened, or are listed in a higher category of threat (e.g. from Vulnerable to Endangered to Critically Endangered) than 5 years ago – an increase of 8% since 2016.

The multiple threats faced by Australia’s threatened species may interact and be cumulative, such that the impacts are increased (see Cumulative pressures). On average, each threatened species faces around 4 different threats (Kearney et al. 2018) (Figure 6). In the past decade, climate change in the form of more severe drought, extreme weather events, fire and habitat modification is becoming a new driver for habitat change and species loss.

Figure 06 Number of threatened species subject to one or more threats

There is a growing trend in Australia of ‘local extirpation’, where species may still survive in protected locations (such as islands or fenced exclosures) but are no longer present across much of their former range. This insidious change can happen slowly over decades and centuries. The mammals considered most at risk from extinction in the next 20 years are the central rock-rat (Zyzomys pedunculatus), the northern hopping-mouse (Notomys aquilo), the Carpentarian rock-rat (Zyzomys palatalis), the Christmas Island flying fox (Pteropus natalis) and the black-footed tree-rat (Mesembriomys gouldii gouldii) from the Kimberley and the Northern Territory (Geyle et al. 2018).

Changes in climate that have been recorded across the Australian landmass are associated with a range of biodiversity responses, including decreases in some species and increases in others. Alpine ecosystems and biodiversity in Australia are particularly vulnerable to climate change that affects snow depth, and the spatial and temporal extent of snow, which have all declined since the late 1950s (CSIRO & BOM 2020). Long-term monitoring (35 years) of alpine vegetation in Australia has shown shifts in the composition and diversity of plant species, changes in the timing of flowering, and significant declines in endangered fauna such as the mountain pygmy possum (Burramys parvus, which is a specialised alpine species) (Hoffmann et al. 2019). Conversely, long-term monitoring in the same region revealed that the average number of bush rats (Rattus fuscipes, which is a generalist species that lives in many regions) has almost doubled (Greenville et al. 2018).

Some species may cope with climate change by moving or extending their range to find more favourable conditions (see Range shifts and extensions). Range shifts and extensions on land can be very complicated because different species have markedly different abilities to shift their location and range in order to cope; many terrestrial species are unable to shift their distribution because of the loss of connecting habitats.

Long-term monitoring data from a wide range of Australian ecosystems confirm that there has been an increase in extreme climate events in the past decade. Coupled with more gradual climate change shifts, extreme events have resulted in lifecycle shifts, changing species abundances, and range expansions and contractions. Approximately two-thirds of threatened species in Australia are threatened by changing fire regimes (usually in concert with other pressures) (Kearney et al. 2020).

Threatened species

The number of threatened species listed under the EPBC Act has risen for almost all taxonomic groups over the past 5 years, by an average of 8%, with listings increasing the most for invertebrates and frogs (22% and 21%, respectively), and the smallest increase being for reptiles and birds (around 5% increase). Although efforts are underway to better align the international, national, and state and territory lists, there are still many discrepancies and differences between the listing processes. The differences between the lists may be justified for wide-ranging species, but should be the same for a species that occurs only in a single state or territory. The adoption (in October 2015) and implementation of a common listing process (known as the Common Assessment Method) for listing threatened species and ecological communities by most Australian jurisdictions allows the outcome of that assessment to be adopted by other relevant jurisdictions, and is helping to improve management and regulation. But this alone is not enough to address the underlying threats. There is concern that our current listing processes are failing to keep up with the actual rate of biodiversity loss.

Long-term timeseries of the populations of threatened species collected by many agencies and collated into the Threatened Species Index, funded through the Australian Government’s National Environmental Science Program (NESP) with National Collaborative Research Infrastructure Strategy support from the Terrestrial Ecosystem Research Network, provides valuable insight into startling trends of ongoing loss of habitat and species.

The index has collated thousands of datasets for multiple species across hundreds of sites, and the results show a worrying trend. For example, monitoring of 112 threatened plant species at more than 600 sites for more than 20 years shows, on average, a 72% decrease in Australian threatened plant populations (TSX 2020) (Figure 7). There is also an overall negative trend for threatened (and near-threatened) mammals and threatened birds, with decreases of 38% and 52%, respectively (TSX 2020).

Figure 07 Threatened Species Index plant populations (1995–2017), mammal populations (1995–2017) and bird populations (1985–2017)

Note: The Australian Government’s NESP Threatened Species Index is based on data from multiple monitoring programs of population trends.

Source: National Environmental Science Program (NESP) Threatened Species Recovery Hub

Lists of threatened species are maintained at different spatial scales: the International Union for Conservation of Nature (IUCN) maintains its ‘Red List’ at a global scale; the EPBC Act lists at a national scale; and each state and territory maintains lists for their jurisdiction. The number and trend of our lists of threatened species is one measure of the health of Australia’s biodiversity. As at June 2021, nationally 533 animal and 1,385 plant species were listed under the EPBC Act, more than half of which were listed as Endangered or Critically Endangered.

The top 3 threats that affect the largest number of listed species are invasive species (82% of all threatened species), ecosystem modifications including changed fire regimes (74% of listed species), and agriculture (57%) (Kearney et al. 2018). All of these major threats that cause population declines for threatened species are associated with different forms of habitat destruction or modification. These can result in fragmented populations in small remnants of habitat, which then become vulnerable to further pressures (e.g. invasive predators), resulting in ongoing population declines. The greatest number of threatened plant species and those at most risk of extinction are concentrated in highly modified agricultural and urban landscapes.

Some threatened species may be considered ‘functionally extinct’, having fallen below the critical number to sustain their populations in the long term. Of the 660 plant species listed as Critically Endangered or Endangered at a national level, 62 are known from fewer than 50 individuals, and 300 from fewer than 250 individuals. These are often restricted to tiny remnants that are vulnerable to further degradation and where population growth is unlikely, with a high risk of extinction within the next 10 years (Silcock et al. 2020).

Threatened ecological communities

Threatened ecological communities are ecosystems that are in danger of being lost and are listed under national and state and territory legislation.

The number of threatened ecological communities listed under the EPBC Act has risen by 20% over the past 5 years. As of June 2021, 88 are listed, of which 41 are Critically Endangered, 44 are Endangered and 2 are Vulnerable. Fourteen new listings have occurred since January 2016, including 9 in the Critically Endangered category. Threatened ecological communities occur mostly in areas that have been heavily modified for agriculture or urban development. Ten of those 14 new listings since 2016 occur in New South Wales. There are 27 recovery plans in place; all EPBC Act–listed ecological communities have either a recovery plan or a conservation advice.

Fauna

Many native animal species in many ecosystems across Australia are in decline.

Terrestrial fauna

Terrestrial mammals across Australia have experienced high rates of extinction, with 10% of endemic species becoming extinct over the past 200 years. Mammals are subject to ongoing population declines, and the numbers of threatened species, including those at high risk of extinction, are increasing. Approximately 21% are now assessed as threatened (Woinarski et al. 2015, Woinarski et al. 2019). Most mammal extinctions in Australia have been driven by predation from introduced species, especially the feral cat and European red fox; extinction rates are particularly high in arid and semi-arid regions of Australia.

The 20 mammal species most at risk from extinction over the next 20 years mostly occur in northern Australia and south-west Western Australia (Geyle et al. 2018).

Many of Australia’s birds are suffering population declines and are at risk of extinction; the most at-risk bird species are found only on islands or in southern Australia (Geyle et al. 2018). The NESP Threatened Bird Index indicates significant declines in abundance of threatened birds for which monitoring data are available. Between 1985 and 2018, the relative abundance of threatened birds decreased by an average of 60%.

Many of Australia’s reptiles also show rates of decline, and the past decade saw the first Australian reptile extinctions in the wild. The proportion of species assessed as Critically Endangered nationally is increasing. Two species currently listed as Critically Endangered – the blue-tailed skink (Cryptoblepharus egeriae) and Lister’s gecko (Lepidodactylus listeri) – are only known to exist in captivity. The Christmas Island forest skink (Emoia nativitatis) was officially declared Extinct in March 2021 and was last seen in the wild in 2010; the last known individual died in captivity in 2014. Reptile experts suggest that, by 2040, up to 11 snakes and lizards, all with restricted ranges and threatened by invasive plants and animals, could become extinct (Geyle et al. 2020).

About half of the 25 species of Australian freshwater turtles are in serious population decline and are listed as Vulnerable, Endangered or Critically Endangered. Nest predation by invasive foxes has driven declines in freshwater turtles in the Murray–Darling Basin (Van Dyke et al. 2019). Turtle declines of up to 91% have also been observed in sections of the Murray River, linked to drying climate and nest predation.

A recent assessment of all our frogs against the IUCN Red List criteria found 18.5% as either extinct or threatened. Most of the threatened frog species occur along the east coast of Australia and the Great Dividing Range (Heatwole & Rowley 2018, Gillespie et al. 2020). Most threatened species of amphibians are restricted to the south-east, the wet tropics and the south-west of Australia. Disease is a persistent pressure in eastern Australia (see Diseases). Drought and fire are increasing pressures.

Figure 08 Threatened fauna, from left to right: thick-billed grasswren; Carpentarian rock-rat; painted button-quail

Coastal and marine species

Most Australians live within 50 kilometres of the coast, and more than half of all Australian species listed as nationally threatened occur within the coastal zone; 56% of the species listed under the EPBC Act were coastal, based on data released in 2019. Of these, 94% were impacted by habitat loss, fragmentation or degradation; invasive species, including weeds, and predators; disease; and fires (Ward et al. 2021). The highest density of threatened species was found along the east coast of Australia, particularly around the urban centres of Brisbane, Cairns, Melbourne and Sydney, and along the increasingly populated coast between Sydney and Brisbane.

Nationally, 88 species and 4 ecological communities with marine and coastal distributions are listed under the EPBC Act. In the past 5 years, 2 species and 1 ecological community were added to the threatened list, including the cauliflower soft coral (Dendronephthya australis), which was listed as Endangered in 2020. No marine species have been removed from the EPBC Act list during this period.

Some marine species are restricted to particular latitudes, such as the endemic Australian sea lion (Neophoca cinerea) which is listed as Endangered in Australia under the EPBC Act and globally on the IUCN Red List (Goldsworthy 2015), and has been assessed as in a very poor and deteriorating state. Some species are limited to bays and estuaries within specific regions – for example, the endemic Australian snubfin dolphin (Orcaella heinsohni), which has been noted as having decreasing population trends under the IUCN Red List. There were no national estimates for dolphins, but Australian humpback (Sousa sahulensis) and snubfin dolphins are considered declining in the North-west Marine Region (Raudino et al. 2019).

All 6 Australian species of marine turtle are also listed under the EPBC Act, half of which are Endangered: loggerhead (Caretta caretta), olive ridley (Lepidochelys olivacea) and leatherback (Dermochelys coriacea). The pressure of greatest concern for marine turtles and sea snakes is climate change and resultant habitat loss from coral bleaching, seagrass loss, mangrove dieback, sea level rise and extreme weather events. Marine debris, pollution, fisheries bycatch, light pollution, and the harvesting of eggs or their consumption by predators also threaten Australian turtles.

Sea snake populations are considered to be poor and declining, with recent dramatic reductions in the spatial distributions of some species (Udyawer et al. 2020). Two endemic sea snake species are listed as Critically Endangered under the EPBC Act and the IUCN Red List; a further 2 endemic species are listed as Endangered and Near Threatened on the IUCN Red List but have not been assessed under the EPBC Act (Eifes et al. 2013). There is limited information on the resilience of sea snakes; however, as they spend most of their lives foraging in surface waters (Udyawer et al. 2016) where temperatures are increasing the fastest, they are potentially vulnerable to climate change (Udyawer et al. 2018).

Fishes

Currently, 62 Australian fish species are listed under the EPBC Act; of these, 38 are freshwater fish (see Freshwater ecosystems). This is considered an underestimate because recent analysis shows that 20 freshwater fish species have more than a 50% risk of extinction in the next 20 years, but only 3 are currently listed. The freshwater Pedder galaxias (Galaxias pedderensis) is known to be extinct in the wild (Chilcott et al. 2013), and the marine smooth handfish (Sympterichthys unipennis) was listed in the IUCN Red List as extinct in 2018, but this is not yet reflected under the EPBC Act listings.

Since 2016, several major fish deaths occurred in our waterways, most prominently in the lower Darling, and both surface water and groundwater ecosystems were affected. Major bushfires also impacted water quality and aquatic species. The long-term decline in populations of Macquarie perch (Macquaria australasica), once the most abundant native fish in the Murray–Darling Basin, was showing signs of stabilising in late 2019 in the Snowy Mountains region. But as the rains followed the bushfires in early 2020, ash and mud were washed into the river system, suffocating much of the remaining population (Productivity Commission 2021b).

Our estuaries and coastal bays are highly productive environments and provide essential nursery grounds, migration routes, and refuge and feeding opportunities for many species. They also suffer immense pressure and, in general, estuarine fish populations remain in poor condition. The pressures of local human activities and climate change (Warwick et al. 2018, Gillanders et al. 2021), combined with legacy contamination in many places (e.g. heavy metals) and emerging contaminants (e.g. pharmaceuticals, microplastics, perfluoroalkyl substances), pose an ongoing threat to estuarine fish populations, particularly near urban and industrial areas (Taylor et al. 2018c, Anim et al. 2020).

In Antarctica and the surrounding Southern Ocean, fish are the most diverse vertebrate group. Evolving over millions of years in subzero temperatures, Antarctic fish (around 200 species) have many physiological and biochemical traits (e.g. antifreeze in their blood) that enable them to thrive in their chronically frigid environment (Beers & Jayasundara 2015) in the vast and variable Southern Ocean, which covers about 10% of Earth’s oceans and is up to 5,000 m deep. Little is known about their capacity to adapt physiologically to increasing ocean temperatures and acidification, but experimental research has shown that heat stress can cause changes in metabolic processes and enzyme activity (Forgati et al. 2017). Annual surveys, stock assessments and tagging studies of species fished within catch limits provide some indications of the state of fish populations since 2016. Populations of schooling mackerel icefish (Champsocephalus gunnari) and the large deep-sea Patagonian toothfish (Dissostichus eleginoides) are assessed as good, comparable to 2016. The population of the deep-sea Antarctic toothfish (Dissostichus mawsoni) is good and has improved since 2016.

Invertebrates

It is estimated that Australia has approximately 320,465 invertebrate species, of which about 35% have been described. Many invertebrates are of significant cultural importance to Indigenous Australians, particularly those that were, and are, valued as a nutritional food source (entomophagy) or used for medicinal purposes.

A total of 285 invertebrate species are listed as threatened under various state and territory conservation Acts, the EPBC Act and the IUCN Red List (Taylor et al. 2018a), but this is considered an underestimate because a vast number are undescribed, and knowledge of their distributions is poor. Most threatened species have been listed from the wetter areas of Australia, with particularly high concentrations of species in coastal regions of eastern Australia.

However, little data are available in either the marine or terrestrial domains to be able to describe trends in species abundance and diversity. Major threats to insect biodiversity come from habitat loss through broadscale clearing of native vegetation, invasion by weeds, habitat fragmentation, loss of natural corridors and inappropriate fire regimes (Braby 2019). Other threats include disturbance of plant communities on hilltops, on creek embankments and in water courses; pesticides; trampling and grazing by stock and feral animals; and non-native predators (Sands 2018). Invertebrates are an important food source at many levels of the food chain. However, this role means that they can also facilitate the transfer of contaminants, such as heavy metals and pesticides, to other species. Climate change affects insects that have limited thermal and moisture tolerances. Changes in temperature and rainfall potentially affect their distribution, development and reproduction (Sands 2018).

Subterranean fauna

Subterranean ecosystems form important ecological communities in Australia. The diversity of Australian subterranean fauna is extremely high. Living underground, they are an inconspicuous but important part of biodiversity that represent outstanding examples of adaptation and ongoing evolutionary processes, with many ancient lineages of high scientific value and conservation significance. More than 4,100 species are estimated to occur in Western Australia alone, based on the rate of species discovery in the early part of last decade (Guzik et al. 2011). At least 3 fish species also occur in groundwater systems. The blind cave gudgeon (Milyeringa veritas) and the blind cave eel (Ophisternon candidum) are both listed as Vulnerable freshwater fish species under the EPBC Act.

Knowledge gained in the past decade shows that much of the Australian subterranean fauna occurs nowhere else (Mokany et al. 2019) and has highly restricted ranges (Hyde et al. 2018). This makes these species extremely vulnerable to extinction from environmental changes and human impacts. For example, in south-west Western Australia, unique stygofaunal communities are associated with mats of submerged rootlets of trees in limestone caves underneath the Leeuwin–Naturaliste Ridge. Several of these communities have been listed as Endangered under the EPBC Act.

Plants

More plant than animal species are listed as threatened under national, state and territory legislation. As of June 2021, 1,385 plant species are listed under the EPBC Act, compared with 533 animal species. The number of plant species listed nationally increased from 1,252 in 2015 to 1,344 in 2020, a marked increase from the previous 5-year period. Orchids are the most threatened group of flowering plants in Australia, with 10% (184 species of a total of around 1,794) of our orchid species listed as threatened under the EPBC Act (Wraith & Pickering 2019). In 2017, the NESP Threatened Plant Index was 0.28, indicating that, on average, the size of threatened plant populations decreased by 72% between 1995 and 2017.

Overall, the major pressure causing population declines for threatened plant species is habitat destruction. Declining species and those at most risk of extinction are concentrated in highly modified agricultural and urban landscapes. Changes in fire regimes – fires that are either too frequent or too infrequent – are also a significant pressure for many plant species.

Case Study Australian sandalwood – native forest product or threatened species?

Richard McLellan, Charles Sturt University

The Australian sandalwood (Santalum spicatum), also known as walarda (Wajarri), waang (Noongar) and dutjahn (Martu), is a tree native to semi-arid and arid areas in southern and western Australia. This important tree is in dramatic population decline – it is estimated that only around 10% of its original extent remains, and it appears that virtually no new trees have emerged in the wild for 60–100 years. 

Indigenous people revered the tree for thousands of years, using it, for example, in smoking ceremonies and bush medicine. Commercially harvested since the 1840s, forest products from Australian sandalwood have been widely used as aromatics and cosmetic products. Over the past 175 years, it has become one of the world’s most valuable timbers. Although extensive plantations have been established for domestic use and export, wild populations continue to be commercially harvested because of commercial expediency and the fact that old-growth trees produce the best-quality oil.

The species is being affected by the cumulative impacts of commercial harvesting, land clearing, altered fire regimes, overgrazing (mainly by introduced herbivores) and lack of regeneration, all compounded by the effects of climate change. Sandalwood seedlings require 3 consecutive good years of rainfall to establish from seed, which, in the current climate regime, is a rarity in arid and semi-arid Australia. The loss of commensal species, such as burrowing bettongs that provided seed dispersal services, has also impacted the recruitment of new individuals.

The fate of the Australian sandalwood tree demonstrates the combination of land-use and climate stressors that are currently impacting many old-growth, slow-growing native species. Dramatic declines are overlooked until the population crash becomes unequivocally evident, requiring immediate and reactive responses. Yet often the cascading signs of collapse in many species can be predicted decades earlier by understanding their biology, ecology, land-use history, and altered climate and disturbance regimes that lead to changes that adversely impact the species’ persistence.  

Figure 09 Dead sandalwood tree

Fungi and microorganisms

Despite the very important roles that fungi and microorganisms play in ecosystems and ecological processes, the overall level of knowledge about Australian nonvascular flora (algae, liverworts, mosses), fungi and lichens is very limited. Thirty-six Australian fungi species are listed under the global IUCN Red List, including 1 Critically Endangered and 4 Endangered species, most of which occur in temperate forests. No fungi are currently listed under the EPBC Act, and only a few are listed under state or territory legislation.

Migratory species

Australia’s migratory species include birds, turtles, marine mammals (such as whales and dugongs) and fish, including the world’s largest shark. Many of these are listed under international agreements (see International obligations and treaties) and protected under the EPBC Act. The EPBC Act’s Migratory Species List as at June 2021 includes 114 birds, 20 marine mammals, 17 fishes (including sharks and rays) and 7 marine reptiles.

Understanding the state and trend of migratory species and the pressures affecting them is complex and requires collation of data from different sites across multiple countries.

Millions of migratory shorebirds fly from breeding grounds in northern China, Mongolia and Russia to East Asia and Australia each year, traversing more than 20 countries while migrating. Thirty-seven species regularly and predictably visit Australia during their nonbreeding season, from spring to autumn. Some shorebird populations are in severe decline, and future extinctions are expected without urgent management interventions. Loss and degradation of ‘stopover habitat’ on tidal mudflats in the Yellow Sea region of East Asia has reduced this habitat by more than 65% in recent decades. Consequently, the populations of migratory species that rely heavily on this region to rest and refuel show significant declines. For example, populations of the great knot (Calidris tenuirostris) and far eastern curlew (Numenius madagascariensis), both of which are listed as globally threatened taxa, have declined more than 5% per year on average since 1993 (Studds et al. 2017).

Twelve out of 19 migratory shorebird species (and 17 out of 19 species in southern Australia) have been declining nationally for several decades. Since 2016, as new trend analyses became available, 4 populations of migratory shorebirds have been listed as Critically Endangered, 5 as Endangered and 3 as Vulnerable under the EPBC Act. Four additional populations that use Australia are listed globally as Near Threatened.

Around 60 species of seabirds are known to breed in and around Australia and its external territories, including albatrosses, boobies, cormorants, frigatebirds, gulls, noddies, pelicans, penguins, petrels, prions, shearwaters, storm petrels, terns and tropicbirds. Their overall state is good and stable (Woehler 2021); however, there have been widespread decreases in the populations of some species of petrels, shearwaters and tropicbirds (Garnett & Baker 2021, Woehler 2021). Many species of seabirds are listed as Threatened under the IUCN and are also listed under the EPBC Act.

Threats to seabirds include the ingestion of marine debris; fisheries bycatch (although this is decreasing); the redistribution of their prey in response to climate change; and competition for breeding habitat as a result of development, feral predators, and the southwards movement of some species due to climate change.

Few surveys have been done of the 7 species of migratory flying seabirds on the Antarctic continent; more is known about the 13 species on the subantarctic Heard, McDonald and Macquarie islands, which include albatrosses, diving petrels, cormorants and shearwaters. Because these islands support threatened and endangered seabird species, they are declared Important Bird Areas (IUCN). Some populations have benefited from the eradication of introduced predators, rabbits and rodents (McInnes et al. 2019), and the management of commercial fishing.

All of Australia’s 48 species of cetaceans (whales and dolphins), 3 species of pinnipeds (seals) and a single sirenian, the dugong (see Coasts), are listed under the EPBC Act. Key pressures include bycatch in commercial fishing operations, interactions with vessels (tourism operations and recreational vessels), ship strike, entanglement in debris and fishing gear, coastal habitat loss from development, temporary disturbance caused by vessels and noise, and changes to breeding and feeding habitats and marine food webs associated with climate change (Speakman et al. 2020).

Information on the status of most whales and dolphins is not available (Evans & Harcourt 2021, Evans & Raudino 2021), but their state is assumed to be good. Available Australian estimates are generally positive. Population growth rates for northward-migrating east coast humpback whales (Megaptera novaeangliae)are estimated at 10% per year (Pirotta et al. 2020). The population has likely fully recovered from commercial whaling and may soon surpass original population levels (Noad et al. 2019). Population growth rates of southern right whales (Eubalaena australis) in south-eastern Australia were estimated to be 4.7% per year, but with no significant change in the numbers of cow–calf pairs at the only recognised calving ground in the region (Stamation et al. 2020). There are no national estimates for dolphins, but Australian humpback and snubfin dolphins are declining in the North-west Marine Region (Raudino et al. 2019).

Blue whales (Balaenoptera musculus) are the largest creature on earth, reaching 27 m in length. The Antarctic blue whale population is only 3% of the population in the pre-whaling era and is recovering slowly, despite prohibitions on hunting in the Southern Ocean from 1965–66 and elsewhere from 1972. The greatest threats the whales now face are declining food sources associated with ocean warming and increasing ocean acidification (Cooke 2018). Blue whales are among 6 species of baleen whales found in Antarctica that sieve or filter krill, plankton and crustaceans from sea water through a hairy plate in their mouth (baleen). Baleen whales include humpback whales, the majority of which migrate to Antarctic waters. Recent surveys indicated that populations of the 7 breeding groups of humpbacks that use the Southern Ocean are increasing, and consultation is in progress on the possible delisting of humpback whales from the EPBC Act (DAWE 2021f).

The 9 species of tuna and billfish that migrate through Australian waters support valuable fisheries (Mobsby et al. 2020). All species are wide-ranging, with populations that extend well beyond the Australian exclusive economic zone. The main pressure on populations is the harvesting of wild stocks. Populations of southern bluefin tuna (Thunnus maccoyii), one of 8 fish species identified as Conservation Dependent under the EPBC Act, have increased as a result of the implementation of a rebuilding strategy that includes harvest limits.