State and trends of marine biodiversity: Species Groups

2016
Marine environment
State and trends
Marine Temperate East
Marine South West
Great Barrier Reef
Marine North
Marine North West
Marine South East
Marine Coral Sea

Species groups

The Australian marine environment is home to a plethora of species; 33,000 have been catalogued, 17,000 remain to be catalogued, and there may be 5–10 times as many yet to be discovered (Butler et al. 2010, Poore et al. 2015). Surveys of the marine environment regularly record new species even in areas that have been surveyed before, and half of the taxa captured in deep-sea environments may be new to science.

Fourteen species groups for which information and data were available were assessed for SoE 2016. These groups largely comprise those caught by fisheries or protected under the EPBC Act. Information for some species, including marine turtles and seabirds, is largely limited to information on land-based nesting or breeding areas (discussed in greater detail in the Coasts report), with little information available about their life at sea. Several species that use the marine environments of Australia (e.g. marine turtles, marine mammals, seabirds, billfish, tunas, sharks) demonstrate connectivity with regions outside the Australian EEZ, and many of the pressures currently affecting these populations are associated with high fishing effort or high bycatch rates in areas external to the Australian EEZ. Within the Australian EEZ, varying pressures are exerted on species and species groups across their range, because many species and species groups are widely distributed throughout Australia’s marine environment.

Even in areas where biodiversity has been surveyed, a good understanding of what ecosystems may have looked like before they were modified by human impacts is lacking. Apart from assessments on commercially caught species, very few species groups are regularly monitored. Consequently, empirical information on species status and trends is not available. It is also not possible to determine whether local declines in some species groups (e.g. sea snakes at Ashmore Reef) have resulted from declines in overall populations or distributional shifts in populations at particular sites. Species groups that have important ecosystem roles (e.g. algae, sponges, phytoplankton, zooplankton) are covered under assessments of habitats and communities, or biological processes.

The current status of those species targeted by fisheries has been derived from the most recent assessments available and, where possible, under single reporting frameworks. However, not all species are reported under single reporting frameworks. Reporting frameworks differ in their methodologies and may differ slightly in their assessments. Where relevant, details of the reporting framework from which assessments have been derived are provided.

Most species groups assessed are in good condition overall, although information is lacking to assess the condition or trend of some groups. Trends are stable or improving for most fish species, except inner shelf reef species, which are highly spatially variable, with some in good condition and stable, and others in poor condition and deteriorating. State and trends often vary for species within groups:

  • Some species have improved from past declines (e.g. long-nosed fur seals—Arctocephalus forsteri, southern Great Barrier Reef green turtles—Chelonia mydas, humpback whales—Megaptera novaeangliae, the eastern stock of orange roughy—Hoplostethus atlanticus).
  • Other species are currently stable (e.g. mesopelagic and epipelagic fish species, shy albatross—Thalassarche cauta).
  • Several species have declined because of cumulative impacts associated with degradation of their nesting habitat (see the Coasts report for further details); and high mortality as a result of bycatch within fisheries, climate change and potential ingestion of marine debris (e.g. flesh-footed shearwater—Puffinus carneipes, Australian sea lions—Neophoca cinerea, north Queensland hawksbill turtles—Eretmochelys imbricata, some demersal shark species).

Within the Great Barrier Reef Marine Park, the status of populations of most species has been assessed as good, although it had deteriorated from previous assessments; inshore and southern parts of the Great Barrier Reef are in worse condition than those in the north (GBRMPA 2014a). Declines have been reported in some fish, shark and seabird species, and dugongs (detailed in the Coasts report). The bleaching event associated with climate extremes in 2015–16 that had an extensive impact on the less disturbed northern areas of the Great Barrier Reef should be noted (see also Quality of habitats and communities). The flow-on impacts on species and species groups are yet to be quantified. Further detail on the state of species groups in the Great Barrier Reef Marine Park is in GBRMPA (2014a).

North Marine Region

Long-term monitoring of populations of species within the marine environment of the North Marine Region—other than those that are the target of commercial fisheries—is sparse. As a result, identified trends in populations are few. Similar to marine habitats and communities, species groups found within, and using, the region are assumed, in the absence of supporting information, to be in good condition, because of the relatively lower use of the marine environment and the remoteness of much of the North Marine Region. Several species that use the area (e.g. marine turtles, dolphins, sharks, rays) demonstrate connectivity with regions to the north, and some populations are impacted by pressures (e.g. high fishing effort, high bycatch rates) in areas external to the Australian EEZ (e.g. Gunn et al. 2010). Sea snakes are known to be regularly caught in trawl fisheries in the region (see Commercial fishing); however, there are no ongoing monitoring programs to identify the current state of populations or trends in populations throughout the marine region. Some sawfish species that occur through the region are listed under the EPBC Act, and research aimed at quantifying population abundance and connectivity of stocks has been initiated since SoE 2011. Recent assessments of species and their stocks currently targeted by fisheries in the region (noting that some also occur within the Coral Sea and North-west marine regions; Flood et al. 2014 and references therein) have classified:

  • 24 species or species stocks in good condition and sustainably fished
  • 1 species or species stock recovering from past depletion
  • 2 species or species stocks in poor condition and currently overfished
  • 8 species or species stocks undefined (not enough data to determine state).
Coral Sea Marine Region

Long-term monitoring of populations found within the Coral Sea Marine Region and those that use the region—other than those subject to commercial fishing—is sparse. As a result, identified trends in populations are few. Again, similarly to marine habitats and communities, species groups in the Coral Sea Marine Region are assumed, in the absence of supporting information, to be in good condition because of the remote and offshore nature of the region. Several species that use the area (e.g. marine turtles, whales, tunas, billfish, sharks, rays) demonstrate connectivity with regions to the north and east of the region, and some populations are impacted by pressures (e.g. high fishing effort, high bycatch rates) in areas external to the Australian EEZ; these include hawksbill turtles and many shark species.

Recent research suggests that, in terms of fish communities, the region is more biogeographically complex than previously thought (Last et al. 2011b). Recent assessments of the Coral Sea Fishery managed by the Australian Government (Flood et al. 2014, Hansen & Mazur 2015 and references therein) have classified:

  • 5 species or species stocks in good condition and sustainably fished
  • 6 species or species stocks in poor condition and currently overfished
  • 2 species or species stocks undefined (not enough data to determine state).

Many tunas and billfish commercially caught by fisheries within the region (also caught within the Temperate East Marine Region) are currently regarded to be western and central Pacific Ocean stocks. These species are assessed at a regional level across the western and central Pacific Ocean. Most species are in good condition and not overfished, except for bigeye tuna (Thunnus obesus), which is currently considered to be overfished (Harley et al. 2014), and broadbill swordfish (Xiphias gladius), which is currently likely to be subject to overfishing but not currently overfished. However, uncertainties associated with the biology of broadbill swordfish mean that this assessment is highly uncertain (Davies et al. 2013). Recent research quantifying the age and growth rates of the species (Farley & Clear 2015) will reduce uncertainty when the species is next assessed in 2017.

Temperate East Marine Region

Overall, populations of species groups are in good condition in the Temperate East Marine Region, although—as with other marine regions—populations demonstrate species-specific state and trends. Long-term monitoring of populations found within, and using, the marine region—other than those subject to commercial fishing—is sparse. As a result, identified trends in populations are few (see Box MAR7). Several species that use the area (e.g. marine turtles, whales, seabirds, tunas, billfish, sharks, rays) demonstrate connectivity with regions to the north and east of the region, and some populations are impacted by pressures (e.g. high fishing effort, high bycatch rates) in areas external to the Australian EEZ; these include bigeye tuna, hawksbill turtles, some species of shearwaters and many shark species.

Populations of inner reef fish and invertebrate populations demonstrate varying trends, with most invertebrate populations stable. There is some indication that populations of fish species in marine reserves are in better condition than those in areas that are not protected (Figure MAR27).

Humpback whales, which seasonally migrate through the region to breed and calve each winter on the Great Barrier Reef (see also the Antarctic report for details of baleen whales that seasonally feed in Antarctic and subantarctic waters), are increasing at close to their maximum rate and are considered to be close to carrying capacity (Noad et al. 2011). Trends for all other marine mammals are uncertain because they are only irregularly monitored or not monitored at all. State and trends of most sharks and rays are also uncertain for the same reasons. The only eastern population of flesh-footed shearwaters occurs in the Temperate East Marine Region on Lord Howe Island. The population has steadily declined because of high fisheries bycatch by Australian and international fisheries, degradation of nesting habitat, and potential marine debris ingestion (Priddel et al. 2006, Lavers 2015). Small pelagic (epipelagic and mesopelagic) fish species are in good condition, with those subject to fishing being sustainably fished (Moore & Mazur 2015). Fisheries management measures limiting catches of some species have stopped the overfishing of some species groups. However, no signs of recovery have been observed to date for some species, such as eastern gemfish (Rexea solandri), blue warehou (Seriolella brama) and redfish (Centroberyx affinis)—the reasons are currently unclear (Georgeson et al. 2015b). Since 2011, blue warehou has been listed as conservation dependent under the EPBC Act. Changing environmental conditions because of the southern extension of the East Australian Current (EAC) separation and associated eddies may be a component of this lack of recovery. Recent assessments of species currently targeted by fisheries in the region (noting that some also occur in the Coral Sea and South-east marine regions; Flood et al. 2014 and references therein) have classified:

  • 20 species or species stocks in good condition and sustainably fished
  • 1 species or species stock recovering from past depletion
  • 4 species or species stocks in poor condition and currently overfished
  • 11 species or species stocks undefined (not enough data to determine state).
South-east Marine Region

Of all marine regions, the species and species groups of the South-east Marine Region can be considered to be the most affected by past exploitation, declining habitat conditions and, in some areas, lack of recovery of habitats. As with other marine regions, populations of species vary in their state, and, because many populations are not monitored routinely, many trends are unclear. Fisheries management measures reducing capacity, and therefore catches, and the closure of particular areas have helped to reduce overfishing and led to improvements in the population abundances of some species throughout the region. The clearest example of this improving trend is the recovery of the eastern zone stock of orange roughy. Since the closure of the fishery in 2006 because of a low biomass of mature fish, sufficient juveniles have recruited to the mature population to permit a limited commercial fishery to recommence in 2015 (Upston et al. 2014; Figure MAR28). The impacts of the broader fishery on future recruitment of the species remain unknown.

SoE2016_mar_fig27_A_Abundance_fishes.png
soe2016_mar_fig27_b_abundance_invertebrates-01.png

Note: The y axis represents the mean indicator value for reef sites in that year relative to the highest value at each site across years. Trends that are significant for all species pooled are identified by a solid trend line.

Source: Data from the Reef Life Survey, the Long-Term Temperate Reef Monitoring Program (Barrett et al. 2009) and the Australian Institute of Marine Science Long-term Reef Monitoring Program

Figure MAR27 Trends in the abundance of (a) all shallow reef fish and (b) invertebrate species at long-term reef biodiversity monitoring locations around Australia.

*Due to the complexity of the graphs they are not rendered here. Click the following links to view each graph individually:

Beware Reef (a), (b); Encounter Bay (a), (b); Jurien Marine Park (a), (b); Lord Howe Island (a), (b); Maria Island (a), (b); Ningaloo Marine Park (a), (b); Rottnest Island (a), (b)

State and trends of marine biodiversity: Species Groups

Populations of inner reef fish and invertebrate populations demonstrate varying trends, with most largely stable (Figure MAR27). There is a likelihood that some invertebrate species have deteriorated, such as rock lobster (Jasus edwardsii), which has been heavily exploited but is not currently considered as overfished (Hartmann K et al. 2013, Flood et al. 2014, Lyle & Tracey 2014, Linnane et al. 2015a,b). Catches of giant crab (Pseudocarcinus gigas) in Victoria are currently less than 5 per cent of their peak (Linnane et al. 2015b), suggesting that this stock is in poor condition. Small pelagic (epipelagic and mesopelagic) fish species are in good condition, with those subject to fishing being sustainably fished. Most stocks of demersal and benthopelagic species are similarly considered to be in good condition, although gulper sharks (Centrophorus spp.) within the Commonwealth Southern and Eastern Scalefish and Shark Fishery are assessed as being in an overfished state (Georgeson et al. 2015b). Since SoE 2011, Harrisson’s dogfish (C. harrissoni) and southern dogfish (C. zeehani) have been listed as conservation dependent under the EPBC Act, spotted handfish (Brachionichthys hirsutus) has been uplisted from endangered to critically endangered, and red handfish (Thymichthys politus) has been uplisted from vulnerable to critically endangered. Recent assessments of species currently targeted by fisheries in the region (noting that some also occur in the Temperate East and South-west marine regions; Flood et al. 2014 and references therein) have classified:

  • 24 species or species stocks in good condition and sustainably fished
  • 2 species or species stocks recovering from past depletion
  • 11 species or species stocks subject to overfishing, but not yet in a state of being overfished
  • 6 species or species stocks in poor condition and currently overfished
  • 18 species or species stocks undefined (not enough data to determine state).

The only albatross species to breed in continental Australia, the shy albatross, occurs in this marine region. Although demonstrating recovery from past exploitation in recent decades, it appears to have plateaued at around half its original population size as a result of high juvenile mortality associated with bycatch in commercial fisheries (Alderman et al. 2011). Kelp (Larus dominicanus), silver gull (Chrolocephalus novaehollandiae) and Australasian gannet (Morus serrator) populations have been observed to be increasing (e.g. Pyk et al. 2013, Woehler et al. 2014). The state and trend of most marine mammals that are either resident in the region (e.g. Australian fur seals—Arctocephalus pusillus doriferus, inshore bottlenose dolphins—Tursiops aduncus) or seasonally migrate to the region (e.g. pygmy blue whales—Balaenoptera musculus intermedia, the eastern population of southern right whales—Eubalaena australis) are unclear, although populations of long-nosed fur seals are reported to be increasing (McIntosh et al. 2014).

South-west Marine Region

Species and species groups within the South-west Marine Region are in poor to good condition. Those in poor condition are largely associated with past exploitation of populations of species, declining habitat conditions and, in some areas, lack of habitat recovery. Recent assessments of species targeted by fisheries (noting that some also occur in the South-east and North-west marine regions; Flood et al. 2014 and references therein) have classified:

  • 28 species or species stocks in good condition and sustainably fished, although Indian Ocean yellowfin tuna (Thunnus albacares) has since been classified as overfished by the Indian Ocean Tuna Commission
  • 2 species or species stocks recovering from past depletion
  • 11 species or species stocks subject to overfishing but not yet overfished
  • 2 species or species stocks in poor condition and currently overfished
  • 12 species or species stocks undefined (not enough data to determine state).

A further 2 species or species stocks are considered to have been reduced to the point where average recruitment levels are significantly reduced, primarily because of substantial environmental changes or disease outbreaks (rather than overfishing).

Several Australian Government, state and international management measures aimed at recovering populations have been put in place across the region, reducing overfishing (see Box MAR6). Observations of inner reef fish and invertebrate species suggest that, in general, populations are stable (Figure MAR27). Western populations of southern right whales and long-nosed fur seals are increasing from past exploitation (Campbell et al. 2014, Bannister 2015, Shaughnessy et al. 2015). Overall numbers of Australian sea lions remain low after past exploitation, and pup abundance has decreased at 82 per cent of sites in South Australia that have been regularly monitored (e.g. Figure MAR29; Goldsworthy et al. 2015b), despite fishery bycatch management measures implemented in Commonwealth and state fisheries. Information on population numbers and recent trends for most cetaceans, seabirds and sharks is lacking (see Box MAR7). However, active programs focused on coastal dolphins in particular locations are beginning to provide information that will enable future assessment of trends in these populations (e.g. Smith et al. 2013). Recent surveys of flesh-footed shearwaters across the region have identified populations that are substantially lower than previously reported (Lavers 2015).

Source: Upston et al. (2014)

Values representing the upper limit of the confidence interval have been labelled "95% Confidence Interval" for graphing purposes. Confidence interval span values (ie the upper CI limit less the lower limit) are available for download.

Figure MAR28 Spawning biomass of the east coast population of orange roughy, 1980–2015

State and trends of marine biodiversity: Species Groups

Source: Goldsworthy et al. (2015a)

Values representing the upper limit of the confidence interval have been labelled "95% confidence interval" for graphing purposes. Confidence interval span values (ie the upper CI limit less the lower limit) are available for download.

Figure MAR29 Abundance of Australian sea lion pups at Seal Bay (Kangaroo Island), based on maximum live pup counts, 1985–2015

State and trends of marine biodiversity: Species Groups
North-west Marine Region

Species and species groups in the North-west Marine Region are largely assumed to be in good condition because of the relatively lower use of the marine environment and the remoteness of much of the northern parts (i.e. north of Broome) of the region. Because of this remoteness, however, long-term monitoring of many marine populations is sparse, and trends in populations are poorly understood. This precludes determination of the status of many species throughout the region. Inner shelf reef fish are in good condition, particularly in northern regions. However, within the Ningaloo region, increasing numbers of some reef fish species are also associated with declining overall community biomass, so care must be taken in interpreting trends, as they may not always be associated with improving conditions (Figure MAR27). The western population of humpback whales, which breeds in the region, is continuing to increase following past exploitation (Salgado-Kent et al. 2012). The state and trend of most marine mammals that are resident in the region (e.g. snubfin dolphin—Orcaella heinsohni) or seasonally migrate to the region (e.g. Brydes whales—Balaenoptera edeni) are unclear (e.g. Ross 2006, DoE 2015c). Research programs focused on coastal dolphins are beginning to provide information that will enable assessment of trends in these populations in the future (e.g. Brown et al. 2016).

Expansion has been observed in populations of roseate (Sterna dougallii), crested (S. bergii), sooty (Onychoprion fuscatus) and bridled (O. anaethetus) terns; brown noddys (Anous stolidus); and red-tailed tropicbirds (Phaethon rubricauda) (Clarke et al. 2011). The Christmas Island frigatebird (Fregata andrewsi), which is unique among frigate birds in nesting on only 1 island, has declined and is listed as vulnerable under the EPBC Act (Tirtaningtyas & Hennicke 2015). Also endemic to Christmas Island and undergoing a decline in numbers is the Christmas Island white-tailed tropicbird (Phaethon lepturus fulvus), which the EPBC Act lists as endangered (CIEWG 2010).

Several species that use the area (e.g. marine turtles, whales, seabirds, tunas, billfish, sharks) demonstrate connectivity with regions to the north and west of the region, and some populations are impacted by pressures (e.g. high fishing effort, high bycatch rates) in areas external to the Australian EEZ; these include Christmas Island frigatebirds, yellowfin tuna and whale sharks. Recent assessments of species targeted by fisheries (noting that some also occur in the South-west and North marine regions; Flood et al. 2014 and references therein) have classified:

  • 26 species or species stocks in good condition and sustainably fished, although Indian Ocean yellowfin tuna has since been classified as overfished by the Indian Ocean Tuna Commission
  • 3 species or species stock recovering from past depletion
  • 7 species or species stocks undefined (not enough data to determine state).

Populations of Shark Bay saucer scallops (Amusium balloti) and blue swimmer crabs (Portunus armatus) are considered to have recruitment levels that are significantly reduced, primarily because of substantial environmental changes or disease outbreaks (rather than overfishing). These declines have been associated with the marine heatwave of 2010–11 (see Interannual and subdecadal variability). Sea snake populations at Ashmore Reef, an isolated and remote Commonwealth marine reserve (see Environment protection systems), have declined, with observations dropping sharply from more than 45 sea snakes per day from 9 species to 1–7 sea snakes per day from 1 or 2 species. The cause of this decline remains unexplained, and there is insufficient information to distinguish population decline from population redistribution (Lukoschek et al. 2013). Since SoE 2011, short-nosed (Aipysurus apraefrontalis) and leaf-scaled (A. foliosquama) seasnakes have been listed as critically endangered under the EPBC Act. Research aiming to establish the status of these species has been initiated since SoE 2011.

Box MAR6 Southern bluefin tuna

Southern bluefin tuna is an important apex predator (at the top of the food chain) in Australia’s marine environment. Juveniles aggregate in the Great Australian Bight during the summer, and subadults and adults use southern and south-eastern waters primarily during winter. Adults aggregate in an area to the north-west of Australia and south of Indonesia to breed, primarily during the spring and summer months; this is the only spawning ground for the species (Basson et al. 2012).

Southern bluefin tuna is a highly prized target species for international commercial fisheries, and national commercial and recreational fisheries. Within Australian waters, a purse-seine fishery catches juvenile (2–4-year-old) tuna in the waters of the Great Australian Bight during summer for ranching operations, and is of significant value to the regional economy (worth around $150 million each year). A longline fishery targeting large individuals off the eastern Australian seaboard during winter and early spring catches a smaller amount of Australia’s commercial allocation (Patterson et al. 2015b). This fishery is one of few in the world where catches of southern bluefin tuna are managed spatially to ensure that bycatch of the species by fishers without allocated quota is minimised (Hobday et al. 2010).

Issues of importance

The southern bluefin tuna spawning biomass (a measure of the adult population) is estimated to have been depleted by fishing to a low fraction of its original size (CCSBT 2014). This low state of the population led to the listing of the species as conservation dependent under the Environment Protection and Biodiversity Conservation Act 1999 and critically endangered by the International Union for Conservation of Nature (Collette et al. 2011).

Current state

The status of the southern bluefin tuna population and the development of a management plan incorporating a rebuilding program have led to the advancement of new fishery-independent methods for monitoring the population in recent years (Bravington et al. 2016). The data provided by these monitoring methods are highly informative and have been integrated into the internationally agreed stock assessment frameworks (Preece et al. 2015). These methods are being applied more broadly, and are leading to improved methods for estimating the abundance and trends of populations of other listed species (see Box MAR7).

Recent assessment and research results indicate that recruitment (the number of younger fish maturing into the age groups of fish that are commercially fished) has increased from a historical low in 2000 and that the mortality associated with commercial fishing has decreased because of the reduction in global catches since 2006 (CCSBT 2014). The spawning biomass is currently estimated at around 9 per cent of its initial size (CCSBT 2015a).

Management measures

Management of the international commercial fishery is overseen by the Commission for the Conservation of Southern Bluefin Tuna, with global total allowable catches for the species determined by a management procedure since 2011 (Hillary et al. 2015). The management procedure is designed to recover the spawning biomass to 20 per cent of the pre-fishing biomass by 2035 (CCSBT 2014; Figure MAR30). This is the first time such a framework has been introduced to an international tuna fishery. Domestic management of Australia’s allocation of the global total allowable catch is the responsibility of the Australian Fisheries Management Authority. Domestic recreational catches of southern bluefin tuna are managed by individual state agencies, largely through daily boat catch limits.

SoE2016_mar_fig30_Trajectory_of_spawning_stock_biomass_for_southern_bluefin_tuna.png

A line graph showing the trajectory of spawning stock biomass for southern bluefin tuna under the base case of the operating model used under the management procedure from 1930 to 2040. After falling steadily from 1930 to 2010, the line begins to rise again, based on management as outlined in the figure notes. The dotted demarcation line occurs in about 2012 to 2013.

SSB = spawning stock biomass

Note: The red line with the pink region shows the median and 90% intervals of the current base case of biomass. The dotted line demarcates the boundary between the observation-based estimates of biomass and future projected biomass based on management measures implemented.

Source: CCSBT (2015a)

Figure MAR30 Trajectory of spawning stock biomass for southern bluefin tuna under the base case of the operating model used under the management procedure, 1930–2040

Outlook

The next full assessment for the species is planned for 2017, when current management measures aimed at rebuilding the population can be assessed and the state of the population can be identified. The management procedure will also be reviewed at this time. Initial indications from fishery-independent methods for monitoring the population in recent years suggest that the population is beginning to show positive signs in terms of rebuilding objectives (CCSBT 2015a).

Unaccounted mortalities associated with discards, unreported catches and recreational catches of southern bluefin tuna can affect the achievement of current rebuilding targets set by the Commission (CCSBT 2015a). Urgent efforts to quantify this mortality have been recommended to the Commission. In association with this, Australia has identified that it intends to begin making an allowance for unaccounted catches of southern bluefin tuna that are attributable by 2018 (CCSBT 2015b).

The draft report from a recent inquiry into the regulation of fisheries across Australia highlighted that management of southern bluefin tuna should include catch limits that are applied across all fishery sectors (commercial and recreational), and that day-to-day management of recreational fishers targeting southern bluefin tuna should be negotiated by fishers, and the Australian and state governments (PC 2016). If implemented, this recommendation would result in all catches across sectors within Australian waters being able to be attributed and included in future assessments for the species.

CCSBT (Commission for the Conservation of Southern Bluefin Tuna) (2015a). Report of the twentieth meeting of the Scientific Committee, Incheon, South Korea, 5 September 2016, CCSBT, Canberra.

Box MAR7 White shark

The white shark (Carcharodon carcharias; also known as great white shark or white pointer) is a large, globally distributed apex predator, and one of the few shark species that have been definitively identified as responsible for human fatalities in Australia. It is a target species for ecotourism, with the South Australian industry valued at more than $6 million annually (Bradford & Robbins 2013). In Australian waters, white sharks occur from north-western Western Australia around the south coast to central Queensland as 2 populations, separated east and west by Bass Strait (Blower et al. 2012). Biologically important areas for white sharks occur in all marine regions except the North Marine Region.

A geographically discrete nursery area spanning 65 kilometres of coast is centred on Port Stephens in central New South Wales, and a second more geographically extensive nursery area is situated off Ninety Mile Beach in south-eastern Victoria (Bruce & Bradford 2012). Similar discrete nursery areas have not yet been identified for the western population. Movements are extensive across the range of each population, primarily focused across continental-shelf and continental-slope waters, with occasional open-ocean excursions (Bruce & Bradford 2012, Francis et al. 2015, McAuley et al. 2016).

Current state and trends

The key factor hampering the determination of the current status of white sharks in the marine environment is a lack of information on current population size and trends in populations (Taylor et al. 2016). Recent research has focused on new methodologies to estimate abundance that will allow monitoring of current status and future trends (Bax & Hedge 2015, Bravington et al. 2016).

Although impacts associated with fishing have no doubt decreased since the species was listed as vulnerable under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), white sharks are still taken as bycatch in commercial shark fisheries. They are also caught under shark control programs and are targeted in response to shark attack or potential hazards. The overall impact of these mortalities on populations is unknown. Although catch rates in the New South Wales shark control meshing program have declined from around 0.3 sharks per 100 net-days to around 0.1 sharks per 100 net-days since the 1950s, there has been a minimal increase in white shark catch per unit effort (a measure of relative species abundance through time) since the mid-1990s (Reid et al. 2011). Whether this reflects overall changes in population size, changes in species distribution or changes in species behaviour is unknown. The impact of shark ecotourism cage-diving operations on white shark physiology is also unknown and subject to current research.

Research since 2011 has improved information on habitat use (Bruce & Bradford 2015, Robbins et al. 2015, McAuley et al. 2016), food-web interactions (Semmens et al. 2013, Pethybridge et al. 2014), and the interactions between white sharks and cage-diving operations (Bradford & Robbins 2013, Bruce & Bradford 2013, Huveneers et al. 2013, Bruce 2015) across the South-west Marine Region.

Management measures

As a result of listing under the EPBC Act, white sharks are subject to a national recovery plan, initially drafted in 2002 and revised in 2013 (EA 2002, DSEWPaC 2013). They are listed under the Convention on International Trade in Endangered Species (Appendix II) and the Convention on Migratory Species (Appendixes I and II), and are listed as vulnerable by the International Union for Conservation of Nature. Recent management changes to the cage-diving industry in South Australia have been implemented to minimise impacts on the species (DENR 2012, Smith & Page 2015). In addition, management changes limiting the use of commercial gillnet gear to target commercial sharks and replacing that effort with longline gear are likely to change the catchability of white sharks in southern Australian waters. In 2014, the Western Australian Government introduced a drumline program to catch and kill sharks that posed a threat to public safety (DPC 2014). This program was subsequently withdrawn, although a catch-and-kill policy remains in relation to sharks perceived as posing a threat.

Outlook

The outlook for white sharks is uncertain because of a lack of reliable data to estimate population size and trend. However, new techniques are currently being developed that may allow these parameters to be estimated and monitored in the future.

Pitcher CR, Williams A, Ellis N, Althaus F, McLeod I, Bustamante R, Kenyon R & Fuller M (2016b). Implications of current spatial management measures on AFMA ERAs for habitats, report 2014/204 to the Fisheries Research and Development Corporation, CSIRO Oceans and Atmosphere, Brisbane.

GBRMPA (Great Barrier Reef Marine Park Authority) (2014a). Great Barrier Reef outlook report 2014, GBRMPA, Townsville.

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