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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

805: Arafura - Carpentaria

Major Habitat Type:

tropical and subtropical coastal rivers

Author:

Peter Unmack

Reviewers:

Helen Larson, Curator of Fishes, Museum and Art Gallery of the Northern Territory, Australia

Countries:

Australia

Boundaries:

This ecoregion begins at the Berkeley River Basin in the west and extends east across northern Australian drainages to the Herbert River, incorporating all rivers draining to the northern coastline. This region includes Arnhem Land, the Gulf of Carpentaria, Cape York Peninsula, and the wet tropics.

Drainages flowing into:

Timor Sea, Arafura Sea, Gulf of Carpentaria, and Coral Sea.

Main rivers or other water bodies:

The main coastal rivers in this ecoregion are from west to east the Ord, Victoria, Daly, Adelaide, South Alligator, Liverpool, Blyth, Goyder, Roper, McArthur, Nicholson, Flinders, Norman, Gilbert, Mitchell, Archer, Wenlock, Jardine, Normanby, Tully and Herbert.

Topography:

Most northern coastal rivers descend from an interior plateau at about 200 m elevation to sea level. The Durack Range and Eastern Highlands with maximum elevations of about 600 m occur in the western and eastern parts of the ecoregion, respectively. There is also a large sandstone massif with elevations up to about 350 m asl in Arnhem Land in the northern portion of the ecoregion. Most rivers flow across flat region with low gradients, except those draining to the eastern coastline. River gradients in the east tend to be higher as the main Eastern Highlands are close to the coastline.

Climate:

There is a seasonal, monsoonal climate, with a short wet season from November to March and then a long dry period for the rest of the year. Rainfall is high at the coast at about 1800 mm and declines moving inland to about 600mm (World Wildlife Fund 2001a). Temperatures also change moving inland with higher average temperatures in January and lower average temperatures in July (Unmack 2001).

Freshwater habitats:

This is a large ecoregion, covering 1,077,000 square kilometers or 13% of Australia. Massive flooding may be caused by large tropical depressions and cyclones. Most of the large rivers of this ecoregion have vast floodplains. Rivers in the southern Gulf of Carpentaria portion of this ecoregion typically rise in relatively low hills, and many of these rivers are somewhat intermittent throughout much of their length. In contrast, many rivers in the “Top End” of the Northern Territory rise on a large plateau and have large waterfalls that restrict the upstream movement of most fishes. These rivers tend to have more permanent flow for much of their length. Rivers draining to the eastern coast tend to be much shorter but originate in much higher mountains with high rainfall. These are some of the few high gradient rivers in northern Australia. There are almost no major dams in this ecoregion, although one, the Ord River Dam, is the largest in Australia at 741 sq. km.

Terrestrial Habitats:

Tropical savannas dominated by open eucalypt forests interspersed with small patches of rainforest occur along the coast. Eucalypt woodland with a grassy understory occurs further inland (World Wildlife Fund 2001b).

Fish Fauna:

There is a strong relationship between the fish fauna of southern New Guinea (especially the Fly River) and this ecoregion, with over thirty freshwater fish species shared between these two regions. The eastern side of Cape York Peninsula tends to have high elevations and the highest rainfall on the Australian continent. It shares a number of species with the rest of the ecoregion but also has a number of distinct species not found further north or west. Twenty-nine families are present in this ecoregion. The ecoregion is dominated by the following families: Eleotridae (gudgeons or sleepers), Terapontidae (grunters), Gobiidae (gobies), Melanotaeniidae (rainbowfishes), Plotosidae (eel-tailed catfishes), Ambassidae (glass perches), and Ariidae (sea catfishes, or fork-tailed catfishes). The remaining 22 families are represented by three species or fewer.

Description of endemic fishes:

Over twenty species are endemic to this ecoregion, including two monotypic genera: Guyu and Cairnsichthys. Each has a small distribution in the wet tropics of northeastern Queensland. Endemics from the genus Melanotaenia and the family Terapontidae are most numerous, although there are also endemic Gobiidae, Soleidae, Percichthyidae, Ambassidae, Eleotridae, and Carcharhinidae.

Other noteworthy fishes:

The bizarre Kurtus gulliveri, nurseryfish, is present in many coastal drainages. Females somehow attach the eggs to a hook on the head of males (Berra & Humphrey 2002). Several other fish species are unusual in that they are mouth brooders. These include the two Scleropages spp. (females hold eggs), all ariid catfish (males hold eggs), and Glossamia aprion, mouth almighty (males hold eggs) (Allen et al. 2002). All of these groups are found in surrounding ecoregions and/or New Guinea.

Other noteworthy aquatic biotic elements:

Emydura victoriae, the Victoria river red-faced turtle, is apparently restricted to the Daly and Victoria river systems (taxonomy unresolved). Emydura tanybaraga, northern yellow-faced turtle; Elseya lavarackorum, gulf snapping turtle; and Chelodina burrungandjii, sandstone long-necked turtle, are all endemic to this ecoregion. The Daly River has the highest species richness of turtles in Australia with eight species (Cann 1998). The palaemonid shrimp, Macrobrachium koombooloomba, is endemic to the upper Tully River (Short 2004), while the palaemonid genera Kakaducaris and Leptopalaemon are restricted to the Arnhem Land plateau (Bruce 1988, 1994). Several freshwater crayfishes are also endemic. Euastacus fleckeri is restricted to a small area of higher elevation near Mossman, and its range is drained by the Mitchell River to the west and south and by the Mossman River to the east (Morgan 1988). Three further species of Euastacus --E. yigara, E. robertsi and E. balanensis -- are endemic to the Northeastern Sub-province and have restricted, montane distributions (Morgan 1988; Short & Davie 1993). Of the seven species of Cherax that are endemic to the ecoregion, Cherax barretti, C. nucifraga, C. rhynchotus, C. wasselli, C. cartacoolah, and C. parvus have limited ranges, whereas Cherax quadricarinatus occurs naturally across the whole ecoregion (Austin 1996; Short 1991, 1993, 2004; Short and Davie 1993; Wingfield 2002). 

Justification for delineation:

This vast region is likely typified by high connectivity between rivers during low sea levels. Most of the area between northern Australia and southern New Guinea becomes terrestrial, and many rivers coalesce together thus allowing their faunas to mix. The separation between Kimberley [803] is likely due more to decreasing connectivity between rivers and the isolated, localized occurrence of endemic species there. The break between Northern and Eastern Coastal Australia [807] is probably due mostly to differences in climate as rainfall drops very rapidly from the wet tropics south (Unmack 2001).

Level of taxonomic exploration:

Taxonomic exploration varies between good and fair. Few species have been studied in any detail and several areas remain poorly sampled. The high faunal similarity within this ecoregion implies a lack of isolating mechanisms. But some widespread groups have diversified, with multiple taxa likely being recognized in the genus Mogurnda (M. Adams, unpub data), Craterocephalus, and within some species of Melanotaenia (Unmack 2005) and Pseudomugil signifer (southern blue-eye) (Wong et al. 2004).

References/sources:

Allen, G. R., Midgley, S. H., et al. (2002). "Field guide to the freshwater fishes of Australia" Perth: Western Australian Museum.

Austin, C. M. (1996). "Systematics of the freshwater crayfish genus Cherax Erichson (Decapoda: Parastacidae) in south-western Australia: electrophoretic, morphological and habitat variation" Australian Journal of Zoology 44 223-58.

Berra, T. M.,Humphrey, J. (2002). "Gross anatomy and histology of the hook and skin of male nurseryfish, Kurtus gulliveri, from northern Australia" Environmental Biology of Fishes 65 263–270.

Cann, J. (1998). "Australian freshwater turtles" Singapore: Beaumont Publishing.

Coughran, J.,Leckie, S. (2007). "Euastacus pilosus n. sp., a new crayfish from the highland forests of northern New South Wales, Australia" Fishes of Sahul 21(1) 308-316.

Coughran, J.,Leckie, S. (2007)"Invasion of a New South Wales stream by the tropical crayfish, Cherax quadricarinatus (von Martens)" In Lunney, D.;Eby, P.;Hutchings, P.;Burgin, S. (Ed.). Pest or Guest: the zoology of over abundance. (pp. 40 - 46) Mosman, NSW, Australia: Royal Zoological Society of New South Wales.

Doupé, R. G., Morgan, D. L., et al. (2004). "Introduction of redclaw crayfish Cherax quadricarinatus (von Martens) to Lake Kununurra, Ord River, Western Australia: prospects for a ‘yabby’ in the Kimberley" Journal of the Royal Society of Western Australia 87 187-191.

Morgan, G. J. (1988). "Freshwater crayfish of the genus Euastacus Clark (Decapoda: Parastacidae) from Queensland" Memoirs of the Museum of Victoria 49(1) 1-49.

Short, J. W. (1993). "Cherax cartacoolah, a new species of freshwater crayfish (Decapoda: Parastacidae) from northeast Australia" Memoirs of the Queensland Museum 33 55-59.

Short, J. W. (2004). "A revision of Australian river prawns, Macrobrachium (Crustacea: Decapoda: Palaemonidae)" Hydrobiologia 525 1-100.

Short, J. W. (1991). "Cherax nucifraga, a new species of freshwater crayfish (Crustacea: Decapoda: Parastacidae) from the Northern Territory, Australia" The Beagle, Records of the Northern Territory Museum of Arts and Sciences 8 115-120.

Short, J. W.,Davie, P. J. F. (1993). "Two new species of freshwater crayfish (Crustacea: Decapoda: Parastacidae) from northeastern Queensland rainforest" Memoirs of the Queensland Museum 34 69-80.

Unmack, P. J. (2001). "Biogeography of Australian freshwater fishes" Journal of Biogeography 28(9) 1053-1089.

Unmack, P. J. (2005). "Historical biogeography and a priori hypotheses based on freshwater fishes" Unpublished Thesis. Arizona State University.

Wingfield, M. (2002). "An overview of the Australian freshwater crayfish farming industry" Freshwater Crayfish 13 177-184.

Wong, B. B. M., Keogh, J. S., et al. (2004). "Current and historical patterns of drainage connectivity in eastern Australia inferred from population genetic structuring in a widespread freshwater fish Pseudomugil signifer (Pseudomugilidae)" Molecular Ecology 13 391–401.

World Wildlife, Fund (2001). "Arnhem Land tropical savanna (AA0701)" 2005 (2005; www.worldwildlife.org/wildworld/profiles/terrestrial/aa/aa0701_full.html).

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