WEST KIMBERLEY PLACE REPORT - Department of Sustainability ...

number of endemic freshwater fish in comparison to any other region in Australia
(ANHAT 2009, Allen et al. 2002, Morgan 2008, Unmack 2001). While over 30
species are confined to Cape York in Australia, over 20 of these have a transcontinental
distribution, with many occurring in Papua New Guinea or further afield
in the Pacific (Allen et al. 2002). It should be noted however that the large number of
endemics that have been recorded within the Kimberley may in part relate to limited
historical surveying. This is largely due to the general isolation of the region and
seasonal access difficulties (Morgan et al. 2004).
In their paper on the fishes of the Kimberley, Allen and Leggett (1990) speculate that
the highly dissected nature of the landscape has served as an isolating mechanism
between species, with the numerous large and deep waterholes acting as refugia, and
resulting in centres of speciation, which are speculated to have been in existence since
the fluctuating climate of the late Cenozoic. The authors also point out that the
Kimberley landmass is isolated, and mostly surrounded by the sea or the desert, with
only a narrow corridor of high rainfall that links the Kimberley with the northwestern
corner of the Northern Territory (Allen and Leggett 1990). In his 2001 paper on the
biogeography of Australian fishes, Unmack notes that the Kimberley region has a
very high endemism, along with a number of species that have disjunct populations.
At the time, the author recorded a total of 13 species that were endemic to the west
Kimberley, compared with a maximum of six endemics confined to any single
drainage basin for the remainder of northern Australia and the entire east coast of
Australia. The only basins that rivalled the Kimberley at that time for numbers of
endemics were the Lake Eyre Basin (12 species) which is approximately five times
larger that the west Kimberley and the Murray Darling Basin (9 species), which is
likewise around four times larger. Since 2001, another five species have been
recorded as endemic to the west Kimberley (Morgan 2008), which is a relatively high
rate of discovery and lends support to the likelihood of a high ongoing rate of
discovery of new species in the west Kimberley in general.
Rivers that are particularly important for species that are either endemic to the
Kimberley, or to one or two river systems within the Kimberley, are those that lie in
the far north and west of the west Kimberley and include the Drysdale River (6
species), the Prince Regent (6 species), the Roe and Moran Rivers (4 species), Carson
River (4 species) and Isdell River (3 species) (Morgan 2008, Allen et al. 2002). The
Kimberley fish endemism also extends to the Fitzroy River (1 species with 2 near
endemics) (Dave Morgan pers. comm. April 2010), however, the catchment size of
the Fitzroy is far larger than the northern and western rivers, being roughly equivalent
to all the above mentioned river catchments combined. The rate of fish endemism
within the Fitzroy is comparable with other rivers across tropical Australia of
approximately equivalent size. For example, there are four species that are endemic to
the Flinders River system, which flows into the Gulf of Carpentaria; and four species
endemic to the Daly River in the Northern Territory. This is in contrast to the 18
species in total that occur in the eight river systems of the far north and west
Kimberley. This combined with the fact that many of these rivers are relatively short
in length, highlights their significance for overall numbers of endemic species, in
comparison with other rivers across northern Australia, including the Fitzroy.
The fossil evidence across Australia for freshwater fish demonstrates persistence of
some families up to 45 million years (Crowley 1990; Unmack 2001). Unmack (2001)
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