DISTRIBUTION, IDENTIFICATION AND BIOLOGY OF FRESHWATER FISHES IN SOUTH-WESTERN AUSTRALIA

WA Museum Records and Supplements | Updated 9 years ago

Abstract - A total of 410 sites in the major watersheds in the south-western corner of Australia, bounded by Bunbury in the north-west and just east of Albany in the south-east, were sampled for fish. Sampling of the different sites was carried out using one or more of the following methods, namely seine netting, scoop netting, trapping and electrofishing to catch juvenile and adult fish, and light trapping, scoop netting and haul netting to collect larval fish. The fish caught at each site were identified and the number of each species recorded. These data were then collated, both with those derived from the studies of Christensen (1982) and Jaensch (1992) and with the records of the Western Australian Museum (WAM), to elucidate the distributions of each of the fish species found in freshwater in south-western Australia. The eight species endemic to south-western Australia are Tandanus bostocki, Lepidogalaxias salamandroides, Galaxias occidentalis, Galaxiella nigrostriata, Galaxiella munda, Bostockia porosa, Edelia vittata and Nannatherina balstoni. The other species found in this region include Galaxias truttaceus and Galaxias maculatus, which are also represented in south-eastern mainland Australia and Tasmania, the anadromous lamprey Geotria australis, and those teleosts which are commonly found in freshwater, but belong to predominantly marine families, i.e. Leptatherina wallacei, Pseudogobius olorum and Afurcagobius suppositus. Finally, there are those species that have been introduced into the region, i.e. Oncorhynchus mykiss, Salmo trutta, Gambusia holbrooki and Perca fluviatilis.

The most common and Widespread endemic freshwater species in southwestern Australia are G. occidentalis, B. porosa and E. vittata, which are found in the majority of rivers and lakes and many of the pools in the region. Within the sampling region, the freshwater catfish Tandanus bostocki, was caught at only two sites during the present study (Alexander Bridge on the Blackwood River and at Lake Smith in the D'Entrecasteaux National Park), and was only recorded from Lake Wilson by Jaensch (1992) and from Pemberton and Nannup in the Western Australian Museum records.

The other four endemic species, namely L. salamandroides, G. nigrostriata, G. munda and N. balstoni, are effectively restricted to the region bounded by Margaret River in the west and by Albany in the east. However, G. nigrostriata, G. munda and N. balstoni have disjunct distributions, each having an isolated population near Gingin, which is well to the north of the other populations of these species. Disjunct populations of G. nigrostriata and N. balstoni have recently been found near Bunbury and Collie, respectively. Lepidogalaxias salamandroides and G. nigrostriata are generally restricted to the small ephemeral pools in the southern peat flats. Although N. balstoni is likewise abundant in the pools of the peat flats, it is also present in very low numbers in some rivers and lakes. Galaxiella munda is also found in a number of pools in the peat flats, but is most common in the headwaters of the major rivers of this area.

The two freshwater species, that are also found in south-eastern Australia, namely G. truttaceus and G. maculatus, were only found in the catchments of the small nature reserve at Two People's Bay. However, G. maculatus is known to be most common eastwards of the sampling region, i.e. within the coastal streams and rivers between Albany and Esperance.

Adult G. australis were recorded migrating up the Warren, Donnelly and Margaret Rivers during winter and spring. Although the precise locations at which they spawn are unknown, a number of maturing adults were caught in autumn and winter in both isolated pools and the main channel of the headwaters of the Warren River. The larvae (ammocoetes) of G. australis were collected from within shallow silty banks in the Capel, Margaret, Donnelly, Warren, Gardner, Shannon, Deep, Kent and Denmark Rivers, while the fully-metamorphosed young adults were typically found in the sandy substrates of these rivers.

Those fish species with marine affinities, that are abundant in freshwater in south-western Australia, namely L. wallacei, P. olorum and A. suppositus, are generally associated with coastal water bodies. However, these species were found considerable distances inland in, for example, the Blackwood River and a number of isolated lakes, such as Lake Jasper in the D'Entrecasteaux National Park.

Gambusia holbrooki, a small introduced species, is extremely common and Widespread in south-western Australia. Perca fluviatilis, a large introduced species was often locally abundant. These two species are often associated with habitats that have been substantially altered by human activity. For example, they were often common in reservoirs, e.g. Big Brook Dam, in mined areas, e.g. Collie River South Branch and the wetlands of RGC Mineral Sands, and in those systems subject to enrichment through agricultural run-off, e.g. certain areas of the Capel River, Blackwood River, Warren River and Lake Unicup. The two introduced trout species, O. mykiss and S. trutta, were only found in those systems where stocking had taken place, i.e. predominantly in the streams of the Pemberton area, and they were rarely captured in large numbers.

Habitat alteration, and possibly also the introduction of exotic species, pose the main threats to the highly endemic fish fauna of the south-western corner of Australia. Habitat alteration is likely to occur through those agricultural and forestry practices in the uppermost catchment that cause alterations to inflow, increased salinisation, siltation and eutrophication, and through dam construction, mineral sand exploration and mining, groundwater extraction, the construction of water points for fire fighting and road maintenance. Although three of the endemic species, namely G. occidentalis, B. porosa and E. vittata, are typically represented by large populations in most types of habitat throughout their extensive ranges, and are thus currently under no threat, local populations of these species may be threatened. In contrast, four of the endemic freshwater species L. salamandroides, G. nigrostriata, G. munda and N. balstoni, have a very restricted range and are generally represented by small populations in very specific habitats. There is also strong circumstantial evidence that the abundance of the pouched lamprey G. australis, has declined in recent years. This decline may reflect the influence of dams, which act as at least partial barriers to the upstream migration of the adults towards their spawning areas and leads to alterations in water flow and thus a decline in the areas of silty substrate in which their larvae (ammocoetes) live. These latter five species are therefore considered potentially vulnerable to the continuing loss or alteration of habitat and, in some cases, also to the introduction of non-native species.

The accounts of the distribution of each species in our study area, together with records of these species to the east and north of our study area, is accompanied by resume's of the taxonomic characters and biology of that species.

Author(s) David L. Morgan, Howard S. Gill and Ian C. Potter : Part 1
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