Fish and crayfish fauna of Ellen Brook, Cowaramup Brook and Gunyulgup Brook in the Cape to Cape Region of Western Australia
Morgan, D. and Beatty, S. (2005) Fish and crayfish fauna of Ellen Brook, Cowaramup Brook and Gunyulgup Brook in the Cape to Cape Region of Western Australia. Murdoch University. Centre for Fish & Fisheries Research, Western Australia.
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During September 2004 a total of 25 sites were sampled for fish and freshwater crayfish in Ellen Brook, Cowaramup Brook and Gunyulgup Brook. This included 11 sites on Ellen Brook, six sites on Cowaramup Brook and eight sites on Gunyulgup Brook. A total of 1270, 720 and 1450 m2 were sampled on Ellen, Cowaramup and Gunyulgup Brooks, respectively.
Five species of fish were captured in the 11 sites sampled in Ellen Brook. These included two freshwater species that are endemic to south-western Australia, i.e. the Western Pygmy Perch and the Nightfish, the marine-estuarine opportunistic Sea Mullet, the marine Zebra Fish and the introduced Mosquitofish. The only fish species captured in the six sites sampled in Cowaramup Brook was the introduced Mosquitofish. Three species of fish were captured in the eight sites sampled in Gunyulgup Brook. These include the estuarine Swan River Goby and Black Bream and the marine/estuarine opportunistic Sea Mullet. All three species were found at the mouth of the brook, with the Black Bream (1 specimen, 43 mm TL) and Sea Mullet (5 individuals, 34-43 mm TL) being small juveniles. In contrast, the 60 Sea Mullet captured at Caves Rd were much larger and ranged in length from 204 to 261 mm TL.
The largest Western Pygmy Perch captured in Ellen Brook was 78 mm TL, a size considerably longer than previously reported for the species (i.e. 68 mm TL, from almost 3000 individuals measured) (see Pen and Potter (1991) in the Collie River. Furthermore, 13 of the 268 individuals captured and measured in Ellen Brook were larger than the largest reported from the Collie River. This high proportion of large individuals is unusual in that most populations of Western Pygmy Perch are represented by the 0+, 1+ and 2+ cohorts, which comprised 99% of all fish examined in the Collie River. In the Collie River, Western Pygmy Perch attain lengths of ~42 and 51 mm TL at the end of their first and second year of life, respectively (Pen and Potter 3 1992). Based on this length at age data, almost 43% of Western Pygmy Perch in Ellen Brook would have been in their fourth, fifth or sixth year of life. The population of Nightfish in Ellen Brook is similarly dominated by larger, older fish. For example, in the Collie River 98.5% of the population is < than three years old (<85 mm TL), whereas in Ellen Brook, over 70% of the population is > three years old (i.e. >85 mm TL) (see Pen and Potter 1990). These dramatically contrasting population demographics are important, particularly in terms of ensuring the survival of what may be an aging population. It is possible that either predation is high on juvenile fish or that the high degree of water extraction is impacting on the fishes. The considerable number of new dams in the catchment, increased land clearing and long term drought experienced in the region again may be affecting environmental flows to the degree that only the few larger fish are surviving, possibly as they are more capable of competing for habitat as it becomes limited.
Four species of endemic freshwater crayfish were captured in Ellen Brook, including the widespread smooth Marron (Cherax cainii), the common Gilgie (Cherax quinquecarinatus), the restricted Gilgie (Cherax crassimanus) and the widespread Koonac (Cherax preissii). While only two, eight and four individuals of the Marron, the restricted Gilgie and the Koonac were captured, respectively, over 500 Gilgies were found throughout Ellen Brook, with densities peaking at 3.0 Gilgies m-2 at site 10 (Garstone Rd, the second uppermost site). Only one Gilgie was found at the uppermost site (site 11) which offered little habitat or shade. The restricted gilgie in Ellen Brook represents the northern-most extent of its range and reflects its preference for small waterbodies. The overall mean density of common Gilgies throughout Ellen Brook was high, with approximately every 2 m2 of stream bed being occupied by one animal. The densities of the widespread Gilgie were highest in Cowaramup Brook, with an average mean abundance of 1.62 Gilgies m-2. A total of 963 Gilgies were captured in Cowaramup Brook and they were found in all sites, including the mouth of the brook. A total of six Marron was also captured in three of the six sites sampled. 41 Yabbies were captured in Gunyulgup Brook. There appeared to be three age cohorts (year classes) present including newly released (0+) individuals, indicating that this species was a self-maintaining population. In Gunyulgup Brook Gilgies were captured in all sites with the exception of the mouth, while Marron were only found in the large dam at site 7, where they were probably introduced. The presence of a Yabbie below this dam (site 6) suggests that this is also the most likely avenue of their introduction into this part of the brook. The fact that the majority of Yabbies were caught on another branch of the brook implies that there have been multiple introductions to the system. A wild population of Yabbies in the Hutt River (near Geraldton) has recently been found to have the serious porcelain disease caused by the microsporidian Thelohania parastaci, a disease that has also impacted on 4 the aquaculture industry in this State. This disease is contracted by a crayfish consuming infected tissue. It is possible that the endemic crayfish may be able to contract this disease by consuming infected Yabbie tissue. Therefore, the potential accompanying spread of this and other diseases by Yabbie introductions is of considerable concern in this region. The identification of this, and other diseases, in the yabbies of Gunyulgup Brook should be assessed.
The high abundance and success of Gilgies in these streams is no doubt a reflection of their adaptive life history strategy adapted to these water bodies which includes: the ability to burrow into the water table in temporary waterbodies, a relatively small size at first maturity reproducing after the first year of life, and being able to spawn multiple times over the annual breeding period (spring-summer). Therefore, the wide distribution and large abundance in all three streams in the current study reflects this species adaptiveness to such small lotic systems, subject to low summer water levels.
|Murdoch Affiliation:||Centre for Fish and Fisheries Research|
|Series Name:||Murdoch University Report to Ribbons of Blue/Waterwatch WA|
|Publisher:||Murdoch University. Centre for Fish & Fisheries Research|
|Copyright:||2005 Murdoch University. Centre for Fish & Fisheries|
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