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Aquatic macrofauna of Ellen Brook and the Brockman River: fresh water refuges in a salinised catchment

Beatty, S.J.ORCID: 0000-0003-2620-2826, Morgan, D.L., Klunzinger, M.W. and Lymbery, A.J.ORCID: 0000-0002-0542-3446 (2010) Aquatic macrofauna of Ellen Brook and the Brockman River: fresh water refuges in a salinised catchment. Murdoch University. Centre for Fish & Fisheries Research, Western Australia.

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The South West Coast Drainage Division houses a highly endemic assemblage of aquatic fauna. For example, the region’s freshwater fish (80% endemic) and crayfish (100% endemic) endemicity is unsurpassed within the continent. However, this fauna has been severely impacted by habitat change and introduced aquatic species. Understanding the distribution and population viability of these aquatic organisms allows for the development and implementation of effective river action plans that can utilise these organisms as long‐term bioindicators of ecosystem health, but can also aid in the recognition of fauna that is in need of special protection.

The Brockman River and Ellen Brook are both major tributaries of the Swan River. While the fishes of the Swan River and the Swan‐Canning estuary have been well studied, the freshwater fishes of its major tributaries have received far less research attention. This study aimed to collate previously existing data on the fishes in the freshwaters of Brockman River and Ellen Brook and survey additional sites in both systems in spring and summer 2009/2010 to gather information on the distribution and abundance of native freshwater and estuarine fishes, feral fishes, native and feral freshwater crayfishes, and a freshwater mussel. By undertaking this research, the study aimed to determine whether changes in the fish fauna had occurred and to set a basis for predicting future changes of the aquatic fauna.

A total of 11342 fish, crayfish and turtles were captured during the survey of 10 sites on the Brockman River and seven sites on Ellen Brook in 2009/2010. Of these captures, 1707 (15.1%) were native freshwater fish, 4392 (38.7%) were native estuarine fish, 3323 (29.3%) were feral freshwater fish, 421 (3.7%) were native freshwater crayfish, 1431 (12.6%) were native freshwater shrimp, 25 (0.2%) were a feral freshwater crayfish, and 43 (0.4%) were the native Oblong Turtle (Chelodina oblonga).

There were six species of native endemic freshwater fishes recorded during the survey and from the collated existing information, including: the Western Minnow (Galaxias occidentalis), Western Pygmy Perch (Edelia vittata) and Nightfish (Bostockia porosa) which were all present in both the Brockman River and Ellen Brook catchments. The Freshwater Cobbler (Tandanus bostocki) and Western Mud Minnow (Galaxiella munda) were recorded only from the Brockman River and Ellen Brook catchment, respectively, the latter species only being found in Lennard Brook. A further native endemic freshwater fish species recorded within the Ellen Brook system is the Black‐stripe Minnow (Galaxiella nigrostriata), which is known from Melaleuca Swamp (Smith et al. 2002a, b) and very recently from Lake Chandala (McLure and Horwitz 2009). As these represent the only known populations of these two species in the entire Swan‐Canning catchment (which is south‐western Australia’s largest), and that they are outlying populations compared to their next nearest populations, indicates that they require specific conservation consideration.

There were two estuarine species recorded in both systems: the Western Hardyhead (Leptatherina wallacei) and the Swan River Goby (Pseudogobius olorum) that have penetrated these systems. The feral fish species captured consisted of the Eastern Mosquitofish (Gambusia holbrooki) and the Goldfish (Carassius auratus). While the Eastern Mosquitofish was widespread, the Goldfish was restricted in distribution. The native freshwater crayfishes recorded were the Gilgie (Cherax quinquecarinatus), which was the most widespread species and the Marron (Cherax cainii) that was much more restricted in distribution in both systems. The feral Yabbie (Cherax destructor) was also recorded in the Ellen Brook catchment. Eradication of these established feral species would be very unlikely, however, there is the potential to control or remove the Goldfish given its apparent restricted distribution in both systems.

The extreme rarity of Carter’s Freshwater Mussel (Westralunio carteri), the south‐west’s only endemic freshwater mussel, in both these systems is cause for concern. This species is likely to play an important role in ecosystem health and its larval phase is reliant on fish hosts. Although the life‐cycle is poorly understood, but is under current investigation by one of the authors, this study implies that it may have undergone a large range reduction in Ellen Brook, the Brockman River and other salt‐affected systems in the region. Further, if the range reductions of fishes that are hosts to the larval stage of the mussel have occurred, then this may have led to a concomitant decline in mussel distribution.

Item Type: Report
Murdoch Affiliation(s): Centre for Fish and Fisheries Research
Series Name: Murdoch University Report to the Ellen Brockman Integrated Catchment Group
Publisher: Murdoch University. Centre for Fish & Fisheries Research
Copyright: 2010 Murdoch University. Centre for Fish & Fisheries Research
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