Friday, August 12, 2011

Western Yabby / Black Crayfish / Cherax Preissii / Cherax Glaber / Koonacs

Cherax Preissi / Black Yabby / Black Crayfish

Species Name: Cherax Preissi & Cherax Glaber
Common Names: Western Yabby, Black Crayfish, Black Yabby, Blue Black Australian Crayfish, Koonacs
Family: Parastacidae
Order: Decapoda
Class: Malacostraca

Two species of freshwater crayfish native to the south-west of Western Australia – Cherax Preissii and Cherax Glaber are called Koonacs. Cherax Preissii is widespread throughout much of Western Australia's South-West and Wheatbelt. Cherax Glaber is restricted to some coastal waterbodies in the far south. Koonacs are found further inland than their larger cousin, the Marron.

Cherax Preissi / Australian Black Crayfish / Western Yabby

Koonacs can grow to 20 cm in length and have four keels on their heads and no spines on the rostrum or
telson. They are usually dark coloured, ranging from brown-black to blue-black. Koonacs are arthropods, like insects and spiders, but have two pairs of antennae (the larger ones are called antennae and the smaller ones are called antennules). Their bodies are divided into three sections – the head, the thorax and the abdomen.
Blue Black Australian Crayfish / Cherax Preissi

Ecology/Way of Life:Koonacs are usually found in swamps that dry up. They spend the summer in deep burrows, low in the water table. They dig using their claws, cap their holes, and remain burrowed until winter rains fill their swamp. They mate and spawn in their burrows, to avoid predation. They are usually able to spawn at two years of age, but observations suggest that some animals mature earlier. Growth occurs primarily in the rainy season, winter. This differentiates them from Marron and Yabbies where growth is achieved primarily in summer. Koonacs, like all freshwater crayfish, can have several species of epibionts attached to their bodies. These tiny animals are usually not harmful to the crayfish but can reach very high numbers under certain conditions.
Cherax Glaber / Koonacs

Interaction with Humans/Threats:
have been present in local Aboriginal diets for thousands of years. They are considered to be a relatively hardy species, but display slower growth than yabbies and Marron under commercial conditions. Koonacs are farmed commercially on a small scale, usually targeting niche markets. Care should be taken to preserve their natural habitat and they are very vulnerable to diseases that may be introduced by the translocation of non-endemic species.

Other Comments:

Two species of freshwater crayfish are refereed to as Koonacs, Cherax preissii and Cherax glaber.
Further Reading:

Western Australian Department of Fisheries. (2004). Identifying Freshwater Crayfish in South West WA. 

This species is endemic to south-west coastal areas of Western Australia and has a relatively uniform distribution due to its ability to tolerate a range of habitat types (Morgan and Beatty 2005). This species ranges from Cannington near Perth, to Albany. The area in which this species is distributed is approximately 50,000 km2.

This is a burrowing species and is found in a range of habitat types including rivers, streams, ponds and swamps indicating that it is a habitat generalist. It occurs in both permanent and temporary freshwater systems (Morgan and Beatty 2005). It has an active dispersal rate and is able to survive extended periods out of water (Gouws, Stewart and Daniels 2006).

This species is locally threatened by competition from both Cherax Destructor and Cherax Quinquecarinatus to a lesser degree (Lynas et al. 2007). It is also likely to be impacted by drought in areas of water abstraction, urbanization, and land conversion for agriculture (C.M. Austin pers. comm. 2008). However, this species is widespread and common throughout much of its range implying it may only be locally threatened. This species is undergoing more significant declines in the northerly extent of its range, around Perth, where it is threatened by intense urbanization (C.M. Austin pers. comm. 2008).

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