Publication Date

11-2001

Series Number

129

Publisher

Department of Fisheries, Western Australia

City

Perth, Western Australia

ISBN

0 7309 8457 5

ISSN

1035 - 4549

Abstract

Yabby (Cherax albidus) burrows were recorded from dams, channels and ponds in Western Australia. Twenty five sites were sampled during Spring, 1998 and the burrow morphology and density was described from six of these locations where burrows were present. To improve the sample size and address seasonal trends 49 commercially harvested yabby dams were sampled over the summer of 1999/2000 and the number and density of yabby burrows were recorded. Burrow incidence and morphology was also recorded from 25 research ponds at the Avondale Research Station between 1995-1997. Soil and water chemistry values are presented and their relationships with burrow morphology are discussed. Burrow density (number of burrows/m2) was also recorded. Burrowing activity was investigated against the density, sex, and feeding regime of yabbies.

Different techniques for casting and excavating the casts of burrows were evaluated. Expanding polyurethane foam was better than concrete, plaster or resin as it was lighter, less brittle and gave a three dimensional representation of the burrow. Excavating the casts of burrows using high pressure water was better than digging as it was more efficient and preserved the shape of the casts.

The morphology of burrows was characterised by burrow length, depth into dam wall, width, number of entrances and cavern width in the Spring 1998 survey. The average burrow length was 25.8 cm. The maximum distance a burrow penetrated directly into a dam was 64.5 cm, while the longest burrow was 148 cm. Based morphological features burrows were classified as either depressions, angular pits, U-shaped tunnels or networks.

The incidence of yabby burrows increased from 25% of dams in Spring 1999 to 70% in Autumn 2000. Burrow density increased significantly from 0.02 burrows/m2 of bank 0.5m above and below water level in Spring to 0.11 burrows/m2 in Autumn, but did not increase significantly between Summer and Autumn.

The majority of burrows (64%) had only 1 entrance to a simple tunnel (mean width 6.4 cm) leading to a terminal cavern (mean width 12.5 cm). Channels and large dams tended to have longer (22 - 40 cm) and more complex burrows than small dams or ponds (8 - 21 cm). Burrows were more complex where there was a greater variation in water table height. Consequently, burrows in levee banks of channels and dams tended to be more complex than those in the bottom of ponds.

In the research ponds, burrowing activity was less in ponds containing only males or unfed yabbies. Similarly the density of burrows during the spring 1998 survey was generally higher where there were more females than male yabbies. Fed yabbies are larger and fitter (physically and reproductively) possibly resulting in increased burrowing activity. There was no relationship between the density of yabbies and the number of burrows in the research ponds.

There was a strong relationship between soil type and burrowing in survey 1, with yabbies burrowing more in soil containing high levels of silt. This finding was not supported by the data from survey 2 which involved more dams.

Similarly, there was also a strong relationship between water chemistry and burrowing in survey 1. Yabbies burrowed more where calcium, potassium, sodium, chloride and conductivity levels were high, while there was a negative relationship between yabby burrowing and hardness. However, in survey 2 there was no significant relationship between water chemistry and burrowing.

When C. albidus burrows were present in a dam, pond or channel they were relatively abundant. However, the burrows were generally much shorter than those described in published reports for crawfish (Procambarus clarkii) and in anecdotal reports for C. destructor, the commonly farmed yabby from South-eastern and Central Australia

Number of Pages

26

Keywords

Yabby, Cerax albidus, Yabber, Freshwater crayfish, Burrowing, Soil type, Research ponds

Disciplines

Aquaculture and Fisheries | Environmental Monitoring | Marine Biology

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