Journal of the Royal Society of Western Australia, 87(4), December 2004 
themselves), food web perturbations, habitat alterations, 
and disease introductions (Horwitz 1990; Holdich 1999; 
Lodge et al. 2000). There may be an increased likelihood 
that translocated redclaw crayfish could escape and 
contribute to these types of ecological impacts because 
their propensity to climb and move out of the water 
means that they are very difficult to contain (Jones et al. 
2000). How many redclaw crayfish are now in Lake 
Kununurra or adjacent waterways is also unknown, but 
given the potential ecological problems associated with 
the translocation of freshwater crayfish (and aquatic 
species generally, see also Doupe & Lymbery 2000; 
Morgan & Gill 2001; Morgan et al. 2002), this introduction 
should not be ignored. Indeed, Lake Kununurra and the 
greater Ord River system has been, and continues to be, 
subjected to a variety of proposed species introductions 
(e.g. Doupe & Bird 1999; Doupe & Pettit 2002; Doupe et 
al. 2005) and escapement from aquacultures (Doupe & 
Lymbery 1999). 
Relatively high fecundity, mobility to invade new 
habitats, and the ability to compete for available 
resources, are prominent ecological attributes commonly 
shared by successful invaders (Elton 1958; Fox & 
Adamson 1986). Nevertheless, the single-most significant 
factor affecting their eventual distribution in the new 
environment concerns the level of ensuing predation of 
them by resident species (Krebs 1985), and from that end, 
food webs can form a useful starting point for the 
theoretical analysis of community organisation (Cohen 
1978; Pimm 1982). In this paper, we present the results of 
a preliminary survey intended to investigate the extent 
to which redclaw crayfish have thus far been assimilated 
into the Lake Kununurra ecosystem using a gut survey 
of the resident fish community. We use those findings to 
provide a baseline for future research on redclaw crayfish 
distributions, and to discuss the potential impacts of 
introducing redclaw crayfish to the waterways of the 
Kimberley region. 
Materials and Methods 
The irrigation water supply reservoir of Lake 
Kununurra (128°46 / E 15°57 / S) is a very large, linear 
wetland approximately 55 km long and with a full 
supply surface area of about 100 million m 2 . During 
daylight hours in December 2002, we surveyed the fish 
fauna of Lake Kununurra by sampling 12 recognisably 
different habitats in the lake proper and associated 
lagoons, and six sites in a major side-creek that connects 
Lake Kununurra to Lake Argyle (z.e. Spillway Creek; see 
Fig 1). Fishing gear comprised monofilament gill nets (50, 
100, 125, 150 and 200 mm stretched mesh width), seine 
nets (5 and 15 m nets of 3 mm woven mesh width), and 
rod and line. On capture, all fish were identified and 
counted. 
We also collected 38 lesser salmon (or blue) catfish 
Arius graeffei Kner & Steindachner from one site in Lake 
Argyle and 56 lesser salmon catfish and 20 barramundi 
Lates calcarifer (Bloch) from three sites in the lower Ord 
River (approximate locations are given in Fig 1), and 
whole guts were checked only for the presence of 
redclaw crayfish remains. 
For fishes taken from Lake Kununurra, between 6 and 
60 individuals of each species were retained for dietary 
analyses. The whole stomach was removed for dietary 
examination, and diets were analysed using the 
frequency of occurrence (Hynes 1950) and points (Ball 
1961) methods; the frequency of occurrence method 
represents the incidence with which a particular prey 
type is consumed by a species, whereas the points 
method gives the relative contribution of each prey type 
to the total volume of the stomach contents. 
Results 
Of the 19 fish species collected from Lake Kununurra 
(see Gill et al 2005), the guts of the freshwater longtom 
Strongylura krefftii (Gunther), black catfish Neosilurus ater 
(Perugia), and Macleay's glassfish Ambassis macleayi 
(Castelnau) were empty, and because only three northern 
trout gudgeon Mogurnda mogurnda and a solitary sleepy 
cod Oxyeleotris lineolatus (Steindachner) were collected, 
dietary data for these species were not recorded. Morgan 
et al. (2004) provide a detailed description and discussion 
of the component diets of all species. 
Claw remnants of redclaw crayfish were found in both 
the lesser salmon catfish and silver cobbler A. viidgleyi 
Kailola & Pierce taken from Lake Kununurra. The 
frequency of occurrence of redclaw crayfish in the guts of 
each species was 3.57% and 8% respectively, and this low 
rate was reflected in a correspondingly small 
contribution of redclaw crayfish to the total stomach 
volume of each (2.84% and 7.97% respectively). We also 
found remains of another decapod, the endemic 
freshwater prawn or cherabin Macrobrachium sp., in the 
guts of lesser salmon catfish, silver cobbler, barramundi, 
and Jenkins' grunter or black bream Hephaestus jenkinsi 
(Whitley). Cherabin frequently occurred in the guts of 
lesser salmon catfish (32.14%) and barramundi (29.79%), 
and to a lesser extent in Jenkins' grunter (14.81%) and 
silver cobbler (12%), but contributed significantly less to 
the total gut content of lesser salmon catfish (7.15%) and 
Jenkins' grunter (1.10%) than for either silver cobbler 
(10.95%) or barramundi (26.42%). 
No redclaw crayfish were found in either lesser 
salmon catfish or barramundi taken from Lake Argyle or 
the lower Ord River, however most guts of both species 
from all sites contained remnants of cherabin and other 
species of teleost. 
Discussion 
Considering that redclaw crayfish was found in 
very low numbers in lesser salmon catfish and silver 
cobbler, and contributed similarly low levels to the 
total volume of their guts, do these results mean that, 
(1) there are few redclaw crayfish in Lake 
Kununurra? (2) Predation of redclaw crayfish by 
these catfishes is a relatively opportunistic event? 
And/or (3), that the time of sampling (i.e. late 2002) 
was too soon post-discovery to establish the extent to 
which redclaw have been assimilated into the lake 
ecosystem? We are also unsure of the significance of 
redclaw crayfish to the diets of lesser salmon catfish 
or silver cobbler, or indeed other fish species of the 
lake; we expect that barramundi would also predate 
188 
