ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.

Movement Patterns and Habitat Preference of the Endangered Eastern Freshwater Cod (Maccullochella ikei) in the Mann-Nymboida Rivers of Northern NSW.

Gavin Butler

GRAFTON, AUSTRALIA

THEME: ASFB

As with many of Australia's freshwater fish species, the behavior of the endangered eastern freshwater cod (Maccullochella ikei) remains poorly understood. Ongoing stream degradation and increasing water demands throughout M. ikei's range has only further accentuated the need to better understand the species spatio-temporal requirements. Therefore the aim of this study was to determine the short-term movements and habitat preference of the species in the Mann-Nymboida River systems. Radio transmitters were used to monitor the activities of M. ikei, with two attachment techniques trailed over the study period. Initially transmitters were fitted externally to the dorsal surface of the five fish. However, all external tags detached within two days of the fishes' release. Radio transmitters were subsequently fitted internally in the peritoneum cavity of six adult cod ranging in size from 350-665mm. Tagged cod were monitored for four weeks post-release throughout the months of August and September 2001. All tagged individuals remained in the release pool throughout the study period. No significant differences in total movement were apparent between sample periods for all cod (P<0.05). Significant differences were apparent in diel movements, with cod found to be more active nocturnally than diurnally (P<0.05). Home range was estimated using the Home Ranger 1.5 software package. Home ranges of tagged M. ikei varied considerably in size. The distinct patchiness apparent in home-range estimates was attributed to feeding and resting behaviour of M. ikei. Comparisons between the availability of habitat types and the frequency of their use, revealed that M. ikei preferred boulders over any other structure type. A linear relationship was apparent between the length of M. ikei and the size of structure utilised. The results of this study suggests that the effective management of M. ikei requires a more holistic approach when identifying areas of habitat critical to the species. Recommendations for further research include extensive studies of movement and habitat usage of M. ikei at all life history stages throughout the species entire range.