Patterns of movement and habitat use were examined in Queensland (Australian) lungfish Neoceratodus forsteri (Krefft, 1870). Data were collected at different spatial and temporal scales from three stages of the lungfish life cycle. The results were derived principally from radio telemetry studies in the Mary and Burnett River systems in southeast Queensland. A mark-recapture program and laboratory studies complemented the telemetry results. Field studies in the Burnett River compared lungfish movements in flowing river reaches with those in impounded sections (i.e. weir pools) to assess the impacts of river regulation on lungfish passage and habitat quality within the species' restricted distribution.
Daily activity patterns were described from 20 radio-tagged individuals in the Mary River and video footage of 30 juvenile lungfish in an above ground swimming pool. Both groups conformed well to predominantly nocturnal activity patterns described previously in captive specimens. However, crepuscular activity was also common. During daylight juvenile and adult lungfish were relatively inactive and sheltered in complex underwater habitat, particularly in shaded or darkened areas. Juvenile lungfish (<300mm) occupied dense macrophyte beds more frequently than other shelter types, while sub-adult and adult fish utilised a wider range of underwater structure, particularly submerged riparian vegetation and woody debris. Adult lungfish occupied depths between 2-3m more often than was predicted based on measures of their availability. Lungfish were less active and occupied smaller daily ranges during winter than the other seasons.
Total linear ranges of 49 radio-tagged lungfish varied from 300-47 900m. The mean total range of lungfish in impounded sections of the Burnett River was considerably higher than in flowing reaches of the Mary River or the Burnett River. Home range estimates for 20 radio-tagged individuals in the Mary River were smaller than total ranges. Mean home range was estimated as 1470m and was not a function of lungfish sex, total length, condition factor or the number of radio fixes. Radio-tagged lungfish exhibited strong site fidelity, frequently returning to specific landmarks within their home ranges. Lungfish withstood major flooding with minimal downstream displacement by making lateral movements to shelter amongst flooded riparian cover.
Long-term movements of sub-adult and adult lungfish were interpreted from radio telemetry and mark-recapture data. The distribution of movements from 124 mark-recapture events was leptokurtic and right skewed. Despite movements up to 25.4 km 56% of recaptures occurred within 1 km of the tagging location. Both sexes moved in a similar fashion, with no directional trend in the movements of either males or females. A wider range of movements was recorded in impounded sections of the river than in flowing reaches. Four lungfish tagged in the main river channel, were recaptured from a group of spawning fish in the lower reaches of a tributary stream (the Boyne River).
Long-term movement data from radio-tagged lungfish were consistent with the mark-recapture results. Longitudinal movements were rare in flowing reaches of the Mary and Burnett Rivers. Only 5 of 32 lungfish radio-tagged in flowing reaches moved more than 5km from the release point. In contrast, nine out 10 radio-tagged lungfish released in an established weir pool on Burnett River made regular longitudinal movements exceeding 5km. At least 5 fish in this group approached the fishlock on the Walla Weir, but none entered the lock and continued upstream. One radio-tagged fish descended into the Burnett River estuary and was unable to ascend a vertical-slot fishway on the tidal barrage and re-enter freshwater. There was good evidence that the substantial longitudinal movements observed in impounded sections of the Burnett River were part of an annual cycle related to spawning. Prior to consecutive spawning seasons, some radio-tagged lungfish left the weir pool and moved upstream into shallow, heavily vegetated sections where spawning activity was observed. Return (downstream movements) from the spawning grounds occurred on a staggered basis, often coinciding with periods of elevated flow.
This study demonstrated that lungfish spawning grounds, nursery areas and adult growth areas share similar characteristics unified by the occurrence of submerged aquatic macrophytes. In flowing river reaches these fundamental habitats frequently overlapped and therefore longitudinal movements were rare. Suitable spawning habitat rarely occurred in impounded river sections due to increased water depth and steep bank profiles. In these areas, lungfish made substantial longitudinal movements. These results confirm that patches of deep still water are largely unsuitable for lungfish spawning. The long-term impacts of this situation require urgent consideration given the apparent inevitability of further lacustrine habitat being created in the future.