Doctor of Philosophy
School of Biological Sciences
Walsh, Christopher Timothy, Ecology and movement behaviour of two co-occurring estuarine-dependent fishes, Macquaria colonorum and Macquaria novemaculeata, Doctor of Philosophy thesis, School of Biological Sciences, University of Wollongong, 2012. http://ro.uow.edu.au/theses/3650
The coastal riverine systems of south-eastern (SE) Australia are characterised by high biological productivity and diversity, associated with highly variable environmental and climatic conditions, as well as detrimental anthropogenic influences. To deal with the climatic variability, many of the fishes endemic to these systems have evolved specialised physiological and life history adaptations, which allow them to utilise a variety of habitats over a range of spatial and temporal scales. Consequently, to sustainably manage impacts on these populations, including any recreational or commercial fisheries based on the fish species, a thorough knowledge of their ecology, life history and habitat requirements is required. Two such species, estuary perch, Macquaria colonorum and Australian bass, Macquaria novemaculeata, are members of a global family of fishes of high ecological and recreational fishery importance and represent the only catadromous Percichthyids found world-wide. The present research was initiated to address the lack of biological and ecological data available for these co-occurring closely related species, in particular for M. colonorum, and to provide the additional life history information required to assist in their conservation and management.
The spatial and temporal variability in life history characteristics, including age, growth, recruitment and reproductive status of M. colonorum populations were examined in three coastal catchments in SE Australia: the Hawkesbury; Clyde; and Bemm rivers. Validated age and reproduction data from 1 644 fish indicated that M. colonorum is a long-lived species (up to 41 years), that exhibits a flexible spawning strategy. Somatic growth was found to be rapid up until 3 to 4 years of age, after which fish matured and growth slowed considerably. Sex-dependent growth differences were evident in all three rivers, with females of M. colonorum reaching significantly larger asymptotic lengths than males. Population age structures indicated variable year class strengths and there was an absence of larger, older (>10 years) individuals in the two rivers subject to commercial fishing. Peak spawning periods for M. colonorum occurred earlier (June-August) in the two most northern populations (Hawkesbury and Clyde) compared with the Bemm River (September- November) further south. Ripe females were captured only in the lower estuarine reaches and displayed a group synchronous pattern of oocyte development. Similar to M. novemaculeata, M. colonorum was found to be a highly fecund species with larger fish having greater reproductive potential. This, combined with their longevity, suggests that M. colonorum possess a long reproductive lifespan, which may ultimately provide populations with resilience in times of unfavourable conditions.
An acoustic telemetry array was used to monitor the residency and movement behaviour of adult M. colonorum and M. novemaculeata in the freshwater and estuarine reaches on the Shoalhaven River. Both species displayed significant shifts in seasonal and size-related habitat use. Specifically, M. colonorum predominantly resided in deep (> 5 m) areas within the middle (mesohaline) reaches of the estuary during the spring to autumn months. In winter, individuals made frequent downstream migrations, often to localised areas within the lower estuary. In contrast, M. novemaculeata were distributed in shallow (< 2 m) habitats throughout the year, within the upper (oligohaline) estuarine reaches of the river, as well as in fresh water. Like M. colonorum, M. novemaculeata made extensive downstream and upstream movements, often coincident with reproductive behaviour, changes in water temperature and increased freshwater inflows. It appears that the high-site fidelity and repetitive homing displayed by both species is influenced by ontogenetic behaviour and prey availability. Furthermore, the previously reported ‘catadromous’ life cycle of these fish species (in particular, for M. novemaculeata), may not be obligatory.
Potential biological processes and environmental variables responsible for influencing the spatial ecology and movement behaviour of M. colonorum and M. novemaculeata were also investigated. Overall, large-scale movements (nonspawning and spawning) for both species were correlated with flood events, as well as trends in seasonal cooling and warming of water temperatures. For M. novemaculeata there was no evidence for increased numbers of migrants with higher river flow pulses while, in contrast, the frequency of individual M. colonorum migrations to the spawning grounds was consistently higher during ‘wetter’ periods. Behavioural rhythms in both species were consistent over broad temporal and spatial scales and often influenced by diel or tidal state. In particular, migrants of both species exhibited a preference for dusk to dawn activity. Location, visitation rates and occupation of spawning grounds by M. colonorum, along with the importance of maintaining base river flows for M. novemaculeata migrants to negotiate natural barriers, highlights the need for managing each species in terms of their particular environmental and habitat requirements.
This study provided new information on key biological and ecological characteristics of two endemic, co-occurring catadromous fishes inhabiting the complex riverine environments of SE Australia. It also highlighted the implications and considerations for managing these highly flexible riverine fish, their fisheries and their environment. Further research is recommended to provide a greater understanding of physiological, behavioural and ecological linkages through which environmental factors influence the distribution, movement and recruitment success of M. colonorum and M. novemaculeata populations.