Quantifying multi-scaled movements of Australian riverine fish to inform environmental flow management and conservation

Abstract

Variation in river flow is a strong behavioral determinant for the movement of many freshwater fish species, and it enables them to complete key aspects of their life cycle. The alteration of natural flow regimes to meet human water demands has contributed substantially to declines in water-dependent biota in many parts of the world. Consequently, environmental flows are used as a remediation tool in some regulated rivers with the intention of restoring aspects of the natural flow regime to benefit native flora and fauna. Specification of appropriate environmental flows ideally requires empirical data on flow-ecology response relationships. This thesis aims to use bio-telemetry to evaluate the effects of variations in hydrology and other environmental and biological factors on freshwater fish movement behaviours over a range of spatio-temporal scales in eastern Australian rivers. It also aims to understand how changes in natural flow regimes have affected fish movements by comparing the movement behaviours of several species in regulated and unregulated systems. In order to supplement knowledge gained on hydroecological relationships, this thesis also aims to assess the effects of other factors, such as translocation for conservation and in-stream barriers, on fish movements. Translocation is a widely used tool in the conservation of threatened species. The movement behaviours of translocated individuals in their new environment is a key factor that can influence translocation success (i.e. survival and reproduction). In Chapter 3, freshwater catfish (Tandanus tandanus) and Murray cod (Maccullochella peelii) movements were monitored using fine-scale acoustic telemetry over a fivemonth period in the Gwydir and Mehi Rivers, northern Murray-Darling Basin (MDB). Fine-scale movement and habitat selection were compared among translocated lacustrine and resident riverine freshwater catfish, and between species. Although freshwater catfish translocated from a reservoir had never experienced riverine environments, individuals still responded to hydrological variations in the same ways as resident riverine fish, suggesting an innate behavioural response. However, this was not the case for habitat selection, where translocated individuals preferred deep, slowflowing habitats more common in their source population’s lacustrine environment. Despite providing considerable benefits to society, dams and weirs threaten riverine ecosystems by disrupting movements of aquatic animals and altering and fragmenting riverine habitats. Chapter 5 examined the effects of a low-head weir on fine- and broad-scale movements, habitat use, and breeding behaviour of three species of native freshwater fish over a four-month period in the Nymboida River in coastal eastern Australia. Eastern freshwater cod (Maccullochella ikei) and freshwater catfish exhibited few broad-scale movements, but Australian bass (Percalates novemaculeata) upstream of the weir were significantly more mobile than those below the weir. No individuals of any species crossed the weir during the study period and freshwater catfish nesting behaviour varied greatly above and below the weir, with those in the impounded area above the weir occupying lower quality nesting sites. Although the effects of the weir may have been further reaching for Australian bass linear movement, possibly impeding migration and routine movements of the longer ranging species. Broad-scale movements were quantified in Chapter 4 in order to assess the movements of fish under a regulated flow regime and the behavioural response of fish to environmental flow releases. The movements of freshwater catfish and Murray cod were recorded for two years in the Gwydir and Mehi Rivers. The flow regimes of these connected distributary rivers are highly altered by regulation and extraction, but both receive environmental flows. Environmental flow releases increased the likelihood of fish movement for both species, particularly during the spawning season, or when temperatures were lowest at the beginning of the environmental watering season immediately following winter. There was also a notable difference between rivers in the effect of flow on the likelihood of movement for both species. To quantify fish movements and their responses to environmental variation under a natural flow regime, Chapter 6 used broad-scale acoustic telemetry to track the movements of eastern freshwater cod and freshwater catfish in the unregulated Nymboida River for two years. Over this period both species exhibited limited movement, being of both short distances and low frequency. Although eastern freshwater cod movements showed little relationship with environmental variation, freshwater catfish were found to use rising limb and peak of the hydrograph to move and showed an increased likelihood of movement in the breeding season. Comparisons between freshwater catfish in the Nymboida and Gwydir Rivers, and Murray cod in the Gwydir River system and eastern freshwater cod in the Nymboida River, show that fish movement behaviours can vary within a species, or genus, among flow regimes and among rivers. The combined findings of this thesis present new knowledge to multiple facets of riverine fish movement ecology and the management of rivers. Both fine- and broadscale studies support that the process of translocation does not influence the movement behaviours of fish, however the suitability of habitat at a release site may have implications for the success and persistence of translocated populations. The thesis also found that small instream barriers not only act as a physical and ecological barrier to large-scale breeding migrations, but also to regular small-scale movements and non-migratory breeding behaviours. Several key findings of this thesis can help to refine the environmental flow requirements of fish species in Australian rivers. The shorter and less frequent movements, and lack of pronounced relationship with flow, exhibited by fish in the unregulated Nymboida River compared to the more mobile fish in the regulated Gwydir River system, suggests that characteristics of flow regime variability and alteration are key determinants of intra- and interspecific variation in movement behaviours of fish. Fish in the regulated rivers showing increased movement during elevated river discharge and environmental flow release periods suggests that environmental flows may benefit non-migratory species by facilitating rather than cueing breeding or other movements, allowing individuals improved connectivity to, and inundation of, higher quality nesting habitats. These conclusions suggest that environmental flows targeting non-migratory species should be used to increase baseflows and connectivity, rather than using larger flow pulses, such as those aimed at stimulating movement of migratory species.