Considerable technical developments over the past half century have enabled widespread application of electronic tags to the study of animals in the wild, including in freshwater environments. We review the constraints associated with freshwater telemetry and biologging and the technical developments relevant to their use. Technical constraints for tracking animals are often influenced by the characteristics of the animals being studied and the environment they inhabit. Collectively, they influence which and how technologies can be used and their relative effectiveness. Although radio telemetry has historically been the most commonly used technology in freshwater, passive integrated transponder (PIT) technology, acoustic telemetry and biologgers are becoming more popular. Most telemetry studies have focused on fish, although an increasing number have focused on other taxa, such as turtles, crustaceans and molluscs. Key technical developments for freshwater systems include: miniaturization of tags for tracking small-size life stages and species, fixed stations and coded tags for tracking large samples of animals over long distances and large temporal scales, inexpensive PIT systems that enable mass tagging to yield population-and community-level relevant sample sizes, incorporation of sensors into electronic tags, validation of tag attachment procedures with a focus on maintaining animal welfare, incorporation of different techniques (for example, genetics, stable isotopes) and peripheral technologies (for example, geographic information systems, hydroacoustics), development of novel analytical techniques, and extensive international collaboration. Innovations are still needed in tag miniaturization, data analysis and visualization, and in tracking animals over larger spatial scales (for example, pelagic areas of lakes) and in challenging environments (for example, large dynamic floodplain systems, under ice). There seems to be a particular need for adapting various global positioning system and satellite tagging approaches to freshwater. Electronic tagging provides a mechanism to collect detailed information from imperilled animals and species that have no direct economic value. Current and future advances will continue to improve our knowledge of the natural history of aquatic animals and ecological processes in freshwater ecosystems while facilitating evidence-based resource management and conservation.

Globally, freshwater fishes are declining at an alarming rate. Despite much evidence of catastrophic declines, few Australian species are listed as threatened under national legislation. We aim to help redress this by identifying the Australian freshwater fishes that are in the most immediate risk of extinction. For 22 freshwater fishes (identified as highly threatened by experts), we used structured expert elicitation to estimate the probability of extinction in the next ~20 years, and to identify key threats and priority management needs. All but one of the 22 species are small (<150mm total length), 12 have been formally described only in the last decade, with seven awaiting description. Over 90% of these species were assessed to have a >50% probability of extinction in the next ~20 years. Collectively, the biggest factor contributing to the likelihood of extinction of the freshwater fishes considered is that they occur in small (distributions ≤44km2), geographically isolated populations, and are threatened by a mix of processes (particularly alien fishes and climate change). Nineteen of these species are unlisted on national legislation, so legislative drivers for recovery actions are largely absent. Research has provided strong direction on how to manage ~35% of known threats to the species considered, and, of these, ~36% of threats have some management underway (although virtually none are at the stage where intervention is no longer required). Increased resourcing, management intervention and social attitudinal change is urgently needed to avert the impending extinction of Australia’s most imperilled freshwater fishes.

Barriers to migration are a major threat to freshwater fish populations. A novel measurement of swimming speed performance and an analytical model were used to calculate the probability that endangered Macquarie perch, Macquaria australasica Cuvier, can swim through instream structures. Over the range of river discharges (2.7-166 ML day )1 ) and temperatures (10-22°C) examined, M. australasica could successfully pass through a rock-ramp fishway and nearby natural riffles under most river discharges, whilst pipe culverts were passable only to large individuals (>17.7 cm total length) under a high river discharge. Cold water temperatures (below 16°C) significantly reduced the likelihood of passage in each case. It was concluded that both the volume and thermal characteristics of environmental flow releases should be considered when assessing and remediating potential instream barriers to fish passage in regulated river systems.