Distribution patterns and habitat associations of Sandelia bainsii (Teleostei: Anabantidae), a highly threatened narrow-range endemic freshwater fish

Sandelia bainsii is a range-restricted and highly threatened freshwater fish endemic to South Africa. Recent genetic evidence suggests that this species comprises three allopatrically distributed lineages that have been informally designated as Sandelia sp. "Kowie," Sandelia sp. "Keiskamma" and Sandelia sp. "Buffalo." As these lineages have only been recently identified and are likely to face a high risk of extinction because of restricted distributions, there is a critical need for generating ecological information to guide conservation prioritisation. The present study compared the historical and current distribution patterns, together with the habitat associations of Sandelia sp. "Kowie" in the Koonap and Kat rivers, tributaries of the Great Fish River. This study indicated that this lineage has been extirpated from one of the three localities in the Koonap River where it was historically abundant. In the Kat River, the current distribution of Sandelia sp. "Kowie" was comparable to its historical range, but its future persistence is threatened by the presence of non-native piscivores, instream physical barriers and potential future exploration for shale gas and infrastructure development in the Karoo Basin. A generalised hurdle negative binomial model revealed that although this lineage's probability of occurrence was high in habitats with boulder and sand substrates, and low conductivity, habitat characteristics were poor predictors of its abundance. Thus, it was postulated that the current range of this lineage probably represents the only available habitats for the persistence of different life stages for this taxon. Alternatively, the observed patterns may suggest the possibility of a shift in habitat associations, possibly for optimum utilisation of the remaining refugia within this river system. Immediate conservation measures should focus on preventing the spread on non-native invasive fishes, whereas future studies should evaluate the impacts of population fragmentation and identify appropriate intervention measures to maintain this lineage's long-term adaptive potential.

Effects of a low-head weir on multi-scaled movement and behavior of three riverine fish species

Despite providing considerable benefits to society, dams and weirs threaten riverine ecosystems by disrupting movement and migration of aquatic animals and degrading riverine habitats. Whilst the ecological impacts of large dams are well studied, the ecological effects of low-head weirs that are periodically drowned out by high flows are less well-understood. Here we examine 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 in the Nymboida River in coastal eastern Australia. Acoustic telemetry revealed that eastern freshwater cod (Maccullochella ikei) and eel-tailed catfish (Tandanus tandanus) made few large-scale movements, but Australian bass (Percalates novemaculeata) upstream of the weir were significantly more mobile than those below the weir. Within the weir pool, all three species displayed distinctive patterns in fine-scale movement behaviour that were likely related the deeper lentic environment created by the weir. No individuals of any species crossed the weir during the study period. Tandanus tandanus nesting behaviour varied greatly above and below the weir, where individuals in the more lentic upstream environment nested in potentially sub-optimal habitats. Our results demonstrate the potential effects of low-head weirs on movement and behaviour of freshwater fishes.

Abiotic drivers of activity in a large, free-ranging, freshwater teleost, Murray cod (Maccullochella peelii)

The allocation of time and energy to different behaviours can impact survival and fitness, and ultimately influence population dynamics. Intrinsically, the rate at which animals expend energy is a key component in understanding how they interact with surrounding environments. Activity, derived through locomotion and basic metabolism, represents the principal energy cost for most animals, although it is rarely quantified in the field. We examined some abiotic drivers of variability in locomotor activity of a free-ranging freshwater predatory fish, Murray cod (Maccullochella peelii), for six months using tri-axial accelerometers. Murray cod (n = 20) occupied discrete river reaches and generally exhibited small-scale movements (<5 km). Activity was highest during crepuscular and nocturnal periods when water temperatures were warmest (19-30°C; January-March). As water temperatures cooled (9-21°C; April-June) Murray cod were active throughout the full diel cycle and dormant periods were rarely observed. Light level, water temperature and river discharge all had a significant, non-linear effect on activity. Activity peaked during low light levels, at water temperatures of ~20°C, and at discharge rates of ~400 ML d-1. The temporal changes observed in the behaviour of Murray cod likely reflect the complex interactions between physiological requirements and prey resource behaviour and availability in driving activity, and highlight the importance of empirical field data to inform bioenergetics models.