Dry season habitat use of fishes in an Australian tropical river

Abstract

The modification of river flow regimes poses a significant threat to the world’s freshwater ecosystems. Northern Australia’s freshwater resources, particularly dry season river flows, are being increasingly modified to support human development, potentially threatening aquatic ecosystems and biodiversity, including fish. More information is urgently needed on the ecology of fishes in this region, including their habitat requirements, to support water policy and management to ensure future sustainable development. This study used electrofishing and habitat survey methods to quantify the dry season habitat use of 20 common freshwater fish taxa in the Daly River in Australia’s wet-dry tropics. Of twenty measured habitat variables, water depth and velocity were the two most important factors discriminating fish habitat use for the majority of taxa. Four distinct fish habitat guilds were identified, largely classified according to depth, velocity and structural complexity. Ontogenetic shifts in habitat use were also observed in three species. This study highlights the need to maintain dry season river flows that support a diversity of riverine mesohabitats for freshwater fishes. In particular, shallow fast-flowing areas provided critical nursery and refuge habitats for some species, but are vulnerable to water level reductions due to water extraction. By highlighting the importance of a diversity of habitats for fishes, this study assists water managers in future decision making on the ecological risks of water extractions from tropical rivers, and especially the need to maintain dry season low flows to protect the habitats of native fish.

Use of radiotelemetry to quantify diel habitat preferences and minimum environmental flow requirements of a tropical riverine fish (Sooty grunter Hephaestus fuliginosus)

“…The results of the current study demonstrate that juvenile Sooty grunter exhibit a strong preference for shallow, fast flowing hydraulic habitat during the dry season. These findings are broadly compatible with those of previous studies by Chan et al (2012) and Keller et al (2019), who both concluded that they prefer shallow, fast flowing riffle areas and that preservation of riffles during the dry season is critical to the viability of Sooty grunter populations. However, while Chan et al (2012) emphasised the importance of riffle habitat for juvenile Sooty grunter, their analyses suggested optimal velocities of 0–0.6 m s −1 and depths of 0.3–0.6 m (Table 4).…”

“…A particular concern for water management is that the availability of shallow, fast flowing habitat may be reduced due to increased groundwater abstraction in the dry season, a period when river flows are at their lowest and water abstraction is likely to have its greatest effects (King et al, 2015). Although previous research suggests that juvenile Sooty grunter exhibit a strong preference for shallow, fast flowing habitat during dry season, low‐flow periods (Chan et al, 2012; Keller et al, 2019), these studies have several potential limitations, in that they (1) did not consider diel variation in habitat use (see Davey et al, 2011), (2) developed habitat suitability curves using data from different electrofishing methods (backpack in riffles, boat‐mounted in other habitats) and (3) estimated habitat preference using fish abundance and habitat data that were not spatially matched. The fish abundance data were catch‐per‐unit effort (CPUE) calculated over 5‐min electrofishing ‘shots’ covering an average river length of 77 m (range: 5–263 m), with five replicate measures of depth and velocity taken within each sampled reach (Chan et al, 2012; Keller et al, 2019).…”

“…Although previous research suggests that juvenile Sooty grunter exhibit a strong preference for shallow, fast flowing habitat during dry season, low‐flow periods (Chan et al, 2012; Keller et al, 2019), these studies have several potential limitations, in that they (1) did not consider diel variation in habitat use (see Davey et al, 2011), (2) developed habitat suitability curves using data from different electrofishing methods (backpack in riffles, boat‐mounted in other habitats) and (3) estimated habitat preference using fish abundance and habitat data that were not spatially matched. The fish abundance data were catch‐per‐unit effort (CPUE) calculated over 5‐min electrofishing ‘shots’ covering an average river length of 77 m (range: 5–263 m), with five replicate measures of depth and velocity taken within each sampled reach (Chan et al, 2012; Keller et al, 2019). Chan et al (2012) used this reach scale data to generate habitat suitability curves and then made inferences about hydraulic habitat preference at the microhabitat scale, while Keller et al (2019) analysed 10 years of reach scale data using boosted regression tree modelling to quantify the habitat use of abundant fish species in the Daly River.…”

“…Sooty grunter predominantly inhabit permanent river reaches, large intermittent streams and floodplain wetlands (Pusey et al, 2020). In the wet–dry tropics, males mature at ~200 mm fork length (FL), and females at 250–320 mm FL (Pusey et al, 2004), and they appear to undertake a ontogenetic habitat shift, with small fish utilising shallow, fast flowing habitats and larger fish preferring deep, slow‐flowing pools (Chan et al, 2012; Keller et al, 2019; Pusey et al, 2004).…”

“…The fish abundance data were catch‐per‐unit effort (CPUE) calculated over 5‐min electrofishing ‘shots’ covering an average river length of 77 m (range: 5–263 m), with five replicate measures of depth and velocity taken within each sampled reach (Chan et al, 2012; Keller et al, 2019). Chan et al (2012) used this reach scale data to generate habitat suitability curves and then made inferences about hydraulic habitat preference at the microhabitat scale, while Keller et al (2019) analysed 10 years of reach scale data using boosted regression tree modelling to quantify the habitat use of abundant fish species in the Daly River.…”