Response of two-spined blackfish Gadopsis bispinosus to short-term flow fluctuations in an upland Australian stream

Abstract

Environmental flows are applied to regulated rivers, predominantly with the aim of benefiting native fauna. However, the outcomes for biodiversity and the mechanisms that underpin changes due to these manipulations are poorly understood. We examined the effects of elevated water release, of the magnitude used for riffle maintenance, on the movement and habitat use of the locally-threatened two-spined blackfish, Gadopsis bispinosus, in the Cotter River, a regulated upland stream in south-eastern Australia. We compared the behaviour of radio-tagged individuals during baseline flow conditions (0.12 m 3 s -1 ) and during elevated flow releases (1.74 m 3 s -1 ). Eight individuals (196 ± 8 mm TL) were radio-tracked at one site over 22 days, and six individuals (180 ± 5 mm TL) were monitored by fixed telemetry stations at a second site for 1 month. At both the sites, two-spined blackfish were nocturnal and occupied small linear ranges (23 ± 6 m). They preferentially used pools, but also used runs and riffles. Elevated discharge did not significantly affect movement, activity or dispersal of two-spined blackfish. Two individuals utilised inundated vegetation during high flow. Despite a small number of behavioural changes, there was no response to elevated flow at the population level. It is likely that the benthic nature of this species precludes its behaviour being affected by a 15-fold increase in-stream discharge. However, the indirect effects of flows of this magnitude on two-spined

HYDROLOGIC CORRELATES OF BULL TROUT (Salvelinus confluentus) SWIMMING ACTIVITY IN A HYDROPEAKING RIVER

“…A number of other studies have found no effect of short‐term changes in river discharge on fish movement when locating fish at weekly (Cocherell et al ., ), daily (e.g. Broadhurst et al ., ) and subdaily scales (e.g. Heggenes et al ., ).…”

Reach‐scale movements of bull trout (Salvelinus confluentus) relative to hydropeaking operations in the Columbia River, Canada

“…Cocherell et al, 2010), daily (e.g. Broadhurst et al, 2011) and sub-daily scales (e.g. Heggenes et al, 2007).…”

PIT POP! Bursting the bubble on home-range bias with fine-scale PIT telemetry

“…Whether a species undergoes spawning-related movements or migrations will of course influence temporal movement patterns, with homing ability and site fidelity determining longer-term patterns (Koehn and Crook 2013). A combination of behaviours is important in a population for dispersal, resilience to environmental changes and genetic mixing (Broadhurst et al 2011;Davis 2017), and must be considered when developing species management plans. This is especially important when considering conservation strategies for range-restricted threatened species, with small population sizes and potential threats of genetic bottlenecking, if managed incorrectly (Hilderbrand and Kershner 2000;DeHaan et al 2017;Fluker et al 2019).…”