Constraints upon the Response of Fish and Crayfish to Environmental Flow Releases in a Regulated Headwater Stream Network

Abstract

In dry climate zones, headwater streams are often regulated for water extraction causing intermittency in perennial streams and prolonged drying in intermittent streams. Regulation thereby reduces aquatic habitat downstream of weirs that also form barriers to migration by stream fauna. Environmental flow releases may restore streamflow in rivers, but are rarely applied to headwaters. We sampled fish and crayfish in four regulated headwater streams before and after the release of summer-autumn environmental flows, and in four nearby unregulated streams, to determine whether their abundances increased in response to flow releases. Historical data of fish and crayfish occurrence spanning a 30 year period was compared with contemporary data (electrofishing surveys, Victoria Range, Australia; summer 2008 to summer 2010) to assess the longer–term effects of regulation and drought. Although fish were recorded in regulated streams before 1996, they were not recorded in the present study upstream or downstream of weirs despite recent flow releases. Crayfish (Geocharax sp. nov. 1) remained in the regulated streams throughout the study, but did not become more abundant in response to flow releases. In contrast, native fish (Gadopsis marmoratus, Galaxias oliros, Galaxias maculatus) and crayfish remained present in unregulated streams, despite prolonged drought conditions during 2006–2010, and the assemblages of each of these streams remained essentially unchanged over the 30 year period. Flow release volumes may have been too small or have operated for an insufficient time to allow fish to recolonise regulated streams. Barriers to dispersal may also be preventing recolonisation. Indefinite continuation of annual flow releases, that prevent the unnatural cessation of flow caused by weirs, may eventually facilitate upstream movement of fish and crayfish in regulated channels; but other human–made dispersal barriers downstream need to be identified and ameliorated, to allow native fish to fulfil their life cycles in these headwater streams.

High air humidity is sufficient for successful egg incubation and early post‐embryonic development in the marbled crayfish (Procambarus virginalis)

“…Considering that our trials utilised marbled crayfish females with attached and developing eggs, we believe that our findings are valid also for sexually reproducing species, thus covering both modes of reproduction. Our findings suggests that successful ontogeny under drought‐like conditions for this species is primarily related to the tolerance of crayfish eggs to periods without free water, which is well in line with adaptations of other drought‐tolerant species, such as construction of special aestivation burrows (Chester & Robson, ; Chester et al., ), burrow commensalism with other crayfish (Johnston & Robson, ), and digging deeper burrows to the water‐level during dry seasons (Horwitz et al., ; Riek, ). The tolerance to drought using various traits is probably crucial for inhabiting ecosystems with high water level fluctuations in freshwater crayfish.…”

Drought survival strategies, dispersal potential and persistence of invertebrate species in an intermittent stream landscape

“…). Despite their small size, six of the streams are regulated by weirs for town water supply, reducing flows and often resulting in downstream reaches being completely dry over hundreds to thousands of metres (Mackie et al ., ), with impacts sufficient to cause the local extinction of some species (Chester et al ., ).…”

Impacts of extreme events on southeastern Australian freshwater crayfish

“…This process might increase fire impacts on crayfish aestivating in dry streambeds. The GNP region contains numerous water extraction points and reservoirs that alter stream flow regimes causing substantial negative impacts on algae, fish and invertebrates (e.g., Robson and Mitchell 2010;Chester et al 2014). Many of these impacts are associated with recolonization and movement processes of the biota, because weirs used for water extraction act as barriers to movement both directly and by creating sections of dry streambed immediately downstream (Mackie et al 2012;Chester et al 2014).…”

“…The GNP region contains numerous water extraction points and reservoirs that alter stream flow regimes causing substantial negative impacts on algae, fish and invertebrates (e.g., Robson and Mitchell 2010;Chester et al 2014). Many of these impacts are associated with recolonization and movement processes of the biota, because weirs used for water extraction act as barriers to movement both directly and by creating sections of dry streambed immediately downstream (Mackie et al 2012;Chester et al 2014). Although another GNP study (at a different group of streams) showed that another species of Geocharax was resilient to drought and flow regulation (Chester et al 2014), this resilience was founded on the ability of this species to rapidly build aestivation chambers in stony streambeds.…”

“…Many of these impacts are associated with recolonization and movement processes of the biota, because weirs used for water extraction act as barriers to movement both directly and by creating sections of dry streambed immediately downstream (Mackie et al 2012;Chester et al 2014). Although another GNP study (at a different group of streams) showed that another species of Geocharax was resilient to drought and flow regulation (Chester et al 2014), this resilience was founded on the ability of this species to rapidly build aestivation chambers in stony streambeds. The species of crayfish found in the present study do not share this ability, and channeldwelling species such as E. bispinosus might not be equally able to both resist drying and recolonise locations after disturbance when their movement is blocked by weirs.…”