Effects of flow regulation on carp (Cyprinus carpio L.) recruitment in the Murray–Darling Basin, Australia

Abstract

Carp biomass density and the numbers of 'sub-adult' (juvenile, plus young-of-the-year) carp were used to indicate net recruitment (hereafter 'recruitment') to carp populations in 'regulated' and 'unregulated' lowland rivers (<300 m altitude) and 'slope' rivers (300-700 m) of the Murray-Darling Basin, southeastern Australia. Most recruitment occurred at lower-altitude reaches, during October-March (water temperature 95% confidence limits ¼ 16-32 C). Temporal changes in distribution of juvenile carp and sub-adult carp, and high biomass density and slightly larger carp sizes in slope populations, indicated that slope sites were 'sinks' for downstream 'source' populations. The distribution of sub-adult carp also suggested that recruitment differed between regulated and unregulated lowland sites, and unregulated sites had proportionately more sub-adult carp in the total catch. We suggest that while floods might have enhanced recruitment in unregulated rivers, flow regulation provides long-term refuge from mortality associated with high flows.

Small environmental flows, drought and the role of refugia for freshwater fish in the Macquarie Marshes, arid Australia

“…This ratio is much higher than the 0Ð71 : 1 and 0Ð82 : 1 reported for main-channel habitats by the SRA (Davies et al, 2008) and NSW DPI (unpublished data), respectively. However, these results are consistent with findings from other carp recruitment hotspots in the Murray-Darling Basin, such as the Great Cumbung Swamp on the lower Lachlan River and Barmah-Millewa Forest on the Murray River where European carp outnumber native fish ¾4 : 1 (Driver et al, 2005). These large, low-relief wetlands with shallow, relatively warm semi-permanent water and dense aquatic vegetation (e.g., Phragmites, Carex and Paspalum distichum) provide ideal spawning and nursery habitats for alien species (Driver et al, 2005), unlike habitats in upland areas (Gilligan and Rayner, 2007).…”

“…However, these results are consistent with findings from other carp recruitment hotspots in the Murray-Darling Basin, such as the Great Cumbung Swamp on the lower Lachlan River and Barmah-Millewa Forest on the Murray River where European carp outnumber native fish ¾4 : 1 (Driver et al, 2005). These large, low-relief wetlands with shallow, relatively warm semi-permanent water and dense aquatic vegetation (e.g., Phragmites, Carex and Paspalum distichum) provide ideal spawning and nursery habitats for alien species (Driver et al, 2005), unlike habitats in upland areas (Gilligan and Rayner, 2007). Freshwater fish in arid-zone rivers depend largely on low-flow refugia during dry periods (Arthington et al, 2005;Balcombe et al, 2006).…”

Coping with hydrogeomorphic variations in a prairie river: resiliency in young‐of‐the‐year fishes

“…demonstrated that the riverscape of the Kansas River provides various habitats with sufficient food resources and the physical parameters necessary for YOY growth and survival. Discharge and current velocities have been hypothesized to be the major mechanism limiting YOY distribution among rivers in general and among habitats in a given river (Turner et al, 1994;Humphries et al, 2002;Driver et al, 2005;Pease et al, 2006). Flowing water influences many factors in a fish life including habitat and food availability, energy demand to maintain or change position, suitable sites for spawning and YOY development, abrasion and gill fouling (e.g.…”

When trends intersect: The challenge of protecting freshwater ecosystems under multiple land use and hydrological intensification scenarios

“…Regulation of river flows, initially for navigation but ultimately to provide water for intensive irrigation, provides a refuge for carp in regulated rivers during low flow periods (Driver et al, 2005a) and has drowned seasonal, floodplain lakes, killed river red gum forests in near-channel areas while expanding suitable habitat for emergent species such as Typha (Gell, 2012) and the floating fern, Azolla. The uneven spatial distribution and extreme temporal variability of surface and groundwater supplies in Australia have led to the construction of a multitude of water regulation structures, including many thousands of weirs (3600 in the Murray-Darling Basin alone), locks and floodplain levee banks, 446 large dams (N 10 m crest height) and over 50 intra-and inter-basin water transfer schemes.…”