Regional‐scale effects of flow regulation on lowland riverine fish communities in New South Wales, Australia

Abstract

Lowland reaches of 40 rivers in New South Wales, Australia, were designated as 'regulated' or 'unregulated', depending upon the degree to which flows were modified by the operation of a dam upstream. Five replicate rivers of each type were selected from the North Coast, South Coast, Darling and Murray regions in the State. Fish communities in each river were sampled in summer and winter in two consecutive years. Regulated and unregulated rivers contained significantly different fish communities, although communities in each region retained characteristic features. The proportion of native species in the total catch was greater in unregulated rivers in all regions, ranging from 27% in the Murray region to 100% in South Coast rivers. In regulated rivers, native species made up 20% of the catch in the Murray region compared with a maximum of 99% in the North Coast. Carp, Cyprinus carpio, were the main alien species contributing to changes in the proportional abundance of native fish. Native species most affected by river regulation were western carp gudgeons, Hypseleotris spp., bony herring, Nematalosa erebi, and striped gudgeons, Gobiomorphus australis. Fifteen native species showed some effect of river regulation on their population structures. Individual species showed positive, negative or mixed positive and negative, effects of regulation, at population, species or community levels. Three abundant alien species and seven native species showed only positive or mixed responses, whereas 13 native species exhibited only negative effects. Flow regulation has reduced the resilience of New South Wales rivers and native fish communities to invasion by alien species. New research has commenced to investigate whether recently introduced environmental flow rules are effective in reducing the effects of river flow alteration on fish communities in New South Wales rivers.

Australia's Murray - Darling Basin: freshwater ecosystem conservation options in an era of climate change

“…Native fish now make up only 20% of the total catch in regulated rivers in the MDB, as a result of changes in flow regulation disrupting the natural water-regime triggers for fish spawning, thermal pollution and barriers to movement (Gehrke et al 1995;Gehrke and Harris 2001;Growns 2008). The MDB's aquatic biodiversity has also been severely affected by barriers, cutting access to rivers, and flood levees, cutting access to floodplains, with more than 3600 weirs in the MDB that block longitudinal connectivity (Arthington and Pusey 2003).…”

Climate-change threats to native fish in degraded rivers and floodplains of the Murray–Darling Basin, Australia

“…In their assessment of fish species, hydrology and macroinvertebrates, Davies et al (2010) found 20 of the 24 river basins to be in poor or very poor condition. The impacts of flow modifications, including thermal pollution, have been implicated in the demise of native fish in the MDB-regulated rivers, because of their impacts on physiology, spawning and movement (Gehrke and Harris 2001;Growns 2008). Native fish numbers are now only 10% of pre-European levels (MDBC 2004) because of factors such as changes to the natural flow regime, habitat degradation and barriers to biological connectivity (Pratchett et al 2011).…”

Reconstitution de la dynamique du paysage alluvial de trois secteurs fonctionnels de la rivière allier (1946-2000), Massif central, France

“…Depuis les cinquante dernières années, une abondante littérature fait état de ces perturbations anthropiques et des impacts qu'elles ont eu sur l'écocomplexe alluvial en Europe (Pautou, 1984 ;Pautou et al, 1992 ;Décamps, 1993 ;Hughes, 1994 ;Piégay, 1995 ;Bravard et al, 1997 ;Surian, 1999 ;Piégay et al, 2003a ;Steiger et al, 2005), aux États-Unis (Johnson, 1994 ;Gurnell et Gregory, 1995 ;Miller et al, 1995 ;Johnson, 1998 ;Merritt et Cooper, 2000 ;Cooper et al, 2003) et en Australie (Brierley et al, 1999 ;Kingsford, 2000 ;Gehrke et Harris, 2001). Ces impacts anthropiques se traduisent le plus souvent par la suppression de la dynamique naturelle (Peiry, 1997), la simplification de la morphologie du chenal (Sidle et Sharma, 1986 ;Steiger et al, 2000 ;Pisùt, 2002), l'isolement du chenal principal de sa plaine d'inondation par diminution de la largeur du lit (Eschner et al, 1983) et le changement de physionomie de la plaine d'inondation (Johnson et al, 1992 ;Johnson, 1997).…”