River regulation and fish communities in the Murray‐Darling river system, Australia

Abstract

Fish communities from four catchments in the Murray-Darling river system were analysed in relation to climate, hydrology and river regulation. Using the annual proportional flow deviation as a measure of river regulation, the Paroo River catchment was assessed as unregulated, the Darling River catchment as mildly regulated and the Murrumbidgee River and River Murray catchments as highly regulated. A total of 11 010 fish, representing nine native and three alien species, was caught during high and low flow seasons in the four catchments. Native species, such as golden perch Macquuriu ambigua (Percichthyidae), bony herring Nematalosa erebi (Clupeidae) and spangled perch Leiopotherapon unicolor (Teraponidae), dominated fish communities in the Paroo and Darling catchments, but alien species, mostly carp, Cyprinus carpio (Cyprinidae), were also abundant. Both native and alien species were more abundant in these catchments after flooding, but there was little change in species composition between high and low flow seasons at the catchment level. Carp dominated communities in the Murray and Murrumbidgee catchments. There was a significant trend for reduced species diversity in increasingly regulated catchments. River regulation may alter the relative abundance of native and alien fish by desynchronizing environmental cycles and the reproductive cycles of native species. Ordination of species abundances showed discrete fish communities that reflect the geographical separation between catchments. Differences between communities are related to opportunities for dispersal, the environmental tolerances of dominant species and the modifying effects of river regulation. Fish communities in lakes exhibited less seasonal variation than riverine communities within the same catchment, indicating the greater seasonal stability of lakes compared with regulated and unregulated river reaches. Management of fish resources needs to include catchment-specific strategies within current State and basin-wide management programmes.

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

“…While there are no major diversion weirs or water storages on these rivers, there are many low-level weirs that currently impose the largest threat to fish migration and breeding patterns in the region (Table 2). The fish of these rivers are mostly ecological generalists, adapted to cope with the highly variable flows of these rivers (Gehrke et al 1995;Balcombe et al , 2011. It is unlikely that climate change will substantially change these fish assemblages, given the ability of the species to cope with extremes of climate.…”

“…Generalist species such as eel-tailed catfish, yellowbelly and bony bream may increase in abundance in response to declines in Murray cod. Balanced against this is the potential expansion of the distributions of exotic fish, particularly of common carp and gambusia, which are established and significant competitors for food resources in these rivers (Gehrke et al 1995;Balcombe et al 2011). The combined effects of reduced flows and reduced connectivity from development will also have an impact on species, including carp gudgeons, MurrayDarling rainbowfish and un-specked hardyheads, that use more marginal waterbodies such as anabranches and billabongs (Lintermans 2007).…”

Abundance and spatial variability of invasive fishes related to environmental factors in a eutrophic Yunnan Plateau lake, Lake Dianchi, southwestern China

“…Introduced freshwater fishes, in particular, have commonly been documented to thrive in degraded aquatic environments in many areas of the world (e.g. Leidy and Fiedler 1985;Gehrke et al 1995;Brown 2000;Meador et al 2003). Generally, key attributes of invasive fish successfully thriving in degraded environments include broad physiological tolerances, generalist resource requirements, and a variety of life history traits enabling them to persist where many native species could not (Kolar and Lodge 2002;García-Berthou 2007;Gozlan et al 2010).…”