43 4 Natural flows drive the ‘boom and bust’ ecology of fish in Cooper Creek, an arid-zone floodplain river Angela H. Arthington and Stephen R. Balcombe Introduction Why is the Lake Eyre Basin so special and why should we care so much about the future of its rivers and floodplain wetlands? It covers an area of more than 1 million km2, about one- seventh of Australia (Habeck-Fardy and Nanson 2014), and is one of the world’s largest internally draining river basins, meaning its waters never reach the sea. In Cooper Creek, one of the main catchments of the basin, most stream flow is generated by summer monsoon rainfall in the headwaters of the Thomson and Barcoo Rivers and by periodic local rainfall (see Chapter 1). Episodic floods can inundate tens of thousands of square kilometres of floodplain, and reconnect channels, anabranches, and isolated channel and floodplain waterholes (Fig. 4.1), turning a fragmented river network into a mighty floodplain river, occasionally helping to fill Kati Thanda-Lake Eyre, the largest lake in Australia. Lake Eyre Basin catchments have very high conservation values high endemic biodiversity, Ramsar wetland listings, range-restricted species (e.g. the Cooper Creek catfish), relatively few alien fish species (i.e. species foreign to Australia) and few translocated species (see Chapter 3). Rivers and floodplain wetlands of the basin are in very good ecological condition relative to most of the world’s large developed river basins, and especially compared to the Murray–Darling Basin. Cooper Creek is a largely undeveloped catchment with a near natural and very erratic flow regime (Puckridge et al. 1998 see Chapter 2). Aquatic habitats exist for most of the time as isolated waterholes, connected occasionally by channel flows and large overland floods (Fig. 4.1). Rivers of the Channel Country, especially Cooper Creek, have been studied as model arid-zone floodplain systems for understanding the ‘boom and bust’ ecology of fish and other biota. This chapter demonstrates the importance of flow variability and the boom and bust cycle to fish, and outlines threats associated with changing the natural flow regime, concluding with scientific principles for the conservation and wise use of arid-zone rivers. Cooper Creek fish Twelve native fish species in eight families, two translocated species (Murray cod, Maccullochella peelii, and sleepy cod, Oxyeleotris lineolata) and two alien species (goldfish and mosquitofish) are known from the Cooper Creek catchment (Table 4.1). Both alien species and Murray cod are relatively rare in Cooper Creek, but the sleepy cod is becoming
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