Trout Cod (Muccullochella macquariensis) in the Murray River, Southeast Australia: Prioritizing Rehabilitation Efforts

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Abstract Trout cod (Muccullochella macquariensis Cuvier) were formerly distributed over a substantial proportion of the Murray-Darling Basin in eastern Australia (Douglas et al. 1994). In the last 50 years they have undergone a dramatic contraction in range and are now classified as critically endangered (Australian Society for Fish Biology 2001). At present only two breeding populations are known: a naturally occurring population in a 200-km reach of the Murray River below Lake Mulwala, and a translocated population in an 8-km reach of Seven Creeks below Polly McQuinns Weir (Richardson and Ingram 1989, Ingram et al. 1990). Alteration or destruction of habitat is widely recognized as a major cause of decline in fish native to Australia (Cadwallader 1978; Koehn and O’Connor 1990a, 1990b; Lintermans 1991). In combination with angling pressure, it is thought to be the primary threat to remaining populations (Douglas et al. 1994). Fish habitat has been degraded in the Murray-Darling Basin by the construction of instream barriers to fish passage, alteration of flow regimes and water extraction, reduction in water quality, loss of floodplain habitat, and the removal of instream physical habitat such as woody debris and pools (Lawrence 1991). Large woody debris from trees that have fallen into a river is an important habitat attribute for many Australian freshwater fish species (Treadwell et al. 1999), including trout cod (Koehn and Nicol 1998). The reach of the Murray River where trout cod still occur is large, deep, and slow flowing; has a sand, silt, and clay substrate; and contains abundant large woody debris (Australian Capitol Territory Government 1999). There has been little removal of large woody debris in this reach (Department of Land and Water Resources, unpublished records) in contrast to areas where trout cod no longer occur (Treadwell et al. 1999).