Distribution of large woody debris in the mid-reaches of the Murray River

Removal of large woody debris (LWD) or snags was a common activity in many lowland rivers in southeastern Australia until recent times (Treadwell et al. 1999). Many native fish species in these waters are reliant upon snags and snag piles (aggregations of snags) for habitat, including Murray Cod, Golden Perch and the critically endangered Trout Cod (Koehn & Nicol 1998). Several investigations have identified the importance of snags in forming and providing fish habitats for foraging, predator avoidance, velocity refuge, and habitat landmarks (see review by Crook & Robertson 1999). To improve the habitat available to native fish, responsible agencies are now returning snags (LWRRDC 2000) to these rivers and management guidelines have recently been published to assist resnagging operations (Treadwell 1999). While these guidelines recommend reintroduction of snags as fish habitat, our understanding of the interaction between fish and snag piles is lacking. Information is required on the various configurations of instream snag piles and fish responses to them so that any reconstruction efforts produce the optimal snag habitat necessary to attract and retain the desired species