Australian Bass - Migratory Patterns

Migratory Patterns

Australian bass are primarily a freshwater riverine species, but must breed in estuarine waters. Consequently, Australian bass reside in the freshwater reaches of coastal rivers for the warmer half of the year or slightly more and the estuarine reaches in winter, and are highly migratory in general.

A general description of the migratory pattern for adult Australian bass would be:

• September: re-enter lower freshwater reaches after spawning
• October–November: movement through middle freshwater reaches
• December–February: maximum penetration into negotiable upper freshwater reaches
• March–April: slow movement back down through freshwater reaches in anticipation of spawning run
• May: strong spawning run to estuarine reaches
• June–July–August: aggregation and spawning in estuarine reaches

Obviously the timing of these migratory movements varies slightly from the south to the north of their range. The timing of these migratory movements are also dependent on river flows, particularly freshes and floods that drown out and make larger rapids and cascades passable.

Australian bass are found at their highest altitude in the freshwater reaches of rivers during the months of December, January and February. Research indicates there is sexual segregation in this non-spawning season for resource partitioning purposes. Males inhabit the lower freshwater reaches of rivers while females travel far into the middle and upper freshwater (upland) reaches, up to an altitudinal limit of around 600 metres (if there are no natural or man-made obstructions). For instance, Australian bass originally migrated up to the Dalgety region in the Snowy River, well above Oallen Crossing on the Shoalhaven River and far up the Warragamba River and Coxs River before these rivers were dammed.