Oral Presentation Australian Society for Limnology Congress 2013

Long-term patterns in spawning and early life history of Murray cod (#71)

Paul Humphries 1
  1. Charles Sturt University, Albury, NSW, Australia

Despite their diversity in freshwaters globally, fishes have suffered major declines over many decades, mostly because of habitat and flow alteration, introduced species, over-harvesting and pollution. This is as true in Australia as anywhere else in the world. One conspicuous example of such declines, is the Murray cod. Populations of Murray cod are now much lower than when Europeans first settled along our inland rivers. Yet its ‘equilibrium’ life history strategy and predictable spawning period means that, given the right conditions for recruitment, this species can hang on under extremely harsh environmental conditions. I present the results of a 15-year study of the spawning and early life history of Murray cod in the Broken River, northern Victoria. This period spanned the whole of the millennium drought, the decommissioning of Lake Mokoan – a major off-channel storage in the system - and floods in 2010-2012. Murray cod continued to spawn throughout this whole period, very predictably between early November and mid-December, with drifting of larvae peaking in early December. Spawning occurred irrespective of flow conditions, but instead was related to a temperature threshold. Larvae were typically 8-15 days-old when drifting, but differed substantially in developmental stage and the amount of yolk they retained. Growth of larvae varied inter-annually, and was intimately related to temperature patterns in the week prior to capture in the drift. I will speculate on why I think Murray cod has persisted in the Broken River and how it provides hope for the future of this iconic species.