Oral Presentation Australian Freshwater Sciences Society Conference 2018

Take the long way home: minimal medium-term recovery in a large freshwater crayfish impacted by significant population loss (#72)

Sylvia Zukowski 1 , Nick Whiterod 1 , Marty Asmus 2
  1. Aquasave - Nature Glenelg Trust, Goolwa Beach, SA, Australia
  2. NSW Department of Primary Industries, NSW

Extreme disturbance can cause catastrophic mortality, population collapse and localised extinction in animal species. The ability of species to resist and recover from such disturbance is paramount to the persistent of populations thus regulating species distribution and diversity. This presentation provides assess of the recovery of the slow-growing, long-lived and recreationally harvested freshwater crayfish, the Murray Crayfish Euastacus armatus following significant population loss imposed by an extreme hypoxic blackwater disturbance in the Murray River over 2010−11. Specifically, before-after-control-impact monitoring, which accounted for imperfect and variable detection, was employed to document key population parameters (abundance, sex ratio and length structure) at affected and non-affected sites over 3−7 years following the hypoxic blackwater. A stochastic population model was also utilised to simulate longer term trajectories of recovery under a range of management scenarios. The study revealed minimal recovery with no significant improvement in occupancy or abundance and the continued truncation of length structures across the affected populations. Modelling simulations reinforce these findings with lengthy recovery trajectories (e.g. 50 years to reach pre-disturbance population sizes) forecast under natural recovery scenarios and any scenario involving harvest pressure predicted to delay this recovery timeframe. The findings emphasise the need to acknowledge realistic recovery timeframes for K-selected species impacted by extreme disturbance. It is now a critical time for concerted conservation and fisheries management to facilitate the recovery of the species across its range.