Take the long way home: Minimal recovery in a K-selected freshwater crayfish impacted by significant population loss

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. The present study assessed the status of a slow-growing, long-lived and recreationally harvested freshwater crayfish, the Murray crayfish Euastacus armatus, which experienced significant population loss imposed by an extreme hypoxic blackwater disturbance in the Murray River in the southern Murray-Darling Basin, Australia. Specifically, before-after-control-impact monitoring, which accounted for imperfect and variable detection, was employed to assess indicators of recovery (occupancy, abundance, sex ratio and length structure) at affected and non-affected sites over 3-5 years following the hypoxic blackwater. A stochastic population model was further utilised as an indicator of longer term trajectories of recovery under a range of management scenarios. The indicators employed in the study suggested minimal recovery as there was no significant improvement in occupancy or abundance and length structures emphasising the continued underrepresentation of juveniles 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.