Australian dryland rivers undergo long periods of no flow punctuated by often short-duration flow events. The persistence of resident biota is dependent on the twin processes of drought resistance and resilience; they must survive drought and then repopulate depleted reaches when flow returns. Waterholes form as deepened sections of channel which retain water during drought while much of the channel network dries. They confer drought resistance to species that lack resistance traits, acting as drought refuges essential to the persistence of many aquatic species, especially fish. Fishes move away from refuge waterholes during flow events and for many species, spawning and recruitment success is associated with flow. Movement and recruitment allow repopulation of drought depleted reaches. Flow events that permit fish movement are often short lived and barriers such as dams and weirs impede fish movement. Even small structures dramatically reduce movement opportunities as a consequence of dryland river hydrology.
We investigated the effects of drought refuge availability and movement opportunity on the recovery of fish populations in the Queensland Murray-Darling Basin following one of the region’s most severe recorded droughts.
Results showed that post-drought abundances of fishes, at river segment scales, were significantly determined by remote sensed peak-drought waterhole area, confirming the critical role of waterholes as refugia. Movement opportunity, defined by the interaction of flow and barrier drown-out characteristics, was less influential. Large-scale movement of individual fish, derived from otolith microchemistry assessed against environmental strontium isotope variability, was less prevalent than expected. In combination these results highlight the importance of local processes in regional recovery of fish populations following drought.
Ongoing research is further refining understanding of processes of fish drought resistance and resilience in dryland rivers. This is essential to their management given forecasts of increasing drought frequency, duration, and extent under climate change.