Hydrological manipulation to assist spawning of a threatened galaxiid fish in a highland lake system

Abstract

Hydrological alterations threaten freshwater fishes globally, with infrastructure-related modification of inland waterways (e.g. dams, water diversions) having profound impacts on many species. Adapting existing water-management systems can provide opportunities for undertaking hydrological manipulations to assist management of threatened fishes. The present study conducted two hydrological manipulations in an impounded highland lake system in Tasmania, Australia, under differing hydrological conditions in 2007 and 2009, to assist recovery of an endemic species, Galaxias auratus, following a prolonged drought. Monitoring at egg, larvae, juvenile and adult life stages revealed a positive response by G. auratus in Lake Crescent (recipient of water release), with no adverse impact on the species in Lake Sorell (source of water release). In both years, reproductive constraints imposed by water level-related availability of sediment-free rocky substrata delayed spawning (~1 month) of G. auratus in Lake Crescent. Despite this, spawning and recruitment occurred in 2007 (drought year) and 2009 (drought-breaking year), and the 2007 manipulation resulted in a two-fold increase in the seasonal density of larvae in Lake Crescent and an abundant cohort of YOY fish. Given knowledge of life histories and eco-hydrological relationships, manipulating (or re-instating) hydrologic conditions is a powerful tool for assisting recovery of threatened lacustrine fishes.