Water levels in a highland lake control the quantity and quality of spawning habitat for a littoral‐spawning galaxiid fish

Abstract

Abstract In comparison with other habitats, the littoral zone can be disproportionately important to lentic fishes, especially for species that rely on it for reproduction. Impoundment of lentic waters can alter hydrological regimes, littoral inundation patterns and hydrodynamic processes, which can affect the quantity and quality of littoral habitats. This study examined the effects of water‐level fluctuations on the quantity and quality of rocky littoral spawning habitat for the threatened Galaxias auratus in the Crescent–Sorell lake system, Tasmania (Australia) using GIS analyses, sediment measurements and observations of the composition and condition of littoral substrates under varying hydrological conditions. The extent of littoral rocky substrate was found to be limited in Lake Crescent (<1.3% of the lake's bed). The relationship between water levels and G. auratus spawning habitat (littoral rocky substrates at depths of 0.2–0.6 m) was non‐linear with spawning habitat quantity and quality declining markedly at water levels <802.20 m Australian Height Datum (AHD). Hydrological impacts of global climate change on the Crescent–Sorell lake system are likely to increase the occurrence of water levels below this threshold in Lake Crescent in the future, thereby limiting the ability of G. auratus to sustain its population in this lake. The structure of littoral areas of rocky substrate in Lake Crescent and Lake Sorell, and influential processes acting on these areas under varying hydrological conditions, were conceptualized to assist transferability of this knowledge to other lentic waters and species with similar habitat requirements. Global climate change is predicted to alter lacustrine hydrological regimes and shoreline environments. This is likely to have significant ramifications for fishes that use littoral habitats during their life cycles, especially crucial reproductive phases. We believe the influence of alterations to hydrological regimes on the availability of these habitats to lacustrine fishes requires further investigation globally. Copyright © 2016 John Wiley & Sons, Ltd.