A comparison of temperature regimes in dry-season waterholes in the Flinders and Gilbert catchments in northern Australia

Dry-season waterholes in ephemeral rivers provide vital habitat for aquatic biota, whose survival is dependent on the waterholes lasting throughout the dry season with temperatures that are not lethal. To examine this in the Flinders and Gilbert Rivers, 20-min temperature measurements were taken during the 2012–2013 dry season in 10 waterholes in each catchment. These data were used to derive thermal-frequency curves that quantify how often waterhole temperature exceeds thresholds for (1) the optimum growth of tropical fish and (2) their lethal temperature. Waterholes that remained deeper than ,0.5 m throughout the dry season provided thermally suitable fish refugia, especially if they were turbid, because this decreased the risk of exposure to undesirable temperatures at the bottom of the waterhole. However, surface temperatures in these waterholes often exceeded optimal and even potentially lethal temperatures, so fish may have had to move to cooler water at the bottom of these waterholes. The risk to aquatic species in waterhole refugia is, therefore, primarily determined by depth, with shallow waterholes presenting the greatest risk because they become thermally unsuitable well before (1–2 months) they fully dry out.

Marine and Freshwater Research

Marine and Freshwater Research

68

1448-6059

N/A

4

18