Diving behaviour, aquatic respiration and blood respiratory properties: a comparison of hatchling and juvenile Australian turtles

Australia has a number of bimodally respiring freshwater turtle species that use aquatic respiration to extend their aerobic dive limit. While species variations in reliance on aquatic respiration are reflected in the diving behaviour and ecology of adults, it is unknown whether these relationships also occur in hatchling and juvenile turtles. This study compared the diving behaviour, aquatic respiration and blood respiratory properties of hatchling and juveniles from five species of Australian freshwater turtles: Rheodytes leukops , Elusor macrurus , Elseya albagula , Elseya latisternum and Emydura signata . Both diving behaviour and physiology differed significantly between species as well as age classes. Dive duration in R. leukops was 17 times longer than the other species, with two hatchlings remaining submerged for the entire 72 h recording period. The long dive duration recorded for R. leukops was supported by a high reliance on aquatic respiration (63–73%) and high blood oxygen affinity ( P ₅₀=17.24 mmHg). A correlation between dive duration, aquatic respiration and blood respiratory properties was not observed in the remaining turtle species where, despite the longer dive duration of Els. albagula and Elu. macrurus compared with Em. signata and Els. latisternum , there was no difference observed in per cent aquatic respiration or blood oxygen affinity between these species. When compared with adult individuals (data from previous studies), dive duration was positively correlated with body size in Em. signata , Els. albagula and R. leukops , but a negative relationship occurred in Els. latisternum and Elu. macrurus .