Effect of water depth and water velocity upon the surfacing frequency of the bimodally respiring freshwater turtle,Rheodytes leukops

Abstract

SUMMARY This study examines the effect of increasing water depth and water velocity upon the surfacing behaviour of the bimodally respiring turtle, Rheodytes leukops. Surfacing frequency was recorded for R. leukops at varying water depths (50, 100, 150 cm) and water velocities (5, 15, 30 cm s-1) during independent trials to provide an indirect cost-benefit analysis of aquatic versus pulmonary respiration. With increasing water velocity, R. leukops decreased its surfacing frequency twentyfold, thus suggesting a heightened reliance upon aquatic gas exchange. An elevated reliance upon aquatic respiration, which presumably translates into a decreased air-breathing frequency, may be metabolically more efficient for R. leukops compared to the expenditure (i.e. time and energy)associated with air-breathing within fast-flowing riffle zones. Additionally, R. leukops at higher water velocities preferentially selected low-velocity microhabitats, presumably to avoid the metabolic expenditure associated with high water flow. Alternatively, increasing water depth had no effect upon the surfacing frequency of R. leukops, suggesting little to no change in the respiratory partitioning of the species across treatment settings. Routinely long dives (>90 min) recorded for R. leukopsindicate a high reliance upon aquatic O2 uptake regardless of water depth. Moreover, metabolic and temporal costs attributed to pulmonary gas exchange within a pool-like environment were likely minimal for R. leukops, irrespective of water depth.

Effect of water depth, velocity and temperature on the surfacing frequency of the bimodally respiring turtle Elseya albagula

“…Surfacing frequency of T. sinensis was reduced from 10·2 to 1·5 breaths h −1 when depth was increased from 15 to 45 cm. In contrast, the study by Gordos et al . (2004) on adult R. leukops employed an experimental design similar to the present study (experimental depths of 50, 100 and 150 cm), but found no effect of increasing depth on surfacing frequency.…”

“…), it is possible that negligible travel costs in the shallow (50 cm) flume facilitated aerial respiration to such an extent that any cost applied by water velocity was outweighed. However, Gordos et al . (2004) recorded a 20‐fold decrease in surfacing frequency for R. leukops also in 50 cm of water, when water velocity was increased from 5 to 30 cm s −1 .…”

“…2001). One recent study (Gordos, Franklin & Limpus 2004) showed that water velocity affects surfacing frequency and micro‐habitat selection of the bimodal respirer Rheodytes leukops under laboratory conditions.…”

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

“…Species ecology may also act as an evolutionary driving force for reliance on aquatic respiration and diving behaviour. The remarkable ability of R. leukops to extend dive duration through the use of aquatic respiration is thought be a key factor in the ability of this species to inhabit fast‐flowing riffle zones (Gordos, 2004). A high reliance on aquatic respiration decreases the frequency and therefore the costs associated with surfacing in a high‐velocity environment.…”

“…A high reliance on aquatic respiration decreases the frequency and therefore the costs associated with surfacing in a high‐velocity environment. Within riffle zones, R. leukops has reduced competition from other turtle species for food resources as well as reduced predator exposure (Gordos, 2004). The maximum dive durations of Elu.…”