Abundance and nutritional status of freshwater turtles to guide delivery of environmental flows in the Murray‐Darling Basin, south‐eastern Australia

Abstract

Almost half of Australian freshwater turtle species are formally listed as threatened, but little is known about the effects of water management and other factors on the abundance and health of freshwater turtles in arid and semi‐arid regions. This study investigated how river flows (including the controlled release of water from an upstream storage facility, or ‘environmental flow’) and water quality might affect the abundance and nutritional status of three freshwater turtle species in three dryland rivers of the Murray–Darling basin in south‐eastern Australia. No response in abundance or nutritional status of the broad‐shelled turtle, Chelodina expansa, the eastern long‐necked turtle, Chelodina longicollis, and the Macquarie turtle, Emydura macquarii, was detected in relation to river flows, possibly because of the small magnitude of the environmental flow. However, for C. expansa, the catch per unit effort (CPUE) was negatively related to increasing macrophyte cover, electrical conductivity (EC, an indicator of salinity), and turbidity. CPUE for C. longicollis was positively related to macrophyte cover and EC, and for E. macquarii it was positively related to macrophyte cover. Haematological measurements suggested that the turtles had healthy nutritional status. Body condition and blood glucose and protein were related significantly to EC, whereas haematological measurements varied significantly among species and between spring and summer. The main conclusion is that water management measures to help the conservation of these turtles should include sufficient environmental flow to produce overbank flooding, thereby creating and maintaining a wide range of habitat suitable for the differing needs of the individual species.

Conservation implications of isotopic variation in nails and blood with wetland quality in three species of Australian freshwater turtle

“…At each site, water depth (m), turbidity (NTU), salinity (ppt) (estimated from electrical conductivity within the meter), temperature (°C) and macrophyte cover (%) were measured. Turtles were weighed, measured, sexed and marked in case of recapture (Francis et al, 2022). Methods were in accordance with University of New South Wales Animal Care and Ethics permit number 14/119B and Taronga Conservation Society Australia Animal Ethics Committee permit number 3c/08/14.…”

“…The three turtle species were sampled in three rivers: the Bogan (two sites, Nyngan and Monkey Bridge), Castlereagh (one site, Mendooran) and Macquarie rivers (two sites, Pillicawarrina and Gradgery Lane) in central NSW, Australia (Francis et al, 2022) (Figure 1). Turtles were caught in cathedral traps in spring (November 2014) and summer (January 2015).…”

“…and Macquarie rivers (two sites, Pillicawarrina and Gradgery Lane) in central NSW, Australia (Francis et al, 2022) (Figure 1). For stable isotope analyses ( 13 C and 15 N), 1-2 mL of blood was collected (25 G, 2 mL syringe) from the jugular vein of each individual (Rogers & Booth, 2004), splitting the blood into two microtubes.…”

“…The three study rivers were chosen because of their presence in or around the Macquarie Marshes, an important wetland of the Murray–Darling Basin, which is supported by environmental flows down the Macquarie River. Sites within the Bogan and Castlereagh rivers were selected owing to the presence of water, which was scarce in the sampling periods, and they also varied in water quality and macrophyte cover (see Francis et al, 2022, for more details). The sampling periods fell before and after an environmental flow in the Macquarie River.…”

Opportunities for research and conservation of freshwater turtles in Australia

“…Likewise, conservation translocations of Critically Endangered species such as reintroductions ( Myuchelys georgesi ) and assisted colonization ( Pseudemydura umbrina ) have attempted to mitigate critically low population sizes due to disease (Chessman et al, 2020) and habitat loss and degradation (Bouma et al, 2020; Kuchling et al, 2018). Improved river management, such as managed flow delivery in regulated systems, has attempted to improve wetland habitats and the condition of rivers (Espinoza et al, 2022; Francis et al, 2022). More broadly, technological advances such as biobanking gametes, controlling diseases, and advances in genetic and bioinformatic tools should assist future conservation measures (Clulow et al, 2022).…”