Water regulation and population management : investigation into the impacts of dams and foxes on Murray River turtles and comparison of management strategies

Abstract

Freshwater turtle populations have been declining globally due to a combination of natural and anthropogenic factors, with nearly half of the world freshwater turtles threatened with extinction. Australia is high on the list of contributing countries, with one third of its native species threatened with extinction. The Murray River is an obvious example with populations of its native species Emydura macquarii declining by 69% and Chelodina longicollis declining by 91% over the past 30 years. Nest predation by the red fox and the installation of water regulators, which have affected dispersal and changed water quality, are likely main causes of these population declines This thesis used meta-population and population viability analyses to evaluate the impacts of dams on turtle populations in areas where recruitment may be severely limited because of predation by foxes. The aims are to determine levels of recruitment required throughout a system to eliminate risks of extinction, as well as determine how the placement of dams and weirs may restrict movement and potentially increase risks of extinction. I show that turtle populations of the Murray-Darling Basin (MDB) can sustain relatively high losses of source recruitment populations, if relief populations are located between dams and impoundments. Areas of South Australia are of most concern. The scarcity of available habitats between dams, combined with high nest predation rates, increases the risk of extinction significantly. Water quality is also another significant factor that has hastened population declines and led to localised extirpation of MDB turtle populations. Management of MDB turtles centres on increasing the number of source populations for several species, increasing connectivity between populations and minimising risks for species moving terrestrially. This study also used modelling and population viability analysis to compare the cost to benefit ratio of two management techniques; headstarting and 1080 poison baiting, to determine which management technique would require the least cost to be the most effective. Vortex modelling showed that headstarting is significantly more efficient, economically beneficial, and uniformly more successful than baiting. Headstarting cost up to 40 times cheaper than baiting yet produced the same results. Headstarting cost an average of $0.22 AUD per hectare, whilst baiting cost as much as $8.73 AUD per hectare. Furthermore, modelled headstarting success was unaffected by the proportion of waterbodies in an area, the proportion of waterbodies baited/supplemented into or the proportion of forests (areas of lower nest predation) present, and could be used uniformly throughout the river. However, baiting required more baits when a lower number of waterbodies and low proportion of forests were present and would therefore need to be tailored to the area.

Date of Award	2017
Original language	English