i The comparative ecology of Krefft’s River Turtle Emydura krefftii in Tropical North Queensland.

By

Dane F. Trembath B.Sc. (Zoology)

Applied Ecology Research Group University of Canberra ACT, 2601 Australia

A thesis submitted in fulfilment of the requirements of the degree of Masters of Applied Science (Resource Management).

August 2005. ii Abstract

An ecological study was undertaken on four populations of Krefft’s River Turtle Emydura krefftii inhabiting the Townsville Area of Tropical North Queensland. Two sites were located in the Ross River, which runs through the urban areas of Townsville, and two sites were in rural areas at Alligator Creek and Stuart Creek (known as the Townsville Creeks). Earlier studies of the populations in Ross River had determined that the turtles existed at an exceptionally high density, that is, they were superabundant, and so the Townsville Creek sites were chosen as low abundance sites for comparison.

The first aim of this study was to determine if there had been any demographic consequences caused by the abundance of turtle populations of the Ross River. Secondly, the project aimed to determine if the impoundments in the Ross River had affected the freshwater turtle fauna. Specifically this study aimed to determine if there were any difference between the growth, size at maturity, sexual dimorphism, size distribution, and diet of Emydura krefftii inhabiting two very different populations.

A mark-recapture program estimated the turtle population sizes at between 490 and 5350 turtles per hectare. Most populations exhibited a predominant female sex-bias over the sampling period. Growth rates were rapid in juveniles but slowed once sexual maturity was attained; in males, growth basically stopped at maturity, but in females, growth continued post-maturity, although at a slower rate. Sexual maturity was at 6-7 years of age for males, which corresponded to a carapace length of 150-160 mm, and 8-10 years of age for females, which corresponded to a carapace length of 185-240 mm. The turtles were omnivorous, although in the Ross River they ate more submerged vegetation (by percent amount and occurrence) than those of the Townsville Creeks. Turtles in Townsville Creeks ingested more windfall fruit and terrestrial insects.

v Acknowledgments

I would personally like to thank my three supervisors Prof. Arthur Georges, Dr. Nancy Fitzsimmons, and Dr. Di Barton for making this project work and for their help in obtaining permits and resources, which were needed for this study. I would especially like to thank Dr. Di Barton for helping me realise I could do this kind of research from when I was an undergraduate and for obtaining permits for the original work on Emydura krefftii. Also thanks to my friends Dr. Sean Doody, Dr. Jason Elliott and David Freier for much help with ideas and statistical analysis. I am also thankful to Dr. David Blair for providing me with resources from James Cook University and also for providing keys to the James Cook University Rowing Shed. Also to Steve Patane for drawing turtle shells for me. Thanks also to Dr. Chris Johnson for providing me with a copy of EcoMeth. Also much thanks to Enzo Guarino for providing me with new turtle traps. Additional thanks to Dr Scott Snyder and his wife Maggi for giving me all their turtles to dissect once they were done with them. Much thanks also to my good friend Janet Perry for helping me with the x/ray machine even though we never used it. Thanks also To George Zug for emailing me some references. Thanks to all the volunteers as their help and enthusiasm in the field made the work more bearable: Sarah Bales, Andrea Bogle, Kim Clover, Eloise Crowley, John Dawson, Haley Dingfelder, Jennifer Donnellson, Simon Fearn, Samantha Hanstock, Arliah Hayward, Michael Heslop, Elizabeth Isaacson, Jarle Jorgenson, Ray Lloyd, Anna Lorenz, Chad Martin, Paul McCann, Melinda Mucci, Steve Patane, Reid Perlick, David Poppi, Jodi Rowely, Zubin Saleem, and Jason Schaffer. Additionally much thanks to the American volunteers who travelled across the world to show that greater turtle biodiversity leads to greater turtle capture: Chip Blackburn, York Morgan, Ed Smith, and Alex Stevenson. Lastly I would like to thank my Mum and Dad for encouraging me to fulfil my desire to learn more about turtle and by providing the resources to maintain a large turtle collection when I was younger.

vi Table of Contents Chapter 1: Introduction 1.1 Background………………………………………………………………………….…1 1.2 Superabundance………………………………………………………………………..5 1.3 Demographic Studies on Freshwater Turtles…………………………………………..8 1.4 Aims…………………….…………………...………………………………………..11

Chapter 2: Study Species, Study Area, and Methods ………………………………………..12 2.1 Study Species…………………..……………………………………………………..12 2.1.1 Emydura krefftii...... 12 2.1.2 Elseya latisternum…………………………………………………………….13 2.1.3 Chelodina canni……………………………………………………...... 15 2.2 Study Area………………………………………………………………………………...17 2.2.1 The Townsville Area………………………………………………………….17 2.2.2 The Ross River………………………………………………………………..17 2.2.3 Alligator Creek…………………..……………….…………………………...19 2.2.4 Stuart Creek…………………………………………………………………...23 2.3 Capture, Handling and Measurement………………………………………...... 23 2.4 Population Parameters………………………………………………………………...31 2.5 Growth………………………………………………………………………………..35 2.6 Diet...………………………………………………………………………………….36 2.7 Sexual-Size Dimorphism……………………………………………………………..38

Chapter 3: Results…………………………………………………………………...... 39 3.1 Population Estimation for Emydura krefftii…………………………………………..39 3.2 Size Distribution/Sex Ration…………….…………………………………...... 42 3.3 Size at Sexual Maturity……………………………………………………………….47 3.4 Rates of Survival/Immigration………………………………………………...... 50 3.5 Growth Rates………………………………………………………………………….53 3.5.1 Ross River…………………………………………………………………….53 3.5.2 Townsville Creeks…………………………………………………………….57 3.6 Diet…………………………………………………………………………...... 58 3.6.1 Ross River Emydura krefftii...... 58 3.6.2 Townsville Creeks Emydura krefftii………………………………………62 3.6.3 River/Creek Comparisons…………………………………………………….63

vii 3.7 Sexual Size Dimorphism……………………………………………………………...63

Chapter 4: Discussion………………………………………………………………...... 67 4.1 Population estimation………………………………………………………...... 67 4.2 Population Structure…………………………………………………………………..70 4.3 Growth Rates/Age at Maturity………………………………………………………..74 4.4 Size At Maturity……………………………………………………………...... 76 4.5 Rates of Survival and Immigration……………………………………...…...... 78 4.6 Dietary parameters……………………………………………………...…………….80 4.7 Sexual Size Dimorphism……………………………………………………………...83

Chapter 5: Synopsis…………………………………………………………………………..87 5.1 Demographic affects of Superabundance…………..………………………...... 87 5.2 Freshwater Turtle Conservation in North Queensland………………..……...... 89 5.3 Further Research……………………………………………………………………...91

References……..……………………………………………………………………………...92

Appendix…………………………………………………………………………………….110

viii List of Figures Figure 2.1. Male Emydura krefftii from Alligator Creek, Townsville……..………….……...14 Figure 2.2. Female Elseya latisternum from Alligator Creek, Townsville…………………...16 Figure 2.3. Female Chelodina canni from Ross River, Townsville………………………….16 Figure 2.4. Mean Monthly rainfall and maximum/minimum air temperatures for the Townsville Area………………………………………………………………...18 Figure 2.5. Map of the Ross River throughout the suburbs of Riverside Gardens and Annandale………………………………………………………………………20 Figure 2.6. Turtle Bridge Site, Palmetum Botanical Gardens, Townsville…………………..21 Figure 2.7. Riverside Gardens, Ross River, Townsville……………………………………..21 Figure 2.8. Map showing location of Alligator Creek Sites…..…………….……………….22 Figure 2.9. Alligator Creek Picnic Area in the dry season and wet season…………...….….24 Figure 2.10. Alligator Creek, Bruce Highway Townsville……………………….…………..25 Figure 2.11. Mean water depth of Alligator Creek (1972-2004) and Aplin’s Weir, Ross River (1944-1961)…………………………………………….……………………….26 Figure 2.12. Map of the Southern Townsville area showing location of Stuart Creek Study Sites…………………………………………………………..…………………27 Figure 2.13. Magnetic Island Caravan Park, Stuart Creek, Townsville…………..…………..28 Figure 2.14. Morphometric variables measured in Emydura krefftii from Townsville, Queensland……………………………………………………….….………….30 Figure 2.15. Linear regressions of curved carapace length (mm) versus straight carapace length of male and female Emydura krefftii from Ross River, Alligator Creek, and Stuart Creek……………………………….………………………………..32 Figure 2.16. Sexual dimorphism in tails of Emydura krefftii from Ross River, Townsville...33 Figure 2.17. Diagram of the notching method (Cagle, 1939) used in this study…………….34 Figure 3.1. Size Distribution of Emydura krefftii from Riverside Gardens Ross River and Palmetum, Ross River………………………………………….……………….44 Figure 3.2. Size distribution of Emydura krefftii from Alligator Creek and Stuart Creek…………………………………………………………………………....45 Figure 3.3. Age distribution of Emydura krefftii from Riverside Gardens Ross River and Palmetum, Ross River………………………………………………………..…46 Figure 3.4. Age distribution of Emydura krefftii from Alligator Creek and Stuart Creek…………………………………………………………………………....48 Figure 3.5. Carapace length plotted against tail length of both sexes of Emydura krefftii from all sites…………………………..……………………………………………....52

ix List of Figures Figure 3.6. Von Bertalannffy growth curves and rates for male Emydura krefftii from Ross River and Townsville’s Creeks…………………………………………………55 Figure 3.7. Von Bertalannffy growth curves and rates for female and Emydura krefftii from Ross River and Townsville’s Creeks…………………………………………...56 Figure 3.8. The percentage contribution by frequency of amount and occurrence of major food groups in the diets of Emydura krefftii from Townsville’s Creeks and Ross River’s…………………………………………………………………………..59 Figure 3.9. The percentage contribution by frequency of amount and occurrence of major food groups in the diets of male Emydura krefftii from Townsville’s Creeks and Ross River…………………………………………………………………………….60 Figure 3.10. The percentage contributions by frequency of amount and occurrence of major food groups in the diets of female Emydura krefftii from Townsville’s Creeks and Ross River…………………………………...... 61

x List of Tables Table 1.1. Large densities and biomass of freshwater turtles from around the world………....4 Table 1.2. Causes of exotic and native overabundance of various animals species from around the world………………………………………………………...…………………7 Table 1.3. Summary of published ecolological freshwater turtle research from Queensland..10 Table 3.1. The results of the mark recapture study of Emydura krefftii from the Townsville Region…………………………………………………………………………….40 Table 3.2. The number of times each turtle was caught during the study……………………41 Table 3.3. Comparisons of sex ratios among seasons and sites from the Townsville, North Queensland………………………………………………………………………..43 Table 3.4. Size Distributions of other turtles caught at all study sites…………...…………...49 Table 3.5. Minimum Straight Carapace lengths (mm) of sexually mature Emydura krefftii of both sexes from the Townsville Region……...... 51 Table 3.6. Rates of Survival for Emydura krefftii from the Townsville Region……………...51 Table 3.7. Rates of Immigration for Emydura krefftii from the Townsville Region…………51 Table 3.8. Von Bertalannffy growth parameters for male and female Emydura krefftii from the Ross River and Townsville Creeks.………………………..…………………54 Table 3.9. Dietary overlap (Morista’s original measure) by percentage amount in diets of Emydura krefftii from the Townsville Region…………………...... 64 Table 3.10. Dietary overlap (Morista’s original measure) by frequency of occurrence in diets of Emydura krefftii from the Townsville Region…………………………………64 Table 3.11. Mean ± SE of nine morphological parameters for male and female Emydura krefftii from all localities sampled………………………………………………..65 Table 4.1. Population estimates of Australian freshwater turtles.………..………………….68 Table 4.2. Sex ratios of Emydura spp throughout Australia………………………………….71 Table 4.3. Growth rate parameters used in Von Bertalannffy Growth curve analysis and ages of maturity of various Australian freshwater turtles………..…………………….75 Table 4.4. Carapace Length at Maturity for turtles of the genera Emydura…….……………77 Table 4.5. Survival, and immigration estimates of Australian freshwater turtles.…………....79 Table 4.6. Known diets of Australian freshwater turtles………………………...... 81 Table 4.7. Sexual size dimorphism of Emydura spp. from across Australia………………....84

1 Chapter 1: Introduction 1.1 Background

Freshwater turtles dwell in riverine and wetland habitats many of which have disappeared or been substantially modified in the last 100 years. Human disturbances include habitat alteration, water pollution, terrestrial alteration, channelization, and sand mining, all of which have had a negative effect on freshwater turtles throughout the world (Moll & Moll, 2004). Habitat alteration is the most common. In the United States only 2% of its rivers are still free flowing (Palmer, 1994). In Australia this is also the case, and as development continues, government plan for water resource development of many of its rivers (Tucker, 1999). Many of the turtles impacted by this development are restricted in range to single drainages, greatly increasing their vulnerability to extinction (Georges et al. 1993). Impoundments such as dams and weirs drastically alter the instream and riparian environment, altering suitability for many freshwater species, including turtles. Dams and weirs change waterways from flowing rivers and creeks into a series of large pools which may be very different from the pre-existing conditions of the waterway. Moll & Moll (2004) highlighted that lentic conditions caused by impoundments seriously affect lotic species in a variety of ways, though “river specialist” turtles are most affected. Dams prevent the movement of sediment needed to replace what is regularly lost which can greatly affect sand beach nesting species such as Batagur baska and Callagur borneoensis (Moll & Moll, 2004). Dams and weirs interfere with migratory movements of turtles and can fragment populations and thus leave them open to inbreeding, pollution, and disease. In Alabama such processes have caused the decline of the flattened musk turtle Sternotherus depressus (Dodd, 1990). One of the larger populations suffered 50% mortality because of disease associated with this fragmentation (Dodd, 1988).

More subtly, habitat alteration can change species composition and density. In the Warrior Basin of the USA, upstream waterway alteration has lead to fragmentation of turtle populations and this in turn has lead to altered population structure within species and alteration in species composition (Dodd, 1990). A study by Moll (1980) documented a decrease in abundance of a specialist turtle species following the construction of a dam, with a coincident steady increase in generalist species. Altered conditions created by the impoundment favoured some species but not others (Mills et al. 1966). In Israel, exceptionally high densities (up to 500-2000 turtles per hectare) have been reported for terrapins Mauremys caspica inhabiting sewage polluted waterways compared to 50-100 2 turtles per hectare in unpolluted waterways (Gasith & Sidis, 1984). Similarly, Souza & Abe (2000) described a population of side-necked turtles Phrynops geoffroanus inhabiting a polluted waterway with densities of 170-230 turtles per hectare, however their study did not compare their density to any other populations, but stated that these were high densities for the species. Cases of elevated densities are of value as they allow us to examine how species may change in abundance and population structure over time in response to human disturbance. Comparative studies of impacted and unimpacted areas are required to fully understand the processes and demographic implications of variation in population density (Aresco, 2004), whether natural or human induced. All widely ranging species tend to vary in population density from location to location.

Comparative studies can be very expensive and time consuming, especially for long- lived animals such as turtles, and require study over 20 years or more. To achieve this, different groups of researchers may work on the same populations, leading to problems with data collection, as methods may vary from researcher to researcher (Garber & Burger, 1995). Accurate measures of age structure, size distributions, sex ratio, and survivorship provide more information than regular short term studies (Limpus et al. 2002) but cannot be obtained in the short term. Long term studies on the other hand provide more direct data over time in response to natural and human-induced changes. Population density often has been overlooked in long term studies, but now that population data of turtles is accumulating it is possible to even estimate biomass of turtles (Iverson, 1982). A review by Iverson (1982) found that turtle densities ranged from 1.2 to 1196 individual per hectare showing that the importance of turtles in ecosystems is not fully known or appreciated. Some incredibly large densities though of almost 20,000 Kinsperson integrum (Berry & Legler, 1980) and 10,300 Podocnemis vogli (Marcellini, 1979) per hectare have been recorded but Iverson (1982) found these estimates to probably have been exaggerated. Most high turtle densities range from ca 200-2800 individuals per hectare and the data represent a wide range of genera (Table 1.1).

Turtle species are long lived and have low annual recruitment despite relatively high fecundity, making them especially vulnerable to changes in adult mortality, and recovery may be extremely slow (Iverson, 1982). Even relatively small changes in the density of adults can take decades to recover from (Brooks et al. 1991). Iverson (1982) goes as far as to say that populations of giant land tortoise have yet to recover from past density changes incurred during their long period of human exploitation and have only survived on oceanic islands that were and are rarely visited by humans. Low densities are clearly of concern to conservation

Table 1.1. High densities and biomass of freshwater turtles from around the world.

Species Country Density (turtles/ha) Biomass (kg/ha) Source Aspideretes nigricans Bangladesh 800 Ahsan (1997) Chelodina longicollis Australia 400 Parmenter, 1976 Chrysemys picta United States 576 28.2 Gibbons, 1968 C. picta United States 591 106.4 Ernst, 1971 Clemmys marmorata United States 420 137 Bury, 1979 Hydromedusa maximiliani Brazil 193.5 41.6 Souza & Abe, 1997 Kinosternon leucostonum Mexico 449 364 Morales-Verdeja & Vogt, 1997 K. herrerai Mexico 411 109 Iverson, 1982 K. integrum Mexico 1196 341 Iverson, 1982 K. sonoriense United States 815.4 100.3 Hulse, 1974 Phrynops geoffroanus Brazil 170-230 255-345 Souza & Abe, 2000 Sternotherus minor United States 2857 45.7 Cox & Marion, 1979 S. odoratus United States 700 41.7 Iverson, 1982 Trachemys scripta Belize 315 Moll, 1990

4 5 in this context. In contrast, the implications of high densities for demographic processes have rarely been considered. High densities can lead to competition for breeding sites which could lead to increased rates of nest damage due to overcrowding (Girondot et al. 2002). Increased density could also lead to competition for food which may then lead to a decrease in growth thus affecting size at maturity. Decreases in populations on the other hand lead to smaller densities of animals that have greater access to resources and food. This greater access to food may enable them to grow faster and achieve sexual maturity faster, and thus start reproducing at an earlier age than high densities. Such density dependent responses are clearly important for population modelling, but are rarely considered in demographic models for freshwater turtles.

In this thesis, I present the results of a study of the ecological responses in selected attributes, to exceptionally high abundances of the freshwater river turtle Emydura krefftii. The study draws upon my own data, collected in the Ross River near Townsville, and the data presented for a range of populations in the Emydura macquarii complex (including E. krefftii and E. signata) by Judge (2001) and others.

1.2 Superabundance

Caughley (1981) defines overabundance as simply too many “animals”, and identified three common classes of overabundance:

Class 1: “The animals threaten human life or livelihood”. This definition refers to animals which humans perceive are dangerous to us. An example of this includes tigers which regularly attack humans around the edges of their reserves resulting in hundreds of deaths (Garrot et al. 1993).

Class 2: “The animals depress the densities of favoured species”. Not all organisms on this earth are treated favourable and a lot of wildlife management is aimed at preserving human friendly species. An example of this is that in the 70’s wildlife management authorities’ culled lions and hyenas in Kruger National Park to increase the densities of zebras (Smuts, 1975).

Class 3: “The animals are too numerous for their own good”. This statement applied to the idea that animals which are held at a low density by hunting and culling tend to be healthier that unharvested populations. This idea is what seems to drive the idea of culling of large herbivores in national parks (Caughley, 1981).

6 These categories can further be structured on the basis of whether the animals are exotics or natives (Table 1.2). Exotic overabundance usually arises when the introduced organisms are habitat and dietary generalists. A range of factors, poorly understood, but including low rates of predation and disease, allow their numbers to grow to the point where they have a detrimental affect on native fauna. Boiga irregularis, the Brown tree snake, was accidentally introduced to the island of Guam during WWII (Fritts, 1988). As there were no predators of these snakes on the island they proceeded to increase greatly in numbers. This in turn caused the extinction of most of the island’s native birds (Savidge, 1987) and native nocturnal lizards (Rodda & Fritts, 1992). Overabundance is thought to be an essential element in bringing about the most destructive of impacts of most invasive exotic species. On Matthew Island in the Berring Sea, 29 reindeer were released in 1944 (Klein, 1968). The original 29 reindeer grew to a density of 6,000 animals in 1963, though the population then crashed for lack of food (Klein, 1968). Though exotic overabundance is widely reported (Coblentz, 1990; Soule, 1990) and many control programs exist for control of eradication of exotics, it is the overabundance of native species in human modified systems that are more challenging in terms of wildlife management. A review by Garrot et al. (1993) found that of 341 articles published in the journal Conservation Biology; only 13 dealt with the topic of management of overabundance and of this only one study on white tailed deer, (Alverson et al. 1988), dealt with the management of overabundance of a native species. I believe that this is a serious deficiency in studies to date, as overabundance of species can lead to a loss of diversity through resource competition, spreading infectious disease, changing the species composition of an area, and reducing the relative abundance of a sympatric species (Garrott et al. 1993).

Native overabundance is often associated with human-induced change in native habitats. These changes include the extermination of predators, which in turn allows populations to become overabundant. Human-induced change can also be positive in making resources such as food and nesting banks more extensive, available or accessible. In Europe the expansion of fish farming has lead to greater access to food for otters. This then has lead to an increase in otter abundance which causes considerable damage to the fish stocks (Kranz, 2000). Elsewhere in California sea lions have enjoyed federal protection and have risen in numbers. Unfortunately this increase has lead to an increase in their consumption of an endangered salmon (Demaster & Sisson, 1992). Native overabundance though may also be natural in some areas.

7 Table 1.2. Causes of exotic and native overabundance of various animals species from around the world.

Species Cause Reference Exotic Overabundance Brown Tree Snakes, Guam Lack of predators Fritts, 1988 Common Carp, USA Lack of predators Verrill & Berry, 1995 Reindeer Russia Lack of predators Bolen, 1999 Native Overabundance Elk, USA Climate Change Wang et al. 2002 Koalas, Australia Lack of predators Phillips, 2000 Rock Lobster (juveniles) Harvesting of adults Seiderer et al. 1982 Otters, Europe Greater Resources Kranz, 2000 White-Tailed Dear Greater Resources Alverson et al. 1988 California Sea Lions Lack of Predation Demaster & Sisson, 1992

8 Caughley’s definition of over-abundance is appropriate for studies in a wildlife management context, as it is a terminology useful for flagging situations where management intervention is required. However, the definition cannot be applied without invoking human values on what is desirable or not desirable for the wildlife under consideration. For the purposes of this study, I will use the term “superabundant” to apply to those cases where the abundance and density of individuals within a population is exceptionally high in comparison with the norm for other populations of the same species in natural areas unimpacted or little impacted by human disturbance. Superabundance may occur naturally such as when turtles aggregate in refugial wetlands during periods of drought (Georges & Kennett, 1989) or may occur as a result of modification of habitat through water resource development or other human induced modifications. This study is undertaken in the context of changes in abundance and population density that occur when rivers are impounded by dams or weirs, in some cases favouring some species to the point where they become superabundant to the exclusion of others.

1.3 Demographic Studies of freshwater turtles

Freshwater turtles are long-lived (Stickel, 1978; Williams & Parker, 1987) and readily collected (Ernst, 1971; Georges, 1982a; Souza & Abe, 2000), thus making them a desirable study animal. In the United States accessibility to the largest diversity of turtle species (Ernst et al. 1994) has led to many long-term research projects on a wide array of freshwater turtle species (Stickel, 1978; Williams & Parker, 1987; Ernst, 1986; Gibbons, 1990; Frazer et al. 1991; Congdon et al. 1993; Hall et al. 1999; Schwartz, 2000). In Australia, though, long term studies of freshwater turtles are non-existent except for Pseudemydura umbrina which has been studied since the mid 1960’s by an array of herpetologists (Kuchling, 1998). However P. umbrina is a relict species with no close relatives that only inhabits specialised swamps in Western Australia (Kuchling, 1981), thus making it ecology unlike most other species in Australia. Within Australia, Queensland has the highest biodiversity of turtles in Australia, with 11 species and 2 monotypic genera (Cann, 1998). Despite such a variety of turtles, research into their basic ecology is lacking, especially in regards to life history variation (Table 1.3). No long-term research has ever been conducted on any freshwater turtle populations in North Queensland or the Wet Tropics.

Apart from the lack of long-term research in North Queensland we can infer that the turtles their probably have high adult survivorship and low recruitment (Congdon et al. 1993). High adult survivorship is possible through the evolution of a bony shell, which offers

9 protection from predation (Gibbs & Amato, 2000). Mortality of juveniles may be the greatest factor leading to the low recruitment and persistence of a freshwater turtle population. Studies by Thompson (1983b) and Spencer (2001) have showed populations of E. macquarii macquarii experience up to 95% nest mortality by foxes. This effectively removed most of the recruitment and the population structure was thus composed of older adult turtles with little or no recruitment (Thompson, 1983b). However demographic analyses show that survival of adult females has the greatest influence on population stability (Spencer, 2001).

Growth of the Australian chelids follows the typical growth pattern of rapid juvenile growth with declines after reaching sexual maturity (Chessman, 1978; Burbidge, 1981; Kennett & Georges, 1990; Kennett, 1996). Attainment of sexual maturity tends to vary between species, with fast maturing species Chelodina rugosa and slow maturing species Elseya dentata (Kennett, 1999). Even though sexual maturity is quite easy to ascertain, data has only been presented for the following Australian turtles C. longicollis (Parmenter, 1985), C. oblonga (Kuchling, 1988), C. steindachneri (Kuchling, 1988), Chelodina rugosa (Kennett, 1999), Elseya dentata (Kennett, 1999), Emydura krefftii (Georges, 1983; Limpus et al. 2002), and E. macquarii (Chessman, 1978; Spencer, 2001). Growth and sexual maturity are highly related as sexual maturity is attained as soon as a reptile grows to a certain size, although sexual maturity may be related to an age rather than a size. Comparative studies within Australia of growth and sexual maturity within contrasting study habits are nonexistent. However in the United States studies of Chrysemys picta inhabiting a wastewater lagoon had higher growth and achieved faster sexual maturity than other turtles in natural populations. However, only males were able to achieve rapid sexual maturity and even though females grew faster in the wastewater lagoons they still had to be a minimum age before they could reproduce (Ernst & Macdonald, 1989). Their study though contradicts the results of Gibbons (1970a) who found accelerated growth rates of Trachemys scripta inhabiting a cooling water pond from a nuclear reactor. Increased growth rates in this population had led to sexual maturity at earlier ages than populations inhabiting normal waterways for both sexes.

Dietary components of turtles are widely studied as they swallow whole chunks of food thus making easy identification of stomach contents. Turtles are also very easy to access for stomach contents through the various methods of stomach flushing (Legler, 1977; Fields et al. 2000). In Australia dietary studies have been limited to Carettochelys insculpta (Georges & Kennett, 1989) Chelodina longicollis (Georges at al, 1986), C. expansa (Legler, 1978; Chessman, 1983) , C. rugosa (Kennett & Tory, 1996), Elseya albagula (Armstrong & Booth, 2005) , E. dentata (Kennett & Tory, 1996), Emydura krefftii (Georges, 1982b), E. macquarii

10 Table 1.3. Summary of published ecological freshwater turtle research from Queensland. 1=Emydura maqcuarii krefftii, 2=E. m. maqcuarii 3= E. m. signata, 4=E. subglobosa 5=Chelodina canni, 6=C. expansa, 7=C. longicollis, 8=Elseya latisternum, 9=E. dentata (Johnstone River), 10=E. lavarackorum, 11=E. albagula 12=Elusor macrurus, and 13=Rheodytes leukops.

Species Aspect of Study Reference 11 Dietary Ecology Armstrong & Booth, 2005 3,6,8 Blood Sampling Methods Rogers & Booth, 2004 1 Sexual-Size Dimorphism Trembath et al. 2004 9 Nesting Behaviour Turner, 2004 12 Diving Behaviour Gordos et al. 2003 6 Embryonic Diapause Booth, 2002 2,12 Diving Behaviour Gordos & Franklin, 2002 1 Population Dynamics Limpus et al. 2002 5 Species Description McCord & Thomson, 2002 3,6 Reproduction McCosker, 2002 2,12 Diving Behaviour Priest & Franklin, 2002 1 Disease Tucker et al. 2002 1 Nesting Habitat Carter & Tucker, 2001 12 Home Ranges Tucker et al. 2001 6 Reproductive Effort Booth, 1998 12 Temperature Sex Georges & McInnes, 1998 Determination 3 Basking Behaviour Manning & Grigg, 1997 10 Species Description Thomson et al. 1997 1,2,3,4,8,9,12,13 Electrophoresis of species Georges & Adams, 1996 12 Species Description Cann & Legler, 1994 1-9,12,13 Electrophoresis of species Georges & Adams, 1992 5 Distribution and Ecology Kennett et al. 1992 3,8 Cane toad predation Hamley & Georges, 1985 6 Diet Chessman, 1983 1 Reproduction Georges, 1983 1 Diet Georges, 1982b 12 Species Description Legler & Cann, 1980 6 Behaviour and ecology Legler, 1978 8, 10 Feeding habits Legler, 1976

11 macquarii (Chessman, 1986; Spencer et al. 1998). These studies found that the Australian chelids consume a wide variety of prey from the specialist herbivore Carettochelys insculpta which feeds mostly on ribbon weed (Georges & Kennett, 1989) to the generalist omnivore E. macquarii macquarii (Chessman, 1986; Spencer et al. 1998). Some dietary studies though have shown that diet can affect demographic parameters. Recently Souza & Abe (2000) demonstrated that high densities of Phrynops geoffroanus were able to maintain themselves because they fed on different diets in comparison to other populations. The high protein diet of chironomid larvae in conjunction with greater access to nesting sites had allowed the P. geoffroanus population density to reach between 170-230 turtles per hectare.

1.4 Aims

In this thesis I examine selected population parameters and diet of a superabundant population of the Australian freshwater turtle Emydura krefftii, inhabiting the Ross River, Townsville, North Queensland, with a view to assessing the demographic consequences of abundance at the extreme of those observed for this species. In particular, I aimed to determine size distribution, size at sexual maturity, rates of growth, diet and sexual size dimorphism m across populations varying in density and in relation to estimates from other studies where abundances and densities fall more within the norm.

12 Chapter 2: Study Species, Study Area, and Methods.

2.1 Study Species

The Chelidae and Carettochelydidae are the only two families of freshwater turtles inhabiting Australia. In Australia, the Chelidae are represented by the genera Chelodina, Emydura, Elseya, Elusor, Pseudemydura, and Rheodytes. This family is also present in South America with the genera Chelus, Hydromedusa, Phrynops, and Platemys (Georges et al. 1999). The Carettochelydidae has only one survivor, the Pig-Nosed Turtle Carettochelys insculpta, which occurs in Northern Australia and Papua New Guinea.

Despite having six genera of chelid turtles in Australia, their biology are poorly known with a number of recently described forms such as Chelodina burrungandjii (Thomson et al. 2000) and Elusor macrurus (Cann & Legler, 1994). The genus Emydura is perhaps an exception, with five substantial projects on basic ecology (Chessman, 1978), ecology of insular forms (Georges, 1982a), egg physiology (Thompson, 1983a), regional variation, (Judge, 2001), and population dynamics (Spencer, 2001) completed to date.

These studies have shown that the Emydura can be classed as “river turtles” according to characteristics defined by Moll & Moll (2000). The “river turtles” are known to be one the most endangered turtle groups in the world (Moll & Moll, 2004).

2.1.1 Emydura krefftii

The Genus Emydura is commonly found throughout Australia but also extends in Papua New Guinea. Of these Krefft’s River Turtle was first described by Dr. J. Gray in 1871 from a series of turtles collected by Gerard Krefft from the Burnett River (in central Queensland) that were sent to the British Museum (Cann, 1998). The status of populations of Emydura from southern and eastern Australia has recently come under scrutiny. Recent electrophoresis work has found that all populations of E. macquarii, E. krefftii, and E. signata are the same taxon E. macquarii (Georges & Adams, 1996). They suggested that Emydura signata be subsumed by Emydura macquarii macquarii and that three new subspecies be described. One of these subspecies is E. m. krefftii, with the remaining two recently receiving new names -- E. m. emmottii from Cooper Creek and E. m. nigra from Fraser Island (McCord et al. 2003). Recognition of Emydura krefftii as a subspecies of Emydura macquarii has not

13 received widespread acceptance within or outside Australia, and for the purposes of this thesis, I have chosen to retain the name Emydura krefftii for the species that is the subject of this study.

Emydura krefftii (Figure 2.1) is a medium-large species of turtle that exhibits sexual size dimorphism with females being larger than males (Trembath et al. 2004). Throughout its range it is highly variable in size with the Cooper Creek individuals from south-western Queensland’s being the largest (Cann, 1998). The preferred habitat for E. krefftii is slow moving waterways and creeks that have a large amount of cover in the form of overhanging trees and underwater snags, which provide large amounts of food and cover for the turtles, however E. krefftii is equally at home within freshwater lakes on offshore islands (Georges, 1982a). Demographic studies of mainland populations are limited to a study by Limpus et al. (2002) which described a population of E. krefftii that had a demographic structure composed mostly of large adults with limited juvenile recruitment. Demographic studies from Fraser Island also found a population composed of large adults with few small juveniles found (Georges, 1982a). Studies on growth are limited to the population inhabiting Fraser Island was found to grow relatively fast and then slow down upon reaching sexual maturity (Georges, 1983). Dietary studies of E. krefftii from Fraser Island found that juveniles were carnivorous, whereas adults were mostly omnivorous (Georges, 1982b); however there are no published studies on the diet of E. kreftii from mainland populations, though they have been observed to be opportunistic omnivores (Cann, 1998).

2.1.2 Elseya latisternum

The genus Elseya is a widespread group with representatives in Australia and Papua New Guinea. Georges and Adams (1996) have shown that within Australia, Elseya can be separated into two species groups, the E. dentata complex (6 species, one described) and the E. latisternum complex, (4 species, one described). Recently a species that was thought extinct E. lavackorum was found in western Queensland (Thomson et al. 1997). There is ongoing work to describe all the Elseya sp. in detail (A. Georges, pers. comm.).

Within the Townsville area only one species, E. latisternum has been found. Elseya latisternum was first described in 1867 by Dr. John Gray from a specimen collected from

14

Figure 2.1. Male Emydura krefftii from Alligator Creek, Townsville.

15 Cape York Peninsula. Elseya latisternum (Figure 2.2) is a medium sized turtle. They are easily sexed by the more heavily built tails in the males. They prefer lagoons and creeks to the larger rivers and abundance of them reduces as you near the coast (Cann, 1998). In the Townsville area they seem to be found exclusively in clear flowing water that is highly oxygenated, though a small population of them does exist in the Ross River. There are no demographic studies of this species.

Recent electrophoresis work has found that specimens of E. latisternum inhabiting Cape York are identical to specimens from the east coast (Georges & Adams, 1996). No specimens were examined from the Townsville region, but given the wide geographic distribution in that study, from Cape York to New South Wales, the Townsville form is most likely E. latisternunm.

The diet of E. latisternum has never been studied in detail though they are presumed to be omnivorous. Studies of other Elseya sp. have shown them to be variable in diet ranging from primarily herbivorous E. dentata (Kennett & Tory, 1996) to mostly carnivorous E. georgesi (Allanson & Georges, 1999).

2.1.3 Chelodina canni

The genus Chelodina is represented across the Australian continent by seven species (McCord & Thomson, 2002). Chelodina canni (McCord & Thomson, 2002) occupies the Townsville area. Chelodina canni (Figure 2.3) is a large turtle that prefers large wetlands and salt pans in the Townsville area. Their ecology remains poorly known except for a study by Kennet et al. (1992) who described reproductive data and distribution.

16

Figure 2.2. Female Elseya latisternum from Alligator Creek, Townsville.

Figure 2.3. Female Chelodina canni from Ross River, Townsville.

17 2.2 Study Area

2.2.1 The Townsville Area

Townsville exhibits a wet-dry tropical climate, with high summer (Dec-Mar) rainfall and an extended dry season (Figure 2.4). Temperature is also seasonal with July being the coldest month, although temperatures rarely drop below 13°C (Figure 2.4) and temperature may vary throughout the seasons (Oliver, 1978). The vegetation of Townsville is classed as open woodland (Reid, 1978) dominated by Eucalyptus alba, E. platyphylla, and E. polycarpa, with a riparian fringe along the Ross River.

Four study sites were located in the Townsville area. Two sites, along the Ross River, are located within the city limits and are surrounded by urban development. While the last two sites are located in an area of minimal human disturbance.

2.2.2 The Ross River

The Ross River headwaters are Central Creek, which flows west out of Herveys Range, and Five Head Creek, which flows east out of Mount Stuart (Bell, 2003). After the creeks meet, the river then flows north, and heads east to Cleveland Bay. The entire catchment is only 45 km long with the majority of its length flowing through the middle of Townsville and Thuringowa townships (Bell, 2003).

Between 1912 and 1934 a series of weirs were built to maximise the water storage potential for Townsville. The first of these, Aplins Weir, essentially divided the river into freshwater and saltwater sections (Webb, 1994). Subsequently, Blacks Weir and Gleesons Weir were installed to provide recreational areas. The construction of the weirs turned the river into a series of eutrophic lakes. In addition, they prevented the movement of the Saltwater Crocodile, Crocodylus porosus, into the river above Aplin’s weir as none has been seen since the weirs were put into place. Potential predators of freshwater turtles present in the river include long-finned eels, Anguilla fosteri, barramundi, Lates calcarifer, and an introduced population of freshwater crocodiles, C. johnstoni.

18

350

300

250

200

150

100

50

Mean Monthly RainfallMean Monthly (mm) 0

34

32 30 28 26 24 22 20 18 16 14 Mean Monthly Temperature (C) Mean Monthly 12 l ry ry ch ri ay ne ly st er er er er ua ua ar Ap M Ju Ju gu b ob b b an br M u em ct em em J Fe A pt O ov ec Se N D

Figure 2.4. Mean Monthly rainfall and maximum/minimum air temperatures for the Townsville Area. Data represents means from they years 1940 to 2004, from the Townsville Airport. (Source: Commonwealth Bureau of Meteorology).

19

This study focused on the section of water between Aplin’s and Gleeson’s weir (Figure 2.5) as this area has limited boating facilities and was very accessible for studies of turtles. This section of water is 5275m long with an average width of 212m and it covers an area of 83 ha (Webb, 1994). Two study sites were selected within the Ross River. The first site is the Palmetum Botanical Gardens adjacent to the Ross River above Aplin’s Weir. Jensen Creek, a permanent waterway, flows eastward through the Gardens into the Ross River. The study site in the area was ‘Turtle Bridge” (19°18’34”S, 146°45’57E), an unofficial name coined by the local Townsville residents. It is a metal bridge (Figure 2.6) that spans Jensen Creek just before it empties into the Ross River. The creek here is about 20m wide and ranges from 1m to 3m in depth depending on the season. Throughout the year large numbers of turtles gather under the bridge where they seem to be attracted by local residents who feed them bread. The second site selected was Riverside Gardens, a large suburb on the south bank of the Ross River that has been developed since the late 1990s. In the development are picnic areas, jetties, and a large boathouse for use by the James Cook University Rowing Club (Figure 2.7) (19°15’59”S, 146°45’6”E) which was the location of the study site referred to in Trembath et al. (2004).

2.2.3 Alligator Creek

Alligator Creek is located about 28km south of Townsville. Surrounding it is extensive Eucalypt woodland dominated by Corymbia clarksoniana, Eucalyptus platyphylla, E. tessellaris, and E. crebra (Environmental Protection Agency, 2002). This area receives up to 1200mm of rain per year with the majority falling between December and March (Williams et al. 1993). Alligator Creek (Figure 2.8) starts at the top of Mt Elliott where it cascades down and flows around Mt. Saddle. The creek then weaves it way through Bowling Green Bay National Park before emptying into the sea. There are no weirs constructed along it’s though a weir exists before it empties into the sea. Saltwater crocodiles Crocodylus porosus are present in the area and are probably a major predator of adult E. kreftii.

20

Figure 2.5. Map of the Ross River throughout the suburbs of Riverside Gardens and Annandale. Map reproduced with permission of Townsville City Council. Study sites are represented by stars.

21

Figure 2.6. Turtle Bridge Site, Palmetum Botanical Gardens, Townsville.

Figure 2.7. Riverside Gardens, Ross River, Townsville.

22

Figure 2.8. Map showing location of Alligator Creek Sites. Site A was on the Bruce Highway and Site B was at the Picnic ground. Map reproduced with permission of Townsville City Council. Study sites are represented by stars.

23 Two sampling sites occurred along the Creek. The first site consisted of a seasonal waterhole located (Figure 2.9.) at the Alligator Creek camping grounds (19°26’14”S, 146°56’45”E). This area is characterised by a series of pools that are connected during the wet season. The pools vary in depth but may be up to 3m deep in the wet season. Crocodylus porosus are not present in this stretch of the creek. The second site was where the Bruce Highway crosses Alligator Creek (19°23’18”S, 146°57’25”E). This area is characterised by slow moving water with high sand banks (Figure 2.10); although the water level varies throughout the year (Figure 2.11), it does not isolate into pools. This area is inhabited by C. porosus.

2.2.4 Stuart Creek

Stuart Creek flows (Figure 2.12) southward from Mount Stuart where it is fed by multiple small creeks. The creek then makes it way across a flat area of open vegetation south of Townsville before emptying into the sea. It has a drainage area of 58 km2 and no weirs are constructed along its length. Saltwater crocodiles are not present in the upper reaches of the creek though there is nothing to stop them from entering this area. The site that was chosen was opposite the Magnetic Island Caravan Park (19°19’28”S, 146°50’09”E). Either side of the creek has been heavily modified into pastures or old fruit orchards line the banks (Figure 2.13).

2.3 Capture, Handling and Measurement

Staring in July 2003 to April 2004, the Alligator Creek and Stuart creek sites were sampled for three hours at a time usually. The Ross River sites were also sampled during this period but also had been previously sampled since August 2001. While their may be biases in the extended Ross River sampling their was no way to avoid this.

During this sampling time, turtles were caught using three techniques: diving with the aid of mask and fins, dip netting, and trapping. Trapping was used at all study sites and was the only method used in areas where C. porosus were potentially present. Early in the study, traps consisted of crab pots with floats attached to each

Figure 2.9. Alligator Creek Picnic Area in the dry season (left) and wet season (right).

24 25

Figure 2.10. Alligator Creek, Bruce Highway, Townsville..

26

5.0 Aplins Weir

4.5

4.0

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2.01.0 Alligator Creek (Allendale) 0.9 Mean Water Depth (m)

0.8

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0.3 l t r r r r ary ary rch pri ay ne uly us be be be be nu ru a A M Ju J ug m to m m Ja eb M A pte Oc ve ce F Se No De Figure 2.11. Mean water depth of Alligator Creek (1972-2004) and Aplin’s Weir, Ross River (1944-1961). (Source: Department of Natural Resources and Mines).

27

Figure 2.12. Map of the southern Townsville area showing location of Stuart Creek Study Sites. Map reproduced with permission of Townsville City Council. Study sites are represented by stars.

28

Figure 2.13. Magnetic Island Caravan Park, Stuart Creek, Townsville.

29 corner. Once the project was underway, the traps by the design of Kuchling (2003) with modifications (Georges, pers comm.) were used. These modifications involved designing a separate holding chamber within the traps from which turtles could not escape. At each site two traps were typically set in deep water near cover with access to air so that no turtles would drown. These traps were monitored hourly to make sure that if they captured many turtles, they were emptied before accidental injuries and drowning occurred. Trapping was generally undertaken in the mornings as turtle activity was generally greater then than in the afternoon (D. Freier, pers comm). Traps were initially baited with a range of different baits; it was found that the use of chicken frames was the most effective in catching turtles.

Snorkelling was also undertaken while traps were in place however this method could only be used at Ross River and in parts of Alligator Creek and because of this bias were not used for the populations estimates (See section 2.4). Turtles were easy to locate as they utilised extensive underwater structures so that search effort could be directed at the most favourable areas instead of the whole creek. Turtles were also caught by slowly probing in the leaf litter packs at the bottom as turtles tended to sit in these during the morning where to the untrained eye they escape detection.

Dip netting for turtles was done at all sites while traps were in place. This method involved slowly walking the banks of the creek or river. All turtles that were seen were enticed to come closer by throwing pieces of bread. Once they swam in for the bread they could be caught and processed. Whilst there may be an affective bias with dip netting it did allow for greater capture effort as turtles that may not be near the traps could also be caught and included in the study.

Once caught turtles were held in 40 litre Nally bins containing river water in the shade to minimise stress. For every turtle, the length and width of the carapace, plastron, tail and head were measured in mm and recorded to ± 1mm. Carapace length was measured as curved carapace length, while width was measured as the curved horizontal distance across the highest point of the carapace. Plastron length was measured as the curved distance along the ventral midline, whilst plastron width was measured across the proximal end of the femoral plates (Figure 2.14). All these curved measurements were made with a flexible measuring tape. In order to compare carapace lengths used in other studies these measurements were converted to straight line dimensions using regressions established between the curved measurements and straight-line measurements using callipers applied to animals measured

30

A B

C D

E F

Figure 2.14. Morphometric variables measured in Emydura krefftii from Townsville, Queensland. Curved Carapace Length/Width (A), Plastron Length/Width (B), Cranial Length/Width (C), Tail Length (D), Straight Carapace Length (E), and Mass (F) of Emydura krefftii from Townsville, Queensland.

31 by both approaches (Figure 2.15). Thiry turtles of each sex from Ross River, Alligator and Stuart Creek were measured to obtain these conversions. Tail length was recorded to the nearest mm from the tail tip to the edge of the plastron with vernier callipers. Cranial length was measured, using callipers, from the snout tip to the posterior edge of the tympanic membrane. Cranial width was measured at the widest point, across the tympanic membrane. Turtles were sexed based on a marked sexual dimorphism in tail morphology (Figure 2.16) which is considered a reliable means of sexing adult and sub-adult E. krefftii, with males possessing considerably broader, longer tails than females (Cann, 1998). Additionally all turtles caught were photographed with a digital camera.

Once processed they were released at the site of capture within 20 minutes [SI units] of capture. Turtles that were processed for diet (see section 2.6) were taken to holding tanks at the laboratory for processing and were returned to point of capture within two hours.

2.4 Population Parameters

A mark-recapture regime was utilised at all sites. All turtles of all species were individually tagged using the design by Cagle (1939) by notching the shell in a series of places which allows individual animals to be recognised (Figure 2.17). In the beginning this was done with the use of two files; a triangle file was used to make the initial cut in the marginal scute, then a square file was employed to tidy up the cut and make it more visible. Later, the notches were made with a Dremel Rotary Tool.

Mark-recapture data was analysed with the Open Jolly-Seber method (Jolly, 1965) in the program EcoMeth which provided estimates of population size, rates of survival and immigration. The open method was chosen as all sites were rivers or creeks and not ponds which in essence would be closed populations. In order to compare densities to other published figures, densities were converted to density per hectare. Locations were measured with a handheld geographic positioning system (Magellan 315), boundaries of the study sites were charted, and areas calculated in hectares.

32

Alligator Creek Males y = 0.955x - 2.5666 Alligator Creek Females y = 0.9445x - 2.6833 2 R2 = 0.9988 R = 0.9991 250 300 200 250 200 150 150 100 100 50 50 0 0 0 50 100 150 200 250 0 50 100 150 200 250 300 350

Stuart Creek Males Stuart Creek Females y = 0.9849x - 9.5169 y = 0.9512x - 4.5254 R2 = 0.9903 R2 = 0.9995 250 300 200 250 200 150 150 100 100 50 50 0 0 0 50 100 150 200 250 0 50 100 150 200 250 300

Ross River Males y = 0.9511x - 1.5089 Ross River Females y = 0.9465x - 1.3825 2 R2 = 0.9894 R = 0.9927 250 300 200 250 200 150 150 100 100 50 50 0 0 0 50 100 150 200 250 0 50 100 150 200 250 300

Figure 2.15. Linear regressions of curved carapace length (horizontal axis) (mm) versus straight carapace length (vertical axis) (mm) of male and female Emydura krefftii from Ross River, Alligator Creek, and Stuart Creek.

33

Figure 2.16. Sexual dimorphism in tails of Emydura krefftii from Ross River, Townsville. Female (left) and Male (right).

Figure 2.17. Diagram of the notching method (Cagle, 1939) used in this study. The shell on the right shows the numbers applied to the margninals. The shell on the left shows a turtle marked 7, 8:10. Shell diagrams drawn by Steve Patane

34 35

Size at the onset of sexual maturity was assessed using the methods of Spencer (2001). In males, this involved determining the average carapace length of the five smallest males that displayed the characteristic large tail that sexually mature males possess. Sexual maturity in females was assessed by palpating their abdomen through the inguinal pocket for the presence of eggs (Kennett, 1996) and the five smallest gravid animals were used to determine the average minimum size of maturity.

As part of another project conducted by Dr Scott Snyder of the University of Nebraska in Omaha, specimens of E. krefftii were sacrificed and made available to determine age at minimum sexual maturity through dissection. Thirteen females and eleven males of various sizes were sacrificed. Males were determined as mature it they had large testes and convoluted sperm ducts. Testes width was measured with vernier callipers and a sample of fluid was obtained from the testis and placed under a light microscope to determine the presence of sperm (Georges, 1983). Females were classed as mature if they had follicles that were yellow and contained yolk. All follicles classed as mature were counted and their widths measured with vernier callipers. In addition a smaller number of turtles (n=3) were found dead or were killed owing to fishhook ingestion were also included in the sexual maturity analysis. These methods allowed me to verify that highly developed male tails a good indication of maturity and that palpation could determine sexual maturity in females.

2.5 Growth

Estimates of growth rate were derived from growth interval data of male and female recaptures, following the methods of Fabens (1965). Growth curves of males and females were assumed to follow a von Bertalannffy growth function, as has been exhibited by other freshwater turtle species (Cox et al. 1991; Kennett, 1996; Lindeman, 1996; Lindeman, 1997; Spencer, 2001). The von Bertalannffy equation is:

Lt = L ∞ (1 – exp [-K(t – t0)])

where Lt is length at age t, L ∞ is the theoretical maximum (or asymptotic length), and K is a growth coefficient which is a measure of the rate at which maximum size is reached. As the actual growth curves often cut the X-axis at a value less than zero, the value t0 represents the theoretical age at zero length, and typically has a small negative value.

35 36

Estimates of K and L ∞ were obtained using Gulland-Holt plots, where growth rate (on the Y- axis) is plotted against mean length (on the X-axis) for each individual recapture interval. A regression line fitted through these points has a slope of –K, and cuts the X-axis at L ∞ . Gulland-Holt plots are typically used for the estimate of growth parameters where mark- recapture data are available, but age at length data is not. Estimation of the final parameter, t0, requires re-arrangement of the growth function, together with a single known age at length value. Using the calculated von Bertalannffy growth functions for males and females, age estimates were produced from the carapace lengths for each individual within the study. Age- frequency figures were produced to illustrate the demographic distribution of turtles at the sites.

To analyse data for growth curves I decided to combine the Ross River samples and data from the Alligator and Stuart Creek sites to enable a comparison between the Ross River (abundance high) and the Creeks (abundance moderate).

2.6 Diet

Stomachs of turtles were flushed to release stomach contents (Legler, 1977; Georges et al. 1986). This was done during the months of February, March, and April 2005. Only turtles that appeared in good health were flushed and no turtles recently injured by boat propellers were included in the stomach flushing. The method involves inserting a small tube into the stomach via the mouth and oesophagus; water is then pumped through the tube forcing the stomach to expand and the contents to be expelled out of the mouth. Flushing is considered complete if the pyloric plug is retrieved (a distinct plug of digested food that resides in the pyloric stomach awaiting passage to the duodenum) or after 2 minutes, whichever came first. Contents were then damped dry on gauze and stored in 70 %ethanol for later analysis. Turtles that were found to have no stomach contents or that had eaten large quantities of bread were excluded from the analysis. Previous studies of turtles have found that some items of the diet are overestimated relative to others because of differential digestion rates. This bias is exacerbated in the material found in the pyloric plug. To avoid this bias, I excluded any items found in the pyloric plug.

36 37 Stomach contents were sorted into each of the following categories.

• Windfall Fruit – All items of vegetation and fruits that was not aquatic such as fruit, flowers, leaves, and bark • Aquatic Vegetation – Aquatic plants such as ribbon weed. • Sponge – Freshwater Sponges (Only found in Townsville Creeks). • Terrestrial Insects – All insects of a terrestrial origin such as beetles, grasshoppers, and adult dragonflies. • Aquatic Insects – All insects of aquatic origin such as odonate and chironomid larvae. • Molluscs – Mostly gastropods that were identified only by shell fragments remaining in the stomach. • Crustaceans – Mostly freshwater shrimps (Only found in Ross River). • Vertebrates – Miscellaneous pieces of carrion and small fishes.

Once identified the dietary composition was determined by how many turtles contained a certain type of food (% frequency of occurrence). Turtle diet was also determined by the percentage of certain food groups in a diet using a point’s method. This was achieved by placing all the dietary items from each individual onto a piece of paper and estimated the percentage of diet made up of prey categories. Since most turtles contained aquatic vegetation these estimation methods were used instead of counts to determine dietary importance.

Dietary variation was tested using the Niche Breadth program in EcoMeth. This program outputs a Levin’s niche breadth score which was used to determine the levels of specialist feeding or generalist feeding of both sexes from all sites (Krebs, 1989). Secondly I looked at differences among diets of male and female E. krefftii from Ross River and the Townsville Creeks using Morista’s niche overlap, the least biased of all niche overlap measures even when working with small sample sizes (Smith & Zaret, 1982). Morista’s Niche Overlap produces a C scores in which (C=0) represents no overlap. High overlap is presented by the maximum score of (C=1).

Thirty male and female E. krefftii samples were pooled from within 1000m of each of the Ross River study sites study sites in the Ross River. Additionally thirty male and female E. krefftii samples from Alligator Creek and Stuart Creeks were pooled to form the

37 38 Townsville’s Creeks dataset in order to make direct comparisons of Ross River against natural waterways.

2.7 Sexual Size Dimorphism

Sexual size dimorphism was measured using the methods outlined in Trembath et al. (2004). This involved log transforming all morphological data prior to analysis so as to meet the assumptions of homogeneity of variance. Intersexual comparison of all variables was completed using univariate ANOVA. In order to accurately describe significant differences, the effects of body size were removed by deriving standardised residuals which were calculated from regressions of every morphological variable against weight. These measures of relative morphology were then compared intersexually with univariate ANOVA (Trembath et al. 2004).

38 39 Chapter 3: Results

3.1 Population Estimation for Emydura krefftii

A total of 1681 captures of 1187 individually marked Emydura krefftii were recorded during the study (Table 3.1). Emydura krefftii proved to be readily captured at rates of 5 to 37 turtles per trapping session, with trap success ranging from 5 to 34 turtles in individual traps. Recapture rates were high with some turtles being recaptured three times at some sites (Table 3.2). In order to fit data into the Jolly Seber method every four trapping sessions were combined into one (The Jolly-Seber method can handle multiple trapping sessions and certainly more than 4. What was the real reason?). After this, combined trapping sessions ranged from 8-25 sessions (Table 3.1). The Jolly Seber Method was found to be a good fit to its underlying assumptions for all sites (Table 3.1.). This method was used as all sites were considered open populations as they were creeks and not lakes or ponds. Turtles were most abundant within the Ross River site with a density of 5342 ± 3482 turtles/hectare (Table 3.1.). High densities at this site were evident on visual inspection, with up to 200 heads counted at any one time. High head counts were also noted at the Riverside Gardens on the main Ross River channel, but densities were much lower (684 ± 360 turtles/hectares). Turtle densities within Townsville’s Creeks ranged from high at Bruce Highway, Alligator Creek (2935 ± 2080 turtles/hectares) to the lowest of 491 ± 441 turtles/hectares from Stuart Creek, representing the smallest creek sampled in the Townsville area (Table 3.1.). Emydura krefftii within the Ross River were mostly restricted to the banks where cover and food are in abundance. This in itself may explain why densities between the main channel at Riverside and Palmetum are so different. At the Palmetum site (0.21ha) turtles are densely packed into Jensen Creek very small tributary of the Ross River where they forage for food scraps which are thrown off the bridge by Townsville’s residents. Riverside gardens was the largest site (1.7ha) as it had very good access to the banks where traps could be set however estimates from this site must be viewed with caution as turtles may not use all of the areas available to them as it is quite deep. Emydura krefftii in Townsville Creeks appeared to be mostly associated with cover as Alligator Creek at Bruce Highway and Stuart Creek had a large amount of snags and aquatic vegetation present. Additionally none of the turtles are fed there, which prevents the turtles from forming large aggregations along these waterways. Emydura krefftii abundance was found to not differ greatly between the Ross River sites but was much greater than that of Alligator and Stuart Creek. However very high standard errors were estimated for all sites (Table 3.1.). In conclusion it was found that the E. krefftii populations

39

Table 3.1. The results of the mark recapture study of Emydura krefftii from the Townsville Region. Population size was estimated by the use of the Jolly-Seber Method (Jolly, 1965). Numbers in parentheses are degrees are freedom. Site # of Individuals # of Captures # of Trapping sessions/ χ-square Significance Population Size Population Sessions used in Jolly of χ-square. ± SE Density/Hectare Seber Analysis Riverside, Ross 509 818 100/25 χ= 54 (48) NS 1164 ± 613 684 ± 360 River Palmetum, Ross 324 410 52/13 χ= 24 (24) NS 1122 ± 741 5342 ± 3482 River Alligator Creek 232 308 32/8 χ= 20 (16) NS 5871 ± 416 2935 ± 2080 Stuart Creek 122 145 32/8 χ= 15 (12) NS 105 ± 94 491 ± 441

40 41 Table 3.2. The number of times each turtle was caught during the study. Palmetum Ross River Times Recaught Numbers Recaught 0 269 1 39 2 8 3 4 4 1 5 1 Riverside, Ross River 0 334 1 111 2 42 3 11 4 7 5 3 6 3 7 1 8 1 Alligator Creek 0 155 1 20 2 4 3 3 4 2 Stuart Creek 0 103 1 17 2 1 3 1 4 0

42 inhabiting the Ross River where much larger than the populations inhabiting the Townsville Creeks.

3.2 Sex Ratio/Size Distribution of Emydura krefftii

Sex ratio data was obtained throughout the Townsville area for 1 year at Alligator and Stuart Creeks and for 3-4 years at Riverside and Palmetum, Ross River (Table 3.3). Female bias in sex ratios was found throughout the Ross River at both sites sampled and was also evident throughout all sampling times except for the first year of sampling at Ross River sites. The first year at Palmetum was not tested due to low sample sizes incurred by low sampling effort (Table 3.3). Overall female bias throughout the study was evident for Ross River with significantly more females (515) than males (315) caught (χ2= 23.965, p= 0.001). The Creeks however were found to not have a significant bias in sexes with almost equal numbers of males and females were caught at both creek sites (Table 3.3). These data combined also showed that there was no significant differences in the numbers of males (168) and females (184) present during the study (χ2= 0.279, p= 0.598). The distribution of size classes within the Ross River population was found to be more even than other populations, in that it had turtles of all size classes present for both sexes (Figure 3.1). However within the Ross River, older females were recorded at Palmetum than Riverside (Figure 3.1). Juveniles were found in low numbers at the Riverside site; one juvenile was seen, but not captured, at the Palmetum site (Figure 3.1). The largest females caught within the Ross River came from the Palmetum site and were 284mm, 283mm, and 282mm straight carapace length (Figure 3.1). The largest males caught within the Ross River were 232mm, 229, and 228mm, which were all caught at the Riverside site (Figure 3.1). The size distribution within the Townsville Creeks was made up of lots of different size classes with a large number of juveniles present in the population (Figure 3.2). Both Alligator and Stuart Creeks appeared to have ongoing recruitment of juveniles of both sexes (Figure 3.2). The largest females caught within the creeks came from Alligator Creek and were 288mm, 287mm, and 278mm (Figure 3.2). The largest males also caught at this site were 264mm, 243, and 240mm (Figure 3.2). However within Stuart Creek a gigantic adult male (#0, 10) was caught which measured 296mm straight carapace length making it the largest E. krefftii caught within the Townsville area (Figure 3.2). Ages of E. krefftii were calculated from growth interval data (See Section 2.5). The Ross River male population was estimated to contain turtles of 2-33 years of age (Figure 3.3). The male population ages did vary throughout the river with males at Palmetum averaging 13.7

43 Table 3.3. Comparisons of sex ratios among years and sites of Emydura krefftii from the Townsville, North Queensland. *Significant difference, p<0.05. Site and Season No. of Males No. of Females x2 caught caught Riverside 2001-2002 52 70 1.055 2002-2003 97 163 8.006 * 2003-2004 38 100 13.737 * 2004-2005 58 109 7.337 * Palmetum 2002-2003 11 13 Not Tested 2003-2004 37 93 11.761* 2004-2005 72 149 13.095* Alligator Creek 2004-2005 119 115 0.008 Stuart Creek 2004-2005 53 69 0.807

44 60 Riverside Male Female 50

40

30

Frequency 20

10

0 50 100 150 200 250 300

Straight Carapace Length (mm)

60 Male Palmetum Female 50

40

30

Frequency 20

10

0

50 100 150 200 250 300

Straight Carapace Length (mm)

Figure 3.1. Size Distribution of Emydura krefftii from Riverside Gardens, Ross River and Palmetum, Ross River. Data represents all individuals caught during the time of 2001- 2005.

45 25 Alligator Creek Male Female 20

15

Frequency 10

5

0 50 100 150 200 250 300 350 Straight Carapace Length (mm)

25 Stuart Creek Male Female 20

15

Frequency 10

5

0

50 100 150 200 250 300

Straight Carapace Length (mm)

Figure 3.2. Size distribution of Emydura krefftii from Alligator Creek and Stuart Creek. Data represents all individuals caught during the time 2003-2005.

46

Riverside, Ross River 40 Male Female

30

20 Frequency

10

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 Age (Years)

Palmetum, Ross River 30 Male Female

20 Frequency

10

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 Age (Years)

Figure 3.3. Age distribution of Emydura krefftii from Riverside Gardens, Ross River and Palmetum, Ross River. One female omitted from the Palmetum graph was estimated to be 51 years old. Data represents all individuals caught during the time of 2001-2005.

47 years compared to the average age of 10 years at Riverside (Figure 3.3). The female population within the Ross River ranged from 1-51 years old (Figure 3.3). Average female age also differed between sites in the Ross River with females at Palmetum averaging 13.7 years compared to 9.8 years at Riverside. The male population of E. krefftii inhabiting the Townsville Creeks sample ranged from 2-37 years old (Figure 3.4). The average age of males from Alligator Creek (13.5 years) did not appear to be that different to the average age at Stuart Creek (11.5 years) (Figure 3.4). Female E. krefftii from the Townsville’s Creeks were estimated to have ages from 2-32 years old (Figure 3.4). Average female age at Stuart Creek (14.2 years) did not appear to be that different to Alligator Creek (13.9 years) (Figure 3.4). Throughout the study a number of other species of turtles were caught at all sites and marked and released (Table 3.4). In the Ross River two individual Chelodina canni were found (Table 3.4.). A dead juvenile female was given to me by a local resident on the 5th March 2003 and donated to the Queensland Museum. An adult female was caught in a trap on the 24th September 2003 at the Riverside Site. Additionally three adult male and six adult female Elseya latisternum were caught at Palmetum in traps during the study (Table 3.4.). Of these one male was found dead on the bank at Palmetum. The Townsville Creeks contained much larger populations of other turtles (Table 3.4). Three adult female C. canni were caught in traps during the study (Table 3.4). Thirty three female and 17 male E. latisternum were also caught within the Townsville Creeks (Table 3.4).

These results show that the population of E. krefftii inhabiting the Ross River is made up of larger individuals with few juveniles. These results also show that the population of turtles inhabiting the Ross River is mostly made up of E. krefftii; with few individuals of other species present (same number of species, but fewer individuals). The E. krefftii individuals are larger but not necessarily of different ages in comparison to the Townsville Creeks. This trend is especially evident in the Palmetum population where E. krefftii forage for food scraps thrown from the bridge. This may be the cause of the larger turtles in there as these larger individuals might be more easily sampled than smaller individuals which may not be accustomed to feeding on bread scraps.

3.3 Size at sexual maturity

The dissections revealed that only male E. krefftii with a well developed tail were sexually mature. Females palpated prior to euthanasia for other projects found that the palpation method was able to determine the presence of eggs reliably.

48

10 Alligator Creek Male 8 Female

6

Frequency 4

2

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 Age (Years)

10 Stuart Creek Male 8 Female

6

Frequency 4

2

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 Age (Years)

Figure 3.4. Age distribution of Emydura krefftii from Alligator Creek and Stuart Creek. Data represents all individuals caught during the time of 2003-2005.

Table 3.4. Size Distributions of other turtles caught at all study sites. Values represent that maximum and minimum and values in parentheses are means. Curved Carapace (mm) Plastron (mm) Cranial (mm) N Length Width Length Width Length Width Mass (gm)

Chelodina canni Riverside ♀ 2 26-242 (134) 20-190 (105) 20-187 (103.5) 13-49 (31) 19-40 (29.5) 12-93 (52.5) 3.5-1300 (651.7) Chelodina canni Stuart Creek ♀ 2 222-274 (248) 168-220 (194) 168-207 (187.5) 80-104 (92) 41-48 (44.5) 32-38 (35) 900-1900 (1400) Chelodina canni Alligator Ck ♀ 1 250 203 186 98 46 35 1400 Elseya latisternum Palmetum ♂ 3 135-211 (173) 113-166 (140) 108-165 (136) 50-81 (65.6) 36-47 (40.3) 27-39 (32.6) 300-1200 (683.3) Elseya latisternum Palmetum ♀ 6 257-291 (274) 213-245 (226.8) 197-225 (208.8) 94-108 (99.6) 55-65 (60.1) 48-63 (54) 1700-2900 (2200) Elseya latisternum Alligator Ck ♂ 12 65-202 (145) 64-163 (118.8) 52-162 (111.5) 27-75 (53.2) 19-46 (33.7) 16-37 (27.5) 37-900 (384.7) Elseya latisternum Alligator Ck ♀ 28 33-280 (171.1) 35-238 (145.7) 25-220 (133.3) 13-99 (62.7) 12-62 (39.1) 10-54 (33.8) 5.5-2100 (826.1) Elseya latisternum Stuart Ck ♂ 5 153-200 (177.8) 127-161 (144.6) 115-150 (135.8) 56-69 (62) 35-41 (38.8) 28-35 (32.6) 400-700 (538) Elseya latisternum Stuart Ck ♀ 5 132-299 (250) 116-241 (200) 97-227 (188.6) 52-160 (101) 30-62 (51.8) 24-60 (46.8) 180-3100 (1826)

49 50

A comparison of straight carapace length versus tail length determined that there was a clear distinction in tail growth following sexual maturity of male E. krefftii from all sites (Figure 3.5). Male E. krefftii appeared to attain sexual maturity at the same size across all sites though Riverside was found to attain sexual maturity at 160mm instead of 148mm (Table 3.5). However even with this slight difference it appears that Ross River male E. krefftii and Townsville Creek's E. krefftii mature at the same sizes. Female E. krefftii attained sexual maturity at a much larger range of sizes throughout Townsville (Table 3.5). Females within the Ross River were found to attain sexual maturity at smaller sizes 185-208 mm compared to 232-242 mm in the Townsville Creeks (Table 3.5).

3.4 Rates of Survival/Immigration

Survival rates varied throughout the Townsville area (Table 3.6). Survival rates were higher within the Ross River than the Townsville Creeks. The highest survival rate was reported from Riverside, within the main Ross River. The Palmetum site experienced higher mortality than the main channel (Table 3.6). At he Townsville Creek sites survival rates were found to not differ much between each other. The survival rates though were calculated to have very high standard errors and were derived from and Open Jolly-Seber method used in determining the population size that also had very large standard errors.

Immigration rates were also found to vary greatly throughout the Townsville area (Table 3.7). The highest immigration rates were reported from within the Ross River. The E. krefftii inhabiting this area have a very large amount of water within which to live and this may explain why immigration rates were so high. The Townsville Creeks also experienced high immigration rate showing that this variable is high throughout the Townsville area (Table 3.7). Immigration rates were obtained from a Jolly-Seber estimated that was used to determine the population estimate. The values that were obtained from this output had standard errors that were higher than the values themselves. Only Riverside within the Ross River had estimates with a lower standard error though it was still very high. The Jolly Seber methods rely on equal catchability of turtles throughout the trapping season. Even though the data were found to fit the Jolly-Seber method well (Table 3.1) the turtles may have been exposed to unequal catchability in that turtles were leaving the study sites either through capture or migrating to new water bodies as happened within Alligator Creek. These rates show that immigration within tropical turtle populations may be very high.

51

Table 3.5. Minimum Straight Carapace lengths (mm) of sexually mature Emydura krefftii of both sexes from the Townsville Region. Site Male Sexual Maturity Female Sexual Maturity Straight Carapace Length Straight Carapace Length Riverside, Ross River 160mm 208mm Palmetum, Ross River 148mm 185mm Alligator Creek 148mm 242mm Stuart Creek 148mm 232mm

Table 3.6. Rates of Survival for Emydura krefftii from the Townsville Region. Turtle and Locality Survival Standard Error (PHI) Survival (PHI) E. krefftii (Riverside) 0.81 0.32 E. krefftii (Palmetum) 0.60 0.30 E. krefftii (Stuart Creek) 0.52 0.42 E. krefftii (Alligator Creek) 0.57 0.41

Table 3.7. Rates of Immigration for Emydura krefftii from the Townsville Region. Turtle and Locality Immigration Standard Error (B) Immigration (B) E. krefftii (Riverside) 431.5 376.2 E. krefftii (Palmetum) 843.2 1248.6 E. krefftii (Stuart Creek) 91.2 162.5 E. krefftii (Alligator Creek) 208.4 355.2

52

180 120 Palmetum Riverside 160 100 140 120 80

100 60 80

Tail Length (mm) 60 Tail Length (mm) 40

40 20 20 0 0 50 100 150 200 250 300 50 100 150 200 250 300 Straight Carapace Length (mm) Straight Carapace Length (mm)

180 140 Alligator Creek Stuart Creek 160 120 140 100 120

100 80

80 60

Tail Length (mm) Length Tail 60 Tail Length (mm) Length Tail 40 40 20 20

0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 350 Straight Carapace Length (mm) Straight Carapace Length (mm)

Figure 3.5. Carapace length plotted against tail length of both sexes of Emydura krefftii from all sites. Black dots represent males, white dots females, and grey dots are gravid female. Average size of mean minimum sexual maturity is the dotted line.

53

3.5 Growth Rates

3.5.1 Ross River

Male Ross River Emydura krefftii growth intervals were recorded from 27 individuals representing growth periods of 36 – 109 weeks since last capture. Of these only one adult male (3, 10/10, 211mm) did not grow in 27 weeks, whereas all others experienced growth. The greatest growth recorded was an adult male (5, 7) that grew from 154mm to 191mm in 156 weeks. The greatest short-term growth recorded was an adult male (3, 10/11) that grew from 170mm to 188mm in 61 weeks. Sexual size dimorphism was both evident in the asymptote sizes and intrinsic growth rates (Table 3.8) with males growing faster than females. Juvenile growth was rapid though is mostly unknown because of the lack of recapture small males used in the analysis.

A Von Bertalannffy growth model was applied to the males using growth interval data obtained through mark-recapture of individuals (Figure 3.6). These models showed a very rapid juvenile growth followed by slower growth upon reaching sexual maturity at between 150mm-160mm for the Ross River. This then would allow Ross River male E. krefftii to attain sexual maturity at about 6-7 years.

Female Ross River Emydura krefftii growth intervals were recorded from 154 individuals representing growth periods of 17 – 156 weeks since last capture. Of these 30 individuals did not experience any growth during the study. The greatest growth recorded was an adult female (5, 6/2) that grew from 214mm to 263mm in 48 weeks. This individual also had the greatest short term growth recorded. Sexual size dimorphism was both evident in the asymptote sizes and intrinsic growth rates (Table 3.8) with males growing faster than females. Juvenile growth was rapid though is mostly unknown because of the lack of recapture small females used in the analysis.

A Von Bertalannffy growth model was applied to the females using growth interval data obtained through mark-recapture of individuals (Figure 3.7). These models showed moderate juvenile growth followed by slower growth upon reaching upon reaching sexual maturity at between 242 mm-232 mm. This then would allow female E. krefftii to attain sexual maturity at about 16-18 years.

54

Table 3.8. Von Bertalannffy growth parameters for male and female Emydura krefftii from the Ross River and Townsville Creeks. Models were derived from growth interval data. Locality Asymptote K Mean Adult Size (mm) (mm/week) (mm) Ross River 218 0.32 185 ♂

Townsville Creeks 205 0.32 187 ♂

Ross River 260 0.27 210 ♀

Townsville Creeks 315 0.13 195 ♀

55

240 220 Ross River Townsville Creeks 200

180 Males

160

140 120

100

80 60 Straight Straight Carapace Length (mm) 40

20

0 5 10 15 20 25 Age (Years)

1.2

Ross River

Townsville Creeks 1.0

0.8

0.6

0.4

Growth Rate Growth(mm) Rate 0.2

0.0

80 100 120 140 160 180 200 220 240

Mean Straight Carapace Length (mm)

Figure 3.6. Von Bertalannffy growth curves (top) and rates (bottom) for male Emydura krefftii from Ross River and Townsville’s Creeks.

56

300 Ross River Townsville Creeks 250 Females 200

150

100

Straight Carapace Length (mm) Length Carapace Straight 50

0 0 5 10 15 20 25 Age (Years)

1.2 Ross River Townsville Creeks 1.0

0.8

0.6

0.4 Growth(mm) Rate 0.2

0.0

50 100 150 200 250 300 Mean Straight Carapace Length (mm)

Figure 3.7. Von Bertalannffy growth curves (top) and rates (bottom) for female Emydura krefftii from Ross River and Townsville’s Creeks.

57 3.5.2 Townsville Creeks

Male Alligator and Stuart Creek Emydura krefftii growth intervals were recorded from 15 individuals representing growth periods of 15 – 57 weeks since last capture. Of these only one adult male (7, 5; 195mm) did not grow in 31 weeks, whereas all others experienced growth. The greatest growth recorded was a juvenile male (8, 0) that grew from 92mm to 120mm in 27 weeks. This individual also had the greatest short term growth recorded however another adult male (0, 2) showed rapid growth and grew from 204mm to 220mm in 25 weeks. Sexual size dimorphism was both evident in the asymptote sizes and intrinsic growth rates with males growing faster than females (Table 3.8). Juvenile growth was rapid and validated through the mark recapture of juvenile turtles that could be sexed.

A Von Bertalannffy growth model was applied to the males using growth interval data obtained through mark-recapture of individuals (Figure 3.6). These models showed a very rapid juvenile growth followed by slower growth upon reaching sexual maturity at about 148mm for both Alligator and Stuart Creek. This then would allow Alligator and Stuart Creek male E. krefftii to attain sexual maturity at about 6-7 years.

Female Alligator and Stuart Creek Emydura krefftii growth intervals were recorded from 21 individuals representing growth periods of 28 – 79 weeks since last capture. Of these 5 individuals did not experience any growth during the study. The greatest growth recorded was a sub adult female (0, 2) that grew from 204mm to 220mm in 25 weeks. This individual was also had the greatest short term growth recorded.

A Von Bertalannffy growth model was applied to the females using growth interval data obtained through mark-recapture of individuals (Figure 3.7). These models showed moderate juvenile growth followed by very slow growth upon reaching sexual maturity at between 232mm-242mm. This then would allow female E. krefftii to attain sexual maturity at about 16-18 years.

58 3.6 Diet

3.6.1 Ross River Emydura krefftii

Overall diets of male and female E. krefftii (N=60) were found to be omnivorous by both percentage amount (Levin’s Standardised Niche Breadth =0.32) and frequency of occurrence (Levin’s Standardised Niche Breadth =0.29). Their main dietary components by percentage amount were submerged plants (54%), molluscs (16%), and windfall fruit (16%) (Figure 3.8). The rest of their diet consisted of terrestrial insects (6%), crustaceans (6%), and vertebrates (2%) (Figure 3.8). Submerged plants (65%) and molluscs (20%) were to be the most frequently occurring dietary items. Of lesser occurrence were crustaceans (13%), terrestrial insects (13%), and aquatic insects (7%). The overall diet of Ross River E. krefftii was found to not consume any sponge material (Figure 3.8).

The diet of male E. krefftii from Ross River (N=30) was found to be mostly herbivorous by both percentage amount (Levin’s Standardised Niche Breadth =0.27.) and frequency of occurrence (Levin’s Standardised Niche Breadth =0.37). Their main dietary components by percentage amount were submerged plants (73%) and windfall fruit (16%) (Figure 3.9). The rest of their diet consisted of crustaceans (6%) and terrestrial insects (4%) (Figure 3.9). Submerged plants (87%) and windfall fruit (23%) were to be the most frequently occurring dietary items. Of lesser occurrence were crustaceans (17%), terrestrial insects (7%). The overall diet of E. krefftii males from Ross River was found to not consume any sponge material, aquatic insects, molluscs, or vertebrates. (Figure 3.9).

Female E. krefftii from Ross River (N=30) were found to be mostly omnivorous by both percentage amount (Levin’s Standardised Niche Breadth =0.48) and frequency of occurrence (Levin’s Standardised Niche Breadth =0.63). Their main dietary components were submerged plants (35%) and molluscs (32%) (Figure 3.10). The rest of their diet consisted of windfall fruits (15%), terrestrial insects (8%), aquatic insects (5%), vertebrates (3%) and crustaceans (2%) (Figure 3.10). Submerged plants (43%) and molluscs (40%) were the most frequently occurring dietary items. Of lesser occurrence were terrestrial insects (20%), windfall fruit (17%), aquatic insects (13%), crustaceans (10%), and vertebrates (3%) (Figure 3.10). The overall diet of female E. krefftii from Ross River was found to not consume any sponge material. (Figure 3.10).

59

90 Ross River 80 70 60 50 40 30 20 10 0 ll d n e s s s e fa e a ct ct c at d rg ce ong se se llu br in ta p In In o te W bme s S l c M r u ru ria ti Ve S C st ua rre Aq Te

90 Townsville Creeks 80 70 % Amount % Occurence 60 50 40 30 20 10 0 l d ts s al e ae ge c ct cs te df rg lg n se e lu ra in e A o In ns ol eb m Sp l I M rt W b ia tic e Su tr a V es u rr Aq Te

Figure 3.8. The percentage contribution by frequency of amount and occurrence of major food groups in the diets of Emydura krefftii from Townsville’s Creeks and Ross River’s.

60

100 Ross River Males 90 80 70 60 50 40 30 20 10 0 ll d n s s s e a e a ct ct at df rg ce onge e e lluc br in e ta p Ins Ins o te W s S l c M r ubm ru ria ti Ve S C st rre Aqua Te

100 Townsville Creeks Males 90

80 %Amount %Occurence 70 60 50 40 30 20 10 0 ll d e e s s s e fa e a g ct ct c at d rg lg on se se llu br in e A p n o te W bm S l I In M r u ria tic Ve S st ua rre Aq Te

Figure 3.9. The percentage contribution by frequency of amount and occurrence of major food groups in the diets of Male Emydura krefftii from Townsville’s Creeks and Ross River.

61

70 Townsville Creeks Females 60

50 %Amount %Occurence 40

30

20

10

0 ll d e e s s s e fa e a g ct ct c at d rg lg on se se llu br in e A p In In o te W bm S l c M r u ria ti Ve S st ua rre Aq Te

70 Ross River Females 60

50

40

30

20

10

0 ll e s s s e fa ed an g ct ct c at d rg ce on se se llu br in e ta p In In o te W bm s S l c M er u ru ria ti V S C st ua rre Aq Te Figure 3.10. The percentage contributions by frequency of amount and occurrence of major food groups in the diets of female Emydura krefftii from Townsville’s Creeks and Ross River.

62 3.6.2 Townsville Creeks Emydura krefftii

Overall diets of male and female E. krefftii (N=67) were found to be omnivorous by both percentage amount (Levin’s Standardised Niche Breadth =0.32) and frequency of occurrence (Levin’s Standardised Niche Breadth =0.35). Their main dietary components by percentage amount were windfall fruit (58%) and terrestrial insects (20%) (Figure 3.8). The rest of their diet consisted of submerged plants (10%), vertebrates (5%), sponge (3%) and aquatic insects (2%) (Figure 3.8). Windfall fruit (78%) and terrestrial insects (42%) were found to be the most occurring dietary items. Of lesser occurrence were submerged plants (21%), sponge (9%), vertebrates (7%), aquatic insects (3%), and molluscs (3%). The overall diet of E. krefftii in Townsville Creeks did not include any crustaceans (Figure 3.8).

The diet of male E. krefftii from Townsville’s Creeks (N=35) was found to be mostly omnivorous by both percentage amount (Levin’s Standardised Niche Breadth =0.32) and frequency of occurrence (Levin’s Standardised Niche Breadth =0.41). Their main dietary components by percentage amount were windfall fruits (64%) and terrestrial insects (15%) (Figure 3.9). The rest of their diet consisted of submerged plants (13%), sponge (5%), and vertebrates (2%) (Figure 3.9). Windfall fruit (89%) and terrestrial insects (37%), and submerged plants (29%) were found to be the most occurring dietary items. Of lesser occurrence were sponges (14%), vertebrates (6%), and aquatic insects (3%) (Figure 3.9). The overall diet of E. krefftii males from Townsville Creeks River was found to not consume any molluscs or crustaceans. (Figure 3.9).

Female E. krefftii from Townsville Creeks (N=32) was found to be mostly omnivorous by both percentage amount (Levin’s Standardised Niche Breadth =0.32) and frequency of occurrence (Levin’s Standardised Niche Breadth =0.35). Their main dietary components were windfall fruits (53%) and terrestrial insects (26%) (Figure 3.10). The rest of their diet consisted of vertebrates (9%), submerged plants (8%), aquatic insects (3%), molluscs (1%), and sponges (1%) (Figure 3.10). Windfall fruit (66%) and terrestrial insects (41%) were to be the most occurring dietary items. Of lesser occurrence were submerged plants (13%), vertebrates (9%), molluscs (6%), sponges (3%), and aquatic insects (3%) Figure (3.10). The overall diet of female E. krefftii from Ross River was found to not consume any crustaceans. (Figure 3.10).

63 3.6.3 River/Creek Comparisons

Overall diets of E. krefftii from the Townsville region differed between the Ross River and Townsville Creek’s by both percentage amount in diet (C=0.44 ) (Table 3.9) and frequency of occurrence (C=0.53 ) (Table 3.10). Ross River E. krefftii has a diet more composed of submerged plants in comparison to the Townsville Creek’s diet which was mostly composed of windfall fruit.

Diets of male E. krefftii from the Townsville region differed between the Ross River and Townsville Creek’s by both percentage amount in diet (C=0.40 ) (Table 3.9) and frequency of occurrence (C=0.51 ) (Table 3.10).

Male E. krefftii from Ross River seemed to have a diet mostly composed of submerged vegetation when compared to the Townsville Creek’s diet which was mostly composed of windfall fruits and terrestrial insects

Diets of female E. krefftii from the Townsville region differed between the Ross River and Townsville Creeks by both percentage amount in diet (C=0.44) (Table 3.9) and frequency of occurrence (C=0.52 ) (Table 3.10).

Female E. krefftii from Ross River seemed to have a diet mostly composed of submerged vegetation and molluscs when compared to the Townsville Creeks diet which was mostly composed of windfall fruits and terrestrial insects.

3.7 Sexual Size Dimorphism of Emydura krefftii

Mean body mass was greater in females than males at all sites (Table 3.11). Additionally, mean straight carapace length, curved carapace length/width, plastron length/width, head length/width were also greater in females (Table 3.11). Mean tail length though was found to be greater in males (Table 3.11). All morphological variables were found to be significantly different between the sexes (Appendix A).

Table 3.9. Dietary overlap (Morista’s original measure) by percentage amount in diets of Emydura krefftii from the Townsville Region Species Overall Creek Overall River Male Creek Male River Female Creek Female River

Overall Creek X 0.44 1.00 0.36 1.00 0.44 Overall River 0.44 X 0.46 0.93 0.42 0.91 Male Creek 1.00 0.46 X .40 0.97 0.44 Male River 0.36 0.93 0.40 X 0.33 0.69 Female Creek 1.00 0.42 0.97 0.33 X 0.44 Female River 0.44 0.91 0.44 0.69 0.44 X

Table 3.10. Dietary overlap (Morista’s original measure) by frequency of occurrence in diets of Emydura krefftii from Townsville. Species Overall Creek Overall River Male Creek Male River Female Creek Female River

Overall Creek X 0.53 1.00 0.46 1.00 0.53 Overall River 0.53 X 0.56 0.63 0.49 0.91 Male Creek 1.00 0.56 X 0.51 0.98 0.52 Male River 0.46 0.93 0.51 X 0.39 0.68 Female Creek 1.00 0.49 0.98 0.39 X 0.52 Female River 0.53 0.91 0.52 0.68 0.52 X

64 65

Table 3.11. Mean ± SE of nine morphological parameters for male and female Emydura krefftii from all localities sampled. All

measurements were made in mm except for body mass which is measured in grams.

Riverside Gardens Palmetum Stuart Creek Alligator Creek ♂ N=205 ♀N=305 ♂ N=111 ♀ N=213 ♂ N=53 ♀ N=69 ♂ N=119 ♀ N=114 Straight Carapace Length 177.7±1.61 198.6±1.76 194.6±1.74 223.8±1.61 188.1±4.95 194.6±8.41 186.4±3.42 196.5±5.74 Curved Carapace Length 188.3±1.69 211.4±1.86 206.2±1.81 238.0±1.70 200.6±5.03 209.2±8.83 198.0±3.58 210.8±6.08 Curved Carapace Width 152.5±1.32 175.5±1.57 165.7±1.52 197.7±1.57 165.0±3.68 178.8±7.23 160.7±2.66 176.0±5.26 Plastron Length 147±1.43 165.9±1.47 158.7±1.69 186.1±1.40 156.6±3.98 164.8±7.23 155.1±2.84 165.3±4.95 Plastron Width 59±0.57 67.8±0.64 64.3±0.66 78.0±0.64 63.7±1.67 68.7±2.83 62.1±1.08 68.5±2.23 Cranial Length 35.8±0.32 41.2±0.40 38.6±0.35 44.8±0.35 36.5±0.79 38.2±1.46 35.8±0.52 38.9±0.97 Cranial Width 28.6±0.25 34.5±0.38 31.1±0.29 38.5±0.39 30.3±0.76 35.0±2.10 26.6±0.41 33.4±0.91 Tail Length 85.1±1.10 57.6±0.77 92.4±1.10 65.4±0.74 90.3±2.99 59.0±2.87 87.7±2.14 58.3±1.91 Mass 697.4±18.22 1071±41.93 893.6±24.02 1494.5±32.53 904.9±70.46 1283.5±107.87 839.6±33.00 1217.2±76.34

66 Significant linear relationships, on a log-log scale, were evident between body mass and all other measurements (Appendix C). The slope of each of these relationships approximated isometry (slope=0.33), indicating generally proportionate growth over most of the size range. However with differences in body mass removed utilising residuals male and female E. krefftii were found to not be significantly different in terms of relative size of all morphological variable (Appendix B) with the exception of tail length which was found to be significantly different in the Stuart Creek E. krefftii (ANOVA, F=4.152, P=0.042) (Appendix B).

67 Chapter 4: Discussion

4.1 Population Density

Despite the variety of habitats (rivers, lakes, lagoons, farm dams) included in earlier studies (Table 4.1), turtle densities are typically low for Emydura, ranging from 10 to 114 turtles/hectares (Table 4.1). The lowest densities found in earlier studies came from the populations of E. m macquarii inhabiting Nortons Basins in NSW, these values though represent a population that appears to have been recently introduced and has not reached its full capacity (Judge, 2001). The higher densities reported for E. m.macquarii has been reported for populations inhabiting the Murray River (Judge, 2001) and Hawksview Lagoon in NSW (Spencer, 2001). Higher densities have been reported for Chelodina longicollis in farm dams (26 to 400 turtles/hectares) (Table 4.1) but these are thought to be concentrations of turtles during periods when its normal ephemeral habitats are dry. The lowest estimate for E. krefftii obtained in this study (493 turtles/hectares at Stuart creek) was higher than estimates for turtle density in any previous study (Table 4.1).

All of the previous studies of Australian freshwater turtles, with the exception of Carettochelys insculpta (Georges & Kennett, 1989), have occurred in subtropical or temperate climates (Table 4.1) so that there are no directly comparable studies of other tropical species. As with the study of C. longicollis(Carettochelys longicollis?), the density reported for C. insculpta was recognised by the authors as inflated because the turtles were in a pool of the river as it dried up because of seasonal contractions (Georges & Kennett, 1989). Legler (1980, 1981, and 1983) has conducted the most extensive surveys of freshwater turtles in tropical Australia. He did not estimate population density, but measured trapping success as the number of turtles captured per trap hour, using similar traps to those used in the present study. Legler (1980) regarded 20 turtles of one species caught in 20 traps (trapping success = 0.083) as excellent (Legler's emphasis) in most tropical habitats. For example, his success in billabongs in the Magela system ranged from 0 to a high of 0.033. In contrast, trapping success in the present study ranged from 1 to 18.5, establishing the Ross River populations as exceptional in the broader context of turtles, as well as Australia more generally.

High densities of turtles elsewhere in the world have been interpreted as a response to more productive environments (Moll & Moll, 2004); however only two of these make any reference to why the densities were high. In Israel, Mauremys caspica rivulata occurs at

68

Table 4.1. Population estimates of Australian freshwater turtles. Number in parentheses is turtles per hectare. Species and Locality Population S.E. Number of Estimate Individuals marked E. krefftii (Riverside, QLD) (This Study) 1164 (684) 613 509 E. krefftii (Palmetum, QLD) (This Study) 1122 (5342) 741 324 E. krefftii (Stuart Creek, QLD) (This Study) 105 (493) 94 122 E. krefftii (Alligator Creek Highway, QLD) (This Study) 587 (2935) 416 184 Em. m. krefftii (Fraser Island, QLD) (Georges, 1982a) 718 (87) 14 668 Em. m. macquarii (Norton’s Basin, NSW) (Judge, 2001) 240.77 51.21 263 (10.6 - 12.1) Em. m. macquarii (Murray River, NSW) (Judge, 2001) (111) Em. m. macquarii (Banksview Lagoon, NSW) (Spencer, 2001) (95) 888 Em. m. macquarii (Hawksview Lagoon, NSW) (Spencer, 2001) (114) 794 Carettochelys insculpta (South Alligator River, NT) (Georges 27 (33.8) 21 & Kennett, 1989) Chelodina longicollis (Farm dams, Armidale, NSW) (400) (Parmenter, 1976) Chelodina longicollis (Farm dams, Gippsland, VIC) (240) (Chessman, 1978) Chelodina longicollis (Lagoons, Gippsland, VIC) (Chessman, (160) 1978) Chelodina longicollis(Farm ponds, NSW) (Burgin et al. 1999) 37 (360) 37 Chelodina longicollis (Lake McKenzie, NSW) (Georges et al. (163.8) 34.2 109 1986) Chelodina longicollis (Lake Windermere, NSW) (Georges et al. (26.1) 8.3 100 1986) Elseya georgesi (Bellinger River, NSW) (Blamires et al. 2005) 4468 1409 446

69 densities of 500-2000 turtles/hectares in polluted streams compared to densities of 19-217 turtles/hectares in relatively unpolluted waterways (Gasith & Sidis, 1984). These high densities were thought to result from greater food availability and lower competition from other aquatic vertebrates excluded by the pollution (Gasith & Sidis, 1984). In Brazil Phrynops geoffroanus occurs at densities of 170-230 turtles/hectares in a polluted urban river (Souza & Abe, 2000). These high densities were thought to result from an abundance of food, abundance of nesting areas, and minimal predation (Souza & Abe, 2000). Both studies demonstrate that high turtle abundance can result from a change in environmental conditions, such as pollution, which alter food availability and predation pressure. Both habitats were polluted, had reduced populations of predators and had more available resources.

There are a number of possible explanations for the high abundances of Emydura krefftii in the Ross River:

(a) Eutrophication through increased nutrient run-off and/or pollution/ human disturbance; The Ross River does not receive any industrial or sewage runoff though may receive a small amount of agricultural runoff. The Ross River, however, has been heavily modified by human development and is used for various recreational activities, including water skiing, rowing and as a place to feed the turtles and ducks. The potential negative impacts of such activities on populations of animals within the river system have not been determined. Alligator Creek and Stuart Creek on the other hand have relatively lower densities when compared to Ross River although the density at Alligator Creek is still higher than recorded for most other Emydura spp. These waterways also do not receive any waste though farm runoff would happen as both are in close proximity to agriculture. This runoff probably causes minimal damage as algal blooms and fish-kills associated with runoffs were never seen during the study. Both of these sites are also relatively inaccessible except for the upper reaches of Alligator Creek which we did not include in the population estimates because of low recaptures at the site. The E. krefftii in Alligator and Stuart Creek’s areas are not as disturbed anthropologically as the Ross River populations. Due to the lower anthropogenic disturbance likely to occur to turtles in Alligator and Stuart Creek’s, their population estimates are probably a truer reflection of natural densities of E. krefftii in river systems in northern Qld.

70 (b) Conversion from a lotic to a lentic environment by the construction of weirs; The three weirs that were installed have effectively changed the river into a series of eutrophic lakes. Changes in the flow pattern of rivers have been suggested to be an advantage to Em. macquarii (Chessman, 1988) and Em. signata has also been found to thrive in eutrophic water pools near Brisbane (Booth, 2005), thus showing that E. krefftii thriving in these environments is probably a part of overall Emydura ecology. Alligator and Stuart Creek’s are free flowing during the wet season which would greatly change the habitats within these areas which may effect the turtles as food resources may change throughout the year depending on water levels.

(c) Reduced predation of adults by the elimination of a major natural predator, the crocodile; The Ross River weirs have also effectively stopped the movement of saltwater crocodiles, which are a major predator of adult freshwater turtles (Webb & Manolis, 1989) into this area. An introduced population of freshwater crocodiles is present in the river in low densities but both adult and juvenile freshwater turtles are virtually non-existent in the overall diets of freshwater crocodiles from various localities (Webb & Manolis, 1989). Alligator and Stuart Creek’s are not impounded and free flowing though a weir exists in Alligator Creek before it empties into the sea but thus has not stopped the movement of saltwater crocodiles in the study sites as confirmed by sightings by Queensland Parks and Wildlife Service and local land owners along the banks. Stuart Creek has not been found to have any evidence of saltwater crocodiles but it flows through an extensive mangrove system, which is a favoured habitat of saltwater crocodiles, before emptying into the ocean so their presence must be treated with caution.

4.2 Population Structure

Most sites had a female-biased sex ratio, the exceptions being Alligator Creek and Stuart Creek (Table 4.2). This bias was consistent across years, except for Ross River which showed variation across years, and Alligator and Stuart Creeks for which there were insufficient data.

These results possibly derive from sampling bias from gear selectivity (Ream & Ream, 1966; Gibbons, 1970b; Gibbons, 1990; Gibbons & Lovich, 1990) but the traps used in this study have been shown not to have a sex bias (Georges 1982). However there are a

71

Table 4.2. Sex ratios of Emydura spp throughout Australia. Species and Locality Males Females Ratio M: F E. krefftii (Riverside, QLD) (This Study) 206 303 0.68 E. krefftii (Palmetum, QLD) (This Study) 112 212 0.52 E. krefftii (Stuart Creek, QLD) (This Study) 53 69 0.77 E. krefftii (Alligator Creek, QLD) (This Study) 119 115 1.03 Emydura macquarii krefftii (Fitzroy River, QLD) (Tucker, 1999) Impounded 514 791 0.65 Emydura macquarii krefftii (Fitzroy River, QLD) (Tucker, 1999) Unimpounded 175 169 1.04 Emydura macquarii krefftii (Kolan River, QLD) (Tucker, 1999) Impounded 173 169 1.02 Emydura macquarii krefftii (Kolan River, QLD) (Tucker, 1999) Unimpounded 62 74 0.84 Emydura macquarii krefftii (Burnett River, QLD) (Tucker, 1999) Impounded 631 759 0.83 Emydura macquarii krefftii (Burnett River, QLD) (Tucker, 1999) Unimpounded 387 343 1.13 Emydura macquarii krefftii (Burnett River, QLD) (Limpus et al. 2002) Unimpounded 132 132 1.00 Emydura macquarii krefftii (Mary River, QLD) (Tucker, 1999) Impounded 93 120 0.78 Emydura macquarii krefftii (Mary River, QLD) (Tucker, 1999) Unimpounded 97 81 1.20 Emydura macquarii krefftii (Mundubbera, QLD) (Tucker, 1999) 523 561 0.93 Emydura macquarii krefftii (Fraser Island, QLD) (Georges, 1982) 153 142 1.07 Emydura macquarii macquarii (Brisbane River, QLD (Judge, 2001) 68 60 1.13 Emydura macquarii macquarii (Macleay River, NSW) (Judge, 2001) 82 78 1.05 Emydura macquarii macquarii (Hunter River, NSW) (Judge, 2001) 77 136 0.56 Emydura macquarii macquarii (Murray River, NSW) (Judge, 2001) 94 91 1.03 Emydura victoriae (Daly River, NT) (Welsh, 1999 ) 77 86 1.12

72 Number of other explanations. Gibbons (1990) identified four biological factors affecting sex ratios in turtles.

1. Hatchling Sex Ratio. Turtles that have TSD or temperature sex determination may have more males or females hatch at a certain time depending on the temperature that would greatly skew sex ratios. 2. Differential mortality of the sexes. Turtles may have different mortality based on their sex as adults. Examples of this include that females have to leave the water to nest thus making them more vulnerable to predators. 3. Influence of maturation rate. Male and female turtles tend to mature at different ages. Therefore if male turtles reach maturity faster than females there may always be a male biased sex ratio in the adults because more males are recruiting into sexual maturity each year than females. 4. Differential emigration and immigration of the sexes. One sex might travel further than the other. In the mating season some male turtles may travel outside of the study site thus leaving mostly females to sample, which would skew the sex ratio.

Hatchling sex ratio is unknown in the Townsville area. Chelid turtles do not have TSD (Bull et al. 1985; Georges 1988; Thompson 1988; Georges and McInnes 1998), so the biased sex ratios observed in this study, if accurate, are enigmatic.

Differential mortality of the sexes was not tested in our study as we did not get enough recaptures of males from all sites to test for it. To date no study in Australia has investigated differential mortality between sexes of turtles. Differential mortality has been thought to be the cause behind a female-biased sex ratio of slider turtles in South Carolina. In this population the males are eaten more regularly by alligators than the larger females which have led to the female- biased sex ratio (Gibbons et al. 1979). The Ross River populations are not exposed to predation by crocodiles. However Alligator Creek and Stuart Creek may experience mortality associated with saltwater crocodiles but as their sex ratios are not significantly skewed it shows that differential mortality is not evident in the Townsville area and does not contribute to the skewed sex ratios.

The influence of maturity is considered the single most important factor influencing sex ratios (Gibbons, 1990) with the earlier maturing sex predominating (Lovich & Gibbons, 1990). Judge’s (2001) study found that males which matured more rapidly were the cause of

73 the male bias in sex ratios at these sites. In the Townsville area male E. krefftii are known to become sexually mature before females. As the sex ratios in the Townsville area, are female- biased this theory does not hold as females the later maturing sex dominate.

Of the possible causes identified by Gibbons (1990), differential movements and dispersion of the sexes seems the most likely explanation for the female-biased sex ratios in this study. I did not test movements between sexes, though it was noted that males appeared to be harder to catch during the mating season suggesting that they were moving up and down the river and creeks in search of mates. Females on the other hand were more likely to inhabit the original areas in which they were captured, presumable because they had no reason to move large distances in search of mates. Judge (2001) found a biased sex ratio similar to those found in this study at Hunter River in New South Wales. He suggested that the female bias may have been due to differential distribution of males and females in the river, and that the bias arose because he trapped only at a large sandy area where females lay. This study was done in a variety of habitats and throughout the year thus providing a better insight into sex ratios in the Townsville area, but the sex ratio bias in the present study may have resulted from the same process. Indeed, the Ross River and Townsville Creek’s habitats are drastically different in that the river is impounded whereas the creeks were not. Sex ratios of Em. krefftii are known to differ substantially between unimpounded areas to impounded water bodies (Tucker 1999).

The population size structure observed in the Ross River is similar to that of the Burnett River population – both are skewed towards adults with low levels of recruitment, though the reasons for this remain unknown (Limpus et al. 2002). This lack of juveniles within the Ross River (see Table 4.2) resembles that of fox-predated populations inhabiting the Murray River where egg predation is over 96% (Thompson, 1983b). Thompson’s (1983b) study showed that the Murray River E. macquarii population structure was very different to the Cooper Creek E. macquarii, a population with less egg predation, in that it was mostly made up of older individuals with very little juvenile recruitment in to population.

No hatchlings were captured at Ross River, though hard shelled hatchlings were caught at Alligator and Stuart Creek’s. This can not be due to sampling methods as the same trapping regime was used at all sites. Juveniles may be harder to find within Ross River in that they may not be present at sites where large densities of adults are congregated, as they may be predated upon. Nest predation pressure is unknown for Ross River but as most of the

74 River flows through suburban Townsville the affect of dogs, cats, and rat predation may be intense. Alligator and Stuart Creek’s on the other hand resembled regular populations of turtles with juvenile’s recruitment ongoing. These areas are based in more rural areas of Townsville and are mostly inaccessible. This may deter feral predators from nests allowing recruitment to happen. The Ross River population did have a large number of small turtles suggesting that juvenile recruitment takes place but is very infrequent. The exaggerated densities of the Ross River probably represent a major problem for juvenile recruitment for many reasons. The first of these might be that the Ross River is stocked with Barramundi every year. An ongoing study on fish densities in the Ross River found a direct reduction in fish numbers following stocking of barramundi into the Ross River (Webb, pers. comm.). Barramundi have not been reported to feed on hatchling turtles but other carnivorous fish such as eels (Cann, 1998), catfish (Cann, 1981) and saratoga have been found to prey upon newly hatched E. krefftii although they do not constitute a large proportion of their diet (Phillott & Parmenter,2000). Perhaps the stocking of large predatory fish into the Ross River may account for some of reduction in number of juveniles. The second reason may be that because of the high densities of E. krefftii in the Ross River juveniles are either in direct competition with adults. Only detailed studies on juvenile E. krefftii in the Ross River would be able to determine why their recruitment is limited.

4.3 Growth Rates/Age at Maturity

Emydura krefftii of both sexes inhabiting the Townsville area conform to the typical reptilian growth pattern of rapid juvenile growth followed by slower growth upon reaching maturity (Kennett, 1996). This fast juvenile growth allows reptiles to rapidly attain sexual maturity so they can start reproducing at a young age. In freshwater turtles this rapid growth allows them to attain sizes at which they are less susceptible to predation.

Growth in Townsville E. krefftii was found to be in accordance with other studies done on Emydura spp. (Table 4.3). Spencer (2001) found that E. macquarii males grew at a faster rate than females across the Murray Darling Basin. He also found very rapid juvenile growth for both sexes (Spencer, 2001). Unfortunately in this study we were never able to mark any hatchlings and cannot infer on hatchling growth curves. The closest study to Townsville was by Tucker (1999). He found that male E. krefftii grew at faster rates than females. However his study combined all his growth interval data from across a large range of habitats, both disturbed and undisturbed to do his growth analysis.

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Table 4.3. Growth rate parameters used in Von Bertalannffy Growth curve analysis and ages of maturity of various Australian freshwater turtles. Species Asymptote Rate of growth Age at Maturity (mm) (mm) (years) Male Female Male Female Male Female Emydura krefftii Ross River (This Study) 215 260 0.32 0.27 6-7 8-10 Emydura krefftii Townsville’s Creeks (This Study) 205 315 0.32 0.13 6-7 Emydura macquarii krefftii (Southeast QLD) (Tucker, 1999) 168.8 184.6 0.41 0.32 7-9 7-9 Emydura macquarii macquarii(Macleay River, NSW) (Judge, 2001 163.2 0.13 Emydura macquarii macquarii(Nepean River, NSW) (Judge, 2001) 186.1 224.8 0.37 0.27 4-5 6-7 Emydura macquarii macquarii(Hunter River, NSW) (Judge, 2001 227.8 0.12 Emydura macquarii macquarii(Murray River, NSW) (Judge, 2001 250.8 264.6 0.20 0.18 Emydura macquarii macquarii (Murray River) (Spencer, 2001) Plastron L. 208 214 0.23 0.20 5-6 10-11 Chelodina longicollis (Armidale, NSW) (Parmenter, 1976) 321.6 0.15 7 10-11 Chelodina rugosa (Knuckey's Lagoon, NT) (Kennet, 1996) 197.5 246.2 0.41 0.29 4 6 Elseya dentata (Douglas River, NT) (Kennet, 1996) 258.1 307.2 0.20 0.16 8 13 Elseya georgesi (Bellinger River, NSW) (Blamires et al. 2005) Plastron L. 137.9 176.1 0.11 0.14 7-9 Elseya latisternum (Southeast QLD) (Tucker, 1999) 210 280 0.23 0.12 8 12

76 The male E. krefftii grew at the same rates regardless of location and had similar asymptote sizes and mean adult sizes (Table 4.3). The study also found that females inhabiting the abundant sites within the Ross River grew at almost twice the rate of those from the less abundant population. My expectation, outlined in the introduction to the thesis, was that more abundant populations would lead to a decrease in growth through resource competition. For example, a study Trionyx sinensis found that individuals of both sexes maintained at densities of 9.49 turtles m/2 had significantly lower growth compared to individuals kept at 0.83 turtles m/2 (Choo & Chou, 1987). This bias in growth rates was based probably on dominance hierarchy as the females of this species display the aggressive tendencies of soft-shelled turtles (Lardie, 1964). Clearly this study does not support the hypothesis that high abundance leads to lower growth rates in this species. This conclusion will be discussed further in the synopsis.

4.4 Size at Maturity

Various methods exist for determining sexual maturity from examination the collection and systematic dissection of a large series of turtles is today not considered an ethical option (Kuchling, 1999). The methods of determining sexual maturity through palpation of female turtles has been used in many studies on Australian freshwater turtles (Kennett, 1999; Judge, 2001; Spencer, 2002) and has been found to be a reliable determination of sexual maturity in females. Kuchling (1999) mentioned that palpation is not 100% effective at determining minimum female maturity as it has been found to not be accurate for large specimens carrying small clutches of eggs and small specimens that carry one or two eggs a clutch.

The palpation method used in this study was thus deemed suitable as we aimed at determining the minimum reproductive sizes of females E. krefftii which are known to lay multiple clutches of eggs (Georges, 1985). Mature male E. krefftii are easily distinguished from other turtles by the elongation of the preanal portion of the tail which coincides with male maturity (Georges, 1983). This elongation of the tail is very readily visible in males however a closer inspection of if the tail was well formed in terms of build was the basis to determine sexual maturity in males. This technique worked and is non-invasive.

Size at maturity varies widely amongst populations of turtles within the Townsville area and throughout Australia (Table 4.4). However male E. krefftii appeared to reach sexual

77

Table 4.4. Carapace Length at Maturity for turtles of the genera Emydura. Species Carapace Length at Maturity Males Female Emydura krefftii Riverside, Ross River (This Study) 160mm 208mm Emydura krefftii Palmetum, Ross River (This Study) 148mm 185mm Emydura krefftii Alligator Creek (This Study) 148mm 242mm Emydura krefftii Stuart Creek (This Study) 160mm 232mm Emydura macquarii krefftii (Fitzroy River) (Tucker, 1999) 183mm 205mm Emydura macquarii krefftii (Kolan River) (Tucker, 1999) 189mm 191mm Emydura macquarii krefftii (Burnett River) (Georges, 1985) 180mm Emydura macquarii krefftii (Burnett River) (Tucker, 1999) 191mm 216mm Emydura macquarii krefftii (Burnett River) (Limpus et al. 2002) 189mm 211mm Emydura macquarii krefftii (Mary River) (Tucker, 1999) 178mm 205mm Emydura macquarii krefftii (Fraser Island) (Georges, 1985) 110-117mm 150-155mm Emydura macquarii signata (Brisbane River, QLD) (Judge, 2001) 170-195mm 211-215mm

78 maturity at smaller sizes in the more dense areas of Alligator Creek and Palmetum, Ross River, however differences between these sites were very small. Smaller sizes at maturity have been linked to fast growth rates which are maintained by E. krefftii in the Townsville region (See section 4.5). Faster growth allows males to attain sexual maturity at an earlier size than turtles with slow growth that usually attain maturity at larger sizes. As sexual maturity is most often associated with attainment of a minimum size rather than age (Bury, 1979, Moll, 1979; Thornhill, 1982; MacCulloch & Secoy, 1983; Ernst & Macdonald, 1989) it allows turtles living in enriched environments to mature faster that other populations. This theory has been shown in freshwater turtles throughout the world inhabiting a range of different habitat types and that age at maturity varies considerably among some species (Gibbons et al. 1981). Most of these studies documenting differences in sexual maturity involved turtles living in either different latitudes or different environments (Gibbons, 1970a; Gibbons et al. 1981; Thornhill, 1982; Ernst & Macdonald, 1989). In more productive environments, such as thermally enriched ponds, Gibbons (1970a) found that Pseudemys scripta inhabiting a thermally polluted pond when compared to normal thermal ponds were reaching sexual maturity at earlier ages than co-specifics in normal waterways.

Females were found to become sexually mature at smaller sizes in the Ross River when compared to the Townsville Creek’s (Table 4.4). Differences in sexual maturity appeared to be strongly linked to growth rates where species that have faster growth mature at smaller sizes. Species with slower growth tend to become sexually mature at larger sizes. The female E. krefftii inhabiting the Ross River grew at a much faster rate than the females inhabiting Alligator and Stuart Creek’s and were consequently are able to reach sexually mature at earlier ages. Female E. krefftii from Ross River appeared to reach sexual maturity at the same sizes exhibited by Emydura throughout Australia (Table 4.4). Turtles from Alligator Creek and Stuart Creek’s appeared to reach sexual maturity at larger sizes than most other species (Table 4.4). This is probably due to slower growth rates for females within Alligator and Stuart Creek’s.

4.5 Rates of Survival and Immigration

Survival rates have only been reported from two other studies on Australian freshwater turtles (Table 4.5). Judge (2001) found that the introduced population of E. macquarii inhabiting Norton’s Basin had a very low survival rate. He attributed this to the

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Table 4.5. Survival, and immigration estimates of Australian freshwater turtles Annual S.E. Annual S.E. Survival Immigration (PHI) (M) E. krefftii (Riverside, QLD) (This Study) 0.81 0.32 431.5 376.2 E. krefftii (Palmetum, QLD) (This Study) 0.60 0.30 843.2 1248.6 E. krefftii (Stuart Creek, QLD) (This Study) 0.52 0.42 91.2 162.5 E. krefftii (Alligator Creek, QLD) (This Study) 0.57 0.41 208.4 355.2 Em. m. macquarii (Norton’s Basin, NSW) (Judge, 2001) 0.470 0.08 44.18 6.43 Em. m. macquarii (Murray River, NSW) (Judge, 2001) 0.94 0.18 31.08 81.44 Em. m. macquarii (Banksview Lagoon, NSW) (Spencer, 2001) 0.95 Em. m. macquarii (Hawksview Lagoon, NSW) (Spencer, 2001) 0.96

80 population being introduced and still adjusting to the new environment and that mortality may be high among adult turtles through recreational fishing (Judge, 2001). In contrast Spencer (2001) reported very high rates of survival within his two lagoons. He found that there appeared to be almost no predation on adults, but predation on hatchlings was much higher. This was probably attributed to the fact that adult predation was only observed during nesting season when females left the water and were predated by foxes (Spencer, 2001). Survival rates within the Ross River varied greatly between the two sites whereas the Townsville Creek’s estimates did not vary greatly. These estimates did suggest that survival within the Ross River was higher than the Townsville Creek’s. During the study it was noted that there did not appear to be any major predators of adult E. krefftii within the Ross River. The Townsville Creek’s sites, especially Alligator Creek, are home to adult saltwater crocodiles which are known to be a major predator of adult freshwater turtles (Webb & Manolis, 1989).

Immigration rates for Townsville were found to vary greatly but were associated with very high standard errors. The general trend showed high immigration within the Ross River with lower values for the Townsville Creeks. As the standard errors were more than the values itself, care must be taken in trying to interpret the data. More work is required on the rates of immigration of freshwater turtles.

4.6 Dietary Parameters

The Emydura spp. have consistently been found to be omnivorous as adults (Welsh, 1999; Tucker, 1999; Cann, 1998; Chessman, 1986; Georges, 1982b) (Table 4.6). These dietary shifts which are usually from carnivory to omnivory, probably allow a high density of turtles to survive without any competition between juveniles and adults, thus increasing resources. Omnivorous turtles usually only have a small percentage of animal matter in their diets with plant material making up most of their diet (Kennett & Tory, 1996). This can also be on the reverse especially in areas where plant matter may be harder to obtain. On Fraser Island E. krefftii seemed to consume more animal matter because plant material is not common in the unproductive environment of the dune lakes (Georges, 1982b).

Emydura krefftii from the Townsville region were found to be omnivorous with little dietary specialisation. Freshwater turtle diet seems to be more decided by the circumstances

81

Table 4.6. Known diets of Australian freshwater turtles. Species Major Reference Diet Carettochelys insculpta Omnivore Georges & Kennett, 1989; Welsh, 1999 Chelodina burrungandjii Carnivore Thomson et al. 2000 Chelodina expansa Carnivore Legler, 1978; Chessman, 1983 Chelodina longicollis Carnivore Parmenter, 1976; Chessman, 1983, 1984; Georges et al. 1986 Chelodina rugosa Carnivore Welsh, 1999, Kennett, 1994 Elseya albagula Herbivore Thomson et al. 2005, Armstrong & Booth, 2005 Elseya dentata Herbivore Legler, 1976; Kennett, 1994; Welsh, 1999 Elseya sp. aff. dentata (Johnstone) Herbivore Pers obs Elseya georgesi Omnivore Allanson & Georges, 1999 Elseya latisternum Omnivore Tucker, 1999 Elseya purvisi Omnivore Allanson & Georges, 1999 Elusor macrurus Herbivore Flakus, 1999 Emydura m. krefftii (Se QLD) Omnivore Tucker, 1999 Emydura m. krefftii Fraser Island Omnivore Georges, 1982b Emydura krefftii Ross River Omnivore This study Emydura krefftii Townsville Creeks Omnivore This study Emydura macquarii Omnivore Chessman, 1978; Chessman, 1986; Spencer et al. 1998 Emydura subglobosa Omnivore Welsh, 1999 Emydura tanybaraga Omnivore Welsh, 1999 Emydura victoriae Omnivore Welsh, 1999 Pseudemydura umbrina Carnivore Burbidge, 1981 Rheodytes leukops Carnivore Legler & Cann, 1980

82 of opportunity, rather than searching for particular items. Since turtles are generally not agile, herbivory has been one option, but this requires specialisation of the digestive system (Pritchard, 1984). This has lead to the trend of omnivory within most freshwater turtles (Moll & Moll, 2000). Diet though is not that restricted but seems to be more determined by where turtles lives, its age, and where in its reproductive cycle it is.

In the Ross River E. krefftii of both sexes primarily fed upon vegetation compared to the more diverse diet of Stuart and Alligator Creek’s males of windfall fruit and terrestrial insects. Females from the Ross River, Stuart Creek, and Alligator Creek consumed a variety of prey items. Ross River female E. krefftii though was found to consume more molluscs and submerged vegetation than the Alligator Creek and Stuart Creek females.

The diet of Ross River E. krefftii before impoundments is unknown but was probably very similar to the Alligator Creek and Stuart Creek diet. However as Ross River has been impounded their have been changes to the water flow of the River by the construction of the weirs that may have led to an increase in the amount of submerged vegetation, so that turtles in the Ross River have more opportunity to ingest it, rather than the terrestrial-originating items that the Townsville Creek’s turtles utilise. Turtles within the Ross River are also readily fed by the residents of this area but the dietary analysis found this supplemental feeding to not constitute a major percentage of the diet, though it may increase the availability of food available to turtles. Tucker (1999) stated that a ready availability of food will coincide with higher turtle densities than areas with lesser availability of food. This study found very high densities of E. krefftii inhabiting the Ross River which is a testimonial to the large amount of resources present in the river to support this population. Tucker (1999) however reported that in impoundments dietary variation of E. krefftii was lower than compared to unimpounded habitats. This study found the complete opposite with overall diets being more diverse in Ross River than in Alligator and Stuart Creek’s.

In Alligator and Stuart Creek’s all E. krefftii appeared to have a reliance on windfall fruit and terrestrial insects. Windfall fruit and terrestrial insects were also observed in the diet of Ross River E. krefftii but not at the greater amount and frequency of Alligator and Stuart Creek. Both of these food items are abundant along the banks of the Ross River but with higher densities of E. krefftii than Stuart and Alligator Creek’s the reliance on this resource seems to have shifted the diet of Ross River E. krefftii to submerged plants, a resource not readily utilised in the other areas. Dietary shifts are common within freshwater turtles they

83 are highly opportunistic especially in generalist species (Moll & Moll, 2004). Georges (1982b) study of E. krefftii on Fraser Island found they consumed mostly animal matter because plant material was not common in the unproductive environment of the dune lakes (Georges, 1982). Elseya dentata from Daly River, Northern Territory, have a diet of primarily aquatic vegetation where it is abundant, however in the Douglas River, Northern Territory E. dentata feed on a diet of windfall fruit and leaves, where aquatic vegetation may be absent (Welsh, 1999). Across the world, unproductive environments, such as deeper areas of the Mississippi, force turtles such as Graptemys pseudographica ouachitensis to switch their diets to terrestrial vegetation and insects if aquatic vegetation is not present (Moll, 1976). Freshwater turtles that do exhibit a diet change are easily able to readily change some of their demographic factors. Recently Souza and Abe (2000) studied a population of Phrynops geoffroanus in a polluted river in Brazil. Their findings were that P. geoffroanus inhabiting these areas had switched from a diet of seeds, fruits, and leaves (Fachin-Teran et al. 1995) to a diet of entirely Chironomid larvae had then lead to P.geoffroanus being able develop high densities of 170-230 turtles/hectares (Souza & Abe, 2000).

Little information exists for the nutritional requirements of turtles; however studies have shown that species which feed on a higher percentage of protein have faster growth rates. Mayeaux et al. (1996) found that Chelydra serpentina had faster growth rates when fed an experimental diet that was 66% protein. This study also showed that turtles were able to effectively utilise high levels of vegetable protein and in conjunction had a better growth response than turtles fed on diets of animal protein (Mayeaux et al. 1996).

4.7 Sexual Size Dimorphism

Sexual size dimorphism was found to be evident in all populations of E. krefftii that were studied in the Townsville region with the females being larger than males. The one exception to this was a giant male (0, 10, Carapace Length, 296mm, mass 3150gm) that was caught 16/3/04. This turtle was the largest by straight carapace length E. krefftii ever seen in the Townsville area. This turtle was included in the sexual size dimorphism analysis, but as the sexual size dimorphism index relies on the largest turtle caught it was omitted as I thought it was not a representative of the mean of the male population as it was 108mm larger than the mean of males at Stuart Creek (Table 4.7). However the overall results agree with other studies from around the world on freshwater turtles that have found that most riverine species display sexually dimorphic characters in the terms of shell size (Moll & Moll, 2004).

84

Table 4.7. Sexual size dimorphism of Emydura spp. from across Australia. Sexual size dimorphism index was determined by the methods defined in Gibbons & Lovich (1990) in which the maximum size of the larger sex is divided by the maximum size of the smaller sex, these result in either a positive value when females are larger or a negative value if males are larger. Species and Locality Straight Carapace Length (mm) SSD

♀ ♂ E. krefftii (Riverside) This study 278 232 +1.20 E. krefftii (Palmetum) This study 284 228 +1.26 E. krefftii (Alligator) This study 288 264 +1.09 E. krefftii (Stuart) This study with Giant male 278 296 -1.07 E. krefftii (Stuart) This study excluding Giant male 278 255 +1.09 Emydura macquarii krefftii (Fitzroy River) (Tucker, 1999) 308 269 +1.14 Emydura macquarii krefftii (Fitzroy River) (Georges, 1985) 281 277 +1.07 Emydura macquarii krefftii (Kolan River) (Tucker, 1999) 282 264 +1.07 Emydura macquarii krefftii (Burnett River) (Tucker, 1999) 303 281 +1.08 Emydura macquarii krefftii (Burnett River) (Limpus et al. 2002) 291 270 +1.08 Emydura macquarii krefftii (Mary River) (Tucker, 1999) 274 252 +1.09 Emydura macquarii krefftii (Fraser Island) (Georges, 1982) 246 197 +1.25 Emydura macquarii signata (Brisbane River) (Judge, 2001) 280 259 +1.08 Emydura macquarii macquarii(Macleay River) (Judge, 2001) 185 153 +1.21 Emydura macquarii macquarii(Hunter River) (Judge, 2001) 242 212 +1.14 Emydura macquarii macquarii(Nepean River) (Judge, 2001) 260 227 +1.15 Emydura macquarii macquarii(Murray River) (Judge, 2001) 303 278 +1.09 Emydura macquarii macquarii(Murray River) (Chessman, 1978) 324 272 +1.19 Emydura macquarii macquarii(Coopers Creek)(Doddridge, 1992) 335 281 +1.20

85 Specifically though turtles of the genus Emydura have also been found to be sexually dimorphic in all species studied (Table 4.7)

Sexual size dimorphism is most often attributed to differences in reproductive strategies with females being larger than males (Gibbons and Lovich 1990a) though other theories do exist (Berry & Shine, 1980). This is thought to enable the females to have greater clutch sizes because of the larger area to accommodate eggs. Clutch size in E. krefftii has been found to be positively correlated with larger females producing larger clutches (Georges, 1982a) however no data exists on clutch sizes from the Townsville area. Sexual size dimorphism has also been found to be related to frequency of clutching (Forsman & Shine, 1995) though this has never been shown for the genus Emydura. The other theory suggests that sexual size dimorphism evolved independently with habitat type and male mating strategy (Berry & Shine, 1980). This theory states that turtles in which the males are smaller force the males to adopt complex mating strategies as has been observed in Emydura spp. which adopt an array of eye blinks and nose squirts to attract females (Murphy & Lamoreaux, 1978; Norris, 1996; Cann, 1998).

The largest sexual size dimorphism differences were found between the male and female E. krefftii from the high density sites of Riverside and Palmetum (Table 4.7) suggesting that sexual size dimorphism is most evident in these populations compared to the low density sites. The sexual size dimorphism index showed Riverside and Palmetum were more closer to that of the populations of E m. macquarii inhabiting Coopers Creek and Macleay River, and also E. m. krefftii inhabiting Fraser Island (Table 4.7). This is interesting as sexual size dimorphism has been found to vary geographically due to local variations in environmental conditions (Gibbons & Lovich, 1990a). No study has studied the reasons behind differences in sexual size dimorphism in any Australian turtles. Of these populations the comparison with Coopers Creek is relevant because this site has exaggerated densities of Em. macquarii that are also the largest in body size of all the Emydura (George’s pers. comm.) suggesting that maybe sexual size dimorphism is related to density. The Fraser Island and Macleay River forms appear to display the smallest body size of the Emydura studied to date and also display high degrees of sexual size dimorphism (Table 4.7). These size differences in these forms though are more related to the environment in which they live as Fraser Island is considered an unproductive insular environment (Georges, 1985) and that the Macleay River is one of the more colder environments studied by Judge (2001), suggesting lower productivity and growth overall.

86

Differences in sexual size dimorphism between populations have been attributed to a wide array of factors and have been studied in other parts of the world. Rowe (1997) studied four different population of Chrysemys picta belli in Nebraska and found that sexual dimorphism with females larger than males was most evident in population with slower growth rates. Differences in growth rates and mortality were hypothesised to affect sexual size dimorphism in Sternotherus odoratus from Ontario with males being larger than females (Edmonds & Brooks, 1996).

Recently Trembath et al. (2004) described sexual size dimorphism from the Riverside population that was also studied in the present study. In that study they found that females had significantly larger relative cranial length, cranial width, and carapace width. In this study we utilised their methods and found there to be no relative difference in sexual size dimorphism between males and females with the exception of relative tail length from Stuart Creek. This is of interest as this study was conducted at the same sites and failed to find any differences in relative morphology between the sexes. This study spanned four years and data was taken from 509 E. krefftii whereas the Trembath (et al. 2004) study only one season and caught 126 E. krefftii. This shows that in order to get accurate measures of sexual size dimorphism from a turtle population much greater effort must be put in to enable the researchers to gather larger sample sizes of turtles that may be needed for the analysis than was thought before.

87 Chapter 5: Synopsis

5.1 Demographic affects of Superabundance

This study was the second in Australia to determine demographic characters of a population of freshwater turtles inhabiting the seasonally wet/dry tropics of North Queensland. This thesis provides a study on how population density may affect the demographic parameters of Emydura krefftii. Specifically this thesis also compared the life histories of populations of E. krefftii inhabiting large rivers in comparison to small creeks within the North Queensland Area.

The densities recorded in this study were the highest recorded for freshwater turtles in Australia. Few studies have documented population sizes of freshwater turtles throughout Queensland for comparison, and the closest population estimate for E. krefftii come from Fraser Island, where their ecology is unique in being an insular form (Georges, 1985). The superabundance recorded in this study may be a natural effect as freshwater turtles have been found to occur in large densities throughout the world, however few of these studies aimed to determine the cause of these elevated densities. Throughout the study casual observations were made at other sites along the Ross River that determined that populations were indeed very high throughout the river. As expected smaller freshwater creeks throughout Townsville had much lower densities. These lower densities are probably a factor of smaller freshwater environments that may lower productivity. The smallest site sampled, the Palmetum, had the highest density of turtles compacted into a very small creek which flowed into the Ross River. The turtles inhabiting the Ross River had a high number of recaptures, which may indicate that there is little movement from sites. The turtles within the Creek’s were recaptured on a lower basis suggesting that they may have to move farther to find food and nesting areas which appear to be in abundance at Ross River.

This study found that the population of E. krefftii within the Ross River were all female biased in sex ratios and also appeared to be made up of older individuals. The Townsville Creek’s populations of E. krefftii were mostly evenly distributed with a large number of juveniles present in the population whereas Ross River had few juveniles. This may be cause for concern as turtle populations that are mostly made up of older individuals may not have adequate recruitment for continued survival (Thompson, 1983b). Thompson’s (1983b) study found that the cause of the population dominated by older individuals may have

88 been fox predation which effectively eliminated juveniles from the population through nest mortality. Nest mortality of E. krefftii is unknown at the sites and few predated nests were found on the banks of the Ross River site throughout the study. The predated nests that were found were quite old and it was impossible to determine the predator. This leaves the question as to what is limiting the recruitment of juvenile E. krefftii into the population? This can be answered two ways. The first is that juvenile E. krefftii are scarce as other studies have never reported many hatchlings caught (Georges, 1982; Limpus et al. 2002), thus recruitment into any population is low. The second reason could be that there is a high mortality associated with juvenile E. krefftii within the Ross River. Juveniles are probably present in the river as the population structures found were not as dramatic as those reported by Thompson (1983b). However the superabundance of turtles might make life short for a high percentage of the hatchlings through either direct predation of hatchlings or resource competition between adults and juveniles. Unfortunately, this study was not able to determine a cause for the biased sex ratio within the river. The creek’s were only sampled for one season and thus should be sampled over many seasons as sex ratios changed drastically from the first season at Ross River. Survival estimates were made for the populations in the Townsville area and reported that survival was highest within the Ross River and lower in Alligator and Stuart Creek’s. The impoundments within the Ross River has possible increased survival of turtles as their main predator, the saltwater crocodile, is no longer present in these stretches of the Ross River. These crocodile however are present at Alligator Creel and might be at Stuart Creek. Within the Ross River estimates were very high at Riverside but quite low at Palmetum, which was the highest density. This is very interesting in that this might show that very dense populations of E krefftii might experience lower survival rates through competition for resources. Immigration rates reported in this study were found to be very high also but also had very high standard errors. With such large populations present there is probably a large amount of movement between these areas. However the large standard errors associated with this parameter meant that any interpretation of the data needed much care.

Growth rates reported in this study were within the ranges reported on Australian freshwater turtles. Originally it was thought that because of higher temperatures and abundance of food, the growth rate of tropical E. krefftii would be higher than that reported for other populations. The study however found that E. krefftii from the Townsville had similar growth rates compared to some populations. No difference in growth was found for male E. krefftii from either the Ross River or Townsville Creek sites but a large difference in growth was found between female E. krefftii. The females inhabiting the Ross River grew at

89 almost double the rate of the Townsville creek sites. This is probably a consequence of resource availability as diets were found to be completely different between the sites with minimal overlap. Perhaps the diet of female E. krefftii within the Ross River is of a higher nutritional value that would allow the females to grow faster to maturity. The maturity estimates recorded in this study were very different. As growth is intrinsically linked to sexual maturity it seems that the difference in diets of E. krefftii from the two sites is a major factor influencing their demographic parameters. As stated in the thesis differences in diet have been found to produce very different demographic parameters among turtle populations throughout the world. This one factor is probably causing the superabundance of turtles in the Ross River. Turtles within Townsville’s Creek include windfall fruits and insects, which would not be available on an everyday basis and may also explain why turtles in these systems might move farther distances in search of prey, which may explain the low-recapture rates for the creeks.. The Ross River on the other hand is a large permanent waterway that has a lot of aquatic vegetation which E. krefftii of both sexes feed on. This availability of food would allow faster growth to be maintained and also limits competition between individuals which may lead to decreased growth. Lastly this study found that sexual-size dimorphism was evident within all populations studied.

As this study contrasted two very different habitat types, of which one was impounded, there may be possible effects of weirs/impoundments on freshwater turtles in North Queensland. Weirs and impoundments have been found to seriously affect freshwater turtles through a variety of ways (Moll, 2004). Elseya latisternum is known to possess a very efficient cloacal breathing system (King, 1994) in which it obtains oxygen through a pair of vascularised sacs inside it cloaca (King & Heatwole, 1994). Impoundments would have lower dissolved oxygen content which may affect the ecology of these turtles though this remains unknown (Limpus et al. 2002). This may reflect why this species was not found to be as common within impounded areas such as the Ross River . Chelodina canni was encountered rarely but the habitats sampled were not ideal habitats for this species as it prefers seasonal floodplains areas (McCord & Thomson, 2002).

5.2 Freshwater Turtle Conservation in North Queensland

Prior knowledge of the biology and ecology of the turtle fauna of North Queensland was of only a handful of turtle species that were placed into existing species descriptions or were unknown at the time. In 1994 Elseya irwini was discovered inhabiting the Burdekin

90 River (Cann, 1998). Four years later the existing turtle Chelodina novaeguinea was redescribed as C. canni and shown to be mostly present in North Queensland (McCord & Thomson, 2002). Within the waterways of the Johnstone River system lives an undescribed Elseya sp. (Georges & Adams, 1996) that appears to be a North Queensland endemic and still awaits formal species recognition. North Queensland is now known to be home to the following species Chelodina canni, Emydura krefftii, Elseya sp. (Johnstone River Form), Elseya irwini, and Elseya latisternum. While all of these species are reasonably common with the exception of E. irwini, they all share the fact that very little research has been undertaken on populations of these turtles inhabiting North Queensland. The present study described demographic changes associated with overabundance caused by effects of change from impoundments. However it was only able to focus on E. krefftii, which is the most common of all these turtles throughout the area. North Queensland has been extensively modified since human settlement causing vast areas of lowland rainforest to be converted to sugar cane production. While no turtles inhabited these lowland forest areas they did inhabit the range of wetlands that flowed through them. Through the processes of habitat change many of North Queensland waterways have been modified into water storage for agriculture and other purposes. Unfortunately no historical data on turtle populations exist for North Queensland as it does for other parts of the world. This problem makes predictions of effects of impoundments on turtle fauna difficult as we have no baseline to compare these populations to.

Of particular concern was the apparent small population of Elseya latisternum within the Ross River. As stated before the Ross River has been changed drastically into a series of eutrophic ponds that may not present the ideal habitat of E. latisternum which may restrict them to only inhabit Jensen’s Creek at the Palmetum Botanical Gardens. North Queensland has inherited many of the problems associated with any waterways that are in close proximity to people. Through the various recreational activities of people, turtles continue to be affected. Of major concern is fishing and boating in the Ross River. While doing fieldwork many turtles were seen with fishing line dangling from their mouths and a large number had injuries consistent with boat strike. Unfortunately these turtles that were damaged proved to be harder to catch than normal ones due to stress of a fish hook lodged inside their body. Recreational fishing practise, both legal and illegal, probably contribute to mortality of turtles that is never seen or known of.

91 5.3 Further Research

This study was not able to ascertain the very important questions of how does superabundance affect clutch sizes and frequency. This study did however find many other interesting differences between the high density populations of the Ross River in comparison to the low densities of Townsville creeks. A study on clutch frequency/size would determine if the Ross River females have reduced fecundity in order to not overpopulate. The Ross River might also have greater fecundity in order to combat the apparent recruitment issues that appear for juveniles in the Ross River.

Hopefully this thesis will promote more research to be initiated in the Ross River and the entire North Queensland area. Specifically the Ross River presents an ideal study site to test predictions concerning management of natural populations. Additionally, with its ideal setting close to major university and city would enable other researchers to have a valuable study site at a low cost with a high return in data, an exchange not usually possible in other situations.

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110 Appendix. A. ANOVA results for eight morphological parameters comparing male and female Emydura krefftii from all localities sampled.

Riverside Gardens Palmetum Stuart Creek Alligator Creek H Significance H Significance H Significance H Significance Straight Carapace Length 73.400 0.001 111.486 0.001 4.606 0.032 12.792 0.001 Curved Carapace Length 77.133 0.001 114.782 0.001 5.201 0.023 14.539 0.001 Curved Carapace Width 102.363 0.001 128.685 0.001 7.523 0.006 18.524 0.001 Plastron Length 77.691 0.001 113.191 0.001 5.957 0.015 13.707 0.001 Plastron Width 89.270 0.001 127.185 0.001 6.266 0.012 20.449 0.001 Cranial Length 91.217 0.001 101.587 0.001 3.889 0.049 18.384 0.001 Cranial Width 120.417 0.001 124.153 0.001 5.294 0.021 20.303 0.001 Tail Length 202.937 0.001 183.272 0.001 42.607 0.001 94.346 0.001 Mass 83.270 0.001 125.284 0.001 4.894 0.027 15.051 0.001

111 Appendix B. ANOVA results for eight relative morphological parameters (Calculated utilising residuals) comparing male and female Emydura krefftii from all localities sampled. All values are from nonparametric ANOVA except for values with * which are F values derived from parametric ANOVA.

Riverside Gardens Palmetum Stuart Creek Alligator Creek H Significance H Significance H Significance H Significance Straight Carapace Length 0.0594 0.807 0.162 0.687 0.000* 1.000 0.296 0.586 Curved Carapace Length 0.0697 0.792 0.537 0.464 0.000* 1.000 0.363 0.547 Curved Carapace Width .038 0.845 0.720 0.396 0.000* 1.000 2.486 0.115 Plastron Length 0.0167 0.897 1.356 0.244 0.000* 1.000 0.0474 0.828 Plastron Width 0.002 0.959 0.408 0.523 0.070 0.790 0.575 0.448 Cranial Length 0.005 0.940 0.294 0.588 0.00* 1.000 0.103 0.748 Cranial Width 0.001 0.970 0.493 0.482 0.00* 0.998 0.00* 1.000 Tail Length 0.157 0.692 0.146 0.703 4.152 0.042 0.00* 1.000

112

2.6 A B

2.4

2.2

2.0 Log Carapace (mm) Carapace Log

1.8 2 CCL=1.38+0.32,r2=0.96 CSL=1.34+0.32,r =0.96 2 CCL=1.34+0.33,r2=0.95 CSL=1.31+0.33,r =0.95

1.62.5 2.2 C D 2.4 2.0

2.3

1.8 2.2

2.1 1.6

2.0 1.4 Log Carapace(mm) Log Tail Length (mm) Tail Length Log 1.9

CW=1.31+0.31,r2=0.95 TL=0.66+0.37,r2=0.74 1.2 1.8 CW=1.31+0.31,r2=0.94 TL=0.90+0.36,r2=0.51

1.7 1.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Log Mass (g) Appendix C. Linear regressions of Log Curved Carapace Length (A), Log Straight Carapace width (B), Log Carapace Width (C), and Log Tail Length (D) of Emydura krefftii from Riverside, Ross River. The solid dots and lines represent females, and the open dots and dash lines represent males.

113

2.6 A B 2.4

2.2

2.0

1.8 Log Plaston (mm) Plaston Log

1.6

2 PL=1.27+0.32,r2=0.97 PW=0.85+0.33,r =0.93 1.4 2 PL=1.32+0.33,r2=0.93 PW=0.83+0.33,r =0.89

2.01.2 C D 1.8

1.6

1.4

Log Cranial (mm)Log Cranial 1.2

2 1.0 CL=0.73+0.30,r =0.81 CW=0.53+0.36,r2=0.83 CL=0.74+0.29,r2=0.79 CW=0.65+0.29,r2=0.81

0.8 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Log Mass (g) Appendix C. Linear regressions of Log Plastron Length (A), Log Plastron Width (B), Log Cranial Length (C), and Log Cranial Width (D) of Emydura krefftii from Riverside, Ross River. The solid dots and lines represent females, and the open dots and dash lines represent males.

114

2.6 A B

2.5

2.4

2.3

2.2 Log Carapace (mm) Carapace Log

2 2.1 CCL=1.44+0.30,r2=0.90 CSL=1.40+0.30,r =0.91 2 CCL=1.42+0.30,r2=0.83 CSL=1.39+0.30,r =0.83

2.02.6 2.2 C D 2.1 2.5

2.0

2.4 1.9

2.3 1.8

1.7 2.2 Log Carapace(mm) Log Tail Length (mm) Tail Length Log 1.6

2.1 CW=1.27+0.33,r2=0.89 TL=0.97+0.27,r2=0.34 CW=1.32+0.31,r2=0.79 TL=1.47+0.17,r2=0.17 1.5

2.0 1.4 2.4 2.6 2.8 3.0 3.2 3.4 3.6 Log Mass (g) Appendix C. Linear regressions of Log Curved Carapace Length (A), Log Straight Carapace width (B), Log Carapace Width (C), and Log Tail Length (D) of Emydura krefftii from Palmetum Ross River. The solid dots and lines represent females, and the open dots and dash lines represent males.

115

2.6 A B

2.4

2.2

2.0 Log Plaston (mm) Plaston Log

1.8

2 PL=1.27+0.32,r2=0.93 PW=0.82+0.34,r =0.88 2 PL=1.25+0.32,r2=0.82 PW=0.80+0.34,r =0.78 1.61.9 CW=0.39+0.38,r2=0.76 C D CW=0.74+0.26,r2=0.56 1.8

1.7

1.6

Log Cranial (mm) Cranial Log 1.5

1.4 CL=0.72+0.30,r2=0.76 CL=0.86+0.25,r2=0.52 1.3 2.4 2.6 2.8 3.0 3.2 3.4 3.6 Log Mass (mm)

Appendix C. Linear regressions of Log Plastron Length (A), Log Plastron Width (B), Log Cranial Length (C), and Log Cranial Width (D) of Emydura krefftii from Palmetum, Ross River. The solid dots and lines represent females, and the open dots and dash lines represent males.

116

2.6 A B 2.5

2.4

2.3

2.2

2.1 Log Carapace (mm) Carapace Log 2.0 2 CCL=1.37+0.32,r2=0.98 CSL=1.32+0.33,r =0.98 2 1.9 CCL=1.28+0.35,r2=0.95 CSL=1.24+0.36,r =0.94

1.82.5 2.4 C D 2.4 2.2

2.3 2.0

2.2 1.8 2.1 1.6 2.0 Log Carapace (mm) Carapace Log

1.4 (mm) Tail Length Log 1.9 CW=1.33+0.31,r2=0.98 2 TL=0.66+0.37,r =0.92 1.2 1.8 CW=1.29+0.32,r2=0.96 TL=0.40+0.53,r2=0.86

1.7 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Log Mass (g) Appendix C. Linear regressions of Log Curved Carapace Length (A), Log Straight Carapace width (B), Log Carapace Width (C), and Log Tail Length (D) of Emydura krefftii from Alligator Creek. The solid dots and lines represent females, and the open dots and dash lines represent males.

117

2.6 A B 2.4

2.2

2.0

1.8 Log Plastron (mm)

1.6 2 PL=1.21+0.38,r2=0.98 PW=0.87+0.32,r =0.98 2 PL=1.14+0.36,r2=0.95 PW=0.83+0.33,r =0.94 1.4

1.8 C D 1.7

1.6

1.5

1.4 Log Cranial (mm) 1.3

CL=0.82+0.26,r2=0.97 2 1.2 CW=0.68+0.28,r =0.96 CL=0.79+0.27,r2=0.93 CW=0.72+0.26,r2=0.94

1.1 1.5 2.0 2.5 3.0 3.5 4.0 Log Mass (g)

Appendix C. Linear regressions of Log Plastron Length (A), Log Plastron Width (B), Log Cranial Length (C), and Log Cranial Width (D) of Emydura krefftii from Alligator Creek. The solid dots and lines represent females, and the open dots and dash lines represent males.

118

2.6 A B

2.4

2.2

2.0

1.8 2 CCL=1.31+0.34,r2=0.99 CSL=1.25+0.39,r =0.99 2 CCL=1.34+0.33,r2=0.97 CSL=1.26+0.35,r =0.97

1.62.6 2.4 C D

Log Carapace (mm) 2.2 2.4

2.0

2.2 1.8

1.6 2.0

1.4 Log Tail Lenght (mm)

1.8 2 2 CW=1.32+0.31,r =0.99 TL=0.61+0.39,r =0.89 1.2 CW=1.38+0.29,r2=0.95 TL=0.47+0.50,r2=0.76

1.6 1.0 1.01.52.02.53.03.54.0 Log Mass (gm)

Appendix C. Linear regressions of Log Curved Carapace Length (A), Log Straight Carapace width (B), Log Carapace Width (C), and Log Tail Length (D) of Emydura krefftii from Stuart Creek. The solid dots and lines represent females, and the open dots and dash lines represent males.

119

2.6 A B 2.4

2.2

2.0

1.8 Log Plastron(mm)

1.6 2 PL=1.30+0.36,r =0.99 PW=0.85+0.33,r2=0.98 PL=1.22+0.22,r2=0.97 2 1.4 PW=0.80+0.34,r =0.94 1.8

1.7 C D

1.6

1.5

1.4

1.3 Log Cranial(mm) 1.2

2 2 1.1 CRL=0.76+0.28,r =0.98 CRW=0.67+0.29,r =0.97 CRL=0.77+0.27,r2=0.95 CRW+0.56+0.32,r2=0.91

1.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Log Mass (gm) Appendix C. Linear regressions of Log Plastron Length (A), Log Plastron Width (B), Log Cranial Length (C), and Log Cranial Width (D) of Emydura krefftii from Stuart Creek. The solid dots and lines represent females, and the open dots and dash lines represent males.