Mark A. Read

Estuarine crocodiles ride surface currents to facilitate long-distance travel

1. The estuarine crocodile (Crocodylus porosus) is the worlds largest living reptile. It predominately inhabits freshwater and estuarine habitats, but widespread geographic distribution throughout oceanic islands of the South-east Pacific suggests that individuals undertake sizeable ocean voyages. 2. Here we show that adult C. porosus adopt behavioural strategies to utilise surface water currents during long-distance travel, enabling them to move quickly and efficiently over considerable distances. 3. We used acoustic telemetry to monitor crocodile movement throughout 63 km of river, and found that when individuals engaged in a long-distance, constant direction journey (>10 km day(-1)), they would only travel when current flow direction was favourable. Depth and temperature measurements from implanted transmitters showed that they remained at the water surface during travel but would dive to the river substratum or climb out on the river bank if current flow direction became unfavourable. 4. Satellite positional fixes from tagged crocodiles engaged in ocean travel were overlaid with residual surface current (RSC) estimates. The data showed a strong correlation existed between the bearing of the RSC and that of the travelling crocodile (r(2) = 0.92, P < 0.0001). 5. The study demonstrates that C. porosus dramatically increase their travel potential by riding surface currents, providing an effective dispersal strategy for this species.

Satellite tracking reveals long distance coastal travel and homing by translocated Estuarine Crocodiles, Crocodylus porosus

Crocodilians have a wide distribution, often in remote areas, are cryptic, secretive and are easily disturbed by human presence. Their capacity for large scale movements is poorly known. Here, we report the first study of post-release movement patterns in translocated adult crocodiles, and the first application of satellite telemetry to a crocodilian. Three large male Crocodylus porosus (3.1–4.5 m) were captured in northern Australia and translocated by helicopter for 56, 99 and 411 km of coastline, the last across Cape York Peninsula from the west coast to the east coast. All crocodiles spent time around their release site before returning rapidly and apparently purposefully to their capture locations. The animal that circumnavigated Cape York Peninsula to return to its capture site, travelled more than 400 km in 20 days, which is the longest homeward travel yet reported for a crocodilian. Such impressive homing ability is significant because translocation has sometimes been used to manage potentially dangerous C. porosus close to human settlement. It is clear that large male estuarine crocodiles can exhibit strong site fidelity, have remarkable navigational skills, and may move long distances following a coastline. These long journeys included impressive daily movements of 10–30 km, often consecutively.

Diving Behaviour of a Reptile (Crocodylus johnstoni) in the Wild: Interactions with Heart Rate and Body Temperature

The differences in physical properties of air and water pose unique behavioural and physiological demands on semiaquatic animals. The aim of this study was to describe the diving behaviour of the freshwater crocodile Crocodylus johnstoni in the wild and to assess the relationships between diving, body temperature, and heart rate. Time‐depth recorders, temperature‐sensitive radio transmitters, and heart rate transmitters were deployed on each of six C. johnstoni (4.0–26.5 kg), and data were obtained from five animals. Crocodiles showed the greatest diving activity in the morning (0600–1200 hours) and were least active at night, remaining at the water surface. Surprisingly, activity pattern was asynchronous with thermoregulation, and activity was correlated to light rather than to body temperature. Nonetheless, crocodiles thermoregulated and showed a typical heart rate hysteresis pattern (heart rate during heating greater than heart rate during cooling) in response to heating and cooling. Additionally, dive length decreased with increasing body temperature. Maximum diving length was 119.6 min, but the greatest proportion of diving time was spent on relatively short (<45 min) and shallow (<0.4 m) dives. A bradycardia was observed during diving, although heart rate during submergence was only 12% lower than when animals were at the surface.

Body Temperatures and Winter Feeding in Immature Green Turtles, Chelonia mydas, in Moreton Bay, Southeast Queensland

Body temperatures of immature Clenonia mydas does not deviate significantly from water temperature in the range of 15-22.7 degrees C. Additionally, there was no correlation between Tb and body mass, indicating that larger turtles in the sampled range of sizes (9.2 - 39.5 kg) were not gaining a thermal advantage over smaller individuals.

Remote monitoring of crocodilians: implantation, attachment and release methods for transmitters and data-loggers

Crocodilians are by their very nature difficult animals to study. However, research on wild animals is essential for the development of reliable long-term management. Here, we describe methods for the acquisition and monitoring of behavioural and physiological variables from free-ranging crocodilians through the use of archival tags (data-loggers) and via satellite, radio and acoustic telemetry. Specifically, the attachment or implantation of electronic tags is described and examples provided of the type of data that can be collected. Our research group has used a combination of approaches to monitor the movements, diving activity, body temperatures and heart rates of crocodilians, including studies on the Australian freshwater crocodile (Crocodylus johnstoni), the estuarine crocodile (Crocodylus porosus) and the caiman (Caiman latirostris). Each approach or method presents unique challenges and problems, chiefly as a consequence of differences in body morphology and size of the crocodilian species, their behaviours and the habitats they occupy.

The distribution and abundance of the estuarine crocodile, Crocodylus porosus, in Queensland

A total of 6444 Crocodylus porosus (4303 non-hatchlings and 2141 hatchlings) were recorded during 196 vessel-based surveys of 103 waterways to determine the distribution and abundance of Crocodylus porosus in Queensland. The surveys, conducted from January 1994 to December 2000, covered 4174.3 km of waterway. Population structure was biased towards immature crocodiles, with 91% of all animals sighted being less than the minimum breeding size for individuals in the Northern Territory. The mean relative density of non-hatchling C. porosus was highest in waterways of north-western Cape York Peninsula and Lakefield National Park, and lowest for waterways along the populated east coast of Queensland. The highest numbers of hatchlings were recorded from waterways of north-western Cape York Peninsula, where nearly 74% of all hatchlings were recorded during the seven-year survey period. The C. porosus population in northern Queensland appears to be undergoing a limited recovery, with marginal increases in the mean relative density of non-hatchlings in seven of the eight crocodile biogeographic regions. On the basis of the distribution and abundance of hatchling and non-hatchling crocodiles, the north-western Cape York Peninsula region contains the best habitat for C. porosus in Queensland, particularly in the Wenlock River and Tentpole Creek area.

Home range and movements of radio-tracked estuarine crocodiles (Crocodylus porosus) within a non-tidal waterhole

We radio-tracked five male and eight female estuarine crocodiles (Crocodylus porosus) in a non-tidal waterhole in Lakefield National Park in northern Queensland during the late dry/mid-wet season (2003-04) and the following dry season (2004). Individual crocodiles occupied larger home ranges (River Channel Areas (RCA) during the late dry/mid-wet season (10.64 ± 2.86 ha) than in the dry season (3.20 ± 1.02 ha), and males occupied larger home ranges (23.89 ± 2.36 ha) than females (5.94 ± 1.34 ha) during the late dry/mid-wet season. There were no obvious differences in home range between sexes during the dry season. During the late dry/mid-wet season, adult males often travelled long distances along the waterhole while females moved less. During the dry season, movement patterns were quite variable, with no clear difference between sexes. All crocodiles were most active from late afternoon (1500-1800 hours) until midnight. Individual home ranges (RCA) overlapped considerably during the late dry/mid-wet season. The extent of home-range overlap between three adult males and the number of times they either passed each other or were located near each other was particularly striking. Previous research has come to conflicting conclusions about the extent of territoriality in wild estuarine crocodiles, although it has been widely believed that males are highly territorial. The findings imply that large adult male estuarine crocodiles are not highly territorial in non-tidal freshwater systems that are geographically confined.

A review of fibropapillomatosis in Green turtles (Chelonia mydas)

Despite being identified in 1938, many aspects of the pathogenesis and epidemiology of fibropapillomatosis (FP) in marine turtles are yet to be fully uncovered. Current knowledge suggests that FP is an emerging infectious disease, with the prevalence varying both spatially and temporally, even between localities in close proximity to each other. A high prevalence of FP in marine turtles has been correlated with residency in areas of reduced water quality, indicating that there is an environmental influence on disease presentation. Chelonid herpesvirus 5 (ChHV5) has been identified as the likely aetiological agent of FP. The current taxonomic position of ChHV5 is in the family Herpesviridae, subfamily Alphaherpesvirinae, genus Scutavirus. Molecular differentiation of strains has revealed that a viral variant is typically present at specific locations, even within sympatric species of marine turtles, indicating that the disease FP originates regionally. There is uncertainty surrounding the exact path of transmission and the conditions that facilitate lesion development, although recent research has identified atypical genes within the genome of ChHV5 that may play a role in pathogenesis. This review discusses emerging areas where researchers might focus and theories behind the emergence of FP globally since the 1980s, which appear to be a multi-factorial interplay between the virus, the host and environmental factors influencing disease expression.

First record of sea snake (Hydrophis elegans, Hydrophiinae) entrapped in marine debris.

Entanglement in derelict fishing gear and other marine debris is a major threat to the survival of large marine wildlife like cetaceans, seabirds and sea turtles. However, no previous reports of entanglement or entrapment have been recorded in sea snakes (Hydrophiinae). We report here on a sea snake (Hydrophis elegans) found with a ceramic washer encircling its body captured from the north-east coast of Queensland, Australia. The ring had constricted the body and over time caused extensive damage to the underlying tissues. A post-mortem examination showed the snake was severely emaciated as the ring restricted the passage of food to the stomach and intestine. This is the first record of mortality due to marine debris entrapment in sea snakes.

When Is a Male Turtle Not a Male?—Observations on Intersex Turtles

Abstract We report on an intersex green turtle, Chelonia mydas, observed at Raine Island, Australia that externally resembled an adult male but internally—based on laparoscopic examination—had both ovarian and testicular structures resembling those of an adult. This individual was the first intersex turtle that has been recorded on a nesting beach during the 39 years of extensive census studies in Queensland. Its observation confirms that the definitive identification of sex with marine turtles remains dependent on observations of their gonads or on observing eggs being laid.