21 research outputs found
Comment on “Insulative capacity of the integument of the dugong (Dugong dugon): thermal conductivity, conductance and resistance measured by in vitro heat flux”
No full textCommunicated by U. Sommer.
This article presents original research to investigate the relationship between integumentary composition and predictive thermal capacity. The authors suggest that cold stress syndrome (CSS) is unlikely to occur in dugongs, a claim that is at odds with a recent study from our group where we described the local appearance of mortality cases consistent with this syndrome. Horgan et al. (2014) made two statements, in particular, which disregarded a diagnosis following observations by specialist veterinary pathologists, yet without, to our knowledge, accessing the material themselves and instead quoting ‘unpublished data’ to support their conclusions. Further, and importantly, Horgan et al. (2014) ignore the pathological changes we described in other organ systems, which were consistent with changes noted during CSS in manatees and led to our diagnosis.
Cold stress syndrome is an incompletely understood but clearly very complicated, multisystemic entity that has been described as affecting Florida manatees chronically exposed to cold water (Bossart et al. 2002). Florida and south-east Queensland (QLD) are very similar in climate, species composition and marine environment. In 2013, our group published an article comparing the lesions described in manatees with those we were seeing in many of the dugongs presenting to our post-mortem room during the colder months of the year in Queensland. This description was combined with presentation of supporting environmental data (Owen et al. 2013).
Horgan, Booth, Nichols and Lanyon have made statements contradicting our argument in their article, namely: “with no credible pathological evidence of CSS (cf. Owen et al. 2013)” and “Skin lesions suggested as characteristic of cold stress and reported for dugongs by Owen et al. (2013) are grossly and histologically different to those reported for the Florida manatee, are found in dugongs throughout the tropics (Woolford and Lanyon unpublished data) and are also found in dugongs in cooler waters outside the winter period (the latter point also reported by Owen et al. 2013). Each of these factors casts serious doubt as to these skin characteristics being thermally related”. These statements are not based on sound scientific principles.
In the former instance, this statement has been made without offering any supporting or qualifying evidence and is therefore an unsubstantiated opinion. The dugong samples used for Owen et al. (2013) were assessed and compared by experienced pathologists and experts in marine population health, one of whom (MF) is in the unique position of having first-hand experience with disease in both manatees in Florida and dugongs in southeast QLD. Data and the resulting interpretations in this article were also deemed as credible by multiple reviewers. The qualifying evidence in support of the second unsubstantiated statement by Horgan et al. (2014) is that dugongs do not exhibit cold stress at 15 °C, which has been linked to Bossart et al. (2002, 2004) studies on manatees. Neither of these articles have any reference to dugongs, raising question as to where this information was derived. Further, the evidence offered by Horgan et al. (2014) in this statement is logically questionable in the way it concludes dugongs cannot get cold stress and is insufficient, based on unpublished data and misleading for other studies into this syndrome.
It is inadequate to suggest that skin lesions in the two species are different without supportive data and a reasonable scientific basis. A major concern of this rebuttal of our work is that the authors are hinging their scientific arguments by making a statement about lesions in cases they have not seen (grossly or histologically) and are then using this unfounded opinion to dismiss peer-reviewed scientific data. In addition, the precise nature of these “differences” identified by the authors needs to be described in order for their significance to be determined by the reader. Even without this information, we are sceptical that diagnostically significant differences exist as skin has a very stereotypical and non-specific range of responses to any chronic injury. Chronic lesions that are essentially indistinguishable, particularly on gross examination, can be produced by a wide array of triggers. For this reason, even though the authors have noted similar lesions in “dugongs throughout the tropics”, these lesions could have a completely different cause to those reported in our study. Also, it is diagnostically dangerous to assume that an animal in one region requires the same conditions (in this case, the same low-temperature trigger point) as an animal in another region to express the clinical signs of a disease. We do not understand the influences of geography and species differences on precipitating environmental conditions, and it is important that researchers keep an open mind and report without bias. Finally, the authors’ suggestion that these lesions are seen in dugongs throughout the tropics is misleading given dugongs’ vast range and the nature of response to syndromes. The dugong’s range spans estimated tropical and subtropical coastal and island waters of some 40 countries encompassing approximately 860,000 km2 (Marsh et al. 2012) and would require a range of trigger points unique to each locale to manifest skin lesions. Even if the authors have noted these lesions in their study sites, they cannot extrapolate to all dugong habitat and aetiologies to draw their presented conclusions.
This article highlights how misleading it can be to examine one lesion in isolation rather than the animal as a whole and to make generalizations on syndromes without solid evidence, particularly in species where response to disease is not well documented or understood. Cold stress syndrome is also obviously a complicated disease, and a multifactorial aetiology is likely, given that some animals in a particular environment can be affected while others are not. Expecting a direct cause-and-effect relationship with water temperature risks oversimplifying the syndrome and will encourage future researchers to overlook data that could be vital to increase our understanding.
A holistic and multidisciplinary approach is required in order for us to progress our understanding of this entity. We hope researchers in this field are not swayed or discouraged by the opinion presented in Horgan, Booth, Nichols and Lanyon’s recent article and rather view the data presented as a potential piece in the CSS puzzle that requires a collegial effort to solve
Ocean-finding in marine turtles: the importance of low horizon elevation as an orientation cue
No full textSea finding behaviour in hatchling sea turtles is widely believed to be guided by orientation towards the brightest horizon and away from high silhouettes. We propose that the horizon profile at the lowest angle of elevation is a more important cue for ocean finding than light intensity. Examples of hatchling orientation occurring at natural nest sites, at preselected beach release sites, and within a walled wooden arena under various conditions in the field, are presented. We conclude that hatchlings orient as follows: (1) Hatchlings move towards the horizon line at the lowest angle of elevation; (2) Hatchlings move away from high silhouettes, in a direction that remains close to the horizon line at the lowest angle of elevation; (3) Should a conflict exist regarding the direction of lowest horizon elevation, hatchlings move towards the brightest lowest horizon. This refinement to current theory explains numerous instances of natural non-ocean-finding behaviour in marine turtles, which occur both by day and by night, and in the absence of artificial lighting. We propose that the disruption caused to hatchling orientation by artificial lighting close to nesting beaches occurs because bright lights mask the horizon line as a cue by making it impossible to discern, causing the hatchlings to move towards the only visible "horizon" — the artificial lights. Consequently, we recommend that managers of sea turtle rookeries where turtles have an ocean-finding problem should manipulate the beach profile to ensure the direction of the ocean matches the lowest angle of elevation, in combination with light reduction strategies — as the most effective means of preventing disrupted orientation
Temporal changes in artificial light exposure of marine turtle nesting areas
No full textArtificial light at night poses a significant threat to multiple taxa across the globe. In coastal regions, artificial lighting close to marine turtle nesting beaches is disruptive to their breeding success. Prioritizing effective management of light pollution requires an understanding of how the light exposure of nesting areas changes over time in response to changing temporal and spatial distributions of coastal development. We analyzed multitemporal, satellite night-light data, in combination with linear mixed model analysis, to determine broadscale changes in artificial light exposure at Australian marine turtle nesting areas between 1993 and 2010. We found seven marine turtle management units (MU), from five species, have experienced significant increases in light exposure over time, with flatback turtles nesting in east Australia experiencing the fastest increases. The remaining 12 MUs showed no significant change in light exposure. Unchanging MUs included those previously identified as having high exposure to light pollution (located in western Australia and southern Queensland), indicating that turtles in these areas have been potentially exposed to high light levels since at least the early nineties. At a finer geographic scale (within-MU), nine MUs contained nesting areas with significant increases in light exposure. These nesting areas predominantly occurred close to heavily industrialized coastal areas, thus emphasizing the importance of rigorous light management in industry. Within all MUs, nesting areas existed where light levels were extremely low and/or had not significantly increased since 1993. With continued coastal development, nesting females may shift to these darker/unchanging 'buffer' areas in the future. This is valuable information that informs our understanding of the capacity and resilience of marine turtles faced with coastal development: an understanding that is essential for effective marine turtle conservation
Coastal light pollution and marine turtles: assessing the magnitude of the problem
No full textGlobally significant numbers of marine turtles nest on Australian beaches; however,the human population of Australia is also heavily concentrated around coastal areas. Coastal development brings with it increases in artificial light. Since turtles are vulnerable to disorientation from artificial light adjacent to nesting areas, the mitigation of disruption caused by light pollution has become an important component of marine turtle conservation strategies in Australia. However, marine turtles are faced with a multitude of anthropogenic threats and managers need to prioritise impacts to ensure limited conservation resources can result in adequate protection of turtles. Knowledge of the extent to which nesting areas may be vulnerable to light pollution is essential to guide management strategies. We use geographical information system analysis to over-lay turtle nesting data onto night-time lights data produced by the NOAA National Geophysical Data Center, to assess the proportion of marine turtles in Australia potentially at risk from light pollution. We also identify the Australian nesting sites which may face the greatest threat from artificial light. Our assessment indicates that the majority of nesting turtles appear to be at low risk, but population management units in Western Australia and Queensland are vulnerable to light pollution. The risk to turtles from light generated by industrial developments appears significantly higher than at any other location. Consequently, managers of turtle management units in regions of proposed or on-going industrial development should anticipate potentially disrupted turtle behaviour due to light pollution. Our methodology will be useful to managers of turtles elsewhere
Influence of industrial light pollution on the sea-finding behaviour of flatback turtle hatchlings
No full textContext: Numerous studies show that artificial light disrupts the sea-finding ability of marine turtle hatchlings. Yet very little has been published regarding sea-finding for flatback turtles. Given the current industrialisation of Australia's coastline, and the large potential for disruption posed by industrial light, this study is a timely investigation into sea-finding behaviour of flatback turtle hatchlings.
Aims: We investigate sea-finding by flatback turtle hatchlings in relation to ambient light present in areas of planned or ongoing industrial development, and evaluate the fan and arena-based methods that are frequently used for quantifying hatchling dispersion.
Methods: Using a combination of methods, we assessed the angular range and directional preference of sea-finding hatchlings at two key flatback turtle rookeries, Peak and Curtis Islands, during January–February 2012 and 2013, and at Curtis Island in January 2014. Relative light levels at each site were measured using an Optec SSP-3 stellar photometer, and moon phase, moon stage and cloud cover were also recorded.
Key results: We found no evidence of impaired hatchling orientation, and observed very low levels of light at Peak Island. However, at Curtis Island, hatchlings displayed reduced sea-finding ability, with light horizons from the direction of nearby industry significantly brighter than from other directions. The sea-finding disruption observed at Curtis Island was less pronounced in the presence of moonlight.
Conclusions: The reduced sea-finding ability of Curtis Island hatchlings was likely due to both altered light horizons from nearby industry, as well as beach topography. Both methods of assessing hatchling orientation have benefits and limitations. We suggest that fan-based methods, combined with strategically placed arenas, would provide the best data for accurately assessing hatchling sea-finding.
Implications: Sky glow produced by large-scale industrial development appears detrimental to sea-finding by flatback turtle hatchlings. As development continues around Australia's coastline, we strongly recommend continued monitoring of lighting impacts at adjacent turtle nesting beaches. We also advise rigorous management of industrial lighting, which considers cumulative light levels in regions of multiple light producers, as well as moon phase, moon-stage, cloud cover and time of hatchling emergence. All these factors affect the likelihood of disrupted hatchling sea-finding behaviour at nesting beaches exposed to artificial light-glow, industrial or otherwise
A new species of Freshwater Turtle in the Genus Elseya (Tesudines: Chelidae) from Central Coast Queensland, Australia
No full textInter-nesting habitat use by green turtles Chelonia mydas in the Great Barrier Reef
No full textUnderstanding green turtle habitat use during the nesting season is important for informing management decisions relating to green turtles and ecosystems that support them. Despite patterns such as migration being described, few studies investigate behaviour during the inter-nesting period. This research aims to describe and quantify the spatial distribution patterns of green turtles during 2 nesting seasons on Raine Island in the northern Great Barrier Reef. Satellite telemetry data were used to analyse the inter-nesting movements and patterns of green turtles in 2017 (n = 19) and 2018 (n = 20). The inter-nesting period ranged from 51 to 100 d (76.33 ± 15.98 d) across both seasons. The average inter-nesting area of individual turtles did not differ between nesting seasons (2017: 12.31 ± 13.22 km2, 2018: 12.01 ± 21.92 km2). In addition, it was established that 39 individuals are a sufficient sample size to describe the spatial distribution. Approximately half of the tracked individuals remained at the same reef for their entire inter-nesting season (n = 19), and half used habitat on nearby reefs (n = 20). Most turtles showed fidelity to Raine Island as a nesting site (n = 37), laying all their clutches on the island. However, 2 individuals travelled 479 and 337 km during the inter-nesting period. This study thus highlights where the habitats used by green turtles during the inter-nesting season are and how they are used. Therefore, management strategies and conservation decisions can be informed to maintain the viability of these essential habitats.Full Tex
Genetic identification of Australian marine turle stocks and their representation at feeding grounds and regional harvests
No full textPopulation ecology, ecophysiology, phylogenetics and taxonomy of the threatened western sawshelled turtle, 'Myuchelys bellii', from the Murray-Darling Basin of Australia
No full textResolving the evolutionary relationships among species remains an important focus of biodiversity conservation, and is key for assessing and reversing global trends in biodiversity decline. International and national systems of biodiversity protection rely on good taxonomic knowledge at the species level and good information about their biology and life history traits, knowledge that is often incomplete and therefore an impediment to effective conservation action. Over half of the world's turtle species are considered threatened, yet the taxonomy of many turtles species is not adequately resolved, and much work needs to be done to understand relationships between closely related taxa, and for uncovering cryptic species and genera. The 'Myuchelys' genus is a little known group of Australian freshwater turtles. The focal species, the vulnerable western sawshelled turtle 'Myuchelys bellii' located in the Murray-Darling Basin in eastern Australia, is both taxonomically confused and poorly studied. ... In summary, the molecular and morphological evidence of this research do not support the presence of a cryptic species within 'M. bellii'. Consequently, the three major populations of 'M. bellii' from the Gwydir, Namoi and Border Rivers need to be managed as a single species entity. The relatively small size and extent of each population also means that 'M. bellii' is certainly worthy of its national vulnerable status and international endangered status. Of particular concern for 'M. bellii', is the long term conservation of the isolated Queensland population. This thesis provides a clear foundation and insight into the conservation priorities for 'Myuchelys' species, and in particular, for the threatened western sawshelled turtle 'M. bellii'
A veterinarian’s guide for sea turtle post mortem examination and histological investigation
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