An investigation into the stranding of Australian sea snakes

Abstract

Strandings of marine animals are a regular occurrence both on Australian and international beaches and provide an opportunity for gathering data on the anatomy, health, and ecology of many ocean- dwelling species that might be unattainable otherwise. Analysis of stranding data has revealed many important diseases, anthropogenic injuries (primarily as a result of commercial or recreational fishing and boating) and other potential threats in a number of marine species. As such, stranding information is important to include when evaluating the conservation status of marine species whilst developing processes to mitigate declines. Stranding analyses and scientific reports are readily available for a range of marine species, including cetaceans, pinnipeds, dugong and marine turtles, but have not been previously undertaken in sea snakes. True sea snakes (subfamily Hydrophiinae: Hydrophiini) spend their entire life in the marine environment, as opposed to their amphibious counterparts the sea kraits (genus Laticauda). Sea snake species inhabiting Australia’s waters are almost exclusively Hydrophiinae, yet are regularly found beach-washed on Australia’s coastline, particularly in Queensland. As such, stranded sea snakes in Australia are likely ill or injured individuals. Despite frequent sea snake strandings, demonstrated population declines in some species and recognition that sea snakes are likely to be bio-indicators of the health of the marine ecosystem, an epidemiological investigation of sea snake strandings has not been conducted. The main objective of this thesis was to help address gaps in the literature about sea snake health, disease and stranding events, with particular focus in south east Queensland, where stranding reports occur most frequently. A comprehensive analysis of information from multiple stranding databases was undertaken to assess: (i) species occurrence, (ii) the cause of strandings (where known), (iii) sex predisposition (where identified), (iv) biometrics, (v) stranding locations, and (vi) times of year when strandings occur. This information was from stranding reports, and was collated to provide a comprehensive assessment of reported sea snake stranding events in Queensland, identifying key ‘hot-spots’ for stranding observations, seasonal occurrence of strandings, and factors that are likely to influence stranding events. Abnormally high numbers of stranded animals were reported in 1996 and 2009 and this appeared to coincide with times of higher than average rainfall, as well as increased onshore winds and wind speed (Chapter 2). To address the paucity of information in the literature about normal clinical health parameters for sea snakes an antemortem assessment guide was developed, detailing procedures for the clinical assessment and diagnostic investigation of sea snakes by veterinarians and researchers (Chapter 3). In addition, the first comprehensive set of haematological and biochemical reference ranges for three species of Australian sea snakes were developed from blood collected during an intensive field survey of wild caught sea snakes (Chapter 4). A comprehensive examination of sea snakes found stranded on beaches in south east Queensland and presented to the Australia Zoo Wildlife Hospital, was conducted from 2009 to 2015. Gathered information was used to develop the first sea snake postmortem guide, illustrating normal anatomy and outlining common diseases and pathology found in stranded animals. Traumatic injuries, including eye injuries, spinal fractures and jaw amputations, were prevalent in examined snakes and neoplasia (predominantly pancreatic ductal adenocarcinoma) was identified as one of the most common disease conditions (Chapter 5). In addition to the presence of trauma and neoplasia, granulomas were also found in the hypaxial and epaxial musculature of a small number (4) of necropsied snakes and contained dense aggregations of microsporidial organisms. Ultrastructural examination using transmission electromicroscopy suggested these organisms were most similar to the genus Pleistophora affecting the muscle of many species, including marine and freshwater fish, and terrestrial reptiles. However, Bayesian and maximum likelihood analysis of ssrRNA placed the sea snake microsporidia within the Heterosporis clade, known most notably to affect the muscle of freshwater eels. Although molecular analysis appeared to place the sea snake microsporidia within this clade, our specimens lacked a key defining morphological feature of this group, a sporophorocyst. Microsporidial infection was previously undescribed in sea snakes and the identified organism may represent a novel species. Due to the disparity between morphological and molecular identification methods complete classification was not possible with the current sample set (Chapter 6). The investigation on sea snakes undertaken for this thesis is the first of its kind anywhere in the world, and has made a significant contribution towards closing the gaps in our knowledge of this group. This body of work revealed that stranded sea snakes are often suffering from injuries and diseases that predispose them to stranding. Anthropogenic, environmental, infectious and natural causes are all implicated. Stranded individuals are likely to only represent a very small proportion of overall morbidity and mortality in these animals. In order to determine the true impact of these conditions on sea snake populations both in Australia, and globally, further research is required.