Behavioural ecology of the yellow-lipped sea krait, Laticauda colubrina, in the Fiji Islands SOHAN SHETTY A thesis submitted in fulfilment of the requirements for the degree of Master of Science (Environmental) School of Biological Sciences University of Sydney August 2000 This thesis is my own original work, except where specifically acknowledged. \.S Sohan Shetty August 2000 DEDICATED TO EVOLUTION .......the creator of these awesome beasts. ABSTRACT Yellow-lipped sea kraits (Laticcauda colubrina) are large (> 1.5 m body length, 1.5 kg) amphibious snakes widely distributed throughout the Pacific region. They forage in the ocean, but frequently return to land. I captured, measured and individually marked > 1,100 sea kraits between September 1998 and December 1999, on Mabualau and Toberua Islands (Fiji), Female sea kraits grow much larger than males, and the sexes differ in head sizes even at the same snout-vent length (females have longer, wider heads), The sex differences in mean adult body length and in relative head size probably reflect a combination of evolutionary processes involving fecundity selection, sexual selection and natural selection, Female sea kraits eat much larger prey items than do conspecific males (mostly conger eels) and usually contained only a single prey item when examined. In contrast, male sea kraits eat smaller prey items (mostly moray eels) and often contain multiple prey. The sex divergence in relative head sizes may be an adaptation to this sex difference in dietary habits. Interestingly, the prey taken by female sea kraits are larger relative to the snake's head length, as well as its snout- vent length, than is the case for prey items in males. I quantified various facets of terrestrial behaviour in the sea kraits of Mabualau. Intensive surveys and radiotelemetry were used to monitor daily activity and movement patterns of sea kraits, and to suggest causal influences on these traits, Behavioural patterns including activity levels, activity type and microhabitat use differed significantly between juvenile and adult snakes, and between adult males versus females. Juvenile sea kraits rarely ventured far from water, whereas adults moved much further. Adult snakes were generally most active at night. The movements of adult male snakes were influenced not only by the location of females, but also by tidal conditions and physical attributes of the island. Radiotelemetric monitoring of 16 adult snakes indicated that most of these animals spent relatively equal amounts of time on land and at sea, moving between the two habitats about once every ten days. In keeping with this pattern resampling of individuals showed that they required about eight days to digest a large prey item, and about 12 days to complete the sloughing process. Radio-tracked male sea kraits maintained higher body temperatures than females throughout the day. I collected groups of courting snakes and placed them in outdoor arenas to obtain data on courtship and mating behaviour. These behaviours observed differ substantially from published descriptions of courtship in other snake species. First, males in courting groups displayed overt courtship only rarely, remaining immobile the rest of the time. Second, males exhibited body spasms during the occasional periods of intense courtship. I did not see any overt physical interactions among rival males within courting groups, and body sizes of copulating males compared to unsuccessful suitors suggest that larger body size does not enhance mating success. The intensity of courtship behaviour differed substantially among groups. Larger females attracted more intense courtship, and significant temporal variation in courtship behaviour suggests that environmental factors or attributes of males may also influence these reproductive interactions. I used a simple raceway to measured locomotor speeds of these snakes in water and on land. The resulting data were used to investigate two topics: (1) to what degree have adaptations to increase swimming speed (paddle-like tail, etc.) reduced terrestrial locomotor ability in sea kraits?; and (2) do a sea krait's sex and body size influence its locomotor ability in these two habitats, as might be expected from the fact that different age and sex classes of sea kraits use the marine and terrestrial environments in different ways? To estimate ancestral states for locomotor performance, I measured speeds of three species of Australian terrestrial elapid snakes that spend part of their time foraging in water. The evolutionary modifications of Laticauda for marine life have enhanced their swimming speeds by about 60%, but decreased their terrestrial locomotor speed by about 80%. Larger snakes moved faster than smaller individuals in absolute terms but were slower in terms of body lengths travelled per second, especially on land. Male sea kraits were faster than females (independent of the body-size effect), especially on land. Prey items in the gut reduced locomotor speeds both on land and in water. Proteroglyphous snakes may offer exceptional opportunities to study phylogenetic shifts in locomotor ability, because (1) they display multiple independent evolutionary shifts from terrestrial to aquatic habits, and (2) one proteroglyph lineage (the laticaudids) displays considerable intraspecific and interspecific diversity in terms of the degree of reliance upon land versus water. Based on growth of marked snakes in my study, I can estimate the "typical" growth trajectory for Fijian sea kraits. Snakes of both sexes grow rapidly during the first year of their lives, from about 30 cm SVL at in hatching to about 55 to 65 cm SVL at 12 months of age. Male sea kraits mature at 18 months of age, and females at 30 months. In both sexes, growth rates slow dramatically after maturation. At the same body length, male sea kraits on Mabualau grew more rapidly than did those on Toberua. Several of my results are relevant to the conservation and management of these snakes. However, the most striking of these results was the extreme site fidelity of the individually marked animals. All snakes displaced from Toberua Island and relocated to Mabualau Island rapidly returned to their "home" island. Similarly, none of the snakes from Mabualau Island were ever captured on Toberua Island, Population estimates from the mark-recapture data reveal that there were over 2,300 snakes on Mabualau. Toberua had a resident population of approximately 900 snakes. Because of the high site fidelity, human activities such as commercial harvesting of snakes, or anthropogenic modifications to island habitats, are likely to have intense but highly localised effects on sea krait populations. IV ACKNOWLEDGMENTS This project involved a fair amount of input from folks in Australia, Fiji and home, who not only offered financial and technical support, but a lot of moral support as well. I am grateful to each one of them irrespective of the magnitude of help rendered. I would like to highlight the support of a few people and organisations whose role was vital during the project. Rick Shine. His role as a supervisor in my project was more than significant. I thank him sincerely for accepting me as a student in spite of me not having a scholarship or funds. I guess he recognised my potential to carry out field work and took a risk. From grant applications and planning every detail of the project, implanting transmitters, to offering moral support during field work his role is indeed commendable. His presence in Mabualau was a great source of inspiration for me. Rick also made significant contributions to the making of this thesis. His literary skills and experience enhanced the progress of the work and helped me convey the results in a broader sense. Besides that, I think he is a truly insane person, who believes the meaning of life has something to do with snakes! His efficiency is addictive and I hope a minute fraction of it has rubbed off on me during my interactions with him. Funding for the project was provided by The Australia and Pacific Science Foundation, National Geographic Society (Committee for Research and Exploration) and The Australian Research Council. I am grateful to them for recognising the need for information on sea kraits. Marine Studies Program, University of the South Pacific. I collaborated with USP to carry out my research in Fiji. Prof Robin South, Sunia Lavaki, Nanise Bulai, Litia Konusi - helped me get through the red tape and offered tremendous amount of logistic support in terms of organising permits, boats, equipment, lab space, chemicals, and a million other things, They made my stay at MSP very comfortable. Many thanks indeed. Owners of Mabualau Island: I wish to offer my sincere gratitude to the chiefs of Bau Island. Vinaka vakalevu for accepting my sevu sevu and granting me permission to work on Mabualau. Your open-mindedness and continuing support to researchers wanting to work at Mabualau highly regarded among the scientific community, both in Fiji and overseas. You may have already realised that Mabualau and indeed the resources in Fiji, are valuable not only to the world, but most importantly to you and Fiji. I sincerely hope you continue to have the long term benefits of these resources in mind and preserve Mabualau for future generations. I am sure your regard for the dadakulaci will payback in terms of prosperity for the coral reefs in the Bau waters and for future generations of Bau Islanders. My stay at Mabualau has been a fantastic experience both as a researcher and as a human being. I will cherish this experience for the rest of my life. Vinaka vakalevu once again. Michael Dennis and Caz Tebbut of Toberua Island Resort - for your constant logistic and moral support throughout the study, One of the most interesting results of this study was an outcome of your cooperation and the help rendered by your staff. My parents supported my study at Sydney University.