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The Feeding Behaviour of Humpback Whales While on Migration

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The Feeding Behaviour of Humpback Whales While on Migration The feeding behaviour of humpback whales while on migration: methods, driving factors and its importance to whale ecology Kylie Owen Bachelor of Science (First Class Honours) A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2014 School of Veterinary Science Abstract Many migratory species use stopover sites to reduce the cost of transport or increase energy intake. In terrestrial taxa, the quality of prey at these sites is linked to future survival and reproductive success with animals spending more time feeding when prey quality is high. The humpback whale (Megaptera novaeangliae) makes annual migrations between high latitude feeding grounds and low latitude breeding grounds, with historical data indicating that whales fast while migrating. However, there is growing evidence of whales feeding while on migration, yet little research describing or understanding this behaviour. The aim of this thesis was to develop appropriate methods to study the feeding behaviour of whales while on migration, determine factors that elicit feeding, and, from these results, infer the potential importance of feeding at migratory stopovers to whale ecology. Data were collected off the coast of Eden, NSW, Australia for three weeks in 2011 and five weeks in 2012, during the southward migration of the whales towards feeding grounds. Behavioural data were collected using group surveys (n = 82), digital tag (DTAG) deployments (n = 9) and focal follow sampling (n = 18). Data on the prey type and density available to the whales was also collected concurrently. First, a method was developed to detect both surface-feeding lunges and lunges at depth using accelerometer data from the DTAG. The lunges detected from the DTAGs were then used to determine the amount of time spent feeding and the rate of energy intake in relation to the prey species available. Given that whales in the east Australian population feed predominantly on krill on their main feeding grounds, it was hypothesised that the availability of krill along the migratory route would provide an opportunity for whales to consume a familiar prey item and begin to accumulate energy reserves prior to reaching feeding grounds. It was assumed that if the feeding behaviour observed was important to whale ecology, the behaviour of whales would be more similar to the behaviour described on main feeding grounds and different from the behaviour of whales during migration. When fish were available, whales had relatively straight track lines as well as group sizes and compositions that were similar to those of whales on migration. In contrast, when krill were available, whales regularly looped back through the same area and had group sizes and compositions that were more similar to those on the main feeding grounds. Additionally, individual whales spent a significantly greater amount of time feeding and a larger proportion of the groups observed were determined to be feeding when krill, rather than fish, were available. Therefore, feeding behaviour on migration may be more important to whale ecology than previously thought and is likely influenced by the type of prey available. Given this observation, the influence of prey type, and prey depth on the rate of energy intake was investigated. Whales lunged at a significantly higher rate when feeding on krill compared to when feeding on fish, consuming prey at a rate of up ii to 3.7 times their energetic requirements. Therefore, feeding on migration may contribute more to annual energy budgets than previously thought and allow whales to begin to restore their energy supplies prior to reaching the Antarctic. As changes in the prey species available influenced the behaviour of whales while on migration, a technique to determine the diet of migrating whales is required. Whales often feed underwater and migrate through remote areas, which can make the observation of feeding during migration difficult. This thesis tested whether stable isotope analysis of the skin of the whales would reflect the short-term dietary changes that occur on migration. Stable isotope analysis of skin was not a suitable technique as the skin still displayed historical dietary signatures of Antarctic prey. Therefore, further development of a technique to determine the most recent diet of whales is required in order to determine the diet of whales while on migration. This study is the first to investigate the factors that influence the fine-scale feeding behaviour of whales while migrating. The results suggest that a change in the type of prey that is available at migratory stopovers influences behavioural characteristics of whales such as the amount of time spent feeding and the rate at which energy is consumed. Future research should focus on determining how often feeding occurs over larger spatial and temporal scales, and whether the rate of energy intake observed is sustained for longer periods. This will assist in determining the contribution of feeding behaviour while on migration to the annual energy budgets of humpback whales. iii Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the General Award Rules of The University of Queensland, immediately made available for research and study in accordance with the Copyright Act 1968. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. iv Publications during candidature Peer reviewed publications Miller BS, Barlow J, Calderan S, Collins K, Leaper R, Olson P, Ensor P, Kelly N, Peel D, Donnelly D, Andrews-Goff V, Olavarria C, Owen K, Rekdahl M, Schmidt N, Wadley V, Gedamke J, Gales N, Double MC (In Press) Validating the reliability of passive acoustic localisation: a novel method for encountering rare and remote Antarctic blue whales. Endangered Species Research. Owen, K., Donnelly, D. (2014) The most southerly worldwide sightings of pygmy killer whales (Feresa attenuata). Marine Biodiversity Records 7(e46): 1-4 Owen, K., Dunlop, R., Donnelly, D. (2012) Seaweed interactions by humpback whales (Megaptera novaeangliae): A form of object play? Aquatic Mammals 38(4): 418-422. (Appendix 3) Double, M. C., Barlow, J., Miller, B. S., Olson, P., Andrews-Goff, V., Leaper, R., Ensor, P., Kelly, N., Wadley, V., Lindsay, M., Peel, D., Calderan, S., Collins, K., Davidson, M., Deacon, C., Donnelly, D., Olavarria, C., Owen, K., Rekdahl, M., Schmitt, N., Gales, N. (2013) Cruise report of the 2013 Antarctic blue whales voyage of the Southern Ocean Research Partnership. Report to the International Whaling Commission. Report Number SC/65a/SH21. Conference abstracts Owen, K., Noad, M., Goldizen, A., Donnelly, D., Dunlop, R. (2012) What drives migratory feeding and foraging in humpback whales (Megaptera novaeangliae)? Living whales in the Southern Ocean: Advances in methods for non-lethal cetacean research, Puerto Varas, Chile. Owen, K., Donnelly, D., Goldizen, A., Noad, M., Warren, J., Dunlop, R. (2013) Fast food not so appealing for migrating cetaceans? The impact of prey species and depth on migratory feeding behaviour. Society for Marine Mammalogy biannual conference, Dunedin, New Zealand. James, A., Owen, K., Dunlop, R., Weeks, S., Noad, M. (2013) Identifying key environmental conditions driving opportunistic feeding of migrating humpback whales (Megaptera novaeangliae) off Eden, NSW, Australia. Society for Marine Mammalogy biannual conference, Dunedin, New Zealand. v Publications included in this thesis No publications included. Contributions by others to the thesis All four data chapters outlined below have been prepared for submission to relevant journals but are yet to be submitted or accepted for publication. Owen K, Dunlop R, Monty J, Chung D, Donnelly D, Noad M, Goldizen A, Mackenzie T (In Review) Breaking the surface: a method to detect surface-feeding behaviour of whales in accelerometer data. Prepared for submission to Marine Mammal Science. TM assisted with MATLAB programming to develop the algorithm code, and along with JM and DC provided guidance on the interpretation of the data with respect to the physics influencing the data. DD assisted with data collection. DD, RD and MN were responsible for obtaining the project funding. DD, RD, JM, DC, TM, AG and MN all assisted with editing the final manuscript. KO developed the research concept, collected and processed the data, completed the data analysis, interpreted the results, wrote the manuscript. Owen K, Donnelly D, Warren J, Noad M, Goldizen A, Dunlop R (2014) Is feeding by humpback whales during migration a ‘quick snack’ or more important to their ecology? Prepared for submission to Marine Ecology Progress Series. DD assisted with data collection and RD, DD and MN were responsible for obtaining the funding for the project. JW assisted with data collection and processed the prey availability data. RD assisted with development of the research concept. RD, DD, JW, MN and AG all assisted with editing the final manuscript.
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