Ecology of Hector’s dolphin (Cephalorhynchus hectori): Quantifying diet and investigating habitat selection at Banks Peninsula Elanor J. Miller A thesis submitted for the degree of Doctor of Philosophy June 2014 ABSTRACT Hector’s dolphins (Cephalorhynchus hectori) are endangered and endemic to New Zealand. Although their distribution and abundance have been thoroughly described, little is known about Hector’s dolphin ecology. Being small cetaceans living in a cold water environment, Hector’s dolphins have high energy requirements, and prey abundance and movements are often assumed to be a major driver of distribution patterns. This thesis aims to increase our understanding of Hector’s dolphins in a wider ecosystem context, by quantifying their dietary preferences and investigating the influence of prey availability on their habitat selection. Using stomach contents collected from beachcast and bycaught dolphins throughout New Zealand between 1984 and 2006 (n=63), the diet of Hector’s dolphin was quantified for the first time. The dolphins were found to feed throughout the water column, with 29 prey taxa identified in total. Red cod (Pseudophycis bachus), ahuru (Auchenoceros punctatus), arrow squid (Nototodarus sp.), sprat (Sprattus sp.), sole (Peltorhamphus sp.) and stargazer (Crapatalus sp.) were most commonly consumed. Red cod contributed most in terms of mass (37%), while ahuru and Hector’s laternfish (Lampanyctodes hectoris) were consumed in large numbers. Prey length ranged from <1 cm to over 60 cm, but the majority were <10 cm long. To help overcome inherent biases of stomach content analysis, complementary stable isotope analysis was used to examine long-term dietary preferences on the South Island east coast. Comparison of δ13C and δ15N signatures of dolphins (n=42) and potential prey (n=19 species) using mixing models, revealed that bony fish contributed most to the dolphins’ diet. While stomach content results showed demersal prey to contribute most over spring and summer seasons, stable isotope analysis suggested that epipelagic fish have a greater long-term contribution. The influence of prey availability and oceanography on Hector’s dolphin habitat selection was assessed at Banks Peninsula, a stronghold for this species on the South Island east coast. Concurrent dolphin, demersal prey, and oceanographic surveys ii were carried out offshore, alongshore, and within Akaroa harbour. For all three regions, generalised additive models indicated that Hector’s dolphins strongly correlated with areas of greater red cod mass. The offshore distribution of dolphins was also associated with areas of higher chlorophyll-a and salinity. Alongshore, dolphins were found in areas of higher prey diversity, chlorophyll-a, salinity, and warmer water. The performance and feasibility of two methods for sampling the demersal prey of Hector’s dolphins were assessed. Fish traps sampled a greater number of species, and were more effective at sampling the important prey, red cod. Baited stereo-video sampled greater fish diversity, but was limited by the prevailing water clarity. This study represents the first attempt to study Hector’s dolphin ecology in relation to their prey, addressing fundamental knowledge gaps in what the dolphins eat, and the role of prey availability in their habitat selection. The continued survival of Hector’s dolphins relies upon the success of conservation protection measures, and an increased understanding of their ecology and habitat use will help inform spatial management objectives and future conservation tools. iii ACKNOWLEDGEMENTS There have been a great many people involved in this project in one way or another. All that I have learned from you and the time we have spent together are what have made this experience so valuable and memorable to me – thank you all. First of all, a huge thank you to my supervisors Steve Dawson and Liz Slooten for all of your help from start to finish. Thank you Liz for giving me the opportunity to begin this work as a Masters project on Hector’s dolphin diet, and for all of your encouragement and guidance along the way. Thank you Steve for all of your support, even from across the ditch, for your help with fieldwork, and all that you’ve taught me. I have gained so much from this experience and could not have done so without the both of you. Thank you also to Steve Wing for your very helpful guidance and feedback. My project could not have been carried out without financial support from the New Zealand Whale and Dolphin Trust, University of Otago Research Grant, National Institute of Water and Atmosphere (NIWA; in particular Allison MacDiarmid), Department of Conservation (in particular Jim Fyfe), Greenpeace International, New Zealand Lottery Board, Project Jonah (NZ) Inc., World Wildlife Fund (NZ), Pacific Whale Foundation, IBM (NZ) Ltd, and Oceans Society (NZ). During my study I was supported by a University of Otago PhD scholarship. A big thank you to Chris Lalas for all of his help and expertise in the stomach content analyses. Thank you to the fishermen who passed on incidentally caught dolphins for dissection, and to staff of the MAF Lincoln Animal Health Laboratory for allowing access to your autopsy facilities. Laureline Meynier and Wendi Roe (Massey University) provided some stomach samples, and Colin McLay and Rob Mattlin helped identify crustaceans and squid. The stable isotope analyses could not have been conducted without the help and support of Sarah Bury (NIWA). Thank you also to Anton van Helden (Te Papa) and Wendi Roe for providing access to samples, to Nancy Beaven (GNS Science) for help iv with bone collagen extraction, and to Julie Brown (NIWA) for all of her laboratory assistance. The stereo-video system could not have been developed without the expertise and engineering skills of Brian Paavo (Benthic Science). A big thank you to Pascal Sirguey (Otago University Surveying Department) for his generosity and wealth of assistance during camera calibration. Thanks also to the NIWA Fisheries Acoustics Group (in particular Peter de Joux) for providing calibration assistance and access to the SeaGIS software and equipment. I am very grateful for your help. My fieldwork would not have been possible without the generous help of volunteers and friends who made long hours on the water and windy days onshore so memorable. A big thank you to Emma Gates, Leia Howes, Brianna Bowman, Zoe Stevenson, Dipani Sutaria, Jessica Riggin, Phillippa Dell, Maple Greenwood, Petrina Tay, Michael Hutchison, Jennifer Hutchison, Anthony Davidson and Jennifer Turek. Thanks to Will Rayment, Brian Miller, Steve Dawson, and Liz Slooten for your help getting set up in the field. Thanks also to Katt Preston for your company and help while working together on our projects. I am grateful to have had the chance to work with you all in the field and hope to again in the future. I am grateful to everyone who welcomed me into the Banks Peninsula community and shared their local knowledge. Special thanks to Akaroa Auto Centre for the speedy car and boat maintenance, Akaroa Harbour Cruises, and Barrys Bay Cheese Factory for providing year-round delicious distractions just down the road. Thank you so much to Lynette and Ross Curry for putting up with us and all of our field gear in ‘Possum Inn’. Your kindness and support, particularly during the many earthquakes, made Barrys Bay feel like home. I still miss waking up to the sound of the bellbirds and neighbourly cows. Thank you to all of the excellent people at Otago University who have helped me throughout this project. In the Marine Science Department, thanks to Daryl Coup, Bev Dickson, Chris Fitzpatrick, Lynn Paterson, Keith Probert, and Gary Wilson for logistical support and always making me feel welcome. A big thank you to all my fantastic lab mates: Brian, Will, Trudi, Miranda, Dave, Shaun, Judy, Rohan, Lucy, v Hamish, Ant, Jenn, and Abe. Thanks especially to Brian, Judy, Will, and Trudi for giving me the opportunity to work with you in the field and meet my first Hector’s dolphins. I learned so much from you all. Thanks to Will & Trudi, and Brian Paavo, for providing welcoming places to crash on trips back from Banks Peninsula. Thank you to the absolutely amazing group of students with whom I began my post-grad experience: Chelsie, Mara, Nat, Ange, Tracey, Dana, Michelle, Alaric, Celine, Suse, Buzzy, Derek… I couldn’t dream of meeting a better bunch of people. Thanks also to my wonderful flatmates Robynne and Janelle, who introduced me to Dunedin, and made my move down south so much fun. Many thanks to Simon Childerhouse, Lesley Douglas, Emma Gates, and Shannon Troy for all your support during my write-up in Tassie. Special thanks to Takoda for being by my side the entire time, always ready to provide a fun distraction, and for putting up with the countless hours I spent staring at the computer instead of playing with you at the beach. Thank you so much to all of my wonderful family, especially my mum and dad, Catherine and Raymond Hutchison; for always being there for me and keeping things in perspective. I love and miss you all. Brian, your love and support have guided me through this entire journey. I can’t thank you enough for all that you’ve taught me. Thank you for all of the long days on the water, the late night walks, and memories I’ll always hold dear. vi “Honorable scientists: I want to compliment you on your efforts to study my kind … I’m not certain what you expect to gain from invading my privacy. You generate numbing statistics … it merely shows that you have discovered some easy facts about me; most aspects of my life cannot be written in the language of mathematics. How can you understand me? We may seem to share certain moods, but you cannot comprehend mine … Remember, you cannot divide me into independent fragments of existence.