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Sperm Whale Diet in New Zealand

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Sperm Whale Diet in New Zealand Thesis submitted to Auckland University of Technology in partial fulfilment of the degree of Master of Applied Science Sperm whale diet in New Zealand Felipe Gómez-Villota 2007 Table of contents Attestation of authorship .................................................................................... i List of abbreviations.......................................................................................... ii Acknowledgements............................................................................................ i Abstract ........................................................................................................... iii Introduction.........................................................................................................2 1.1 Objectives and thesis structure...................................................................3 1.2 Thesis outline..............................................................................................4 Literature review .................................................................................................8 2.1 Sperm whale biology ..................................................................................8 2.1.1 Anatomy of the sperm whale.............................................................8 2.1.2 Distribution and migration ...............................................................12 2.1.3 Social structure ...............................................................................15 2.1.4 Diving behaviour .............................................................................17 2.2 Sperm whaling..........................................................................................18 2.3 Dietary studies..........................................................................................19 2.3.1 Sources of error ..............................................................................21 2.4 Review of sperm whale diet......................................................................23 2.4.1 Atlantic ............................................................................................24 2.4.2 Pacific .............................................................................................28 2.4.3 Southern Ocean..............................................................................32 2.5 Remarks ...................................................................................................33 Material and methods .......................................................................................47 3.1 Dietary analysis ........................................................................................47 3.1.1 Sample collection............................................................................47 3.1.2 Diet analysis....................................................................................51 3.2 Beak descriptions .....................................................................................52 Results...............................................................................................................56 4.1 Cephalopod component of the diet ...........................................................56 4.1.1 Whale diet from stomachs...............................................................57 4.1.2 Cephalopod species notes............................................................105 4.1.3 Unidentified beaks ........................................................................140 4.2 Non-cephalopod component of the diet ..................................................140 4.2.1 Fish ...............................................................................................140 4.2.2 Other animals................................................................................140 Final remarks .............................................................................140 4.3 Beak descriptions ...................................................................................141 Discussion.......................................................................................................151 5.1 Limitations of this study ..........................................................................152 5.2 The diet of the sperm whale in New Zealand..........................................154 5.2.1 Cephalopod component of the diet ...............................................157 5.2.2 Non-cephalopod component of the diet ........................................185 5.2.3 Size of cephalopod prey................................................................186 5.2.4 Secondarily ingested prey and prey remains retention times........188 5.3 Comparison between whales..................................................................189 5.3.1 Regurgitation and stomach fullness ..............................................190 5.4 Migrations ...............................................................................................192 5.5 Beak descriptions ...................................................................................196 5.6 Recommendations..................................................................................197 5.6.1 Future research.............................................................................198 5.7 Conclusions ............................................................................................199 References.......................................................................................................203 Acknowledgements The author would like to acknowledge the assistance provided by the New Zealand Department of Conservation, and his colleagues at AUT for accessing stranded whales to recover stomach contents, particularly Karl McLeod (DoC), Steve O’Shea (AUT), and Kathrin Bolstad (AUT), who assisted with the unpleasant job of collecting stomach contents. To Steve O’Shea and Steve Cook for all the long hours dedicated to the project. Acknowledgement is also due to the Museum of New Zealand Te Papa Tongarewa, particularly Anton van Helden and Bruce Marshall, both of whom have freely provided information, advice, archived stomach samples, and comparative cephalopod material that enabled this study to proceed, but also Andrew Stewart for help in the identification of fish remains. Finally, thanks are due to the Earth & Oceanic Sciences Research Institute (EOS) at Auckland University of Technology, and Ligia Fernanda Villota and Maria del Pilar Villota, for the financial and logistical support that enabled this project to proceed. i List of abbreviations km kilometre m metre cm centimetre mm millimetre °C degrees Celsius ° degree (e.g., of latitude, longitude) ' minute (e.g., of latitude, longitude) kg kilogram g gram sp. species singular spp. species plural % percentage EOS Earth and Oceanic Sciences Research Institute AUT Auckland University of Technology IWC International Whaling Commission LRL lower rostral length ML dorsal mantle length BM body mass EEZ Exclusive Economic Zone NZMS New Zealand Marine Society DoC Department of Conservation MFish Ministry of Fisheries FoO frequency of occurrence pers. comm. personal communication pers. obs. personal observation t/T tonne SE standard error ii Abstract Stomach contents of 19 mature sperm whales, 18 males and one female, that stranded on New Zealand beaches between the mid 1990s and 2004 were examined, identified and measured. Three of the stomachs were empty. All other samples consisted almost entirely of cephalopod beaks. A total of 23,223 cephalopod beaks (10,647 upper and 12,576 lower), representing at least 36 species in 17 families were found in the remaining 16 stomachs. Non-cephalopod remains in the stomachs of sperm whales stranded in New Zealand included limited quantities of fish, salps, crustacean exoskeletons, a copepod, some wood and sand. The present investigation represents the most comprehensive study of the diet of sperm whales in New Zealand since the early 1960s. The results show that oceanic squid of the families Histioteuthidae, Cranchiidae, Onychoteuthidae and Octopoteuthidae are the most common remains found in the stomachs of sperm whales stranded on New Zealand beaches, with the families Onychoteuthidae, Histioteuthidae, Octopoteuthidae and Architeuthidae being the most important by estimated weight in whale diet, and the families Cranchiidae, Pholidoteuthidae and Ancistrocheiridae secondarily so. The beaks of three cephalopod species thought to be restricted to Antarctic waters (Kondakovia longimana, Mesonychoteuthis hamiltoni and Psychroteuthis glacialis) were found in 12 of the stomachs, suggesting these whales had recently migrated into New Zealand from more southern feeding grounds. The amount of local cephalopod beaks in the stomachs suggests some of the stranded sperm whales did not feed much within New Zealand waters in the days prior to stranding. The beaks of Taningia danae, Octopoteuthis megaptera, Octopoteuthis sp. ‘Giant’ and Lepidoteuthis grimaldii are illustrated and described. Oblique and iii lateral illustrations of the lower beaks are given, as well as sections of the rostrum, jaw angle, shoulder and lateral wall, to show the major identifying features for each of the species. Squid are an important component of food chains in the Southern Ocean and they act as both high-level predators and prey for apex predators. Therefore, seasonal fluctuations in their abundance must have cascading effects on the diets of apex predators. With increasing global fishing effort, and with cephalopods
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