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A key driver in determining the distribution and demography of cetaceans is the dispersion of their prey, in terms of availability, abundance and quality. A Working Group on Resource Depletion has been established within ASCOBANS to review current knowledge and develop recommendations for research and action. It includes members with expertise in veterinary and fishery science, cetacean biology, ecology and conservation. The group has eight terms of reference - reviewing and collating recent information on resource depletion and its impacts, prey distribution and abundance, health and condition indicators, small cetacean diet, spatio-temporal trends in small cetacean species, emerging technologies, integrating information from multiple data sources, and making recommendations for possible mitigation measures to aid conservation. As a first step, the group has summarised information on the diets of all small cetacean species regularly occurring in the ASCOBANS Agreement Area, and explored the parameters required to assess cetacean health and condition at both an individual and population level. The need to better understand prey choice in terms of prey availability and caloric content is highlighted along with the development of indicators of food shortage through necropsies of dead animals and photographic assessments of body condition in live animals. Future research, monitoring and conservation needs include refining the definition of prey depletion, developing prey depletion reference points, and articulating associated conservation objectives. We also need a better understanding of the relationships between cetacean physiology, energetics, body condition, health and diet, and of the population and ecosystem level consequences of prey depletion (e.g. based on the use of ecosystem models). Improved monitoring of prey and cetacean distribution and abundance at relevant spatiotemporal scales would facilitate estimation and mapping of resource depletion risk

Animal welfare science can provide critical knowledge to inform ethical wildlife management and human intervention efforts. Despite live stranding events being recognised by the International Whaling Commission as a major welfare concern for free-ranging cetaceans, little research has to date, been conducted on stranded cetacean welfare. Live cetacean stranding events offer a quintessential exemplar of wildlife management, where assessment or integration of welfare has been limited in the decision-making process. This thesis contributes new understanding of how welfare science can be applied to cetacean stranding events to inform decision-making processes. Here, the first welfare-centric data regarding live stranded cetaceans is presented. Specifically, this research presents novel contributions to science via: (1) conceptualisation of stranded cetacean welfare and survival likelihood; (2) recognition of key knowledge gaps and concerns that must be addressed to ensure optimal welfare and survival likelihood outcomes; (3) identification of potential valuable and practical indicators for assessing stranded cetacean welfare and survival likelihood; (4) evidenced feasibility of welfare indicator application to live cetacean stranding events; (5) incorporation of indicators to undertake holistic welfare assessments; (6) identification of potential welfare implications of strandings management, including efficacy of euthanasia; and (7) provision of key recommendations and requirements to ensure humane end-of-life outcomes for non-viable stranded cetaceans. This thesis documents inextricable links between animal welfare and survival likelihood of stranded cetaceans and demonstrates a clear need for integration of welfare science alongside conservation biology at live stranding events. Systematic, standardised data collection and welfare-centric assessment of stranded cetaceans can, if applied scientifically, inform intervention decisions, to ensure consistent guidance and

Climate impacts affect marine ecosystems worldwide with island nations such as New Zealand being extremely vulnerable because of their socio-economic and cultural dependence on the marine and costal environment. Cetaceans are ideal indicator species of ecosystem change and ocean health given their extended life span and cosmopolitan distribution, but limited data availability prevents anticipating change in distribution under future climate changes. We projected the range shifts of a key odontocete and mysticete species (Physeter macrocephalus and Balaenoptera musculus) in 2100 relative to present day in New Zealand waters, using an ensemble modelling approach, under three climate change scenarios of different severity. The results show a latitudinal shift in suitable habitat for both whale species, increasing in magnitude with severity of sea surface temperature warming. The most severe climate change scenario tested generated 56% and 42% loss and decrease of currently suitable habitat for sperm and blue whales, respectively, mostly in New Zealand’s northern waters. These predicted changes will have a strong impact on the ecosystem functioning and services in New Zealand’s northern waters but also in coastal areas (critical for the species’ foraging and survival). Not only do these simulated range shifts help to identify future potential climate refugia to mitigate a global warming, they also generate a range of socioeconomic consequences for island nations relying on wildlife tourism, industry, and environmental protection.

Species occurring in sympatry and relying on similar and limited resources may partition resource use to avoid overlap and interspecific competition. Aotearoa, New Zealand hosts an extraordinarily rich marine megafauna, including 50% of the world’s cetacean species. In this study, we used carbon and nitrogen stable isotopes as ecological tracers to investigate isotopic niche overlap between 21 odontocete (toothed whale) species inhabiting neritic, mesopelagic, and bathypelagic waters. Results showed a clear niche separation for the bathypelagic Gray’s beaked whales (Mesoplodon grayi) and sperm whales (Physeter macrocephalus), but high isotopic niche overlap and potential interspecific competition for neritic and mesopelagic species. For these species, competition could be reduced via temporal or finer-scale spatial segregation or differences in foraging behaviour. This study represents the first insights into the coexistence of odontocetes in a biodiverse hotspot. The data presented here provide a critical baseline to a system already ongoing ecosystem change via ocean warming and subsequent effects on prey abundance and distributions.