Feasibility study of underwater passive acoustic observations of killer whales using A-tag

It is very important to recognise marine biodiversity and to maintain sound ocean ecosystems for long-term and continuous utilisation of the ecosystems services. To ensure this end, ocean environment and ecosystem should be monitored over the long term and a wide range of ocean areas. The purpose of this research is a feasibility study of underwater acoustic observations of marine mammals using a passive acoustic data logger, A-tag. Final goal of this research is to realise the long-term and wide-range monitoring of ocean ecosystems using autonomous underwater gliders, and to evaluate the soundness of ocean ecosystems and environments. This paper deals with underwater acoustic observations of killer whales (Orcinus orca) and analyses of their vocalisation. Underwater passive acoustic observations were conducted at the Prince William Sound, Alaska, USA in the summer of 2013. Direction of vocalisation source was analysed from the time arrival difference between two hydrophones of A-tag. It was demonstrated that the result of acoustic observations of killer whales' vocalisations agreed well with their actual behaviours by visual observations.