Diving and ranging behaviour of odontocetes: a methodological review and critique

Movements can be analysed in terms of horizontal or vertical dimensions, but cetacean movement is ultimately three-dimensional, and it is the integration of analyses of both horizontal and vertical movements that will provide the most insight about an animal's behaviour. Current field techniques can provide simultaneous information on both diving (vertical movements) acid ranging (horizontal movements). We discuss the considerations, techniques and analyses for diving and ranging studies, together with the advantages and disadvantages of each technique. Ranging studies using VHF or satellite-linked radio-transmitters have evolved alongside studies of diving behaviour using time-depth recorders, and problems associated with deployment and attachment techniques apply to both. The diving (and concurrent ranging behaviour) of 13 species of odontocetes has been studied using time-depth recorders or acoustic transponders with VHF-or satellite-transmitters. However, differences in sampling techniques used, and summary statistics presented, have made comparisons difficult. We review these issues and suggest parameters that should be presented in future studies of diving and ranging. In general, studies should be consistent in their presentation of the basic parameters and statistics, and provide enough information for the reader to assess the limitations of the data.