Detection rates of wild harbour porpoises and bottlenose dolphins using static acoustic click loggers vary with depth

Abstract

AbstractAcoustic echolocation click loggers are widely used to study the presence and behaviour of coastal cetaceans. Various studies have examined their performance and how animal behaviour may affect click detection. This study examined the effect of logger depth in the water column on click detection rates for harbour porpoises (Phocoena phocoena) and bottlenose dolphins (Tursiops truncatus) at a coastal nearshore site. There were significantly more harbour porpoise clicks logged at the click loggers moored in the water column, closer to the surface, compared with those near the seabed. No such difference was recorded for bottlenose dolphins. The results were consistent throughout the study period and across sites, apart from a site closest to a possible feeding site, indicating that cetacean behaviour is among the possible factors explaining these findings. The study emphasizes the need for prior understanding of the target species and its habitat use, and stresses the importance of pilot studies to achieve reliable and meaningful data from static acoustic monitoring programs.Keywords:: C-PODTursiops truncatusPhocoena phocoenapassive acousticsstatic acoustic monitoringdeployment depth AcknowledgementsThe authors acknowledge all the volunteers who helped to prepare, deploy and pick up C-PODs for this study, particularly Gemma James, Elisa Girola and Simon Williams; Nick Tregenza for a significant contribution to all aspects of the project; Jan Hiddink for useful advice on data collection and analysis; Margarida Castro for statistical advice and two anonymous referees whose input greatly improved the manuscript.Notes1. Email: [e-mail]