Who Goes There? Evaluating the Performance of a CNN for Monitoring Delphinid Presences to That of the C-Pod Within Diverse Marine Soundscapes

Passive acoustic monitoring (PAM) is a cost-effective method of gathering big data for monitoring the distribution of cetaceans 1,2 , yielding important insights into occurrence, movements, and behaviour over space and time, for use in species conservation and habitat management 3,4,5,6,7 .Dolphins are an indicator species, common to the British Isles, with the status and health of regional populations acting as important metrics for conservation and in assessing ecosystem health 8,9 .Acoustically they emit a diverse range of signals, employed in hunting, navigation, and communication, consisting of highly directional transient signals (echolocation clicks) and tonal omni-directional, frequency modulated whistles 10,11 .The presence of these acoustic cues within broadband acoustic recordings can be used as a proxy for true animal presence 12 , but manual extraction of signals is laborious and unrealistic on an appropriate timescale for conservation.Automation of the detection of these acoustic signals is therefore an essential component of the analysis pipeline for gathering data on delphinid occurrence.The application of Deep Learning (DL) algorithms is increasingly prevalent within the field of bioacoustics.Convolutional Neural Networks (CNNs), which use image processing techniques to read and classify acoustic data into predetermined classes, have been shown to excel at detecting signals which vary in respect to time, frequency, and amplitude 13,14,15,16 .Using broadband acoustic data as input, CNNs have achieved high accuracies at the task of detecting dolphin vocalisations within variable marine environments 17,18,19,20 .The use of CNNs for monitoring long-term dolphin occurrence in diverse acoustic habitats, beyond proof of concept, is still in its infancy; for such a tool to become part of the standard analysis toolkit we must demonstrate its reliability compared to established methods of detection.