Publication of our article on binning-based inter-click interval data of free-ranging harbour porpoises (Phocoena phocoena)

OSC is pleased to announce publication of the article Presentation of binning-based inter-click interval data from passive acoustic monitoring of free-ranging harbour porpoises (Phocoena phocoena) (Ruffert et al., 2020) in the peer-reviewed journal International Journal of Acoustics and Vibration (IJAV). This article was co-authored by OSC’s Managing Directors, Dr Victoria Todd and Ian Todd, and is our second peer-reviewed paper, after Todd et al. (2019), to be published in IJAV and our tenth on harbour porpoise.

A range of underwater Passive Acoustic Monitoring (PAM) systems can be used to monitor presence of cetaceans. One example of a static (non-towed) PAM echolocation-click detector is the C-POD (Chelonia UK), which has become increasingly popular owing to its accuracy, robustness, and resilience (it can be left in situ for many months), thus covering diel, tidal, and seasonal cycles. C-PODs also contain an automatic processing software (C-POD.exe) which reduces signal analyses time significantly. C-PODs (and their analogue predecessor, T-PODs), have been used widely to study many odontocete species, including, inter alia, harbour porpoises; however, researchers are attempting to address shortcomings in how these echolocation-click data are visualised and interpreted.

Ruffert et al. (2020) focus on the assessment of minimum Inter-Click Intervals (minICIs), defined as the minimum logged temporal separation of clicks emitted by the same vocalising animal. By selecting the appropriate binning widths (either manually or semi-automatically) and an appropriate visualisation of the binned data, the essential structure of the dataset can be unveiled and a smoothed histogram created, which can allow investigation of important patterns in the data that might be overlooked otherwise. Through correct selection of binning widths, we found presence of trains with three distinct ranges of minICI values following diel analysis of echolocation data: (i) long >35 milliseconds (ms), (ii) intermediate 6–28 ms, and (iii) short 1.25–2.00 ms. The two ranges of intermediate and short minICI show diel patterns in harbour porpoises, as follows: (a) rates of short minICIs are high at night, (b) rates of intermediate minICIs are high during the day, (c) rates for long minICIs are equal during night and day. In light of these findings, we suggest that, for harbour porpoise behavioural patterns, the short minICI range indicates that this species feeds more at night and that intermediate range is linked to exploration and search for prey further afield during the day.

First author, Dr Maximilian Ruffert, is Reader at the School of Mathematics and Maxwell Institute, University of Edinburgh, and specialises in theoretical astrophysics and numerical hydrodynamics. OSC has collaborated with Dr Ruffert on two previous peer-reviewed publications, namely the manuscript titled Potential audibility of three Acoustic Harassment Devices (AHDs) to marine mammals in Scotland, UK (Todd et al., 2019), also published in IJAV, and the conference paper titled Diel analysis methodology for offshore porpoise (Phocoena phocoena) echolocation using inter click intervals from PAM data (Ruffert et al., 2012).

REFERENCES

Ruffert, M., Todd, I.B., Todd, V.L.G., and Gardiner, J. (2012): Diel analysis methodology for offshore porpoise (Phocoena phocoena) echolocation using inter click intervals from PAM data. 11th European Conference on Underwater Acoustics (ECUA), 2-6 July, Edinburgh.

Ruffert, M., Todd, V.L.G., and Todd, I.B. (2020): Presentation of binning-based inter-click interval data from passive acoustic monitoring of free-ranging harbour porpoises (Phocoena phocoena). The International Journal of Acoustics and Vibration 25, 209-218.

Todd, V.L.G., Jiang, J., and Ruffert, M. (2019): Potential audibility of three Acoustic Harassment Devices (AHDs) to marine mammals in Scotland, UK. International Journal of Acoustics and Vibration 24, 792-800.

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