Todd, V. L. G., Pearse, W. D., Tregenza, N. C., Lepper, P. A., and Todd, I. B. 2009. Diel echolocation activity of harbour porpoises (Phocoena phocoena) around North Sea offshore gas installations. – ICES Journal of Marine Science, 66: 734–745. Echolocation clicks of harbour porpoises (Phocoena phocoena) were detected with T-PODs, autonomous, passive, acoustic-monitoring devices, deployed from an offshore-exploration-drilling-rig and gas-production-platform complex in the Dogger Bank region of the North Sea from 2005 to 2006. Echolocation-click trains were categorized into four phases of the diel cycle: morning, day, evening, and night. Porpoises were present near (<200 m) the platform, and there was a pronounced diel pattern in echolocation activity; the number of porpoise encounters (visits) was greater by night than by day. The number of click trains with a minimum inter-click interval of <10 ms also increased at night. This was confirmed by a comparison of the ratios of feeding buzzes to search-phase clicks (feeding buzz ratios) and an analysis of the changes in pulse-repetition frequencies within each train. A reasonable interpretation of this pattern was that porpoises were feeding below or around the platform at night. The evidence for changes in activity during the morning and evening was less clear, so these may be transitional phases. The pattern of porpoise-echolocation behaviour around this platform is related most probably to the diel activity of their prey. If porpoises cluster regularly around such installations within 500-m shipping exclusion zones, they may be omitted from population surveys. We conclude that offshore installations may play an important role as nocturnal porpoise-feeding stations in an overfished environment, but that further replicated and controlled studies are required. These findings should be taken into consideration during offshore-installation-decommissioning decisions in the North Sea.

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The detection of odontocete echolocation signals with acoustic loggers has proved to be a very effective way to monitor their distribution, seasonal patterns and habitat use. However, belugas (Delphinapterus leucas) have never been monitored using this methodology. In order to evaluate its viability, echolocation signals of captive belugas were analyzed and the performance of T-POD (Chelonia Ltd., UK) acoustic loggers in captivity and in the Arctic environment was tested. Results from captivity demonstrated the potential of beluga remote monitoring by T-PODs. Field tests were organized in different environmental conditions with different populations of belugas to ensure the validity and detection robustness of this method. T-PODs were deployed in Svalbard (Norway) in Spring 2007, in Yakutat (Alaska) in Spring 2008, and in Solovetsky (Russia) in Summer 2008. Instruments were deployed concurrently with visual observations and hydrophone recordings to compare presence/absence data from the three different methods. Results proved that T-PODs positively detected all the identified periods of beluga presence without false detections and revealed temporal distribution correlations with tide levels, feeding behaviors, and circadian rhythms in the echolocation activity. Results from this project indicate that beluga remote monitoring is feasible in the Arctic environment using acoustic loggers.

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