Fine-scale movement responses of free-ranging harbour porpoises to capture, tagging and short-term noise pulses from a single airgun

Abstract

Knowledge about the impact of anthropogenic disturbances on the behavioural responses of cetaceans is constrained by lack of data on fine-scale movements of individuals. We equipped five free-ranging harbour porpoises (Phocoena phocoena) with high-resolution location and dive loggers and exposed them to a single 10 inch3 underwater airgun producing high-intensity noise pulses (2–3 s intervals) for 1 min. All five porpoises responded to capture and tagging with longer, faster and more directed movements as well as with shorter, shallower, less wiggly dives immediately after release, with natural behaviour resumed in less than or equal to 24 h. When we exposed porpoises to airgun pulses at ranges of 420–690 m with noise level estimates of 135–147 dB re 1 µPa2s (sound exposure level), one individual displayed rapid and directed movements away from the exposure site and two individuals used shorter and shallower dives compared to natural behaviour immediately after exposure. Noise-induced movement typically lasted for less than or equal to 8 h with an additional 24 h recovery period until natural behaviour was resumed. The remaining individuals did not show any quantifiable responses to the noise exposure. Changes in natural behaviour following anthropogenic disturbances may reduce feeding opportunities, and evaluating potential population-level consequences should be a priority research area.

Environmental drivers of harbour porpoise fine-scale movements

“…Turning angles close to 0° represent directed movements, while values close to 180° represent tortuous movements. Location data collected within 24 h after tagging were discarded to ensure that potential capture/tagging-related effects on movement behaviour were excluded from the data (van Beest et al 2018 ). We repeated the above process to create two additional horizontal movement data sets that were regularized using a 30-min interval and a 60-min interval.…”

Harbor Porpoise (Phocoena phocoena) Reaction to a 3D Seismic Airgun Survey in the North Sea

“…However, it is not known whether it was the same animals that remained in the area during the survey or displaced animals were continuously replaced by new animals moving into the area during the seismic survey. Some tagged porpoises exposed to a single small airgun (10 cubic-inch) for only 1 min showed strong responses for up to 8 h and moved 10s of km away from the sound source indicating that some animals leave an area with seismic activity, while others may be more resistant to noise disturbance or move into the area from elsewhere (van Beest et al, 2018b). Marine mammal observers were on board the seismic vessels, but the very few and short encounters with porpoises did not allow for any inference about behavior of individuals.…”

“…A lowering in buzzing has been observed during the passing of noisy vessels (Wisniewska et al, 2018), while CPM and PPM was significantly reduced during wind farm construction and operation (Teilmann and Carstensen, 2012). Changes in behavior may lead to a reduction in echolocation parameters, for example when swimming at the surface, where sound propagation is reduced (van Beest et al, 2018b), if source level of the emitted echolocation clicks are reduced by the animal (Teilmann et al, 2002), or a change from pelagic to bottom feeding occur (Schaffeld et al, 2016). In any case, the reduction of recorded echolocation activity is indicative of a change in behavior, meaning that porpoises were affected by this disturbance.…”

Gemini T-c: aerial surveys and passive acoustic monitoring of harbour porpoises 2015

“…An example of individually different behavioural responses was described by Van Beest et al (2018), who equipped three porpoises with high-resolution location and dive loggers and exposed them to a single airgun noise pulse. One individual displayed rapid movements away from the sound source, and two individuals made shorter and shallower dives (Van Beest et al, 2018). These individual differences might be caused by individually different disturbance levels and may lead to incomplete displacement of porpoises around a piling location.…”

“…In the Gemini wind farm area pile driving lasted on average 127 minutes (76-254 min). The swim speed of harbour porpoise is thought to be 1.4 m/s (Otani et al, 2001), while short bursts up to 6 m/s are possible (Lucke et al, 2000;Van Beest et al, 2018).…”