Anti-masking strategies by marine mammals

Finally, we investigated if blue whales show a response towards anthropogenic sounds from marine vibrator (MV) signals (chapter 3). Little is known about this effect on baleen whales, especially on blue whales. Of all the ways in which noise can affect the lives of marine mammals, auditory masking is perhaps the most pervasive. Masking occurs when the ability to detect a sound of interest is obscured in the presence of another sound (Erbe et al., 2016).

Marine mammals may alter the characteristics of their vocalisation sounds in the presence of noise, known as Lombard effect which includes not only changes in sound intensity but also other acoustic features such as changes in repetition rate, frequency shift, or increase of the signal duration (Lombard, 1911). Not only acoustic communication is at risk of masking (as in the present example), but also echolocation and the detection of environmental, predator and prey sounds (Erbe et al., 2016).

In order to investigate possible effects of the marine vibrator (MV) signal, we defined three different phases: pre-exposure, exposure and post-exposure phase. These controlled exposure experiments (CEEs) provide the best method of proving that a particular sound stimulus causes a response because a specific known dose of sound is broadcast to an animal, and the acoustic exposure and behavioural responses can be directly measured (Tyack, 2009). We developed tools to analyse call characteristics and compare parameters between experimental phases.

Therefore, the number of blue whales down sweeps per hour was analysed. We also determined the signal duration and different frequency parameters such as minimum, maximum, centroid and peak frequency. The results of this chapter give evidence that elevated noise from MV signals has an effect on blue whale vocalisation behaviour. We observed changes in call rate and duration as well as changes in frequency that could be a consequence of the exposure from MV signals. But we did not observe changes in source levels.

Animals that communicate acoustically need to overcome the challenge of successfully transmitting signals in varying conditions of ambient noise (Kragh et al., 2019). Killer whales have been shown to raise the amplitude of their communication signals in the presence of ship noise (Holt et al., 2009, 2011); as have beluga whales (Scheifele et al., 2005). Humpback whales increased the source level of their songs proportionately to increases in wind-dependent ambient noise (Dunlop et al., 2014). Bottlenose dolphins were found to raise the amplitude of their outgoing echolocation clicks when masking noise was added to the environment (Au et

91 al., 1974). A beluga whale adapted its echolocation clicks, shifting to higher intensities and higher frequencies after being moved to a different ambient noise environment (Au et al., 1985).

Certain marine mammals have been reported to alter the frequency content of their calls in the presence of interfering noise, potentially as a way to minimise spectral overlap (reviewed in Erbe et al., 2016). Studies suggest that right whales have vocally adapted to environments with increased low-frequency noise through a shift in vocalisation frequency and duration (Parks et al., 2007, 2009, 2011a), which may have been a response to compensate for a loss in communication range (Clark et al., 2009). Right whales (Eubalaena glacialis) (Parks et al., 2007), beluga whales (Lesage et al., 1999), and common dolphins (Delphinus delphis) (Ansmann et al., 2007) apparently shifted the frequency of their calls away from the environmental frequencies containing the most noise energy. These observations, however, were not made in controlled conditions and more research is needed on the usage and effectiveness of this Lombard response in marine mammals. There is also evidence that odontocetes shift the main energy of their echolocation signals outside of the band of masking noise (Au et al., 1985, 1974; Moore and Pawloski, 1990), another observation that should lead to more systematic investigation of the extent to which frequency-shifting, as an anti-masking strategy, may occur in marine mammals. Increasing repetition rate or redundancy of calls reduces the potential for masking and improves the odds of detection by a listener. Many marine mammals display high redundancy in calling behaviour in typical conditions, presumably as a strategy for increased detectability by conspecifics. Increases in call repetition rates have been documented for bottlenose dolphins (Buckstaff, 2004) and beluga whales (Lesage et al., 1999) in the presence of ship noise. Furthermore, increases in call duration have been reported for killer whales in the presence of masking noise (Foote et al., 2004).

A hydrophone array has the advantage to record ambient noise and all marine mammals in the vicinity of the array to estimate source levels and other signal features received at the hydrophones. But with an array, however only a general statement on vocalisation behaviour and changes towards anthropogenic noise can be made. It is difficult to identify individuals and their possible reactions. Therefore, it is reasonable to also use animal-borne tags together with a hydrophone array. By means of tags, not only the vocalisation, but also diving behaviour and acceleration of an individual can be obtained to have clear proof of the animals respond to the

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introduced noise or not. However, no vocalisation of the tagged animals occurred during the whole experiment.

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Conclusion

The aim of my thesis was to monitor different sound sources with a novel GPS-linked receiver array and to develop customised analytical solutions for targeted data processing of the recordings. The thesis consists of three chapters where we assessed the noise input caused by the construction of seed mussel collectors in the Wadden Sea, we studied the vocal behaviour of blue whales in Skjálfandi Bay, Northeast Iceland and verified if blue whales show a response towards anthropogenic sounds from marine vibrator (MV) signals.

The GPS-linked receiver array used for the investigations within the framework of this thesis can be used for many different marine mammals, from very low-frequency species like blue whales to high-frequency species like harbour porpoises (Phocoena phocoena) and dolphins.

The customised R routines developed to detect and localise cetaceans as well as determine the characteristics of their vocalisation signals can be applied to analyse the vocal behaviour on every marine mammal species amenable.

Not only biological sound sources, but also anthropogenic sounds from any kind of offshore activities, such as drilling, dredging, pile-driving, seismic exploration and many more can be investigated. This study is an example for how an autonomous GPS-linked hydrophone array can be used as a tool to assess the effect of anthropogenic sound. Here, vibration sound caused by two different activities at sea was analysed. This type of sound can be either emitted by construction of anchor pipes or by seismic surveys for oil exploration, e.g., vibroseismic signals from marine vibrators. Our system can also be used to measure sound propagation from passing boats or other anthropogenic activities at sea.

We also provided simple propagation models useful and applicable for different sound types to analyse how these sounds radiate in certain areas of interest. Furthermore, it can be modified as a vertical array to measure the sound propagation with depth. Preliminary results revealed that in certain depth with a certain distance from a loudspeaker the sound is cancelled. This can happen due to constructive or destructive phase shift between direct path and surface reflection.

This information might help to understand, if the whales might use these silent areas caused by the Lloyd’s mirror effect due to surface reflection.

One could use playbacks of sound to perform controlled measurements of sounds of interest from new or advanced techniques of industrial activities less harmful to the marine

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environment. Thus, a sustainable use of the oceans could be ensured. Furthermore, a global use of PAM and the development of effective standardised statistical methods to analyse acoustical data on many cetacean species should increase our knowledge and help to understand their role in marine ecosystems (Mellinger et al., 2007).

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Summary

Johannes Baltzer - Passive acoustic monitoring for evaluating potential impacts of anthropogenic noise on marine animals: Tools for ecological assessment and monitoring

In this thesis, we monitored different natural and anthropogenic sound sources with a novel GPS-linked receiver array and developed tailor made analytical solutions for targeted data processing of the recordings. We assessed the noise of anchor pipe vibration embedment operations during the construction of seed mussel collectors in the Wadden Sea (chapter 1). We studied the acoustic behaviour of blue whales (Balaenoptera musculus) in an Icelandic feeding ground (chapter 2) and we analysed how an anthropogenic sound source (marine vibrator signals) can affect the vocalisation of blue whales (chapter 3).

During this thesis we took advantage of an autonomous drifting lightweight portable passive acoustic array that can be deployed quickly and repeatedly from a small boat. We developed tools to estimate the sound propagation by a non-linear logarithmic regression by means of the intercept, slope and attenuation factor, which allowed us to evaluate the received sound levels that reach an animal in certain distances from the construction site of seed mussel collectors in the Wadden Sea. We provided tools for time-synchronisation, detection of blue whale vocalisations in Skjálfandi Bay, Northeast Iceland. We calculated general sound characteristics and compared them to recorded blue whale calls from other regions of the world. Eventually we used the GPS-linked receiver array to analyse how an anthropogenic sound source can affect the calling behaviour of blue whales. This was realised by a controlled exposure experiment.

We looked at call characteristics of blue whale vocalisation, such as source level (SL), call rate, call duration and frequency parameters (minimum, maximum, centroid and peak frequency) as well as possible changes throughout the experimental phases. In addition, we determined ambient noise levels (NLs) within these phases.

Our study showed that the detected anchor pipe vibration embedment noise might exert a behavioural reaction on a local scale. Marine mammals could be affected by the construction operations up to a distance of 375 m and fish up to a distance of 766 m. These zones of responsiveness for vibration embedment operations are relatively small, compared to pile driving, which is regularly used during construction operations. Our study shows that it is important to monitor and assess any kind of noise introduction to verify, whether a sustainable

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human use with respect to the complied guidelines is ensured without affecting the marine fauna. That is the first step to maintain a good environmental status as implemented in the MSFD.

We evaluated the call characteristics of blue whales in a feeding ground. The source level of the recorded down sweeps was 7 to 17 dB lower than the ones reported in other studies from different regions of the world. This finding suggests that blue whales show the ability to vary their call intensity in order to adapt to their local environment.

Our results showed that elevated noise from marine vibrator (MV) signals has an effect on blue whale vocalisation behaviour. We observed that the pre- and exposure phases showed highest NLs, probably caused by the MV signals and additional boat noise. The call rates increased from 2.0 to 6.2 down sweeps per hour and the down sweeps were lengthened two-fold (2.8 s) in the post-exposure phase, the quietest period of the experiment. This increase was probably caused by the preceding elevated noise in general. However, we could also see that the frequency parameters decreased as a result from the MV signals specifically. In contrast, no changes in source level occurred.

With the array we were able to make good recordings, coupled with advanced propagation estimates we were able to make predictions of impacts, evaluate the vocalisation behavior of blue whales and we could assess potential noise-induced reactions towards a controlled exposure to marine vibrator signals.

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Zusammenfassung

Johannes Baltzer - Passiv akustisches Monitoring zur Bewertung möglicher Auswirkungen von anthropogenem Lärm auf die marine Fauna: Tools zur ökologischen Bewertung und zum Monitoring

In dieser Arbeit haben wir verschiedene natürliche und anthropogene Schallquellen mit einem neuartigen GPS-verbundenen Hydrophonarray aufgenommen und angepassten analytische Lösungen für die gezielte Datenverarbeitung der Aufnahmen entwickelt. Wir haben den Lärm beim Einvibrieren von Verankerungsrohren beim Bau von Saatmuschelgewinnungsanlagen im Wattenmeer untersucht (Kapitel 1). Wir haben das akustische Verhalten von Blauwalen (Balaenoptera musculus) in einem isländischen Nahrungsgebiet untersucht (Kapitel 2) und wir haben analysiert, wie eine anthropogene Schallquelle (Signale mariner Vibratoren) die Vokalisierung von Blauwalen beeinflussen kann (Kapitel 3).

Im Laufe dieser Thesis haben wir ein autonomes, leichtes, tragbares, passives, akustisches Array, das schnell und wiederholt von einem kleinen Boot aus eingesetzt werden kann, verwendet. Wir haben Tools entwickelt, um die Schallausbreitung durch eine nichtlineare logarithmische Regression anhand des Achsenabschnitts, der Steigung und des Dämpfungsfaktors abzuschätzen. So konnten wir die empfangenen Schallpegel, die ein Tier in bestimmten Entfernungen vom Baugebiet erreichen, bewerten. Wir haben Tools für die zeitliche Synchronisation und die Detektion von Blauwal-Vokalisierungen in der Skjálfandi Bucht, im Nordosten Islands, entwickelt. Wir haben die Charakteristika von Blauwallauten berechnet und sie mit aufgezeichneten Blauwallauten aus anderen Regionen der Welt verglichen. Das GPS-verbundene Hydrophonarray wurde weiterverwendet, um zu analysieren, wie eine anthropogene Schallquelle das akustische Verhalten von Blauwalen beeinflussen kann.

Dies wurde durch ein kontrolliertes Expositionsexperiment umgesetzt. Wir haben die Charakteristika der Laute, wie z.B. Quellschallpegel, Dauer und Frequenzparameter des Signals bei der Vokalisierung von Blauwalen sowie mögliche Änderungen während der experimentellen Phasen untersucht. Zusätzlich haben wir den Umgebungslärmpegel innerhalb dieser Phasen bestimmt.

Unsere Studie zeigte, dass der detektierte Lärm beim Einvibrieren der Verankerungsrohre eine Verhaltensreaktion auf lokaler Ebene hervorrufen kann. Meeressäuger könnten bis zu einer

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Entfernung von 375 m und Fische bis zu einer Entfernung von 766 m von den Bauarbeiten betroffen sein. Die Bereiche, in denen eine Verhaltensreaktion durch das Einvibrieren hervorgerufen wurde, sind im Vergleich zu Rammverfahren, welches üblicherweise während Bauarbeiten verwendet werden, relativ klein. Unsere Studie zeigt, dass es wichtig ist, jede Art von Lärmbelastung zu kontrollieren und zu bewerten, um zu überprüfen, ob eine nachhaltige Nutzung durch den Menschen in Bezug auf die eingehaltenen Richtlinien gewährleistet ist, ohne die Meeresfauna zu beeinträchtigen. Dies ist der erste Schritt zur Aufrechterhaltung eines guten Umweltzustands, wie in der MSRL vorgesehen.

Wir haben die Charakteristika von Blauwallauten in einem Nahrungsgebiet. Der Quellschallpegel der aufgezeichneten Down-Sweeps war 7 bis 17 dB niedriger als in anderen Studien aus verschiedenen Regionen der Welt. Diese Erkenntnis legt nahe, dass Blauwale die Fähigkeit zeigen, die Intensität ihrer Laute zu variieren, um sich an ihre Umgebung anzupassen.

Unsere Ergebnisse zeigten, dass zunehmender Lärm, einen Einfluss auf das Vokalisierungsverhalten von Blauwalen hat. Wir stellten fest, dass die Pre- und Exposure-Phasen die höchsten Lärmpegel aufwiesen, was vermutlich auf die Signale des marinen Vibrators (MV) und zusätzlichen Schiffslärm zurückzuführen ist. Die Frequenz, in der Blauwale Laute ausgesendet haben, stieg von 2,0 auf 6,2 Sweeps pro Stunde an. Down-Sweeps wurden in der Postexposure-Phase, der leisesten Phase des Experiments, um das Zweifache (2,8 s) verlängert. Dieser Anstieg wurde wahrscheinlich generell durch den erhöhten Lärmpegel verursacht. Wir konnten auch beobachten, wie sich die Frequenzen aufgrund der MV-Signale verringerten. Im Gegensatz dazu traten keine Änderungen des Quellschallpegels auf.

Mit dem Array konnten wir gute Aufzeichnungen machen, zusammen mit weiterentwickelten Schallausbreitungsmodellen konnten wir Auswirkungen von Lärm vorhersagen, das Vokalisierungsverhalten von Blauwalen bewerten und mögliche Reaktionen auf eine kontrollierte Exposition mit MV-Signalen bewerten.

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