Analysis of the behavioural response of fin and humpback whales to an icebreaker using a thermal imaging based whale detection system
Cetaceans have evolved a sophisticated auditory sense and rely on sound as principal mean for underwater communication and sensing. Hence, they are affected by noise that is introduced in the world’s oceans by various human activities, and disturbance of marine mammals by anthropogenic noise is of g...
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| Format: | Thesis |
| Language: | unknown |
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2015
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| Online Access: | https://epic.awi.de/id/eprint/52685/ https://epic.awi.de/id/eprint/52685/1/2015_MSc_Hanna_Michel.pdf https://hdl.handle.net/10013/epic.03b609ae-b8aa-458f-b86c-57148e830272 https://hdl.handle.net/ |
| Summary: | Cetaceans have evolved a sophisticated auditory sense and rely on sound as principal mean for underwater communication and sensing. Hence, they are affected by noise that is introduced in the world’s oceans by various human activities, and disturbance of marine mammals by anthropogenic noise is of great concern. However, over 30 years after the first studies of the effect of noise on marine mammals, its mechanism is still not understood. Documented effects range from short-term behavioural changes to injury and death, while other studies have shown no effect at all. In this thesis, a ship-based thermal imaging based whale detection system was used for retrospective analysis of the behavioural response of fin and humpback whales to the German research icebreaker Polarstern in the Southern Atlantic Ocean. A total of 17 encounters was analysed; during five of these encounters a behavioural response of the whales was observed. As the vessel approached the whales and came closer, the whales changed their swimming direction from swimming virtually parallel to Polarstern to swimming perpendicularly or in the opposite direction of the ship’s heading. Thereby, the distance between the pods and the ship was increased quickly. The direction change ranged from 43-97°. The five pods showing behavioural responses were observed at minimum distances of up to ~1500 m from Polarstern. Three pods detected in the same range and nine pods observed at greater distances did not show a behavioural change. Therefore, proximity to the ship and, thus, the sound pressure level that the whales received likely played an important role since sound pressure levels decrease with increasing distance to a sound source. The behavioural responses of the five pods suggest that the whales were avoiding high sound levels generated by Polarstern. Furthermore, the behavioural analysis based on thermal imaging turned out better than analysis based on records of visual observers. More whale blows were detected, the distance estimation was more precise, and the behaviour of whales was recognizable in contrast to data recorded by visual observers. To this day, the consequences of short-term behavioural changes due to human disturbance on the population-level are unknown. However, a human-caused increase in low-frequency ambient noise must be considered a potential stressor for all baleen whales, and anthropogenic noise has been hypothesized to be involved in the lack of recovery of several cetacean populations. Additional research is needed to understand its biological significance for marine mammals. Further industrialisation of the oceans would be accompanied by increasing noise levels; however, technological advancements could help to lessen the impact of noise from various anthropogenic activities on marine mammals. |
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