01/08/2025
New Article.
Riona M. McNamara, Rebecca A. Dunlop. 2025/in press. Changes in call rate and call level of migrating humpback whales (Megaptera novaeangliae) in response to seismic air guns. Marine Environmental Research.
https://www.sciencedirect.com/science/article/abs/pii/S0141113625004726
Seismic air gun operations, used for oil and gas exploration, create intense, impulsive signals that can last for days or months. In response to these signals, baleen whales have been shown to change their feeding, breeding, and migratory behaviours, but with highly variable vocal responses. Some studies show an increase in calling activity and call level, suggesting a response indicative of a Lombard response to noise, whereas others found whales decreased call rate and level, suggesting an avoidance response. This study aimed to determine if humpback whales (Megaptera novaeangliae) significantly altered the rate and/or source level of their social calls in response to seismic air gun signals and determined if any changes were outside of ‘normal’ baseline vocal behaviour. Air guns ranged in size from a small 20 cubic inch gun to a 3130 cubic inch large commercial array, firing every 11 seconds and towed along a set transect. Individual humpback whales that were exposed to operational air guns were tagged using suction-cup acoustic tags (n=12). Within these individuals, call rates and call source levels were compared during exposure to air guns, to before exposure. Then, the call rate and source level of whales exposed to air guns were compared to tagged whales that had not been exposed to air guns (n=21). Results show that whales exposed to air guns generally increased their call rate and call source level, and these call rates and levels were significantly greater compared to unexposed tagged whales. This is consistent with a Lombard response to noise. However, not all tagged whales responded, nor was there a dose-response relationship between air gun received level, air gun proximity, and vocal response. Humpback whales’ vocal responses to air guns are inconsistent and may be context-dependent, emphasising the need to understand how whales perceive these signals to assess the true ecological impact of air gun noise.
