Frequencies of Humpback Whale Song Units (Megaptera novaeangliae): Adjustments to Small Boat Noise

Anthropogenic noise has been shown to impair hearing and elicit behavioral changes among marine animals. Humpback whales are known for their complex vocal displays (i.e., song) which can be masked by vessel noise. In the Gulf of Tribugá, a part of the breeding grounds for humpback whale Stock G, a marine port construction project was proposed, and, if constructed, underwater noise levels in the Gulf would significantly increase. To better understand how humpback whales cope acoustically with increases in vessel noise, humpback whales in the Gulf of Tribugá were studied to examine changes in the high and low frequencies of their song units during and/or after boat noise compared to before it was present. Out of 38 high- and low-frequency comparisons, the same song units had frequencies that were significantly different during boat noise 5 times and after boat noise 4 times (as compared to before boat noise). Out of 20 bandwidth comparisons, the overall bandwidth of the units narrowed 11 times, broadened 9 times, shifted higher 6 times, and shifted lower 2 times. These results give insight into how humpback whales are capable of altering their song structure when they may be responding to small boat noise.