Interactions between whale-watching boats and cetaceans can lead to changes in their behavior. From a management perspective, it is important to understand how this type of disturbance can be translated into physiological effects, such as changes in their energetic metabolism. Humpback whales (Megaptera novaeangliae) typically do not feed while in breeding grounds, thus they depend on finite energy reserves. The effect of whale-watching boats on the energetic metabolism of humpback whales, in the breeding ground of northern Peru (4°10′35″S, 81°08′03″W) was evaluated. Groups of humpback whales were tracked from land, under the following scenarios: with, without, and before-during-after the presence of whale-watching boats. Mass-specific cost of transport (COT) was used as a proxy of energetic efficiency and calculated from swimming speed and breath frequency estimations. No differences were detected in breath frequency, swimming speed, and COT when comparing whales with and without boats. However, in the presence of boats, swim speed increased, and COT decreased as the number of boats increased. Exponential increment in breathing frequency at higher swimming speed was not detected. The absence of swimming speeds beyond the assumed optimal range suggested no shifts into metabolic inefficiency. Our results suggest optimal swimming speed between 2 and 4.05 m/s, representing COT values between 0.020 and 0.041 J × (kg × m)–1. In light of our results, we encourage the implementation of regulations of the activity, particularly limiting the number of boats interacting with the same group of humpback whales.
Bibliographical noteFunding Information:
We thank Sebastian Silva, Belen Alcorta, Salvador Gubbins, and all the members of the Pacifico Adventures crew for their support during the realization of this study. Special thanks to Alexander Alburquerque for taking us every day to the land-based observation point. We very much appreciate the comments and corrections to this manuscript made by Nicola L. Ransome, Sebastian Uhlmann and two reviewers that help us to improve an early version of this manuscript. Funding. This study was funded by the Rufford Foundation via Rufford Small Grants for Nature Conservation (RSG: 15903-1). AG-C was also supported by a Ph.D. Scholarship from the Chilean National Commission for Scientific and Technological Research (CONICYT/63140172-2014).
This study was funded by the Rufford Foundation via Rufford Small Grants for Nature Conservation (RSG: 15903-1). AG-C was also supported by a Ph.D. Scholarship from the Chilean National Commission for Scientific and Technological Research (CONICYT/63140172-2014).
© Copyright © 2021 Villagra, García-Cegarra, Gallardo and Pacheco.
- anthropogenic perturbation
- baleen whale
- efficiency of transport
- energy consumption
- mass-specific cost of transport
- optimal swimming speed