Inferring energy expenditure from respiration rates in minke whales to measure the effects of whale watching boat interactions

Quantifying the energetic costs of human induced behavioral disturbance on wildlife is a crucial step to evaluate the potential long-term effects of disturbance on individual vital rates. Standard methods cannot be used for estimating energetic cost of transport because of the large size of most cetaceans, and instead energetic costs are inferred from respiration rates. We quantified the added energetic costs of avoidance to whale watching boats for minke whales (Balaenoptera acutorostrata) in Faxaflói bay, Iceland, by comparing minke whale movement tracks and respiration in the presence (impact) and absence (control) of whale watching boats. Energy expenditure was inferred from respiration rates, using published bioenergetic models for minke whales and mass-specific cost of transport (COT) was estimated for different swimming speeds. The sensitivity of the COT estimate to model assumptions was investigated using resampling methods. ANCOVA was used to investigate the effects of swimming speed and whale watching boats on minke whale respiration rate. Respiration rate increased linearly with swimming speed, while COT decreased nonlinearly with increased speed up to an optimal speed between 2.5 and 7.0ms-1. Respiration rates were higher during interactions with whale watching boats at any given speed, suggesting that boat presence elicited a stress response in the animals, resulting in a 23.2% increase in estimated energy expenditure. Swimming speed also increased during whale watching interactions from 1.62 to 2.64ms-1, resulting in an additional 4.4% increase in estimated energy expenditure during whale watching interactions. Thus, whale watching boat interactions resulted in an overall increase in estimated energy expenditure of 27.6%, from 56.54 to 72.16Jkg-1min-1. During interactions with whale watching boats, minke whales swam at speeds that were within the lower range of the optimal COT. This suggests that minke whales employ similar avoidance strategies towards whale watching boats as towards natural predators. © 2014 Elsevier B.V.