The whale-watching industry can represent a critical anthropogenic stressor for the targeted populations. Identifying and characterizing the individual exposure to wildlife tourism in ...island-associated cetacean communities is especially relevant in small, remote oceanic regions relying on tourism. This study characterized the spatial and temporal variation of the whale-watching pressure on common bottlenose dolphins (Tursiops truncatus) and short-finned pilot whales (Globicephala macrorhynchus) in Madeira Island and identified the most exposed portion of the population, making use of diverse long-term datasets (i.e. sighting data, photographic data and vessels’ tracks) obtained year-round from platforms of opportunity (whale-watching operators) and proposing a new descriptive index which estimates the cumulative exposure rates. Core areas of encounters with the whale-watching vessels were identified off the capital city of Funchal. A daily average of 6.5 (±2.2 SD) vessels were concurring in this area, with a significantly higher number recorded between May and October and a peak of 14 vessels in August. From a total of 367 identified bottlenose dolphins and 536 pilot whales, a minimum of 6% and 10%, respectively, were identified as island-associated individuals. Cumulative exposure rates for these individuals could reach levels over two times higher than the general trend for both species. A higher proportion of island-associated bottlenose dolphins were recorded in the winter season. In contrast, island-associated pilot whales were predominant (over 50%) or in a high proportion (over 40%) year-round. The present study highlights the importance of using data from platforms of opportunity to investigate anthropogenic stressors, as tourism-based cetacean observation. It also provides insights into the whale-watching pressure on island-associated individuals occurring in oceanic areas and calls attention to the need of monitoring the fitness and well-being of these wildlife populations in Madeira Archipelago, an outermost European region.
•A new method based on photographic recaptures is used to estimate the individual exposure of cetaceans to whale-watching.•Cores areas of boat-cetacean encounters (50% Kernel Density Estimation) were identified.•Cumulative exposure rates for island-associated individuals are over two times higher than the general trend.•Seasonal analysis showed a high proportion of island-associated pilot whales exposed throughout the year.•Opportunistic data can effectively contribute to the monitoring of tourism-based cetaceans’ observation activity.
Cetacean watching from tour boats has increased in recent years. However, short- and long-term impacts of this industry on the behavior and energetic expenditure of cetaceans have been documented. ...Although multiple studies have investigated the acoustic response of dolphins to marine tourism, there are several covariates that could also explain some of these results and should be considered simultaneously. Here, we investigated whether common bottlenose dolphins, Tursiops truncatus, inhabiting Walvis Bay, Namibia vary their whistle behavior in relation to boat presence, surface behavior and/or group composition. We detected an upward shift of up to 1.99 kHz in several whistle frequency parameters when dolphins were in the presence of one or more tour boats and the research vessel. No changes were demonstrated in the frequency range, number of inflection points or duration of whistles. Whistle occurrence and production rates increased when tour boats were present. High natural variation was detected in the whistle behavior of bottlenose dolphins over varying behavioral states and group composition. Anthropogenic impact in the form of marine tour boats can influence the vocal behavior of dolphins and such changes could have a long-term impact if they reduce the communication range of whistles or increase energy expenditure.
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