Effects of boats on the surface and acoustic behaviour of an endangered population of bottlenose dolphins

Abstract

Coastal cetaceans are increasingly being exposed to boats and noise as nature tourism grows. Such activity has a wide range of detrimental effects on the surface behaviour of cetaceans, but effects on their acoustic behaviour are poorly understood. We quantified the effects of tour boats and of the observing research boat on the group structure and vocal behaviour of bottlenose dolphins Tursiops truncatus in Doubtful Sound, New Zealand. Acoustic recordings and group follow data were collected from a 5 m research vessel, and analysed via an informationtheoretic approach. Groups with mother−calf pairs were significantly less cohesive and coordinated when tour boats were audible. They were more vocal when boats were close and while moving away, presumably to re-establish group structure. Furthermore, groups with calves increased their whistle rates when tour boats were travelling faster, while groups without calves became quieter. Dolphins also responded to boat noise with alterations in whistle frequency and duration. These findings suggest that elevated boat noise affects communication, and groups with calves are particularly sensitive to boat presence and noise. Group structure and whistle parameters were affected by the research boat, highlighting the importance of accounting for observer effects in studies of tourism impacts. The particular sensitivity of groups with calves to boats has important implications for the management of impacts on this population due to its endangered status and history of low calf survival.

Whistle variation in Mediterranean common bottlenose dolphin: The role of geographical, anthropogenic, social, and behavioral factors

“…These aspects need further investigation to be disentangled. Therefore, this study supports the importance of considering the social and behavioral context of the animals when investigating the acoustic structure of communication signals (Guerra, Dawson, Brough, & Rayment, ; Heiler et al, ; Marley et al, ), and its variability between populations to avoid misleading conclusions.…”

“…Even though in Sardinia average levels of noise (recorded at times that whistles were recorded) were higher than in Croatia, whis- (Guerra, Dawson, Brough, & Rayment, 2014;Heiler et al, 2016;Marley et al, 2017), and its variability between populations to avoid misleading conclusions. Note: The upper section shows the significant effects of the assessed explanatory variables on PC2.…”

The Use of Unmanned Aerial Systems in Marine Mammal Research

“…Secondly, the aerial observation range was limited to a radius of approximately 200 m around the vessel [60], while small multirotor aircraft can be controlled at distances of about 4 km. Therefore, it is possible to observe animals in a disturbance-free context and effectively eliminate the research boat presence bias (e.g., [61]). The idea of combining boat observation with aerial imagery for marine mammal behavior surveys is not new.…”

Spatial and Temporal Variation in the Acoustic Habitat of Bottlenose Dolphins (Tursiops aduncus) within a Highly Urbanized Estuary

“…2004; Morisaka et al, 2005;Guerra et al, 2014;May-Collado and Quiñones-Lebrón, 2014;Heiler et al, 2016). Furthermore, different dolphin populations also appear to vary in the source levels of the whistles they produce (Jensen et al, 2012).…”