Changes in bottlenose dolphin whistle parameters related to vessel presence, surface behaviour and group composition

Abstract

Cetacean watching from tour boats has increased in recent years and has been promoted as an ethically viable alternative to cetacean viewing in captive facilities or directed take. However, short-and long-term impacts of this industry on the behaviour and energetic expenditure of cetaceans have been documented. Although multiple studies have investigated the acoustic 1 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 parameters in relation to boat presence, surface behaviour 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. A similar, although less pronounced difference was observed in response to engine noise generated by the research vessel when idling, suggesting that noise alone plays an important role in driving this shift in whistle frequency. Additionally, a strong effect of surface behaviour was observed, with the greatest difference in whistle parameters detected between resting and other behavioural states that are associated with higher degrees of emotional arousal. Group composition also contributed to the variation observed, with the impact of boats dependent on whether calves were present or not. Overall these results demonstrate high natural variation in the frequency parameters of whistles utilized by dolphins over varying behavioural states and group composition. Anthropogenic impact in the form of marine tour boats can influence the vocalization parameters of dolphins and such changes could have a long-term impact if they reduce the communication range of whistles or increase energy expenditure. Key wordsbottlenose dolphin, marine tourism, Namibia, Tursiops truncatus, vocal behaviour Wildlife tourism involving cetacean (whale, dolphin and porpoise) watching has experienced rapid growth since the 1990s (Hoyt, 2001;O'Connor, Campbell, Cortez, & Knowles, 2009). 2Globally, boat-based cetacean watching generates an estimated 2.2 billion US dollars annually (IWC, 2014). Revenue can provide a valuable subsidy to fishing communities and in some cases wild cetacean viewing has replaced direct hunting of whales and dolphins (Amir & Jiddawi, 2001;Berggren et al., 2007). Compared with captive facilities, responsible boatbased cetacean watching has been promoted as an ethically acceptable option for observing dolphins, providing a valuable forum for environmental education and promotion of conservation efforts (IFAW, 1997). However, a considerable body of work has shown that boats and boat-based cetacean watching can have multiple negative impacts on the behaviour of the focal individual, population or species (Parsons,...

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

“…This rule was applied to reduce the risk of collecting whistles from the same individual (pseudoreplication), thus introducing a bias in the sample because of the repetition of whistles characterized by the same contour (La Manna, Rako‐Gospić, Manghi, & Ceccherelli, ; La Manna et al, ). Following a method already applied in other studies (Heiler et al, ; La Manna et al, , ; Marley et al, ), all whistles were graded on the basis of their signal to noise ratio (SNR) as (a) score 1 (faint whistle with the entire contour not clearly visible on the spectrogram or overlapping with other sounds); (b) score 2 (whistle clearly visible from its start to its end); and (c) score 3 (prominent and dominant whistle). Only whistles scoring 2 or 3 were analyzed further.…”

“…The bottlenose dolphin, Tursiops spp., live in complex fission–fusion societies (Connor, Wells, Mann, & Read, ; Mann, Connor, Barre, & Heithaus, ) and have developed frequency‐modulated, narrow‐band signals, called whistles, used for individual recognition, contact maintenance, and group coordination (Janik & Sayigh, ; MacFarlane et al, ). Many studies have found acoustic variation between different populations of bottlenose dolphin (Azevedo et al, ; Hawkins, ; Jones & Sayigh, ; La Manna, Rako‐Gospić, Manghi, Picciulin, & Sarà, ; May‐Collado & Wartzok, ; Morisaka et al, ; Papale et al, ; Wang et al, ), but understanding such variations without disentangling the concurrent effects of different factors shaping dolphin acoustic behavior may be limiting and frustrating (Gridley, Elwen, Rashley, Badenas Krakauer, & Heiler, ; Heiler, Elwen, Kriesell, & Gridley, ; May‐Collado & Quiñones‐Lebrón, ; Sayingh, ). Because the soundscape of a given environment may change over time, variations in dolphin whistles may be the response to varying background noise levels, for example, to facilitate signal transmission and have an effective communication (Ansmann et al, ; May‐Collado & Wartzok, ; Papale, Gamba, Perez‐Gil, Martin, & Giacoma, ).…”

“…The changes in vocal behavior may also depend on factors, including group behavior and the occurrence of anthropogenic stressors (Gridley et al, ; Hawkins & Gartside, ; La Manna, Manghi, Pavan, Lo Mascolo, & Sarà, ; Marley, Salgado, & C.P., Erbe, C. and Parnum, I.M., ; Rako‐Gospić & Picciulin, ; Romeu, Cantor, Bezamat, Simões‐Lopes, & Daura‐Jorge, ). The features, such as group size and composition, are also known to influence the acoustic properties of whistles and contribute to their variation (Heiler et al, ; Quick & Janik, ). Overall, because of the ability for vocal learning and the vocal plasticity of bottlenose dolphin, the structure and characteristics of whistles are influenced and shaped by social and environmental factors.…”

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).…”

“…In coastal habitats, the most ubiquitous source of anthropogenic underwater noise is vessel traffic, which has resulted in numerous dolphin behavioral response studies. Results have found evidence of physical and acoustical changes to dolphin behavior, such as alterations to inter-breath intervals, inter-animal distances, movement patterns, activity states, whistle duration or rates, and frequency shifts in whistle characteristics, among others (Hastie et al, 2003;Buckstaff, 2004;Bejder et al, 2006;Lusseau, 2006;Nowacek et al, 2007;Weilgart, 2007;Ellison et al, 2012;Steckenreuter et al, 2012;New et al, 2013;Pirotta et al, 2015;Heiler et al, 2016). Significant changes to foraging success or energy demands (from altered movement, behavior or vocal production patterns) could also affect individual health, reproductive rates, or even long-term population survival.…”