Dolphin-Watching Boats Affect Whistle Frequency Modulation in Bottlenose Dolphins

Bottlenose dolphins’ whistles are key in social communication, conveying information about conspecifics and the environment. Therefore, their study can help to infer habitat use and identify areas of concern due to human activities. Here we studied the whistles of bottlenose dolphins (Tursiops truncatus) in two sites of the archipelago of Bocas del Toro, Panama, that contrast in boat traffic. Almirante Bay is a site dominated by taxi-boats and Dolphin Bay is a major location for boat-based dolphin watching. Recordings were made using bottom-mounted hydrophones and from the research boat using an over-the-side hydrophone and a broadband recording system. A total recording effort time of 1,726 h was analyzed. Our results show significant differences in boat detection between sites, and a higher number of whistles detected per minute in the site with tour-boat traffic. Furthermore, whistle modulation accounted for most of the differences between sites, boat presence, and whistle types. Dolphin whistle modulation is thought to be a potential indicator of emotional states including danger, alertness, and stress. In this study, dolphin signature whistle modulation increased significantly with boat presence in both sites but changes in modulation were greater in Dolphin Bay where tour-boats directly and sometimes aggressively interact with the animals. These results support a potential association between whistle modulation and stress (or alertness). These findings indicate that if tour-boat captains behave more like taxi-boat captains by e.g., reducing the distance of approach and contact time during dolphin interactions, dolphin communication, and emotional state would be less disrupted. These measures are implemented in the national guidelines for whale-watching and are known to tour-boat operators. The key to protecting these dolphins is in finding ways to effectively enforce these operator guidelines.

Spatial-temporal dynamics of a local population of Black Sea Bottlenose dolphins (tursiops truncatus ponticus barabash, 1940): visual and acoustic methods of description

This work is devoted to research of the Sudak – Novy Svet (Crimea) local population of Black Sea Bottlenose dolphins. Observations and acoustic records were carried out all the year round in 2014 and 2015. Along with visual identification of individuals, for the first time in our country the method of «acoustic identification» was applied (according to the made catalog of «signature whistles»). «Signature whistles» are defined as tonal signals having a frequency contour, unique for each animal, and dominating in its repertoire. In such aspect «signature whistle» can be considered as a peculiar «acoustic marker» of this individual. In the analysis of all volume of the registered whistles of dolphins (about 30 thousands of signals) 206 dominating types (i.e. «signature whistles») have been defined. On the basis of comparison of visual and acoustic data the structure of groups, making the studied population, has been described; the seasonal picture of visit of the water area by various groups has been presented as well as «transit» and «resident» groups have been allocated.

Pre- and Post-Partum Whistle Production of a BottlenoseDolphin (Tursiops truncatus) Social Group

The signature whistle of the Atlantic bottlenose dolphin (Tursiops truncatus) is a well-studied acoustic signal know for broadcasting identity and maintaining contact with conspecifics. Several studies have investigated the use of this signal surrounding the birth of calves to dolphin social groups, although there appears to be discrepancies between the findings of these studies. We aimed to add to the current literature in an attempt to reconcile some of these inconsistencies through investigation of signature whistle production by a bottlenose dolphin group two months prior to and two months following the birth of a calf to one of the social group members. We found that the production of signature whistles matching the contour belonging to our dolphin mother increased significantly in both the pre- and post-partum period. Heightened production of the mother’s signature whistle type in the first week of our focal calf’s life supports the establishment of a recognition system within this time period. Given that learning processes associated with the sound environment appear to begin shortly after calf birth, we also explored the signature whistle rates of the other social group members in an effort to determine whether any signature whistle production influenced the development of the dolphin calf’s own signature whistle type. We found that the signature whistles of the other social group members were significantly lower than production of the mother’s signature whistle until after the first week post-partum. None of the signature whistle types appeared to influence the signature whistle development of our focal calf within the scope of this study, however, as the calf did not develop a signature whistle in her first two months of life.