In a relatively short time in evolutionary terms, dolphins have been exposed to both passive and invasive human activities which have caused large changes in the marine environment. Of particular concern is the impact that vessel activities may have on dolphins, especially dolphins that are resident throughout the year in coastal waters adjacent to major towns and cities. Bottlenose dolphins have become the major focus of the growing dolphin-watching tourism encounters have been instigated following a substantial growth in regional areas and often after the levels of dolphin-vessel encounters have become unsustainable. There has been a lack of baseline data on populations of dolphins exposed to low levels of commercial dolphin-watching activities.This study aims to provide baseline observations of the influence of vessel-encounters on the behaviour and acoustics of bottlenose dolphins exposed to low levels of vessel-based dolphin-watching activities.
Dolphins rely on acoustic transmissions to transfer information between individuals, maintain group cohesion, find and capture prey and navigate. Few studies have investigated the contextual use of acoustic emissions in wild bottlenose dolphins. Gaining an understanding of the relationship between behaviour and acoustics allows for further insight into the ecology of dolphins and their needs for survival. This project also aimed to investigate the use of acoustics during different contextual situations in a population of wild bottlenose dolphins.
There are few geographic areas in Australia where baseline information on populations of bottlenose dolphins has been obtained. The current knowledge regarding the status of bottlenose dolphins in Australia is ‘unknown’ or ‘insufficient’. This study provides baseline data on the population abundance and characteristics of bottlenose dolphins inhabiting the Byron Bay region of northern New South Wales, Australia.
Research involved land-based and vessel-based surveys in intensive seasonal blocks between 2003 and 2006 in a survey area of 226km². A total of 1008hrs of land-based (N =507hrs) and vessel-based surveys (N = 313hrs) were made over 12 field seasons. Continuous behavioural observations of each pod of dolphins were made from during land based and vessel-based surveys. The location, pod composition, environmental conditions and vessel activities were also noted. During vessel-based surveys, one-hour focal follows were made of each pod. During focal follows acoustic recordings, photo-identification of individuals were made. An Access 2000 database was developed to store all data records. Photo-identification of individual dolphins within pods was made using a Nikon D100 digital camera with 70-300mm zoom. A photographic catalogue was prepared of individual dolphins. Using Program Mark v. 2.0, the population of in shore bottlenose dolphins in the Byron Bay region was estimated. SocProg v. 2.2 (Whitehead, 2005) program was used to model the social structure of resident female groups of dolphins. The home ranges of resident female groups were estimated used home range extension analysis in ArcView v. 9.0 (Ontario Ministry of Natural Resources, 1998). Acoustic recordings were made using a single AP-H1 series hydrophone (Burns Electronics) and a two-channel hydrophone array with MAX amp (Burns Electronics). Acoustic recordings were analyzed using sonograms in CoolEdit 2000. Whistles were categorized into one of five tonal classes; sine, rise, down-sweep, flat and concave. Each whistle was allocated an individual reference number based on the tonal shape and acoustic parameter measurements (e.g. duration, start frequency, end frequency).
The population of bottlenose dolphins inhabiting the Byron Bay area was estimated to be 865 individuals (95% C.I. ± 861-869). This population appears to have a high portion of ‘transient’ individuals. The basic social foundation of this population was found to be similar to that of other societies of bottlenose dolphins previously reported, with apparent sexual segregation. Mother-calf pods (mean pod size = 21; S.D. = 15) were larger than non-calf pods (mean pod size = 5; S.D. = 5). Two ‘resident’ female groups were identified occupying adjacent territorities of between 177km² and 320km². The social structure ofone group of females intensively investigated showed that the associations between individuals were relatively weak (HWI = 0.28; S.D. = 0.66). Analysis of dolphin behaviour states showed that dolphins spent the most time travelling (38%), followed by milling (31%), feeding (19%), and socialising (12%).
Correspondence Analysis using SPSS v. 11.0 was used to examine the strength ofassociations between acoustic emissions and behaviour of dolphins. All whistles used in this analysis were produced by more than one pod on more than one day and recorded greater than or equal to 40 times. Both whistle tonal classes and individual whistle types were found to be associatedwith particular behaviour states and events. Results of this study indicate that whistles maybe used to convey contextual information between dolphins, suggesting that thecommunication system of bottlenose dolphins is highly complex and structured. Thesefindings also indicate that dolphins use referential communication, a rare abilitiy in theanimal kingdom.
The responses of inshore bottlenose dolphins (Tursiops aduncus) to three different types of vessels; a 12m yacht, 6m vessel with two 115hp outboard engines, and a kayak, were examined. Overdispersed Poisson Models (MLwin v. 2.01), Chi-Square tests (SPSS v.11.0) and Univariate General Linear Models (SPSS v. 11.0) were used to test if the type of vessel and behaviour of vessels altered the behavioural and acoustical responses of dolphins. Dolphin behaviour and acoustic responses were found to vary significantly in the presence of different vessel types, the vessel’s behaviour and their proximity. Dolphin responses to vessels also varied between the different behaviour states that pods were engaged in prior to a vessel encounter. These results suggest that group cohesion in a population exposed to low levels of commercial dolphin-watching operations is affected during vessel encounters.
The results of this study are used to recommend improvements in management of human-dolphin encounters from vessels for regional, state and federal management regimes.