Association patterns and population dynamics of bottlenose dolphins in the Strait of Sicily (Central Mediterranean Sea): implication for management (original) (raw)
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PloS one, 2014
We investigated social structure and association patterns for a small population of Mediterranean bottlenose dolphins, Tursiops truncatus, inhabiting the Aeolian Archipelago (southern Italy). Specifically we evaluate the role of sex and age composition, residency patterns and interaction with trammel nets on this social organization. Association data for 23 regularly sighted individuals were obtained from summer photoidentification surveys collected from 2005-2012. Using a combined cluster and social network analysis approach, we found associations between dolphins were hierarchically structured, where two mixed-sex social units were subdivided into smaller temporarily dynamic groups. We found non-random and long-term preferred associations in the population; however, the degree of social cohesion, residence pattern and interaction with trammel nets differed considerably between the two social units. Six of eight females occurred in the more resident social unit-1; in addition, soci...
PeerJ
In a wide variety of habitats, including some heavily urbanised areas, the adaptability of populations of common bottlenose dolphin (Tursiops truncatus) may depend on the social structure dynamics. Nonetheless, the way in which these adaptations take place is still poorly understood. In the present study we applied photo-identification techniques to investigate the social structure of the common bottlenose dolphin population inhabiting the Gulf of Alghero (Sardinia, Italy), analysing data recorded from 2008 to 2019. The social structure analysis showed a division of the entire population into five different communities and the presence of non-random associations, while there was no evidence of segregation between sexes. Furthermore, results highlighted an important change in social structure through time, likely due to a reduction in fish farm activity since 2015. The division of the population into different communities, the presence of segregation based on the foraging strategy (i...
INTRODUCTION Since 1996, a population study has been conducted in Lampedusa Island (Mediterranean Sea, Italy), whose objectives were: a) assess the eventual degree of recidency of bottlenose dolphins (Tursiops truncatus) in the island; b) estimate the population size; c) study habitat use and d) examine the dolphins' behaviour. METHODS Land and boat-based surveys, and photo-identification technique were used to derive the population estimate and to examine distribution and movements of individuals over a three-months summer period (July-September each year, from 1996 to 2000). Land-based observations lasting three hours were made from the two island's higher places (Albero Sole, NW and Capo Grecale, NE) at fixed times, both during the morning (07:00-10:00) and during the afternoon (17:00-20:00). Dolphins number, position, estimate behaviour and direction of movement were recorded onto data sheets. Using a 4,5 inflatable powered outboard, boat-based surveys were made, trying ...
Accurate description of population structure and genetic connectivity is essential for efficient conservation efforts. Along the European coastline, Tursiops truncatus typically shows high site fidelity to relatively small areas, often semi-enclosed waters, but patterns of genetic connectivity among such areas are often poorly understood. In this study, we investigate the patterns of genetic structure and connectivity of Tursiops truncatus in the Adriatic Sea and contiguous Mediterranean, where photo-ID studies suggest the occurrence of local ‘resident communities’, and a complex pattern of geographic population structure has previously been suggested. Our results are consistent with the occurrence of communities with high site fidelity to the Gulf of Ambracia, Croatian island systems and the Gulf of Trieste. Dolphins in this region do not fit a model of complete panmixia, but neither do they exhibit multiple discrete population units. Even for the community in the Gulf of Ambracia,...
Journal of Mammalogy, 2015
A large, but poorly studied, bottlenose dolphin community, Tursiops truncatus, inhabits coastal waters of Normandy (Normano-Breton Gulf, English Channel, France). In this study, the social structure and abundance of this community were assessed using photo-identification techniques. Like other bottlenose dolphin communities worldwide, this resident community has a fission-fusion social structure with fluid associations among individuals (half-weight index = 0.10). Association patterns were highly variable as indicated by a high social differentiation (S = 0.95 ± 0.03). The majority of associations were casual, lasting days to months. However, individuals exhibited also a smaller proportion of long-term relationships. A mean group size of 26 was large compared with other resident coastal communities, and variable, ranging from 1 to 100, which could be the results of ecological conditions, in particular resource predictability and availability. Analyses also showed that the community was organized in 3 social clusters that were not completely isolated from each other. Abundance was estimated at 420 dolphins (95% confidence interval: 331-521), making this coastal community one of the largest identified along European coastlines. Because human activities in the Gulf are expected to increase in the upcoming years, longterm demographic monitoring of this dolphin community will be critical for its management.
Aquatic Conservation: Marine and Freshwater Ecosystems, 2019
1. Previous studies suggest that the common bottlenose dolphin population in the Croatian Adriatic Sea is structured into distinct local communities. However, their home ranges and levels of interaction remain unknown. 2. Dedicated boat-based surveys were conducted seasonally, in three adjacent study sites from 2013 to 2017. Photo-identification data were used to identify distinct local communities by relating the social structure descriptors to the home ranges of individual animals, and to determine the community home ranges and identify the levels of interactions between them. 3. The overlaps between the home ranges of individuals (50 and 95% kernel density estimators [KDE]) were positively correlated to association strengths between them. Three distinct communities were identified by the hierarchical cluster analysis. The individuals' 95% KDE home range overlaps and association strengths were significantly higher within the three communities than between them, indicating both social and spatial segregation. 4. The 95% KDE home ranges of the communities showed very low to no overlap. The individuals ranged mainly centrally within the home range of their respective community. The probabilities of movement, expressed as lagged identification rates, were significantly higher within than between community home ranges. However, 37 out of 1024 identified individuals were observed in more than one community home range, indicating that the communities are not isolated. 5. Four out of the six Sites of Community Importance currently in place within the Croatian Adriatic Sea lie within the home ranges of the three local bottlenose dolphin communities. Once these sites are declared as Special Areas of Conservation, the management scheme will need to accommodate for differences in the spatial and social ecology of these communities, and environmental and anthropogenic factors acting upon them. The results of this work provide baseline information for such tailored management.
Journal of the Marine Biological Association of the United Kingdom, 2013
This paper represents the first quantitative assessment of the distribution and abundance of bottlenose dolphins (Tursiops truncatus) inhabiting the waters around Lampedusa Island, Italy. Eleven years of photo-identification data, collected from 1996 to 2006 by three different research groups, were brought together, reviewed and analysed to fulfil the following objectives: (i) to obtain baseline information on the abundance and residency of the local bottlenose dolphin putative population; (ii) to review the current Marine Protected Area (MPA) boundaries, especially those referred to waters around Lampedusa Island, with a view to establish a new Special Area of Conservation (SAC); and (iii) to explore the potential and limits of analysing heterogeneous datasets to improve future data collection methods. The most resident dolphins were regularly observed in six specific areas around Lampedusa Island. From a total of 148 photo-identified bottlenose dolphins, 102 were classified as wellmarked. The capture histories and the distribution of sightings clearly show a number of dolphins regularly use the study area. Best estimates for the first period within the 'core study area' were obtained for 1998 data. The 2005 estimate was significantly larger than the 1998 estimates (z ¼ 2.160; P , 0.05) compared to that of 1998. Implications of our results for the current MPA, for transboundary conservation initiative involving Italy, Malta and Tunisia and for directing future research within and outside the MPA are fully discussed.
Aquatic Mammals, 2010
The Shannon Estuary is home to Ireland's only known resident population of bottlenose dolphins (Tursiops truncatus) and is designated as a candidate Special Area of Conservation (cSAC) for this species. Proper conservation management of these dolphins requires an understanding of the social structure of this population. Four years of photoidentification data (2005 to 2009, excluding 2007) were used to construct sociograms that complement a cluster analysis of individually marked dolphins and their associates. The results found little evidence of social stability or group fidelity for this study's dolphin population. Analysis of dolphins observed in consecutive years showed that the probability of group members encountering an individual dolphin in the second year did not depart from a random model. The social parameters for this resident population seem to be typical for this species. Bottlenose dolphins are found to exhibit a highly fluid, dynamic social structure within which individuals change their composition and associates regularly. These dolphins in the Shannon Estuary appear to live in a fission-fusion based society.
2010
The Shannon Estuary is home to Ireland's only known resident population of bottlenose dolphins (Tursiops truncatus) and is designated as a candidate Special Area of Conservation (cSAC) for this species. Proper conservation management of these dolphins requires an understanding of the social structure of this population. Four years of photoidentification data (2005 to 2009, excluding 2007) were used to construct sociograms that complement a cluster analysis of individually marked dolphins and their associates. The results found little evidence of social stability or group fidelity for this study's dolphin population. Analysis of dolphins observed in consecutive years showed that the probability of group members encountering an individual dolphin in the second year did not depart from a random model. The social parameters for this resident population seem to be typical for this species. Bottlenose dolphins are found to exhibit a highly fluid, dynamic social structure within which individuals change their composition and associates regularly. These dolphins in the Shannon Estuary appear to live in a fission-fusion based society.