Magalhaes Sara

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Magalhaes
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Sara
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  • Preprint
    Sex bias in biopsy samples collected from free-ranging dolphins
    ( 2009-01-16) Querouil, Sophie ; Freitas, Luis ; Dinis, Ana ; Alves, Filipe ; Cascao, Irma ; Prieto, Rui ; Silva, Monica A. ; Magalhaes, Sara ; Matos, Jose A. ; Santos, Ricardo S.
    Biological samples of free-ranging dolphins are increasingly used to gain information on population structure and ecology. In small cetaceans, the gender of individuals usually cannot be determined at sea, and population sex ratio has to be inferred indirectly. We used molecular sexing to determine the gender of 340 biopsy samples of bottlenose dolphins, Tursiops truncatus, spotted dolphins, Stenella frontalis, and common dolphins, Delphinus delphis, collected around the Azores and Madeira. Sex ratio was globally skewed in favor of males, and differed between species and archipelagos. Skew was probably influenced by the selectivity of biopsy collectors and seasonal or year-round predominance of males in natural populations. Skew was also influenced by sampling duration and intensity. In the Azores, when several samples were successively collected within the same group, the proportion of female samples decreased as a function of sample order. This trend indicated a tendency for females to increasingly avoid the boat while samples were being collected. It showed that males and females reacted differently to the perturbation caused by the biopsy sampling process (i.e. sample collection and driving style).
  • Preprint
    Ranging patterns of bottlenose dolphins living in oceanic waters : implications for population structure
    ( 2008-10) Silva, Monica A. ; Prieto, Rui ; Magalhaes, Sara ; Seabra, Maria I. ; Santos, Ricardo S. ; Hammond, Philip S.
    Very little is known about the ecology of common bottlenose dolphins (Tursiops truncatus) living in oceanic waters. This study investigated the ranging and residence pattern, of bottlenose dolphins occurring in the Azores (Portugal), the most isolated archipelago in the North Atlantic. Data were collected during standardized boat-based surveys conducted over a 6-year period in an area of approximately 5,400 km2 (main study area). To investigate the extent of movements of individual animals. non-systematic surveys were also conducted outside this area. Only 44 individuals out of 966 identified were frequently sighted within and between years. The remaining individuals were either temporary migrants from within or outside the archipelago, or transients. Resident dolphins showed strong geographic fidelity to the area. Long-distance movements (of almost 300 km), consistent with foraging or exploratory trips. were observed among non-resident dolphins. Home range size was estimated for 31 individuals sighted ≥ 10 times. Range areas of these dolphins varied in size and location, but considerable overlap was observed in the areas used, suggesting the absence of habitat partitioning between resident and non-resident dolphins. Estimates of home range size of bottlenose dolphins in the Azores were found to be considerably larger than those previously reported for this species. It is hypothesized that dolphins living in the Azores carry out extensive movements and have large home ranges in response to the lower density and patchy distribution of prey compared to other areas. The extensive ranging behaviour and the lack of territoriality provide an opportunity for interbreeding between dolphins associated with different islands, thus preventing genetic differentiation within the population of the Azores.
  • Preprint
    Incorporating information on bottlenose dolphin distribution into marine protected area design
    ( 2011-10-12) Silva, Monica A. ; Prieto, Rui ; Magalhaes, Sara ; Seabra, Maria I. ; Machete, Miguel ; Hammond, Philip S.
    The steady growth of the whale-watching activities in the Azores and its concentration in a small area that partly overlaps the home range of a resident group of bottlenose dolphins (Tursiops truncatus) was one of the driving forces to proposing part of the range of this group as a Marine Protected Area (MPA). We used 6-years of data collected during boat surveys to investigate how dolphins used the candidate MPA (cMPA) and whether they showed any preference for the cMPA over adjacent areas. We also estimated the fraction of the resident individuals and group’s range included in the cMPA and examined whether there were any temporal changes in its use. Mean daily encounter rate of bottlenose dolphins was higher inside than outside the cMPA. Dolphin sightings inside the cMPA were nearly double than what was predicted by the survey effort. Dolphins used the cMPA with similar intensity throughout the years. Resident dolphins were frequently sighted in the cMPA. However, less than 20% of the known range (650 km2) and 41% (39 km2) of the core area of the group lay within the cMPA. The reliability in the use of the cMPA over a 6-year period suggests its importance for the dolphin population remained relatively stable but its surface area was clearly insufficient to satisfy the spatial requirements of the resident group. Based on these findings, we proposed to the Regional Government of the Azores to extend the boundaries of the cMPA. Accordingly, the modified protected area established in 2008 includes 100% of the core area of the resident group of bottlenose dolphins. This study provides an example of how information on cetacean habitat-use patterns may be used to design ecologically meaningful protected areas for this group.