Cascao Irma

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Cascao
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Irma
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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
    Spatial and temporal distribution of cetaceans in the mid-Atlantic waters around the Azores
    ( 2013-02) Silva, Monica A. ; Prieto, Rui ; Cascao, Irma ; Seabra, Maria I. ; Machete, Miguel ; Baumgartner, Mark F. ; Santos, Ricardo S.
    Cetaceans living in offshore waters are under increasing pressure from anthropogenic activities. Yet, due to the lack of survey effort, relatively little is known about the demography or ecology of these populations. Spatial and temporal distribution of cetaceans in mid-Atlantic waters were investigated using a long term dataset collected from boat surveys and land-based observations around the Azores. From 1999 to 2009, 7307 cetacean schools were sighted during 271717 km of survey effort. In 4944 h of land-based observations, 2968 cetacean groups were detected. Twenty-four species were recorded: seven baleen whales, six beaked whales, eight dolphin species, Physeter macrocephalus, Kogia breviceps and K. sima. Overall, Delphinus delphis was the most frequently sighted species but its encounter rate decreased in June- November, coinciding with presence of Stenella frontalis in the region. Tursiops truncatus, P. macrocephalus and Grampus griseus were frequently encountered yearround, whereas large baleen whales showed a distinct peak in encounter rates in March-May. Mesoplodonts were fairly common and appear to be present throughout the year. These findings fill-in a significant gap in the knowledge of cetaceans occurring in a poorly studied region of the North Atlantic, providing much needed data to inform management initiatives.
  • Preprint
    Macro- and micro-geographic variation of short-beaked common dolphin’s whistles in the Mediterranean Sea and Atlantic Ocean
    ( 2013-09) Papale, Elena B. ; Azzolin, Marta A. ; Cascao, Irma ; Gannier, Alexandre ; Lammers, Marc O. ; Martin, Vidal M. ; Oswald, Julie N. ; Perez-Gil, Monica ; Prieto, Rui ; Silva, Monica A. ; Giacoma, Cristina
    Genetic studies have shown that there are small but significant differences between the short-beaked common dolphin populations in the Atlantic Ocean and those in the Mediterranean Sea. The short-beaked common dolphin is a highly vocal species with a wide sound production repertoire including whistles. Whistles are continuous, narrowband, frequency-modulated signals that can show geographic variation in dolphin species. This study tests whether the differences, highlighted by genetic studies, are recognisable in the acoustic features of short-beaked common dolphin’s whistles in the two adjacent areas of the Atlantic Ocean and the Mediterranean Sea. From a selected sample of good quality whistles (514 recorded in the Atlantic and 193 in the Mediterranean) 10 parameters of duration, frequency and frequency modulation were measured. Comparing data among basins, differences were found for duration and all frequency parameters except for minimum frequency. Modulation parameters showed the highest coefficient of variation. Through discriminant analysis we correctly assigned 75.7% of sounds to their basins. Furthermore, micro-geographic analysis revealed similarity between the sounds recorded around the Azores and the Canary archipelagos and between the Bay of Biscay and the Mediterranean Sea. Results are in agreement with the hypothesis proposed by previous genetic studies that two distinct populations are present, still supposing a gene flow between the basins. This study is the first to compare shortbeaked common dolphin’s whistles of the Atlantic Ocean and the Mediterranean areas.