Browsing by Author "Halicka, Zofia"
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- Temporal distribution of the short-beaked common dolphin (Delphinus delphis) in the south of Madeira Island (Portugal) and relationship with oceanographic variablesPublication . Halicka, Zofia; Barbosa, Ana B.Short-beaked common dolphin (Delphinus delphis) is a small cetacean species that is among the most common marine mammals in Madeira Island. This thesis represents the first study that describes temporal distribution of D. delphis in this region and that relates it with environmental determinants. Results were based on data collected on platform of opportunity on the southern off Madeira Island during the period 2011 – 2014. They revealed that presence of D. delphis varied consistently between warm and cold seasons, with higher occurrences between December and May. This temporal distribution pattern reflects a summer migration probably directed northwards. General Additive Models showed that temperature, chlorophyll concentration, wind intensity and direction, as well as landings of sardine, curled picarel and Atlantic chub mackerel were important factors affecting D. delphis distribution. This study confirms information from previous studies revealing that common dolphin tents to avoid waters warmer than 18ºC. Moreover modelling results can also reflect a trophic cascade, between phytoplankton, pelagic schooling fish and D. delphis. Further studies are needed to evaluate seasonal migration patterns, involving animal telemetry and photo-identification, probably in cooperation with other institutions, as well as exact positioning of dolphin sightings and other potentially relevant environmental variables (e.g., depth, distance from the coast, upwelling intensity).