Browsing by Author "Ribeiro, C."
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- Bottlenose dolphin Tursiops truncatus group dynamics, site fidelity, residency and movement patterns in the Madeira Archipelago (North-East Atlantic)Publication . Dinis, A.; Alves, F.; Nicolau, C.; Ribeiro, C.; Kaufmann, M.; Cañadas, A.; Freitas, LThe bottlenose dolphin Tursiops truncatus is one of the most frequently sighted cetacean species in the Madeira Archipelago (North-East Atlantic); however, little is known about its population ecology in these waters. Photo-identification undertaken during systematic, non-systematic and opportunistic surveys conducted between 2001 and 2012 was used to assess group dynamics, site fidelity, residency and movement patterns of bottlenose dolphins in the archipelago. Three different patterns of residency were assigned, based on individual sighting histories. Group size ranged between 2 and 90 individuals (median 12), with no significant monthly difference in group size. All resident dolphins formed a core, complex network with migrant and transient dolphins. In contrast, satellite clusters were formed exclusively by transient individuals. The lagged identification rate (LIR) model indicated that a dolphin remained in the area for an average of 90 days, whereas the average time an individual spent outside the study area was approximately 313 days. The Madeira Archipelago appears to be only a section of a much larger home range for this population, with the dolphins exhibiting three different patterns of occurrence that associate with each other. The information gained about this poorly studied population contributes to the overall knowledge of bottlenose dolphins in insular oceanic habitats.
- Daytime dive characteristics from six short-finned pilot whales Globicephala macrorhynchus off Madeira IslandPublication . Alves, Filipe; Dinis, A.; Ribeiro, C.; Nicolau, C.; Kaufmann, M.; Fortuna, C. M.; Freitas, L.
- Spatial and temporal distribution of bottlenose dolphins, Tursiops truncatus, in the Madeira archipelago, NE AtlanticPublication . Dinis, Ana; Carvalho, A.; Alves, F.; Nicolau, C.; Ribeiro, C.; Kaufmann, M.; Cañadas, A.; Freitas, L.One of the first steps in understanding the relationships between populations and their habitats is to determine which areas they use with higher frequency. This study used systematic and non-systematic survey data from 2001-2002 and 2004-2012 to determine encounter rates and investigate temporal and spatial distribution of bottlenose dolphins around Madeira, Desertas and Porto Santo islands. A total 24,914 km of search effort was carried out and 199 sightings were recorded. Highest encounter rates were found off the east coast of Madeira and off Porto Santo. Moreover, higher encounter rates occurred over bathymetries ranging between 500-1,000 m during systematic surveys whereas in non systematic surveys relative high encounter rates were found in depths of 2,000-2,500m. Most dolphins were found to be distributed in depths <1,000m and at no more than 10 km offshore indicating a preference for shallower waters. Dolphins were sighted during the whole year and there were no significant differences in encounter rate between months. These results suggest the existence of preferential areas for this species based on static bathymetric features. The fact that the dolphins prefer inshore areas that are more exposed to anthropogenic activities should be taken into account when discussing bottlenose dolphin conservation measures in the Madeira archipelago.