GOLFINICHO - Ecological niche partitioning between two species of dolphins around the Azores and Madeira

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Social structure of a population of bottlenose dolphins (Tursiops truncatus) in the oceanic archipelago of Madeira, Portugal

Publication . Dinis, Ana; Alves, Filipe; Nicolau, Cátia; Ribeiro, Cláudia; Kaufmann, Manfred; Cañadas, Ana; Freitas, Luís

In order to investigate social structure, 11 years of individual photo-identification data of bottlenose dolphin were analysed. We examined the type of association indices between pairs of identified individuals; the patterns of affiliation between indi vidual dolphins and the probabilities of association between individuals over time. Between 2001 and 2012, there were 272 encounters which resulted in the identification of 501 individuals. The discovery curve resulting from the photo-identification analysis indicated an open population with regular recruitment of new individuals. All individuals were found to be asso ciated at an association index of ,0.05. A total of 291 individuals recorded from 2004 to 2012 were used to assess the tem poral pattern of the social structure. The model fit to the Standardized Lagged Association Rate (SLAR) that best described the studied bottlenose dolphin population was ‘casual acquaintances’, and the analysis of associations over time showed a decreasing SLAR curve that falls until reaching the null rate, confirming random associations. The decline of the SLAR curve after 500 days (1.4 years) suggests disassociation over that time period which can be explained by demographic events such as mortality or emigration. In an open ocean habitat like Madeira this is not unexpected, as there are neither geographic boundaries nor enclosed environments. This population presented a dynamic and fluctuating social structure, where groups change in size and composition. In future conservation efforts this population should be considered as one large community, where individuals associate, disassociate and reassociate with each other over time.

2017Journal article

Open access

Spatial and temporal distribution of bottlenose dolphins, Tursiops truncatus, in the Madeira archipelago, NE Atlantic

Publication . 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.

2016Journal article

Open access