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SOLAMAC - Society Latin American of Specialists in Aquatic Mammals

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Occurrence, movements and residency of common-bottlenose-dolphin Tursiops truncatus truncatus in Rio de Janeiro state, Southeastern Brazil
- Name: Guilherme Maricato

- Master's dissertation title: Occurrence, movements and residency of common-bottlenose-dolphin Tursiops truncatus truncatus in Rio de Janeiro state, Southeastern Brazil

- Institution: Federal University of the State of Rio de Janeiro

- Supervisor: Tatiana Maria

- Year of defense: 2019

Although populations of Tursiops truncatus are well studied worldwide, recent studies indicate two subspecies occurring in the Brazilian coast, in which the subspecies Tursiops truncatus truncatus is little known. To fill this gap, the present study aimed to study the occurrence, movements and residency of T. t. truncatus in Rio de Janeiro state. The study area was divided into three subareas: (1) Cabo Frio coast – CF; (2) Rio de Janeiro coast – RJ; and (3) Oceanic subarea – OC. In CF, 475 individuals from 18 groups were photo-identified. In RJ, 110 individuals were photo-identified from six groups. In OC, 45 individuals from 3 different groups were photo-identified. A total of 16 individuals were resighted in both coastal areas, totaling 614 individuals analyzed. In CF, most groups (44.4%) were identified in winter, followed by summer (38.9%) and autumn (16.7%), with no significant differences in group size among seasons (p = 0.6). All groups sighted contained calves. In RJ, five groups were sighted during fall (83.3%) and only one in winter (16.7%). Half of the groups with calves and the group size varied independently of the composition (p = 0.08). In OC, all groups were sighted in spring. Groups sighted near to coast (mean = 36.42, SD = 28.70) tended to be larger than the groups seen in oceanic areas (mean = 18.83, SD = 4.31). Only 9.6% of individuals seen in CF were recaptured. Of these, most (82.9%) were recaptured only once. Individuals with low degree of residence were the majority (low = 65.8%, medium = 17.1%, high = 17.1%). Considering both coastal areas, the pattern remained. Of the 614 individuals analyzed, only 9.3% were recaptured and individuals with low degree were the most frequent in the analyzes (low = 68.4, medium = 12.3%, high = 19.3%). The maximum distance between recaptures varied from 1.2 to 18.1 km in CF (mean = 9.6, SD = 4.5) and 15.2 and 16.2 km in RJ (mean = 15.7, SD = 0.6). The distance between the coastal subareas varied between 112.7 and 137.6 km (mean = 126.5, SD = 6.8). Three pairs of adults were recorded associated on three different occasions. Of these pairs, two were recorded in both coastal subareas and a pair recorded only in CF. The results indicated that the individuals of T. truncatus truncatus found in the study area are transient, presenting, in general, low residency (CF subarea: 65.8%; Coastal subareas: 68.4%) with individuals travelling between the two coastal subareas studied. Given these characteristics, it is likely that there is a metapopulation of the subspecies and that the individuals studied belong to it.

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