Social structure of bottlenose dolphins, <i>Tursiops truncatus</i>, in Panama City, Florida

Social organization is an important attribute of the animal society. We describe the social structure of a bottlenose dolphins population living in Panama City, a seaside resort located on the north-west coast of Florida. Study was conducted with 46 individuals. Dolphins are associated on average half weight index of 0.11. Preferred long-term associations are observed. The proportion of the non-zero association indices suggests that some dolphins seem to avoid others. Associations between and within sex-classes were investigated using only dolphins of known sex and observed at least 4 times. Highly significant differences are found in associations between and within sex-classes (Mantel test, t = 3.7987; P = 1); indeed, male associations are stronger than between inter-sexual associations or between females only. Sociogram of males reveals a complex network with strong associations between pairs or trios that reach up to 0.97, whereas female associations are lower than males. The cluster analysis shows no clear division in the social organization of bottlenose dolphins in Panama City, except for dyads, triads and their multiple networks. The population structure seems to be temporally stable over the study and constant companionships are observed in the dolphin population in Panama City

Harbour porpoises (Phocoena phocoena) stranded along the southern North Sea: An assessment through metallic contamination

International audienceThroughout the last few years, the southern North Sea has witnessed an increase in the number of stranded marine mammals, particularly the harbour porpoise (Phocoena phocoena). This species is subject to several potential threats such as exposure to contaminants, changes in food supply, marine traffic and fishery by-catch. The aims of this study were to investigate potential associations between contaminants and health status and to analyze spatial and temporal trends of metal concentrations in harbour porpoises. Selected trace elements (As, Cd, Cr, Cu, Hg, Mn, Se, V and Zn) were measured in kidneys and livers of 105 harbour porpoises stranded along the southern North Sea (French and Belgian coasts from 2006 to 2013) and 27 stranded along the Bay of Biscay (French coast from 2009 to 2012). Porpoises that died from infectious disease displayed significant higher hepatic concentrations of Cd, Hg, Se and Zn compared to healthy porpoises that died from physical trauma. Adult porpoises displayed significant higher concentrations of Cd, Cr, Hg, Se and V in livers compared to juveniles. No spatial or temporal trends in metal concentrations were detected in our study. The results of the present study suggested that chemical contamination may represent one of many threats encountered by harbour porpoises, but it cannot explain alone the increase in the number of stranded individuals

Using an unbaited stationary video system to investigate the behaviour and interactions of bull sharks Carcharhinus leucas under an aquaculture farm

Bull sharks Carcharhinus leucas are common along the coast of Reunion Island (South-West Indian Ocean) and were suspected to aggregate in the vicinity of an aquaculture farm in Saint-Paul Bay on the west coast. In order to understand the behaviour and interaction of bull sharks near aquaculture cages at Saint-Paul Bay, we deployed an experimental unbaited stationary video camera. From 175 hours of recording during daylight hours from March to April 2012, eight individual female bull sharks (seven adults and one immature) were identified based on their natural markings. These sharks were resighted between 3 and 45 times. Residency analysis revealed site attachment under the aquaculture cages for at least three individuals over the course of the study. Recorded behaviours included intraspecific social interactions such as synchronised swimming. Social interactions and relatively strong paired associations for two pairs of females suggest some level of sociality among bull sharks around Reunion Island. Overall, our results demonstrate the utility of unbaited video systems to monitor the behaviour of adult coastal sharks