Vocal repertoires and insights into social structure of sperm whales (<i>Physeter macrocephalus</i>) in Mauritius, southwestern Indian Ocean

Sperm whales communicate using codas (stereotyped click sequences). Females and juveniles live in long-term social units, and units with similar coda repertoires share vocal clan membership. Vocal clans exhibit culturally defined differences in their multilevel social structure. Here, we aimed to identify different social units among sperm whales in Mauritius in the southwestern Indian Ocean, and to describe and compare their coda repertoires to investigate the presence of different vocal clans. We conducted six boat-based surveys between 2008 and 2013, during which 101 different individuals were photo-identified. Analysis of associations between 22 resighted individuals divided them into four candidate social units, but a lack of resightings impedes solid delineation of social units. Based on number and rhythm of clicks, at least 24 discrete coda types were detected among 4,767 analyzed codas using two different classification methods. Comparison of coda repertoires recorded from seven sperm whale groupings revealed the possible existence of two sympatric vocal clans, but the size differences of recorded repertoires warrant caution of interpretation. To further evaluate social structuring and the presence of different vocal clans in this region, future surveys should aim at obtaining long-term sighting and acoustic data, and cover a more extensive area

Records of pinnipeds in the Mascarene Islands, 1996 - 2014

While no populations of seals are resident in the tropical Indian Ocean, vagrant animals are occasionally sighted in the region. Here we detail two new sightings of pinnipeds in the Mascarene Islands (Mauritius, Reunion and Rodrigues) since 1996 and review a further 15. These include nine records of southern elephant seals (Mirounga leonina) and eight of Subantarctic fur seals (Arctocephalus tropicalis). A possible increase in the number of vagrants over time may be partially due to changes in sighting effort. The majority of sightings for both species were in the austral winter, the period during which vagrants were most commonly recorded elsewhere. The most recent sightings were a juvenile Subantarctic fur seal on the south east coast of Mauritius in July 2013 and another on La Reunion in August 2014. These animals were underweight and in poor condition, as were most Subantarctic fur seal vagrants to the region. This contrasts with the apparently healthy condition of vagrant southern elephant seals. The origin of vagrants to the Mascarene Islands is unknown but the Îles Kerguelen is a likely source of the southern elephant seals, and Ile Amsterdam and Prince Edward Islands for the Subantarctic fur seals, due to the proximity, the size of their populations and the direction of flow of oceanic currents.

Contrasted accumulation patterns of persistent organic pollutants and mercury in sympatric tropical dolphins from the south-western Indian Ocean

Due to their high trophic position and long life span, small cetaceans are considered as suitable bioindicators to monitor the presence of contaminants in marine ecosystems. Here, we document the contamination with persistent organic pollutants (POPs) and total mercury (T-Hg) of spinner (Stenella longirostris, n=21) and Indo-Pacific bottlenose dolphins (Tursiops aduncus, n=32) sampled from the coastal waters of La Réunion (south-western Indian Ocean). In addition, seven co-occurring teleost fish species were sampled and analyzed as well. Blubber samples from living dolphins and muscle from teleosts were analyzed for polychlorinated biphenyls (PCBs), DDT and metabolites (DDTs), chlordanes (CHLs), hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), and polybrominated diphenyl ethers (PBDEs). Methoxylated PBDEs (MeO-PBDEs), reported as having a natural origin, were also analyzed. T-Hg levels were measured in blubber and skin biopsies of the two living dolphin species. δ13C and δ15N values were determined in skin of the dolphins and in the muscle of teleosts. For PCBs, HCHs and T-Hg, concentrations were significantly higher in T. aduncus than in S. longirostris. For other POP levels, intra-species variability was high. MeO-PBDEs were the dominant compounds (55% of the total POPs) in S. longirostris, while PCBs dominated (50% contribution) in T. aduncus. Other contaminants showed similar profiles between the two species. Given the different patterns of POPs and T-Hg contamination and the stable isotope composition observed among analyzed teleosts, dietary and foraging habitat preferences possibly explain the contrasted contaminant profiles observed in the two dolphin species. Levels of each class of contaminants were significantly higher in males than females. Despite their spatial and temporal overlap in the waters of La Réunion, S. longirostris and T. aduncus are differently exposed to contaminant accumulation

Habitat availability and geographic isolation as potential drivers of population structure in an oceanic dolphin in the Southwest Indian Ocean

International audienceDelphinid populations show highly variable patterns of genetic diversity and population structure. Previous studies indicate that habitat discontinuities and geographic isolation are major drivers of population division in cetaceans. Spinner dolphins (Stenella longirostris) are distributed in all tropical oceans, but they are particularly common around islands and atolls. This species occurs in shallow waters at daytime to rest and socialise, and feeds on offshore mesopelagic prey overnight. Here we investigated the genetic population structure of spinner dolphins in the Southwest (SW) Indian Ocean along a west-east geographical gradient, from eastern Africa to the Mascarene archipelago. We combined analyses of 12 microsatellite loci, mtDNA control region sequences, and sighting data to assess genetic differentiation and characterise habitat preferences of these populations. Significant genetic structure among the three sampled sites (Zanzibar, Mayotte and La Réunion) was observed using both types of molecular markers. Overall, our results indicate that geographic isolation, and potentially other factors such as shallow water habitats to rest and socialise, may be important drivers of the genetic population structure of insular spinner dolphins in this region

Linking pollutant exposure of humpback whales breeding in the Indian Ocean to their feeding habits and feeding areas off Antarctica

Humpback whales, Megaptera novaeangliae, breeding off la Reunion Island (Indian Ocean) undergo large-scale seasonal migrations between summer feeding grounds near Antarctica and their reproductive winter grounds in the Indian Ocean. The main scope of the current study was to investigate chemical exposure of humpback whales breeding in the Indian Ocean by providing the first published data on this breeding stock concerning persistent organic pollutants (POPs), namely polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), hexachlorocyclohexanes (HCHs), DDT and its metabolites (DDTs), chlordane compounds (CHLs), polybrominated diphenyl ethers (PBDEs), and methoxylated PBDEs (MeO-PBDEs). Analyses of stable isotopes δ13C and δ15N in skin resulted in further insight in their feeding ecology, which was in agreement with a diet focused mainly on low trophic level prey species, such as krill from Antarctica. POPs were measured in all humpback whales in the order of HCB > DDTs > CHLs > HCHs > PCBs > PBDEs > MeO-BDEs. HCB (median: 24 ng.g-1 lw) and DDTs (median: 7.7 ng.g-1 lw) were the predominant compounds in all whale biopsies. Among DDT compounds, p,p’-DDE was the major organohalogenated pollutant, reflecting its long-term accumulation in humpback whales. Significantly lower concentrations of HCB and DDTs were found in females than in males (p0.05). Differences in the HCB and DDTs suggested gender-specific transfer of some compounds to the offspring. POP concentrations were lower than previously reported results for humpback whales sampled near the Antarctic Peninsula, suggesting potential influence of their nutritional status and may indicate different exposures of the whales according to their feeding zones. Further investigations are required to assess exposure of southern humpback whales throughout their feeding zones