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

Foraging dives of sperm whales in the north-western Mediterranean Sea

Oceanic odontocetes rely on echolocation to forage on pelagic or benthic prey, but their feeding ecology is difficult to study. We studied sperm whale foraging dives during summer in the north-western Mediterranean, using visual and passive acoustic observations. Clicking and creaking activities were recorded during dives of focal whales, at distances 24 tons of estimated mass. For individual whales, creak rates did not vary significantly with size (range 0.78–0.80 creak/minute), but decreased with time of the day, and increased for shorter foraging phases. For different dives, higher creak rates were also observed earlier in the day, and linked to shorter foraging phases and surface durations. Although the exact significance of creak emissions (i.e. foraging attempt or prey capture) is not precisely determined, creak rates may be reliably used to quantify sperm whale foraging when single animal dives can be followed acoustically.Publisher PDFPeer reviewe

Identifying key demographic parameters of a small island–associated population of Indo-Pacific bottlenose dolphins (Reunion, Indian Ocean)

<div><p>Photo-identification surveys of Indo-Pacific bottlenose dolphins were conducted from 2009 to 2014 off Reunion Island (55°E33’/21°S07’), in the Indian Ocean. Robust Design models were applied to produce the most reliable estimate of population abundance and survival rate, while accounting for temporary emigration from the survey area (west coast). The sampling scheme consisted of a five-month (June–October) sampling period in each year of the study. The overall population size at Reunion was estimated to be 72 individuals (SE = 6.17, 95%CI = 61–85), based on a random temporary emigration (γ”) of 0.096 and a proportion of 0.70 (SE = 0.03) distinct individuals. The annual survival rate was 0.93 (±0.018 SE, 95%CI = 0.886–0.958) and was constant over time and between sexes. Models considering gender groups indicated different movement patterns between males and females. Males showed null or quasi-null temporary emigration (γ” = γ’ < 0.01), while females showed a random temporary emigration (γ”) of 0.10, suggesting that a small proportion of females was outside the survey area during each primary sampling period. Sex-specific temporary migration patterns were consistent with movement and residency patterns observed in other areas. The Robust Design approach provided an appropriate sampling scheme for deriving island-associated population parameters, while allowing to restrict survey effort both spatially (i.e. west coast only) and temporally (five months per year). Although abundance and survival were stable over the six years, the small population size of fewer than 100 individuals suggested that this population is highly vulnerable. Priority should be given to reducing any potential impact of human activity on the population and its habitat.</p></div

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.

Results of the assumption tests on population closure and trap-dependence.

<p>Results of the assumption tests on population closure and trap-dependence.</p

Summary of the survey effort deployed over the study period (2009–2014), from June to October, off the west coast of Reunion, and the photo-identification effort applied to <i>T</i>. <i>aduncus</i>: Total and mean number of groups sighted with associated photo-identification data and mean group size.

<p>Summary of the survey effort deployed over the study period (2009–2014), from June to October, off the west coast of Reunion, and the photo-identification effort applied to <i>T</i>. <i>aduncus</i>: Total and mean number of groups sighted with associated photo-identification data and mean group size.</p

Distribution of the number of secondary sampling sessions (months) during which each male, female and unknown-sex individual was sighted (total number of secondary sampling sessions = 30).

<p>Distribution of the number of secondary sampling sessions (months) during which each male, female and unknown-sex individual was sighted (total number of secondary sampling sessions = 30).</p

Distribution of the number of individual dolphins sighted in one to six primary sessions (2009–2014) off the west coast of Reunion, according to gender (female, male or unknown).

<p>Distribution of the number of individual dolphins sighted in one to six primary sessions (2009–2014) off the west coast of Reunion, according to gender (female, male or unknown).</p