Vagrant Subantarctic fur seals at Bouvetøya

Three vagrant Subantarctic fur seals, Arctocephalus tropicalis, were seen amongst a colony of Antarctic fur seals, A. gazella, at the isolated subantarctic island, Bouvetøya. Possible sources of the vagrants are populations at either Gough Island or the Prince Edward Islands Archipelago.Keywords: Arctocephalus tropicalis, Bouvetøya, vagrants, subantarcti

Dispersion of a southern elephant seal Mirounga leonina to Possession Island, Namibia

Whilst southern elephant seals Mirounga leonina inhabit the Southern Ocean, hauling out on sub-Antarctic islands, individuals are frequently encountered further north, on southern hemisphere continents. It is unknown whether these animals are merely vagrants or whether they are individuals using the extremes of their range. A single adult male, identified by characteristic scars, was sighted 37 times from 2008 to 2021 at Possession Island, Namibia. The timing of sightings indicates that this individual must have remained in African waters between at least some of its haul-outs, rather than returning to the Southern Ocean. Similar observations have been reported anecdotally for other individual adult male elephant seals on the southern African coast, whilst adult females pupping in this area are extremely rare. Although records of vagrant southern elephant seals hauling out on the southern African coast remain rare, whether they are single or repeated visits, in some instances repeated haul-outs represent dispersion to rewarding foraging areas.https://link.springer.com/journal/3002023-03-16hj2023Mammal Research InstituteZoology and Entomolog

First record of a vagrant Commerson’s dolphin, Cephalorhynchus commersonii, at the southern African continental shelf

Commerson’s Dolphins Cephalorhynchus commersonii are distributed in two disjunct populations, one around southern South America and the other around the sub-Antarctic Kerguelen Islands. These populations have been shown to be morphologically and genetically distinct and movement between the two populations is unlikely. We report on the sighting of a single specimen over the South African continental shelf on 13 November 2004. To our knowledge this is the first record of this species in South African waters and such a vast distance (over 4000 km) from the known distribution limits.Keywords: Cephalorhynchus commersonii, vagrant, distribution, South Afric

Cranial variation in common dolphins Delphinus spp. off South Africa, with the inclusion of information from the holotype of Delphinus capensis

The common dolphins (genus Delphinus) are widely distributed in all temperate and tropical oceans. Over this wide geographical distribution they show considerable range in morphological variation, which has led to descriptions of several species in the genus. Until recently, only two species of Delphinus were accepted, but this classification has become contentious. This study investigated the occurrence of morphologically different types of Delphinus in South African waters and assessed geographic and morphometric variations within each type. A total of 296 skulls of Delphinus spp., obtained from the Port Elizabeth Museum and the Iziko South African Museum, were photographed in their dorsal and ventral aspects for geometric morphometric analysis. Our results revealed three clusters of specimens based on analysis of the dorsal aspect of the skull, and two clusters for the ventral aspect. Significant differences in cranial size were found between clusters. Both cranial aspects showed that the main variations in skull shape occurred in the rostral region and braincase area, indicating divergent adaptations relating to these features. There was a substantial difference between the composition of the dorsal-aspect and ventralaspect clusters, suggesting the presence of only one species in South African waters. Significant differences between morphological clusters associated with the three regions within the study area (cold-temperate, warm-temperate and subtropical) are probably mediated through differences in local environmental conditions (e.g. different water temperatures and productivity).Keywords: cranial morphology, Delphinus delphis, geographical variation, geometric morphometrics, rostral index, sexual dimorphism, taxonom

Evidence for density dependent population regulation in southern elephant seals in the southern Indian Ocean

The means by which populations are regulated form a central theme in conservation biology, and much debate has revolved around density dependence as a mechanism driving population change. Marion Island (46°54’S, 37°45’E) is host to a relatively small breeding population of southern elephant seals, which like its counterparts in the southern Indian and southern Pacific Oceans, have declined precipitously over the past few decades. An intensive mark– recapture study, which commenced in 1983, has yielded a long time-series of resight data on this population. We used the program MARK to estimate adult female survival in this population from resight data collected over the period 1986–1999. Including concurrent population counts as covariates significantly improved our mark–recapture models and suggests density dependent population regulation to be operational in the population. Although  predation may have been involved, it is far more likely that density dependent regulation has been based on a limited food supply. A significant increase in adult female survival was evident which is likely to have given rise to recent  changes in population growth.Key words: density dependence, southern elephant seals, Marion Island, population regulation

Pup growth and maternal attendance patterns in Subantarctic fur seals

Samples of pups from the expanding populations of Subantarctic fur seals  (Arctocephalus tropicalis) at Marion and Gough islands were weighed at specific ages between birth and weaning in the period 1993-2000. Growth was estimated and compared between years, sexes, sites of different density, and populations. Pups of comparable age were consistently heavier at Marion Island than at Gough Island, probably reflecting relative prey resource abundance. No changes in pup growth rates were apparent over the study period, nor was there any evidence that growth was affected by ENSO events. Measures of pup growth at Marion Island were complemented by measures of maternal attendance behaviour during three summer and winter  seasons. More years of data are required to determine patterns between attendance, growth, resource conditions and population abundance trends.Key words: Subantarctic fur seal, Marion Island, Gough Island, pup growth, maternal attendance behaviour

Disease outbreaks among penguins at sub-Antarctic Marion Island: a conservation concern

In 1992 and 1993, unknown diseases killed 250–300 King Penguins Aptenodytes patagonicus and an estimated 5–10 thousand Macaroni Penguins Eudyptes chrysolophus at sub-Antarctic Marion Island. At the same island, an outbreak of avian cholera Pasteurella multocida during November 2004 killed approximately 2000 Macaroni Penguins at Kildalkey Bay. Other breeding colonies of Macaroni Penguins and other species of seabirds at the island were not affected at the time. Procedures for reporting and dealing with such outbreaks are now being developed.Centre of Excellence for Invasion Biolog

Haulout site selection by southern elephant seals at Marion Island

Using data from an ongoing mark–resight programme at Marion Island, we tested  empirically whether southern elephant seals prefer certain terrestrial sites to others during the breeding, moulting and winter haulouts, and whether the pattern of site use is the same for different age and sex groups. Southern elephant seals preferred some sites, while discriminating against other sites, with different age and sex classes using different sites for certain haulout events. Wintering young animals did not show strong site selection. Some popular sites were used for all haulouts by all age and sex groups, and apparently have all the requirements of a good site for terrestrial haulout by southern elephant seals. Site selection becomes more apparent with age, suggesting the role of haulout experience in site selection.Key words: southern elephant seal, Mirounga leonina, Marion Island, age group, haulout, site selection