Use of acoustic signals in Cape fur seal mother-pup reunions: individual signature, signal propagation and pup home range.

The Cape fur seal (Arctocephalus pusillus pusillus) is one of the most colonial mammals, with colonies of up to hundreds of thousands of individuals during the breeding season. During the lactation period, mothers and pups are regularly separated as females undertake multi-day foraging trips at sea. Mothers and pups use a mutual vocal recognition system to reunite after separation. Such communication is highly constrained by both high background noise and risk of individual confusion owing to the density of seals. This study aimed to experimentally assess the acoustic features relevant for mother-pup vocal identification and the propagation properties of their calls. Playback experiments revealed that mother and pup individual vocal signatures rely on both temporal and frequency parameters: amplitude and frequency modulations, timbre and fundamental frequency (f0). This is more parameters than in any colonial species studied so far. The combinational use of acoustic features reinforces the concept that both environmental and social constraints may have acted as selective pressures on the individual vocal recognition systems. Theoretical propagation distances of mother and pup vocalisations were estimated to be below the range of distances at which mother-pup reunions can occur. This suggests that Cape fur seals may have strong abilities to extract vocal signals from the background noise, as previously demonstrated in the highly colonial king penguin. Investigating the transmission of information throughout the propagation of the signal as well as the ability of the receiving individual to decipher vocal signatures is crucial to understanding vocal recognition systems in the wild.

Geographical, temporal, and individual-based differences in the trophic ecology of female Cape fur seals.

Information on resource use and trophic dynamics of marine predators is important for understanding their role in ecosystem functioning and predicting population-level responses to environmental change. Where separate populations experience different local environmental conditions, geographic variability in their foraging ecology is often expected. Within populations, individuals also vary in morphology, physiology, and experience, resulting in specialization in resource use. In this context, isotopic compositions of incrementally grown tissues such as keratinous hairs offer a valuable opportunity to study long-term variation in resource and habitat use. We investigated the trophic ecology of female Cape fur seals (Arctocephalus pusillus pusillus) using carbon and nitrogen isotopic compositions of serially sampled whiskers collected at four breeding sites along the coast of South Africa. Drawing on over 900 isotopic measurements, we assessed geographic variability in isotopic niche width between colonies and the degree of individual specialization. We found slight, but clear geographic differences in isotopic ratios and isotopic niche widths, seemingly related to ecological setting, with niche widths being proportional to the area of available shelf and shelf-slope habitat surrounding the colony. We further identified periodic oscillations in isotopic ratios, which likely reflect temporal patterns in foraging distribution and prey type, linked to shifts in the availability of prey resources and their interaction with constraints on individual females throughout their breeding cycle. Finally, individual specialization indices revealed that each of the study populations contain specialist individuals that utilize only a small subset of the total population niche width. The degree of individual specialization was, however, not consistent across colonies and may reflect an interactive influence between density-dependent effects and habitat heterogeneity. Overall, this study provides important information on the trophic ecology of Cape fur seals breeding in South Africa and highlights the need to consider geographic and individual variability when assessing the foraging ecology of marine predators.

Disentanglement of Cape fur seals (Arctocephalus pusillus pusillus) with reversible medetomidine-midazolam-butorphanol.

Anaesthesia in pinnipeds is considered a much higher risk than in most terrestrial mammals because of their frequent proximity to water and physiological and anatomical adaptations related to diving, which also influence their anaesthesia management. Anaesthetising and immobilising entangled seals does not allow for selection of animals that are at a safe distance from the water's edge. Medetomidine-midazolam-butorphanol (MMB) sedation was trialled on eight entangled Cape fur seals (CFS) (Arctocephalus pusillus pusillus) to determine if it was safe to use on animals that entered the water post-darting. The MMB was given at an estimated dose of 0.03 mg/kg, 0.2 mg/kg and 0.2 mg/kg, respectively, via remote darting. Sedation was reversed with intramuscular atipamezole (0.15 mg/kg) and naltrexone (0.4 mg/kg) to antagonise the effects of medetomidine and butorphanol, respectively. Moderate sedation was achieved in six animals. Six of the animals entered the water after being darted. There was a single mortality and a single animal that was too lightly sedated for capture. The preliminary results indicate that MMB produces suitable sedation for disentanglement of CFS. Additionally, MMB might be suitable for application to field-based biological research.

Subcutaneous merocercoids of Clistobothrium sp. in two Cape fur seals (Arctocephalus pusillus pusillus).

Fur seals represent intermediate hosts of the cestode Clistobothrium. Large sharks are definitive hosts for these parasites. Two female, 25- and 27-year-old fur seals, caught in the 1980s at the South African coast, were examined pathomorphologically. Both animals showed multifocal, up to 1 cm in diameter large cavities of the thoracic and abdominal subcutaneous adipose tissue containing intraluminal metacestodes of tapeworms, which were surrounded by a locally extensive, pyogranulomatous panniculitis. The metacestodes (merocercoids) of one fur seal were isolated from the subcutaneous adipose tissue and characterized morphologically and for the first time from this host by molecular techniques. The morphometric data corresponded with 'delphini'-morphotype merocercoids, but the sequence of the partial 28S ribosomal RNA gene identified them as conspecific with merocercoids of the morphotype 'grimaldii'. These merocercoid types are morphologically Type XV metacestodes of marine tapeworms and represent different species of Clistobothrium. Sequence data were generated for 18S, ITS1, 5.8S, ITS2, partial 28S ribosomal DNA and partial mitochondrial cox1 gene and phylogenetic analysis of 18S rRNA and partial 28S rRNA genes identified the fur seal merocercoids as Clistobothrium species. However, it cannot yet be assigned to species level because of limited molecular data from adult stages. Most likely, both fur seals were infected as juveniles in their original habitat, the coastal regions of South Africa. The metacestode infection is probably an incidental finding, however, there is a chronic inflammatory reaction next to the subcutaneous merocercoids. It is noteworthy, that the merocercoids remain in a potentially infective stage even after more than 20 years.