W. Chris Oosthuizen

• PhD
• Research Fellow at University of Cape Town

Leopard seals (Hydrurga leptonyx) occur mainly south of the Antarctic Polar Front, but immatures, in particular, seasonally move beyond this range during the austral winter and spring, typically under increased sea ice conditions. Extralimital occurrences of leopard seals can be observed at several sub-Antarctic islands where they haul out to rest....

Animal‐attached devices, or bio‐loggers, that record data on multiple channels are frequently used to study the movement of free‐ranging animals. In recent years, the deployment of animal‐borne video cameras in addition to other time‐series loggers, such as accelerometers and depth sensors, has become popular. Visual observations from animal‐borne...

Historical data on chinstrap penguin (Pygoscelis antarctica) breeding population sizes are sparse and sometimes highly uncertain, making it hard to estimate true population trajectories. Yet, information on population trends is desirable as changes in population size can help inform conservation assessments. Recently, Krüger (2023) (Diversity 2023,...

The Southern Ocean exhibits substantial spatio-temporal variation in biogeochemical processes that shape interactions and productivity across food webs. Stable isotopes in marine predators provide an opportunity to capture such variations, yet few studies have accounted for variability in the isotopic baseline when interpreting predator isotope val...

Marine predators are integral to the functioning of marine ecosystems, and their consumption requirements should be integrated into ecosystem-based management policies. However, estimating prey consumption in diving marine predators requires innovative methods as predator–prey interactions are rarely observable. We developed a novel method, validat...

Antarctic fisheries catch thousands of tonnes of krill each year, and large krill predators such as whales are recovering from heavy harvest. Meanwhile, chinstrap penguins, which depend on krill, have become markedly fewer. Understanding the cause of this decline is critical. Fram Forum FRAM – High North Research Center for Climate and Environment...

Identifying important demographic drivers of population dynamics is fundamental for understanding life‐history evolution and implementing effective conservation measures. Integrated population models (IPMs) coupled with transient life table response experiments (tLTREs) allow ecologists to quantify the contributions of demographic parameters to obs...

The first year of life is critical for large mammals to acquire foraging and predator avoidance skills. Southern elephant seal (Mirounga leonina) pups wean at approximately three weeks of age and depart on their first foraging trips in midsummer, typically remaining at sea for three to four months before returning to their natal islands. We describ...

Introduction The Scotia Sea and Antarctic Peninsula are warming rapidly and changes in species distribution are expected. In predicting habitat shifts and considering appropriate management strategies for marine predators, a community-level understanding of how these predators are distributed is desirable. Acquiring such data, particularly in remot...

Population-level shifts in reproductive phenology in response to environmental change are common, but whether individual-level responses are modified by demographic and genetic factors remains less well understood. We used mixed models to quantify how reproductive timing varied across 1772 female southern elephant seals (Mirounga leonina) breeding...

Most marine apex predators are keystone species that fundamentally influence their ecosystems through cascading top-down processes. Reductions in worldwide predator abundances, attributed to environmental- and anthropogenic-induced changes to prey availability and negative interactions with fisheries, can have far-reaching ecosystem impacts. We tes...

Information on marine predator at-sea distributions is key to understanding ecosystem and community dynamics and an important component of spatial management frameworks that aim to identify regions important for conservation. Tracking data from seabirds are widely used to define priority areas for conservation, but such data are often restricted to...

Fine‐scale knowledge of spatiotemporal dynamics in cetacean distribution and abundance throughout the Western Antarctic Peninsula (WAP) is sparse yet essential for effective ecosystem‐based management (EBM). Cruise vessels were used as platforms of opportunity to collect data on the distribution and abundance of humpback whales (Megaptera novaeangl...

Climate variability and changes in sea ice dynamics have caused several ice-obligate or krill-dependent populations of marine predators to decline, eliciting concern about their demographic persistence and the indirect ecological consequences that predator depletions may have on marine ecosystems. Pack-ice seals are dominant ice-obligate predators...

Phenological shifts are among the most obvious biological responses to environmental change, yet documented responses for Southern Ocean marine mammals are extremely rare. Marine mammals can respond to environmental changes through phenological flexibility of their life-history events such as breeding and moulting. Southern elephant seals (Mirounga...

Variation in the distribution and abundance of food resources are key factors affecting animal sociality. In environments with variable resources, dynamic social organization, such as the fission and fusion of groups, is thought to increase the benefits of group living, while reducing the costs. We investigated the relationship between social organ...

Correlations between early‐ and late‐life performance are a major prediction of life‐history theory. Negative early–late correlations can emerge because biological processes are optimized for early but not late life (e.g., rapid development may accelerate the onset of senescence; “developmental theory of aging”) or because allocation to early‐life...

The large-scale spatial patterns and primary drivers of food web dynamics across seascapes can be investigated using isotope ratios in marine consumers. However, interpreting complex signatures from mobile animals can require good knowledge of spatial isotopic variations in the environment. This is particularly true in the Southern Ocean where regi...

Coastally distributed dolphin species are vulnerable to a variety of anthropogenic pressures, yet a lack of abundance data often prevents data-driven conservation management strategies from being implemented. We investigated the abundance of Indo-Pacific bottlenose dolphins (Tursiops aduncus) along the south coast of South Africa, from the Goukamma...

Killer whales, Orcinus orca, are a cosmopolitan species with large ecological and demographic variation across populations. Population-specific demographic studies are, therefore, crucial in accurately assessing the status and trends of local killer whale populations. Such studies require long-term datasets and remain scarce, particularly in the So...

Individual heterogeneity is variation in trait expression observed among individuals of a population. Individual heterogeneity in the pre‐breeder stage of development is of importance given its eventual contribution to the breeding population's overall reproductive performance. Yet most studies do not consider the role of individual heterogeneity i...

Life‐history trade‐off theory predicts that current reproduction can negatively affect survival and future reproduction. Few studies have assessed breeding costs for males of polygynous species compared to females, despite substantial variation in breeding success among individual males (e.g. subordinate cf. dominant breeders). Specifically, differ...

Monitored seabird populations—useful sentinels of marine ecosystem health—have been declining worldwide at a rapid pace. Yet, lack of reliable long-term monitoring data constrains assessment of the conservation status of many seabird populations. Unmanned aerial vehicles (UAVs) have the potential to increase survey efficiency and count precision of...

The presence of Ross seals (Ommatophoca rossii) throughout the Weddell Sea is at best equivocal although overview articles usually depict this as fact on distribution maps. This study reviewed the appropriate literature on the distribution of Ross seals in the Weddell Sea sensu lato and investigated their presence/absence during two expeditions (su...

We investigated the abundance of Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) along the south coast of South Africa, from the Goukamma Marine Protected Area (MPA) to the Tsitsikamma MPA, between 2014 and 2016. During this period, 662.3h of boat-based photo-identification survey effort was carried out, and the sighting histories of 817 iden...

Recruitment age plays a key role in life‐history evolution. Because individuals allocate limited resources among competing life‐history functions, theory predicts trade‐offs between current reproduction and future growth, survival and/or reproduction. Reproductive costs tend to vary with recruitment age, but may also be overridden by fixed individu...

The region of the Filchner Outflow System (FOS) in the southeastern Weddell Sea is characterized by intensive and complex interactions of different water masses. Dense Ice Shelf Water (ISW) emerging from beneath the ice shelf cavities on the continental shelf, meets Modified Warm Deep Water (MWDW) originating from the Antarctic Circumpolar Current...

Anomalous pelage colourations are not uncommon amongst pinnipeds but have not been documented in sub-Antarctic fur seals (Arctocephalus tropicalis). Fur seals (Arctocephalus spp.) have been monitored on Marion Island since 1973, and as part of the long-term monitoring programme, any atypical sightings of fur seals were recorded. Fourteen sub-Antarc...

Increased environmental stochasticity due to climate change will intensify temporal variance in the life-history traits, and especially breeding probabilities, of long-lived iteroparous species. These changes may decrease individual fitness and population viability and is therefore important to monitor. In wild animal populations with imperfect ind...

Early developmental conditions contribute to individual heterogeneity of both phenotypic traits and fitness components, ultimately affecting population dynamics. Although the demographic consequences of ontogenic growth are best quantified using an integrated measure of fitness, most analyses to date have instead studied individual fitness componen...

ABSTRACT: Insight into the trophic ecology of marine predators is vital for understanding their ecosystem role and predicting their responses to environmental change. Juvenile southern elephant seals (SES) Mirounga leonina are considered generalist predators within the Southern Ocean. Although mesopelagic fish and squid dominate their stomach lavag...

Prey selection for models: A Bayesian statistical mixing modelling approach was used for the dietary reconstruction, using the Stable Isotope Analysis in R (SIAR v. 4.2) package (Parnell et al. 2010). The SIAR method utilises a tissue-and species-specific trophic discrimination factor (TDF) to adjust prey isotopic values to the isotopic values obta...

[This corrects the article DOI: 10.1371/journal.pone.0120888.].

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Central to an animal's fitness is its foraging strategy and understanding the choices made by foraging animals is a fundamental aim in animal ecology. For diving animals, quantifying foraging effort within dives provides a measure of foraging that can be integrated with location information to reveal how animals use their environment as well as the...

Recent pup population estimates of sympatric Subantarctic (Arctocephalus tropicalis) and Antarctic fur seals (A. gazella) at Marion Island are presented. Published pup population estimates of A. tropicalis (1995 and 2004) with an unpublished total island count in 2013, and annual counts on subsets of rookeries (2007–2015) were analyzed using a hier...

Marine predator populations are sensitive to temporal variation in prey availability, but prey dynamics are often difficult to quantify. Long-term measures of offspring growth is a useful performance attribute to gauge the potential demographic direction for such predator populations, especially where other metrics (e.g., population size estimates)...

Very high frequency (VHF) radiotelemetry data has been used for over 30 yr to monitor the behavior patterns of otariid seals. These data have been used in a wide variety of ways, from characterizing the reproductive and foraging ecology of these species to inferring ecosystem changes based on variation in attendance patterns. Yet the accuracy of VH...

Predator populations are likely to respond to bottom-up processes, but there remains limited understanding of how wide-ranging marine predators respond to environmentally driven temporal variation in food availability. Widespread declines of several Southern Ocean predators, including southern elephant seals Mirounga leonina, have been attributed t...

Strategies employed by wide-ranging foraging animals involve consideration of habitat quality and predictability and should maximise net energy gain. Fidelity to foraging sites is common in areas of high resource availability or where predictable changes in resource availability occur. However, if resource availability is heterogeneous or unpredict...

Remote tissue biopsy sampling and satellite tagging are becoming widely used in large marine vertebrate studies because they allow the collection of a diverse suite of otherwise difficult-to-obtain data which are critical in understanding the ecology of these species and to their conservation and management. Researchers must carefully consider thei...

Capturing, immobilizing, and fitting radiocollars are common practices in studies of large mammals, but success is based on the assumptions that captured animals are representative of the rest of the population and that the capture procedure has negligible effects. We estimated effects of chemical immobilization on mortality rates of African buffal...

Southern elephant seals Mirounga leonina within the Kerguelen province disperse between Marion Island (MI), Iles Crozet (IC) and Iles Kerguelen (IK) despite the high site fidelity characteristic of this species. From 1987–2002, 199 IC individuals, or 11.63% of the tagged population there, were resighted at MI. Resights of IC seals at MI peaked duri...

The presence of unmarked individuals is common in mark–recapture study populations; however, their origin and significance in terms of population dynamics remain poorly understood. At Marion Island, southern Indian Ocean, where virtually all southern elephant seal Mirounga leonina pups born annually (1983–2008) were marked in a long-term mark–resig...

The Marine Mammal Programme (MMP) conducts research on pinnipeds and killer whales Orcinus orca at Marion Island, Prince Edward Islands, under the auspices of the Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria. The history of the MMP, which has benefited from collaboration with leading national and internati...

The diet of killer whales Orcinus orca was investigated from 48 predation events observed during 823 sightings at sub-Antarctic Marion Island between 2006 and 2009. From these events, there were 10 cases where prey could be identified. Killer whales fed on fur seals Arctocephalus tropicalis, elephant seals Mirounga leonina and penguins. Constant ef...

Non-offspring maternal care should be rare due to the high costs of raising offspring, particularly lactation, but nonetheless occurs in a variety of taxa. Misguided parental care, associated with recognition errors and/or inattentiveness by lactating females, has been hypothesized as an explanation for allolactation in mammals. In an extension of...

Marker-loss is a common feature of mark–recapture studies and important as it may bias parameter estimation. A slight alteration in tag-site of double tagged southern elephant seals (Mirounga leonina), marked at Marion Island from 1983 to 2005 in an ongoing mark–recapture program, had important consequences for tag-loss. We calculated age-specific...

Vagrant birds recorded ashore at Marion Island and Prince Edward Island from 1987 to 2009 are documented. In total, 101 observations (including multiple sightings of potentially the same individual) of 29 species were made. Palaearctic and Holarctic migrants (17 species), African species (n = 6) and pelagic species with a predominantly Southern Oce...

During three summer surveys at Prince Edward Island (PEI), southern Indian Ocean (2001, 2004 and 2008), 416 southern elephant seals Mirounga leonina were inspected for identification tags. In all, 42 seals that had been tagged as weaned pups at their natal site were found on Marion Island (MI), 38 of which could be individually identified by resigh...

Sixteen lactating subantarctic fur seals Arctocephalus tropicalis were satellite-tracked during the winter of 2006 (n = 6), summer of 2006/07 (n = 6) and autumn/winter (n = 4) of 2007, from Marion Island, Southern Ocean. Despite varied individual movement patterns, a favoured foraging area lay to the northeast of the island. In contrast to findings...

Several studies have developed photogrammetric techniques for indirect mass estimation of seals. Unfortunately, these techniques are often narrowly delineated for specific field scenarios or species. Many require sophisticated, custom-designed equipment or analytical tools, limiting their applicability. We aimed to devise a photogrammetric techniqu...

Interspecific parental care is rare, conveys no ultimate evolutionary advantage, and is usually attributed to reproductive errors in species with analogous habitat, behaviour and diet. We report on interspecific parental care (brooding and “defence” of unrelated chick) provided by a king penguin to a sub-Antarctic skua chick on Marion Island, despi...

Like many pinniped species, southern elephant seals (Mirounga leonina) are conducive to long-term population studies using mark–recapture techniques. The twenty-four year longitudinal dataset at sub-Antarctic Marion Island has already provided much insight into elephant seal population dynamics. However, a limitation of the present dataset is that...