Marthán N. Bester

Marthán N. Bester
University of Pretoria | UP · Department of Zoology and Entomology

D.Sc Zoology

About

493
Publications
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Introduction
Marthán N. Bester currently works at the Department of Zoology and Entomology, University of Pretoria. Marthán does research in Marine Mammal Population Biology. Their current project is 'Foraging Ecology of Ross Seals in the Eastern Weddell Sea'.

Publications

Publications (493)
Article
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, ide...
Article
Full-text available
Aim Climate change will likely lead to a significant redistribution of biodiversity in marine ecosystems. We examine the potential redistribution of a community of marine predators by comparing current and future habitat distribution projections. We examine relative changes among species, indicative of potential future community-level changes and c...
Article
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The degree of dietary generalization versus specialization exhibited by populations can impact their ability to respond to changing environmental conditions. Naturally shed hair and epidermis are easily collected and may provide a suitable substrate for stable isotope analysis to assess trophic niche specialization. Whether fasting influences the i...
Article
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...
Article
Management of gases during diving is not well understood across marine mammal species. Prior to diving, phocid (true) seals generally exhale, a behaviour thought to assist with the prevention of decompression sickness. Otariid seals (fur seals and sea lions) have a greater reliance on their lung oxygen stores, and inhale prior to diving. One otarii...
Article
Full-text available
Focal palatine erosion (FPE) is a misleading term that is used in the literature to describe inflammatory lesions associated with depressions of the palatal mucosa in cheetah. Cheetahs have large cheek teeth and these depressions are formed to accommodate them. Previously FPE was only described as a mandibular molar tooth malocclusion on the hard p...
Article
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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...
Article
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Understanding the determinants of poorly studied species’ spatial ecology is fundamental to understanding climate change impacts on those species and how to effectively prioritise their conservation. Ross seals (Ommatophoca rossii) are the least studied of the Antarctic pinnipeds with a limited knowledge of their spatial ecology. We present the lar...
Article
Some top predator populations in the South Atlantic and South Indian oceans are in decline, presumably contingent upon reduced food availability, precipitated by climate change. This phenomenon impacts on the positions of major ocean frontal zones which are hypothesised to act as natural dispersal borders for fish in the Southern Ocean. We investig...
Article
The status of pinnipeds on mid-Atlantic ridge islands is reviewed to detect trends that may relate to climate change. Small numbers of southern elephant seals Mirounga leonina breed on Gough Island (40°S, 10°W) and at Bouvetøya (54°24′S, 03°21′E) where numbers remained small over ~ 68 years. Vagrant southern elephant seals wandered farther north to...
Article
Knowledge of extra-limital movements of seals improves our understanding of species’ dispersal and dispersion abilities and patterns, and perhaps environmental changes. Canvassing and internet literature searches revealed the sighting of a vagrant adult male sub-Antarctic fur seal Arctocephalus tropicalis on the coast adjacent to George Town (7° 56...
Article
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 ageing”) or because allocation to early life...
Article
The distribution, density and percentage contribution of pack ice seals during ship-board censuses in the marginal sea ice zone beyond the Lazarev Sea in spring 2019 are presented. Adult/juvenile crabeater seals ( n = 19), leopard seals ( n = 3) and Ross seals ( n = 10) were sighted during 582.2 nm of censuses along the ship’s track line in the are...
Article
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...
Article
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...
Article
The most plausible hypothesis for declining population trends of some marine top predators at the northern extent of their breeding ranges in the Southern Ocean is that it results from environmental change. Sub-Antarctic fur seals Arctocephalus tropicalis are opportunistic and pelagic foragers that feed on a variety of fish, cephalopods, and crusta...
Article
The continued decline in the small breeding population of southern elephant seals Mirounga leonina at Gough Island (40°19′S, 9°57′W) over a period of 46 years (1973–2019) signals the likely extirpation of the species at the northernmost extent of its breeding range in the Southern Ocean. The estimated number of births declined from a high (n = 38)...
Article
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An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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Southern Ocean ecosystems are under pressure from resource exploitation and climate change1,2. Mitigation requires the identification and protection of Areas of Ecological Significance (AESs), which have so far not been determined at the ocean-basin scale. Here, using assemblage-level tracking of marine predators, we identify AESs for this globally...
Article
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Remote oceanic islands harbour unique biodiversity, especially of species that rely on the marine trophic resources around their breeding islands. Identifying marine areas used by such species is essential to manage and limit processes that threaten these species. The Tristan da Cunha territory in the South Atlantic Ocean hosts several endemic and...
Article
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Understanding the effects of human exploitation on the genetic composition of wild populations is important for predicting species persistence and adaptive potential. We therefore investigated the genetic legacy of large-scale commercial harvesting by reconstructing, on a global scale, the recent demographic history of the Antarctic fur seal (Arcto...
Article
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The Retrospective Analysis of Antarctic Tracking Data (RAATD) is a Scientific Committee for Antarctic Research project led jointly by the Expert Groups on Birds and Marine Mammals and Antarctic Biodiversity Informatics, and endorsed by the Commission for the Conservation of Antarctic Marine Living Resources. RAATD consolidated tracking data for mul...
Article
The Retrospective Analysis of Antarctic Tracking Data (RAATD) is a Scientific Committee for Antarctic Research project led jointly by the Expert Groups on Birds and Marine Mammals and Antarctic Biodiversity Informatics, and endorsed by the Commission for the Conservation of Antarctic Marine Living Resources. RAATD consolidated tracking data for mul...
Article
Full-text available
Seal biologists at Marion Island (Southern Ocean) are in frequent contact with seals. During research activities, biologists may be bitten by seals, yet no standardised protocol for treating such bites is in place. Information on 22 seal bite cases at Marion Island was collected. Treatment of these bites varied, reflecting a need for standardised p...
Article
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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...
Article
This study investigates three presumed fractured phocid seal bones: An isolated metapodial and an ulna belonging to different individuals of the extinct phocid, Homiphoca capensis, from Langebaanweg and a mandible of a juvenile elephant seal (Mirounga leonina), which was included to assess the validity of the assumption that changes to bones caused...
Article
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...
Article
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Background: To understand and predict the distribution of foragers, it is crucial to identify the factors that affect individual movement decisions at different scales. Individuals are expected to adjust their foraging movements to the hierarchical spatial distribution of resources. At a small local scale, spatial segregation in foraging habitat h...
Article
An adult male sub-Antarctic fur seal, Arctocephalus tropicalis, on Inaccessible Island in the Tristan da Cunha archipelago (TdC), was observed infested with goose barnacles, likely Lepas australis. Although adult females have been recorded to carry goose barnacles, this is the first record from an adult male at a breeding island. Males remain at se...
Article
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Comparison of areas of high and low human activity show no difference in the rate of decline of Southern elephant seals at Marion Island.
Article
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Focal palatitis (also known as focal palatine erosion) is thought to be a developmental disease, specifically of cheetah in captivity raised on a commercial diet. The lack of chewing is thought to cause the mandibular molar to change angulation, contacting the palate and causing the lesions. We followed the development of five captive cheetah cubs,...
Article
Full-text available
White sharks (Carcharodon carcharias) are highly visual predators, leading to the hypothesis that the predation risk for foraging Cape fur seals (Arctocephalus pusillus pusillus) might differ with ambient light conditions. This study investigated the relationship between environmental fluctuations of ambient light and the traversing behaviour of Ca...
Article
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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...
Preprint
Full-text available
Remote oceanic islands harbour unique biodiversity, especially of species that rely on pelagic resources around their breeding islands. Identifying marine areas used by such species is important to reduce or limit threats that may put these species at risk. The Tristan da Cunha group of islands in the South Atlantic Ocean hosts several endemic and...
Article
A sub-Antarctic fur seal, Arctocephalus tropicalis, pup was located on Inaccessible Island in the Tristan da Cunha archipelago (TdC), well before the start of the annual breeding (pupping and mating) season in 2018. It was born a few days before 27 September 2018, at least 59 days before the next pup was observed on the island in 2018 and 75 days b...
Article
Full-text available
Anomalous pelage colourations have been reported to occur in several pinniped species and can potentially be used to assess gene flow amongst conspecific populations. Aberrant pelage colour has not been documented in sub-Antarctic fur seals Arctocephalus tropicalis older than pups. Sub-Antarctic fur seals were inspected on two of the beaches at Gou...
Article
Full-text available
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...
Article
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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...
Article
Full-text available
Evaluating how populations are connected by migration is important for understanding species resilience because gene flow can facilitate recovery from demographic declines. We therefore investigated the extent to which migration may have contributed to the global recovery of the Antarctic fur seal (Arctocephalus gazella), a circumpolar distributed...
Data
R-code for “A global cline in a colour polymorphism suggests a limited contribution of gene flow towards the recovery of a heavily exploited marine mammal.”
Article
Sub-Antarctic fur seal, Arctocephalus tropicalis, pups were counted on some of the beaches on all four Tristan da Cunha (TdC) islands, in January 2017, to determine the status of the population, in the face of climate change that is magnified in polar regions. Compared to counts done 40 years earlier on Gough, the breeding population increased mark...
Article
The distribution, density and percentage contribution of pack ice pinnipeds during ship-board censuses in the eastern Weddell Sea in summer 2015/2016 are presented. Of the four true pack ice seal species encountered, crabeater seals predominated. Despite the low survey effort, Ross seals continued to be relatively abundant in the pack ice off the P...
Preprint
To understand and predict current and future distributions of animals under a changing climate it is essential to establish historical ranges as baselines against which distribution shifts can be assessed. Management approaches also require comprehension of temporal variability in spatial distributions that can occur over shorter time scales, such...
Article
Full-text available
Antarctic (Arctocephalus gazella) and Subantarctic (A. tropicalis) fur seals are important predators in the Southern Ocean. Marion Island (southern Indian Ocean) hosts the largest sympatric breeding populations of these two species. Environmental and population changes here over two decades may have influenced their diet and trophic interactions. T...
Article
To understand and predict current and future distributions of animals under a changing climate it is essential to establish historical ranges as baselines against which distribution shifts can be assessed. Management approaches also require comprehension of temporal variability in spatial distributions that can occur over shorter time scales, such...
Article
The distribution of marine predators is driven by the distribution and abundance of their prey; areas preferred by multiple marine predator species should therefore indicate areas of ecological significance. The Southern Ocean supports large populations of seabirds and marine mammals and is undergoing rapid environmental change. The management and...
Article
Descriptions of several oral, maxillofacial and dental conditions/diseases exist for a variety of captive large felids, but little is reported on the pathology of free roaming large felids. Apart from focal palatine erosions (FPEs) as initially described by Fitch and Fagan (1982) and some reference to absent incisor teeth, few data exist on disease...
Article
Full-text available
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...
Poster
Hunting and other human pressures have reduced many wild animal populations. Understanding how populations respond to these (and other) pressures is a central question in conservation biology. The Antarctic fur seal (Arctocephalus gazella), a marine mammal that breeds on islands all around Antarctica, provides an interesting case study. This specie...
Article
Full-text available
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...
Data
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...
Poster
Full-text available
Herein, we demonstrate how southern elephant seals whiskers can provide fine-scale dietary data. We used the isotopic data contained in the whiskers segments to quantify the contribution of crustaceans to the diet of juvenile southern elephant seals at Marion Island, in the Southern Ocean.
Presentation
Full-text available
Southern elephant seals (Mirounga leonina) periodically haul out during the year to moult, to breed or for a winter rest. During a haulout period, elephant seals remain ashore until they have finished moulting, breeding or resting, although movement between beaches during a haulout is known to occur. Multiple logistic regression analyses showed tha...
Article
Quantification of the physical and biological environmental factors that influence the spatial distribution of higher trophic species is central to inform management and develop ecosystem models, particularly in light of ocean changes. We used tracking data from 184 female Antarctic fur seals (Arctocephalus gazella) to develop habitat models for th...