Marion Island elephant seals: the paucity-of-males hypothesis tested

1999 ◽  
Vol 77 (10) ◽  
pp. 1547-1554 ◽  
Author(s):  
I S Wilkinson ◽  
R J van Aarde
Keyword(s):  
Sexual Activity ◽  
Sex Ratios ◽  
Elephant Seal ◽  
Southern Elephant Seal ◽  
Marion Island ◽  
Mirounga Leonina ◽  
Breeding Sites ◽  
Research Activities ◽  
Mating Opportunities ◽  
The Relationship

The southern elephant seal, Mirounga leonina, population at Marion Island has declined since the start of research activities there in 1973, as have populations at other Indian Ocean breeding sites. One suggested mechanism for the decline at Marion Island is a shortage of males, resulting in low insemination rates. We tested this "paucity-of-males" hypothesis by looking at (i) adult sex ratios, (ii) male sexual activity, and (iii) the relationship between levels of sexual activity and the probability of a cow pupping in the following season. Sex ratios were similar to those at other sites where populations are either stable (South Georgia) or increasing (Peninsula Valdes). Dominant bulls monopolised mating opportunities, achieving 98.1% of 629 observed copulations over three seasons. Of the 138 cows coming ashore, only 4 (2.9%) were not seen mating and 89% copulated with only one bull; dominant bulls copulated with all but 1 of the 134 (99.3%) cows that did mate. Cows were mated more frequently than at sites with stable and increasing populations. There was no difference in the observed level of sexual activity between cows seen pupping in the following season and those who failed to pup. This indicates that bulls monopolising harems are capable of inseminating all the cows. Such findings refute the paucity-of-males hypothesis.

The importance of land-based prey for sympatrically breeding giant petrels at sub-Antarctic Marion Island

2007 ◽  
Vol 19 (1) ◽  
pp. 25-30 ◽  
Author(s):  
P.J. Nico de Bruyn ◽  
John Cooper ◽  
Marthán N. Bester ◽  
Cheryl A. Tosh
Keyword(s):  
Breeding Success ◽  
Population Regulation ◽  
Elephant Seal ◽  
Population Trends ◽  
Southern Elephant Seal ◽  
Marion Island ◽  
Giant Petrel ◽  
Mirounga Leonina

Northern (Macronectes halli) and southern (M. giganteus) giant petrels breed at different times at sub-Antarctic Marion Island. Long-term census and breeding success data are used to test for competitive overlap between the two species by correlating population trends with those of land-based prey/carrion species. No parameter was singularly important in population regulation of either giant petrel species and the assumed dependence of breeding northern giant petrels on southern elephant seal Mirounga leonina carrion is not entirely supported.

Tag-loss in southern elephant seals, Mirounga leonina, at Marion Island

1997 ◽  
Vol 9 (2) ◽  
pp. 162-167 ◽  
Author(s):  
I.S. Wilkinson ◽  
M.N. Bester
Keyword(s):  
Elephant Seal ◽  
Southern Elephant Seal ◽  
Island Population ◽  
Marion Island ◽  
Mirounga Leonina ◽  
Elephant Seals ◽  
Tag Loss ◽  
Southern Elephant Seals ◽  
Marking Technique ◽  
Loss Rates

Rates of tag-loss are determined for Dalton Jumbo Rototags applied to the hind flippers of 4343 (2208 males, 2135 females) southern elephant seal (Mirounga leonina) pups at Marion Island over an eight year period from 1983–1990 as part of a demographic study of the species. Loss rates were the lowest recorded to date for this species (range 0.0–9.1%). No significant relationship existed between age and rate of tag-loss, neither was there any sex or year related differences in age-specific tag-loss rates. The low rates of loss highlight the value of tagging as a marking technique, and allow for high levels of confidence in the reliability of the population parameters that are derived from the tagging data collected for the Marion Island population.

Seasonal movements and foraging areas of adult southern female elephant seals, Mirounga leonina, from Marion Island

1998 ◽  
Vol 10 (1) ◽  
pp. 21-30 ◽  
Author(s):  
F. C. Jonker ◽  
M. N. Bester
Keyword(s):  
Elephant Seal ◽  
Outer Edge ◽  
Foraging Strategies ◽  
Southern Elephant Seal ◽  
Antarctic Polar Front ◽  
Marion Island ◽  
Mirounga Leonina ◽  
Seasonal Movements ◽  
Frontal Zones ◽  
The Antarctic

Seasonal movements and foraging areas of postbreeding (n = 9) and postmoulting (n = 3) adult southern elephant seal females from Marion Island were studied using Geolocation Time-depth Recorders. Movements were classified into three phases – an outbound transit phase, distant foraging phase, and an inbound transit phase. The longest residence time of postbreeding females during their foraging migrations was in areas at the outer edge of their feeding range (± 1460 km) both to the north and south of the island, largely within inter-frontal zones south of the Antarctic Polar Front (APF) and between the Sub-Tropical Convergence (STC) and the Sub-Antarctic Front (SAF). Postmoulting females travelled further afield (2122–3133 km distant) to the APF, to inter-frontal zones south of the APF (within the pack ice outer edge), as well as to the Antarctic Continental Shelf. This study provides additional information on the putative function of dive types in relation to the movement phases of elephant seal females from Marion Island. The relative frequency of assumed ‘foraging’, ‘exploratory’ and ‘transit’ dive types, as well as the duration and location of the different phases of movement suggest two seasonal foraging strategies. Sea floor topography could possibly cue the transit phases of both postbreeding and postmoulting females from Marion Island.

Dynamic age-distributions in a declining population of southern elephant seals

1999 ◽  
Vol 11 (4) ◽  
pp. 445-450 ◽  
Author(s):  
P.A. Pistorius ◽  
M.N. Bester ◽  
S.P. Kirkman
Keyword(s):  
Total Population ◽  
Conversion Factor ◽  
Elephant Seal ◽  
Southern Elephant Seal ◽  
Marion Island ◽  
Elephant Seals ◽  
Breeding Sites ◽  
Seal Population ◽  
Southern Elephant Seals ◽  
The Indian Ocean

Estimates of births and standing age-distributions were combined to estimate the size of the southern elephant seal population at Marion Island at various times during its decline. To estimate births each year from 1986 through 1997 we used the number of adult females hauled out on 15 October, which is the peak haulout date for breeding elephant seal females at all breeding sites in the Indian Ocean. A conversion factor (3.15) was derived from the standing age-distributions, and applied to estimates of annual births to yield total population size. The population at Marion Island declined 37.5% overall from 1986–97 at an annual rate of 4.3% from 1986–91 and c. 2.5% yr−1 afterwards.

scholarly journals The northernmost haulout site of South American sea lions and fur seals in the western South Atlantic

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Natália Procksch ◽  
M. Florencia Grandi ◽  
Paulo Henrique Ott ◽  
Karina Groch ◽  
Paulo A. C. Flores ◽  
...  
Keyword(s):  
Mixed Model ◽  
Linear Mixed Model ◽  
Elephant Seal ◽  
Southern Elephant Seal ◽  
South American ◽  
Mirounga Leonina ◽  
Sea Lions ◽  
Significant Difference ◽  
Northern Portion ◽  
Kernel Density Analysis

AbstractWe present estimates of the seasonal and spatial occupation by pinnipeds of the Wildlife Refuge of Ilha dos Lobos (WRIL), based on aerial photographic censuses. Twenty aerial photographic censuses were analysed between July 2010 and November 2018. To assess monthly differences in the numbers of pinnipeds in the WRIL we used a Generalized Linear Mixed Model. Spatial analysis was carried out using Kernel density analysis of the pinnipeds on a grid plotted along the WRIL. Subadult male South American sea lions (Otaria flavescens) were the most abundant pinniped in the WRIL. Potential females of this species were also recorded during half of the census. The maximum number of pinnipeds observed in the WRIL was 304 in September 2018, including an unexpected individual southern elephant seal (Mirounga leonina), and a high number of South American fur seal yearlings (Arctocephalus australis). However, there was no statistically significant difference in counts between months. In all months analysed, pinnipeds were most often found concentrated in the northern portion of the island, with the highest abundances reported in September. This study confirms the importance of the WRIL as a haulout site for pinnipeds in Brazil, recommends that land research and recreational activities occur in months when no pinnipeds are present, and encourages a regulated marine mammal-based tourism during winter and spring months.

A histochemical examination of the epidermis of the southern elephant seal (Mirounga leonina L.) during the telogen stage of hair growth

1968 ◽  
Vol 16 (1) ◽  
pp. 17 ◽  
Author(s):  
RIC Spearman
Keyword(s):  
Hair Growth ◽  
Outer Part ◽  
Elephant Seal ◽  
Basal Part ◽  
Southern Elephant Seal ◽  
Horny Layer ◽  
Mirounga Leonina ◽  
Disulphide Bonds ◽  
Sulphydryl Groups ◽  
Hair Shafts

The epidermal horny layer in the elephant seal, Mirounga leonina, is formed of dead, flattened, solidly keratinized cells without basophilic nuclear remnants. The basal part is more compacted than the outer part which is loosely arranged and has wide dorsoventral intercellular spaces, but the cornified cells appear firmly stuck together along their lateral junctions. Sloughing of the horny layer at the end of a season's growth appears to take place without the development of a specialized fission zone. This is in contrast to the sloughing mechanism in lizards and snakes. Keratin disulphide bonds are uniformly distributed in the horny layer but bound sulphydryl groups, calcium, and phospholipids are more concentrated in the basal part. At the telogen hair growth stage the epidermal horny layer was found to be closely united with the hair shafts within the insunken follicle necks. In these regions the compact junctional horny layer reacted for disulphide bonds, bound sulphydryl groups, phospholipids, and calcium. These substances also occurred in the hook-like keratinized cells which attached the resting club hair to the base of the follicle, but the hair keratin itself only reacted strongly for disulphide bonds. The possible significance of bound phospholipid in the horny layer in waterproofing the skin is discussed.

Studies on the ectoparasites of seals and penguins. 1. The ecology of the louse Lepidophthirus macrorhini Enderlein on the southern elephant seal, Mirounga leonina (L)

1965 ◽  
Vol 13 (3) ◽  
pp. 437 ◽  
Author(s):  
MD Murray ◽  
DG Nicholls
Keyword(s):  
Stratum Corneum ◽  
Skin Temperature ◽  
Elephant Seal ◽  
The Body ◽  
Southern Elephant Seal ◽  
Mirounga Leonina ◽  
Prolonged Stay ◽  
Blood Sucking ◽  
Southern Elephant Seals ◽  
Causes Of Mortality

Although the southern elephant seals, Mirounga leonina, that breed on Macquarie I., come ashore for only 3-5 weeks twice a year, the hind flippers of most of them are infested with the blood-sucking louse Lepidophthirus macrorhini. L. macrorhini does not oviposit, and eggs do not hatch, in water. Reproduction occurs when the elephant seal is ashore on the beach or in the adjacent tussock. The life cycle can be completed in c. 3 weeks and, because 6-9 eggs are laid daily, multiplication can be rapid. Temperatures greater than 25�C are required for rapid multiplication, and these temperatures occur more frequently on the hind flippers than elsewhere on the body. The number of L. macrorhini on a hind flipper however rarely exceeds 100. The principal causes of mortality of the lice are failure to survive the seal's prolonged stay at sea, the moult of the seal, and transmission to unfavourable sites on the seal. When an elephant seal goes to sea its skin temperature falls to nearly that of the sea. The reduction in the metabolic rate of the louse at low temperatures results in the amount of oxygen obtained from the sea by cutaneous respiration being sufficient for survival. The lice do not enter into a state of complete suspended animation, and a blood meal is required at least once a week to enable sufficient to survive to repopulate the seal. The skin temperature of a seal at sea rises more frequently on the flippers than elsewhere on the body because of the increased rate of blood flow to the flippers after diving and whenever it is necessary to dissipate heat. Consequently, there are more opportunities for the lice on the hind flippers to feed. L. macrorhini burrows into the stratum corneum, thus reducing losses to the population when the elephant seal annually sheds the outer layers of the stratum corneum attached to the hair, because only the roof of the burrow is lost. Lice do not reproduce on the older seals that moult in muddy wallows, and consequently fewer lice are found on these animals. Pups are infested within a few days of birth, and the gregarious habits of the elephant seal spread infestations through the seal population. Lice transfer to all parts of the bodies of seals but it is the multiplication of those on the flippers that maintains the louse population. The abundance of L. macrorhini is determined largely by the frequency and duration of opportunities to reproduce when the elephant seal is ashore, and to feed when the elephant seal is at sea.

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