Female Elephant Seals Research Articles

Southern elephant seal movements and Antarctic sea ice

Weaned pups and post-moult female elephant seals (Mirounga leonina) were fitted with satellite transmitters at King George Island (South Shetland Islands) between December 1996 and February 1997. Of the nine adult females tracked for more than two months, three stayed in a localized area between the South Shetland Islands and the South Orkney Islands. The other six females travelled south-west along the coast of the Antarctic Peninsula up to the Bellingshausen Sea. Two of them then moved north-east and hauled out on South Georgia in October. One female was last located north of the South Shetland Islands in March 1998. In total, eight females were again sighted on King George Island and six of the transmitters removed. The tracks of the weaners contrasted with those of the adults. In January, five juveniles left King George Island for the Pacific sector spending about four weeks in the open sea west of the De Gerlache Seamounts. Three of them returned to the tip of the Antarctic Peninsula in June, of which one was last located on the Patagonian Shelf in November 1997. The juveniles avoided sea ice while the adults did not. The latter displayed behavioural differences in using the pack ice habitat during winter. Some females adjusted their movement patterns to the pulsating sea ice fringe in distant foraging areas while others ranged in closed pack ice of up to 100%. The feeding grounds of adult female elephant seals are more closely associated with the pack ice zone than previously assumed. The significance of the midwater fish Pleuragramma antarcticum as a potential food resource is discussed.

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

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.

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

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.

Physiology of diving of birds and mammals.

This review concentrates on the physiological responses, and their control, in freely diving birds and mammals that enable them to remain submerged and sometimes quite active for extended periods of time. Recent developments in technology have provided much detailed information on the behavior of these fascinating animals. Unfortunately, the advances in technology have been insufficient to enable physiologists to obtain anything like the same level of detail on the metabolic rate and physiological adjustments that occur during natural diving. This has led to much speculation and calculations based on many assumptions concerning usable oxygen stores and metabolic rate during diving, in an attempt to explain the observed behavior. Despite their shortcomings, these calculations have provided useful insights into the degree of adaptations of various species of aquatic birds and mammals. Many of them, e.g., ducks, smaller penguins, fur seals, and Weddell seals, seem able to metabolize aerobically, when diving, at approximately the same (if not greater) rate as they do at the surface. Their enhanced oxygen stores are able to support aerobic metabolism, at what would not be considered unusually low levels, for the duration of the dives, although there are probably circulatory readjustments to ensure that the oxygen stores are managed judiciously. For other species, such as the larger penguins, South Georgian shag, and female elephant seals, there is a general consensus that they must either be reducing their aerobic metabolic rate when diving, possibly by way of regional hypothermia, and/or producing ATP, at least partly, by anaerobiosis and metabolizing the lactic acid when at the surface (although this is hardly likely in the case of the female elephant seals). Circulation is the proximate regulator of metabolism during aerobic diving, and heart rate is the best single indicator of circulatory adjustment. During voluntary dives, heart rates range from extreme bradycardia to well above resting, reflecting metabolic performance. Efferent cardiac control is largely parasympathetic. Reflex cardiorespiratory responses are modulated by conditioning and habituation, but reflexes predominate during extended dives and during recovery, when gas exchange is maximized.

Status of southern elephant seals at South Georgia

Approximately 54% of the world population of southern elephant seals (Mirounga leonina) breeds at South Georgia. A partial survey in 1951 and a complete survey in 1985, together with counts at specific sites between these times, suggested that the population (around 100 000 breeding females) had not changed significantly in 34 years. This was in contrast to marked declines in most other populations. To examine this further, we conducted a third survey in 1995. This produced an estimate of 113 444 (se = 4902) breeding females. Taking into account improved information about the behaviour of female elephant seals since the survey in 1985, there was no significant change in the number of breeding female elephant seals between 1985 and 1995. When combined with information from the 1951 survey, this supports the view that the total population size has not changed significantly during the past 45 years. Evidence for regulation of the population by environmental factors is equivocal. We hypothesize that the lack of any net change in population size may be linked to a limited availability of high quality breeding habitat.

Offspring sex ratio in relation to female size in southern elephant seals, Mirounga leonina

Southern elephant seals Mirounga leonina display extreme sexual dimorphism. In addition females show great variation in size and stored resources at parturition. Therefore they present an excellent opportunity for examination of responses of sex ratio to resource availability. We studied the relationships between the size of southern elephant seal females at parturition and the size and sex of their pups at South Georgia over four breeding seasons. We found a large individual variation in maternal post-partum mass (range 296–977 kg, n=151). Larger mothers gave birth to larger pups, irrespective of the sex of their pup. Male pups were on average 14% larger than females at birth and consequently more costly to bring to parturition. Our results suggest that female southern elephant seals must weigh more than 300 kg if they are to breed at all, and more than 380 kg if they are to give birth to a male pup. Above this threshold the proportion of males among offspring rapidly increases with maternal mass, and stabilizes at a level not significantly different from parity. These results show that smaller females of southern elephant seals vary offspring sex ratio in a way that is consistent with theories on adaptive offspring sex ratio. A smaller mother with a male foetus may benefit from terminating her pregnancy and allocating the resources she saves to her own growth. She could then give birth to and raise a larger pup in the subsequent season.

Seasonal Haul-Out Patterns of the Southern Elephant Seal (Mirounga leonina L.), at Macquarie Island

Numbers of male, female, and juvenile southern elephant seals ( Mirounga leonina ) hauled out on the isthmus of Macquarie Island were monitored for 14 months. Most haul-out patterns could be described by a normal distribution function. The value of using these normal distribution equations as predictive models was assessed. Equations describing the number of breeding females and the number of pups produced were found to be the most precise. Haulouts from other years at Macquarie Island, and from other populations were compared by means of parameters calculated by the function. It was concluded that there has been little change in the order or duration of haul-outs at Macquarie Island since the 1950s, and that there is remarkable synchrony in the timing of the haul-out of breeding females in all major southern elephant seal populations.

The energetics of lactation in the Northern elephant seal, Mirounga angustirostris

The energy and material transferred from Northern elephant seal mothers to their pups during the 26.5‐day lactation interval was measured using mass change and water influx data. The dilution of tritium‐ and deuterium‐labelled water was monitored in six female elephant seals and their pups. During the nursing period, pup mass increased by 10.4% of the initial body mass per day while females lost 4.19% of their initial body mass per day. Over the entire nursing period, females lost 42.2±4.9% of their initial body mass. Maternal mass transfer to the pup was efficient; pups gained 54.9% of the mass lost by their mothers. Females lost only 14.9% of their lean mass compared to 57.9% of their adipose mass. The fasting metabolic rate of females was 66.2±7.5 MJ/day, 2.41 times the predicted standard metabolic rate (SMR) of a terrestrial mammal of equal size; the total energy output was 163±11 MJ/day, 5.98 times the predicted SMR. Energy consumption for the entire lactation interval was 4330±460 MJ. Milk production accounted for 60% of this energetic expenditure. This efficient milk production was made possible by temporal separation of lactation and feeding. Separation of feeding from lactation confers several energetic and ecological advantages: reduction in the metabolic overhead used for maintenance metabolism onshore, reduction of foraging effort required to meet the demands of lactation, since feeding can be spread out over a significantly longer interval, and a greater flexibility while foraging at sea due to the absence of the pup.

Female Incitation of Male Competition: A Mechanism in Sexual Selection

Females that mate with the most fit male available leave more viable offspring than females that mate with males of lesser fitness. We describe a mechanism by which females facilitate mating with a superior genotype, as reflected by age, social rank, and sexual experience, without exerting choice. Female elephant seals increase the probability of mating with a mature, high-ranking male by simply rejecting all copulatory attempts during early estrus. Females protest loudly when mounted; this signals all nearby males and activates the dominance hierarchy. The probability that the mounting male will be interrupted by another male is a function of the mounter's social rank. The lower his rank, the higher the probability of interruption. The result is that mature males of high social rank have more time and freedom to attempt copulation, and they succeed in doing most of the mating. The behavior of the female intensifies this monopoly by making it more difficult for young, subordinate males to copulate. A similar female strategy seems to operate in several species where the female is courted by several males. Influencing the genotype of her offspring is an important means by which a female can increase her inclusive fitness. This aspect of sexual selection has been neglected.

Structure of northern elephant seal population breeding on San Nicolas Island, california, in 1971

The structure of the population of northern elephant seals, Mirounga angustirostris, on San Nicolas Island, California, was studied during the 1970 and 1971 breeding season. At the population peak on 31 January 1971, there were 77 males, 306 females, 315 pups, and 6 yearlings on shore. The breeding population was subdivided into 15 groups containing from 3 to 75 breeding animals. Fourteen of the groups were considered territories defended by individual males, and one group, the largest, was controlled by three males in a social hierarchy. The relatively small size of the San Nicolas population and the large amount of available beach space allowed the existence of numerous small breeding groups. Female elephant seals, although gregarious, apparently prefer to be in small groups when conditions permit it. It is likely that the same males that were territorial would have formed the nucleus of a social hierarchy if space had been limited enough to cause all of the females in the population to congregate in one large group.

Perinatal behavior of northern elephant seal females and their young.

Northern elephant seal females and pups were observed during four breeding seasons at Ano Nuevo Tstand, California. Six to seven days after a female arrived on the rookery she gave birth to a single pup which she nursed for four weeks. Estrus began 24 days after parturition and lasted an average of four days. Females spent a total of 34 days on the rookery before returning to sea. The only other time females came ashore was to moult, a period which lasted a few weeks. Most births occurred in the harem at night during the last two weeks of January. Cephalic presentations were more frequent than caudals (62% vs. 38%) and both were equally rapid. The placenta was delivered immediately after the pup or within an hour after birth. Stillbirths were infrequent and premature pups were never observed. The sex ratio was 49.4 males to 50.5 females. Eight females gave birth for the first time during their third year but most females are believed to give birth later. Three females gave birth on a different rookery than their own birthplace. The time of parturition from year to year was very consistent in individual females. Newborn pups weighed 65 lbs at birth and were 60 inches long. They are precocial and suckled for about four weeks before being weaned. Weaners moulted their natal pelage at four to six weeks of age, a time when they began entering the water. Most weaners left the rookery headed north during the month of April. Females accepted a pup by allowing it to nurse and rejected alien pups by biting them. Females emitted two vocalizations : a pup attraction call and a threat vocalization. Pups emitted a single vocalization which functioned in several situations. Scventy-two percent of the females observed nursed their own pups to weaning and rejected most of the suckling attempts of alien pups. A few females nursed an alien pup in addition to their own. Twenty-six percent of the females became separated from their pups or their pups died. One third of these females adopted an alien pup. Females that gave birth, but did not nurse for several days, did not copulate. The frequency and duration of suckling increased as pups developed. Pups attempted to suckle any available female but were rejected by most alien females. Sixty percent of marked pups suckled their mothers. The remaining forty percent were separated from their mothers and most of them died. Those that survived were adopted by an alien female or were suckled by several different females each day. Pup mortality at Ano Nuevo Island was very consistent over the four year period, ranging from 13.0% to 14.5%. Most mortalities were socially induced; pups separated from their mothers starved or were injured by adult males and females. The probability of separation was increased by high numbers of females and disturbances created by intrusions of breeding hulls into the harem.

The component fatty acids of elephant seal oil

AbstractThe compositions of the blubber fats of a male and female elephant seal were examined. Evidence is presented to show that acids of chain length greater than C22 were absent; there was an appreciable difference in the composition of the fatty acids from the two specimens. The possibility of a dependence of the fatty acid composition on the physiological state of the animal is discussed.The use of methyl esters in preference to fatty acids in the preliminary separation by low‐temperature crystallization has the advantage of obviating the cumbersome steps of saponification, regeneration of the fatty acids and final methylation, since the esters can be prepared directly by methanolysis. The risk of accidental oxidation of the highly unsaturated portion of the fat is also minimized.