• Argos telemetry;
  • foraging strategy;
  • maternal investment;
  • migration;
  • navigation;
  • reporductive strategies


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  • 1
     Female southern elephant seals (Mirounga leonina L.) expend variable, often large, amounts of their stored body resources on their pups during lactation. There is some evidence that pups with higher weaning masses have a better chance of surviving their first year. But in order to understand what level of maternal investment is required to produce successful pups, we need to understand the behaviour and problems faced by naïve pups before nutritional independence.
  • 2
     We used satellite telemetry to track 30 newly weaned pups on their first trip to sea from their natal site at Macquarie Island in 1995 and 1996. Track duration varied from 2 to 179 (mean, 77) days. Seven seals were tracked for the entire duration of their first trip.
  • 3
     The movements were grouped into three phases. Phase 1 (mean duration 30 days) was characterized by rapid and directed dispersal from Macquarie Island at daily travel rates of up to 140 km day−1. Phase 2 (mean duration 67 days) consisted of slower travel rates (generally < 20 km day−1) where activity was often centred on localized patches up to 1900 km from Macquarie Island. This phase was sometimes interrupted by bouts of increased travel rate as the seal moved to another patch. Phase 3 (mean duration 42 days) consisted of prolonged increased travel rates as the seals returned to Macquarie or, in one case, Chatham Island.
  • 4
     The routes of the tracks to the south-east were very similar. Simulated tracks based on a constant heading of magnetic east, at variable swimming speed, and modified by ocean current vectors produced a pattern similar to, but not identical to, the south-east tracks. The tracks to the west and south were more diverse and meandering.
  • 5
     Based on a nearest neighbour analysis, neither sex, year nor weaning mass influenced Phase 1–2 or Phase 2–3 transition locations.
  • 6
     Phase 2 tracks were associated in the south-eastern group with the Pacific Antarctic Ridge and in the south-west group, to a lesser extent, with the Indian Antarctic Ridge. The southern limits of Phase 2 tracks in the south-eastern group aligned with the southern Antarctic Circumpolar Circulation front.
  • 7
     Using calculated estimates of body composition at weaning and estimates of the rate of utilization of body reserves for the period before animals reach phase 2 of their trip, we estimate that large pups will have reserves remaining to supply their needs whereas pups in the small group are approaching critical limits. However, these estimates are based on several assumptions and extrapolations. More information on body composition of pups at weaning and departure is needed along with behavioural information to clarify the value of maternal expenditure in terms of offspring survival.


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Phocid seals provide unique opportunities for studying maternal investment strategies (Fedak & Anderson 1982; Costa 1993; Trillmich 1996). The mothers of many species expend a large fraction of their body reserves on their pups each year during their brief lactation period. The requirements for lactation are largely met by stored reserves and the mothers often do not feed from parturition through to weaning, when all maternal care abruptly terminates (Fedak & Anderson 1982; Anderson & Fedak 1987; Oftedal, Boness & Tedman 1987). Southern elephant seals (Mirounga leonina L.) exemplify this life-history pattern (LeBoeuf & Laws 1994a). Pregnant females come ashore on a few sub-Antarctic islands, give birth and nurse their pups for an average of 24 days (McMahon et al. 1997). After weaning they mate and then abandon their pups, which remain ashore for a further 6 weeks fasting (Arnbom et al. 1993). Mothers may vary in mass by a factor of three at parturition but across the entire size range, they expend material roughly proportional to (35%) their mass at that time (Fedak, Arnbom & Boyd 1996). The pups may treble their birth mass during suckling, but weaning mass is strongly dependent on the mother’s parturition mass, with the pups of larger mothers weighing up to three times those of smaller ones. The value of such a variable maternal investment can only be understood in terms of the pup’s subsequent behaviour.

We would expect the cost of maternal expenditure and the benefit (in terms of pup survival) to be important parameters in determining maternal strategies. Maternal costs are demonstrable in southern elephant seals. Small females that expend a high proportion of their reserves in one year are often missing on breeding beaches the following year (Arnbom, Fedak & Boyd 1997). Furthermore, reserves must be restored quickly since they are required again around 70 days later to sustain the animal over the energetically expensive annual moult in February (Boyd, Arnbom & Fedak 1993). It can also be demonstrated that females appear to be in control of their own expenditure. For example, the rare mothers that feed two pups only expend the amount expected for the mother’s size, in spite of presumably facing double the demand from the pups, and mothers adjust their expenditure from year to year, depending on their mass gain between years (Arnbom et al. 1997).

We would expect that this large, and apparently costly, maternal expenditure would confer benefit in terms of pup survival. Indeed, McMahon et al. (2000) found that southern elephant seal pups that were heavier at weaning (> 135 kg) had higher (72%) chances of first year survival than lighter (< 95 kg) pups (54%). In contrast, LeBoeuf et al. (1994b) found no clear relationship between weaning mass and first year survival in northern elephant seals (M. angustirostris Gill). However, the extent of the costs and benefits depends upon the situations mothers and pups face at sea. Both must retain sufficient reserves at departure to see them through the time it takes to swim to sources of food. But while mothers have previous foraging experience, their pups depart naïve, having never been away from their natal island, and do so at a time when their mothers and all other experienced animals have already left.

By the time the pups finally depart the breeding site, they will have lost, on average, 32% of their weaning mass (Arnbom et al. 1993). During the post weaning fast, behavioural and physiological developments take place in preparation for life at sea. However, the fast has a likely cost in that the body reserves remaining at departure, to provide for the pup until it finds food, will be diminished. The value of the resources passed to a pup by its mother and the cost of its post-weaning fast will depend critically on the time it takes for pups to locate prey. This in turn is influenced by the predictability of prey distribution, and the information and strategy the pups use to help them locate prey.

Therefore, to understand the costs and benefits of maternal investment in phocid seals, we need to know the proximity (in time and space) of foraging areas from natal areas and have an idea of the problems that naïve pups face in locating these areas and how they might solve them. This is the primary aim of this paper. We used satellite telemetry to study naïve southern elephant seal pups on their first trip to sea from their natal site on Macquarie Island in the Southern Ocean. We describe their initial foraging trips and examine both the intrinsic (sex, weaning mass and year) and extrinsic factors (oceanographic and geophysical features) that may influence foraging areas used and how the pups find them. Finally, we estimate how long body reserves in large and small pups would last in relation to the time it takes them to first find food.

Materials and methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

study site

Macquarie Island (54°30′ S, 158°57′ E) is situated in the Southern Ocean between Australia and the Antarctic continent (Fig. 1). It has an associated southern elephant seal population of approximately 78 000 individuals (Laws 1994), which represents about 12% of the world population of 664 000.


Figure 1. Tracks of 30 southern elephant seal pups after their first departure from Macquarie Island. The tracks are colour coded by seal (13 colours are recycled). The mean tracking duration was 84·5 days. The bathymetry is derived from the ETOPO5 data set (NOAA 1988). The white lines indicate the locations of the Subantarctic (SAF), Polar (PF) and southern Antarctic Circumpolar Circulation fronts (SACCF) and the southern boundary of the Antarctic Circumpolar Circulation (SBACC) as described by Orsi et al. (1995). Upper case letters point to locations mentioned in the text.

Download figure to PowerPoint


Forty-four pups were fitted with Argos Satellite Relay Data Loggers (SRDLs, Sea Mammal Research Unit, St Andrews, UK) at Macquarie Island during their post-weaning fast in December 1995 (32) and 1996 (12). Each pup was individually marked and weighed at birth and reweighed at weaning and at the time of SRDL deployment. They were chosen on the basis of sex and the lower and upper quartiles of weaning mass (light < 96 kg and heavy > 135 kg). We code individual seals by their sex and weaning mass. For example, ‘HF1’ is a heavy female. In addition, we include the corresponding Seal Codes used by Hindell et al. (1999) who presented the dive information obtained from this study.

Each pup was lightly anaesthetized with an intramuscular injection of Zoletil (Virbac, France) at an intramuscular dose rate of approximately 0·5 mg kg−1 body weight (Baker et al. 1990). The fur at the site of attachment was dried and cleaned with ethanol and the SRDLs were glued to the fur with a two-part, rapid-setting epoxy resin (Fedak, Anderson & Curry 1983). The SRDLs were placed on the top of the neck just behind the head so that the aerial would emerge when the seal surfaced.

telemetry system

The SRDLs consisted of a data logger interfaced to a 500 mW Argos RF unit (model PTT100, Microwave Telemetry, Columbia, MD, USA) (McConnell, Chambers & Fedak 1992). Detailed dive behaviour information were collected and transmitted. The data collection and analysis have been described by Hindell et al. (1999). The SRDL measured 10 × 9 × 4 cm, weighed 0·7 kg and could resist pressure to a depth of 2000 m. In order to prolong battery life, the SRDLs switched to an energy-saving mode after 50 days when transmissions were inhibited for 10 out of every 15 h, resulting in a decreased rate of location fixes.

data processing

Argos location fixes were filtered by the algorithm described by McConnell, Chambers & Fedak (1992), using a ‘maximum speed parameter’ of 2·0 m s−1. The principle of this filter was to reject locations that would require an unrealistic rate of travel to achieve. Path length and daily travel rate were estimated from mean daily, filtered locations.

movement classification

We classified individual seal tracks into three phases based upon their daily travel rates. The departure date was defined as when a seal had travelled at least 50 km from Macquarie Island. We defined the start of Phase 1 as the departure date and the end when the 5-day running mean of daily travel rates first dipped beneath 20 km day−1. We defined the end of Phase 2 as the date when the 5-day running mean of daily travel rates last rose above 20 km day−1. We defined the end of Phase 3 as the arrival date at Macquarie Island or Chatham Island. These definitions are the same as those used by Hindell et al. (1999). We use the phrase ‘completed Phase n’ to indicate that a phase was completed to its end definition, rather than being terminated by SRDL failure or seal death. In this paper ‘day n’ refers to the nth day after a seal’s departure date.

spatial tests

To test whether a nominal variable (sex or year of deployment) or an ordinal variable (weaning mass) influenced the clustering of locations, we calculated a nearest neighbour test statistic. Two sets of locations were considered separately: the terminal locations of completed Phase 1 and of completed Phase 2.

Let Dij be the Euclidean distance between the location of animal i and the location of its nearest neighbour, j. A measure of nearest neighbour similarity (dij) is defined for nominal variables as:

  • image

and for ordinal variables as:

  • dij = │valuei − valuej

The test statistic (h) is defined as

  • image

The test statistic was calculated for the observations (hobs). We then used a re-sampling procedure to estimate the probability (P) that hobs could have been obtained from a population where the value of h was independent of a given variable. Consider, for example, the nominal variable sex. Each animal location was re-assigned a random value of sex from the original set of sexes and h was recalculated. This process was repeated 1000 times and the mean of h values (hmean) was calculated. If hobs < hmean then P was assigned the proportion of the 1000 hs from resampling that were less than hobs. If hobs > hmean then P was assigned the proportion of the 1000 hs from resampling that were greater than hobs. The tests were programmed in R (Ihaka & Gentleman 1996).

track simulation

In order to examine the possible role of geo-magnetism and ocean currents on the outward tracks from Macquarie Island, we constructed a series of simulated seal tracks. Based on the observed tracks, we constructed a simple rule that the seal should swim due magnetic east. A regional grid of magnetic declinations (the difference between true and magnetic bearing) was constructed from the International Geomagnetic Reference Field (1995) model (Barton 1997). An overlapping grid of ocean current vectors was constructed from the Ocean Circulation and Climate Advanced Modelling Project (Saunders, Coward & deCuevas 1999) at the 100 m depth level for the month of February 1996. The simulated tracks consisted of daily magnetic eastward vectors of 0, 20, 40, 60, 80 or 100 km that were added to the local daily current vector to produce a series of net daily movements.

remotely sensed data

Various remotely sensed data sets were examined using the MAMVIS visualization package (Fedak, Lovell & McConnell 1996) to explore spatio-temporal associations with the seal tracks. Ice concentration data were provided by the EOS Distributed Active Archive Center (DAAC) at the National Snow and Ice Data Center, University of Colorado, Boulder, CO. Sea Surface Temperature data were provided by the NASA Physical Oceanography Distributed Active Archive Centre (DAAC) at the Jet Propulsion Laboratory, California Institute of Technology. Sea colour data were provided by SeaWiFS Project (Code 970·2) and the Distributed Active Archive Center (Code 902) at the Goddard Space Flight Center, Greenbelt, MD 20771.

estimation of time to starvation

We calculated the approximate time to starvation using estimates of body composition of southern elephant seal pups at weaning and during the post-weaning fast (Carlini et al. 2001) and mass loss rate using the equations of Reilly & Fedak (1990) relating total body water to protein and fat. Mean mass loss rates during the post-weaning fast were estimated, separately for the heavy and light categories, from weaning mass and subsequent mass at tag deployment (an average of 38 days later). These mass loss rates were extrapolated to times after departure. Death by protein depletion was estimated to occur when the pup lost 30% of its weaning protein mass (Cahill, Marliss & Aoki 1979). Death by fat depletion was estimated as when fat mass reduced to 10% of body mass (Cahill et al. 1979).


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

telemetry system performance

We include here data from the 30 SRDLs (21 in 1995 and 9 in 1996) that provided data once the seal had travelled at least 50 km from Macquarie Island (the departure date) (Table 1). An initial high failure rate in some of SRDLs that were originally applied was due primarily to aerial breakage while seals were still on land. Due to these failures, heavy pups were under-represented in the remaining study sample: heavy females (HF) n = 6, heavy males (HM) n = 5, light females (LF) n = 9, and light males (LM) n = 10.

Table 1.  Details of the SRDL deployment and tracking of 30 southern elephant seal pups. The departure date was the first day that a seal exceeded 50 km from Macquarie Island. The definitions of the three track phases are given in Results. Summary statistics (mean (SD, SE)), grouped by sex and weaning mass are shown. Summary statistics of durations only include completed phases (durations shown in bold). Durations for uncompleted phases are also shown. Completion of Phase 3 is defined by return to Macquarie or Chatham Island (1 and 2, respectively, in column ‘end date’). No SE statistic is given for the ‘All’ seals category. The date and mass of seals recaptured on their return to Macquarie Island are also shown
SealSeal codeWeaning mass (kg)Departure datePhase 1 duration (days)Phase 1–2 transition Phase 2 duration (days)Phase 2–3 transitionPhase 3 duration (days)End dateTotal duration (days)Recovery dateRecovery mass (gain from estimated departure mass) (kg)
HF122501–9513618 Dec 951603 Jan 96 1720 Jan 96 33  
HF217215–9513918 Dec 9513 –31 Dec 95 13  
HF3 5811–9514525 Dec 9536 –30 Jan 96 36  
HF420916–9515118 Dec 9512 –30 Dec 95 12  
HF520917–9616518 Dec 96 6 –23 Dec 96  6  
HF628482–9617120 Dec 9646 –04 Feb 97 46  
HF 151·2 (14·1, 5·8) 16 (–, –)  – (–, –) – (–, –) 24·4 (16·2, 6·6)  
HM117219–9514008 Dec 952704 Jan 96  609 Jan 96 33  
HM226629–9514114 Dec 9511 –24 Dec 95 11  
HM3 5814–9514309 Dec 953008 Jan 96 6816 Mar 964803 May 961146  
HM422500–9614217 Dec 96 8 –25 Dec 96  8  
HM526623–9616917 Dec 961602 Jan 9712709 May 973613 Jun 97179  
HM 147·0 (12·3, 5·5) 24·3 (7·4, 4·3) 97·5 (41·7, 29·5) 48·0 (–, –) 75·2 (80·9, 36·2)  
H 149·3 (12·9, 3·9) 22·3 (7·3, 3·7) 97·5 (41·7, 29·5) 48·0 (–, –) 47·5 (58·8, 17·7)  
LF117217–95 7806 Dec 953712 Jan 96 5103 Mar 963305 Apr 96112110 Apr 9699 (43)
LF222486–95 8102 Dec 954112 Jan 96 3112 Feb 964427 Mar 9611628 Mar 9687 (32)
LF322500–95 8803 Dec 953103 Jan 96 7417 Mar 964026 Apr 961145  
LF426635–95 8906 Dec 952803 Jan 96 7013 Mar 964628 Apr 961144  
LF526625–95 9105 Dec 953610 Jan 96 4322 Feb 963023 Mar 96109  
LF6 2849–95 9202 Dec 954112 Jan 96 4122 Feb 965719 Apr 96113914 Apr 9688 (12)
LF726633–95 9510 Dec 9511 –20 Dec 95 11  
LF822490–96 9308 Dec 962603 Jan 97  14 Jan 97 2719 Sep 97105 (43)
LF920916–96 9002 Dec 961113 Dec 96 11  
LF 88·6 (5·6, 1·9) 34·3 (6·0, 2·3) 51·7 (17·0, 7·0) 45·5 (12·0, 6·9) 91·5 (57·9, 19·3)  
LM122483–95 8405 Dec 952227 Dec 95 9228 Mar 96805 Apr 96122  
LM222499–95 8410 Dec 953009 Jan 96 8806 Apr 965430 May 962172  
LM326628–95 8802 Dec 952325 Dec 95 6903 Mar 962528 Mar 96111731 Mar 9680 (18)
LM426627–95 8810 Dec 953211 Jan 96 3212 Feb 96 64  
LM522484–95 9029 Nov 9523 –22 Dec 95 23  
LM620918–95 9206 Dec 953207 Jan 96 6815 Mar 963518 Apr 96135  
LM722490–95 9313 Dec 952507 Jan 96 6007 Mar 965429 Apr 961139  
LM828479–96 8511 Dec 96 2 –13 Dec 96  2  
LM922483–96 9205 Dec 962903 Jan 97 2901 Feb 97 58  
LM1026624–96 9210 Dec 963918 Jan 97 5817 Mar 973824 Apr 97135  
LM 88·8 (3·5, 1·1) 29·0 (5·6, 2·0) 72·5 (14·3, 5·8) 37·9 (14·8, 8·5) 96·7 (56·0, 17·7)  
L 88·7 (4·5, 1·0) 31·5 (6·2, 1·6) 62·1 (18·5, 5·3) 44·2 (12·0, 4·5) 94·3 (55·4, 12·7)  
ALL 110·9 (30·8) 29·5 (7·4) 67·1 (24·3) 42·3 (11·0) 77·1 (60·2)  

tracking duration

The mean tracking duration was 77·1 days. The under-representation of heavy pups was exacerbated by the heavier group (especially the females) having shorter tracking durations (mean 47·7, SE 17·8, range 2–179 days) than the light group (mean 94·3, SE 12·7, range 6–172 days).

rate and quality of location fixes

Details of location fixes are given in Table 2. The filtering algorithm rejected 13% of locations. There remained an average of 2·46 locations per day, of which 92% were classed as ‘of unguaranteed accuracy’ (location quality (LQ) 0, A and B (Argos 1989)). For filtered LQs 0, A and B, Vincent et al. 2002) estimated 68th percentile latitude errors as 1851, 678 and 3193 m, respectively, and 68th percentile longitude errors as 3029, 909 and 4815 m, respectively.

Table 2.  Mean number of locations per day for all seals, grouped by Argos location quality index, and by whether locations passed through the location filter
Argos location quality indexMean number of pre-filtered locations per day (percentage of total)Mean number of post-filtered locations per day (percentage of total)
30·02 (0·8)0·02 (0·8)
20·04 (1·5)0·05 (1·9)
10·12 (4·1)0·11 (4·5)
00·16 (5·6)0·15 (6·2)
A0·69 (24·1)0·62 (25·4)
B1·83 (63·8)1·50 (61·2)
All2·86 (100)2·46 (100)


Five study animals were recovered and reweighed at Macquarie Island; four in March–April and one in September. Their mass gain in relation to estimated departure mass varied from 12 to 43 kg (for more detail see Table 1).

overview of movements

All seals dispersed from Macquarie Island to areas up to 1900 km away. There were two main areas, one up to 1900 km to the south-east, and a more diffuse grouping up to 1800 km to the west (Fig. 1). Daily distances from Macquarie Island and travel rates are shown in Fig. 2. Movements were grouped into three phases. Phase 1 was characterized by rapid and directed dispersal from Macquarie Island at daily travel rates of up to 140 km day−1. Phase 2 consisted of slower travel rate (generally less than 20 km day−1) where activity was often centred on localized patches. This phase was sometimes interrupted by bouts of increased travel rate as the seal moved to another patch. Phase 3 consisted of prolonged increased travel rates as the seal returned to Macquarie Island (or, in the case of seal LM2, Chatham Island). Seven seals were tracked to the completion of Phase 3. Their total path lengths ranged from 2671 to 6509 km, with a mean of 4600 km.


Figure 2. Distance from Macquarie Island (line) and daily distance travelled (shaded) plotted against month for each of 30 southern elephant seal pups. The vertical lines indicate the Phase 1–2 and Phase 2–3 transition dates (see Results). Note that the plot of distance from Macquarie Island may start before travel rate if there are no locations in the first few days.

Download figure to PowerPoint

phase 1

The mean of the departure dates was 9 December, and they ranged from 29 November to 15 December. The mean duration of completed Phase 1s was 29·5 days (n = 19, SD = 7·4) (Table 1). This was equivalent to a mean of 73·2 days (SD = 7·81) post-weaning, and the means for the heavy and light groups were not significantly different (t-test, t = 1·42, modified d.f. = 4·12, P = 0·227). The tracks were grouped into those that went generally south-east (n = 20) or south-west (n = 10). For the south-east group the end of Phase 1 was reached after a mean of 71·5 days post-weaning, and for the south-west group at a mean of 79·7 days post-weaning. The difference in the means was not significant (P = 0·08).

All seals undertook directed and rapid travel from Macquarie Island (Fig. 3a). Within the first few days between-seal direction of travel was varied. However, by day 5 there was a distinct grouping of tracks which went east and then south-east, and tracks which were more variable in direction, but headed generally to the west and south. These two groupings were usually, but not always, evident by day 5. Two seals (LF5 and LM7) were exceptional in this respect. Both travelled similar routes to the south for the first 10 days, but thereafter LM7 travelled into the south-east grouping while LF5 travelled into the more diffuse west grouping.


Figure 3. Tracks of seals shown in Fig. 1 grouped by movement Phase 1 (a), 2 (b) and 3 (c) (see Results). The tracks are colour-coded by the seals’ sex-weaning mass code where heavy female (HF) is red, heavy male (HM) is green, light female (LF) is blue and light male (LM) is yellow. The start of each track is shown by a triangle (omitted in (a) since all seals departed from Macquarie Island). A solid circle shows the last location of a completed phase. An open circle shows where transmissions terminated before a phase transition. The frontal systems labelled in Fig. 1 are shown in white. Selected seals mentioned in the text are labelled. In Fig. 3d the Phase 1 tracks (black) overlaid with simulated seal tracks at swimming speeds of 0 (red), 20 (green), 40 (blue), 60 (yellow), 80 (purple) and 100 (orange) km day−1 on a constant magnetic bearing of due east. The tracks were truncated at 180° east and covered periods of 55 days at 0 km day−1, 50 at 20, 31 at 40, 21 at 60, 17 at 80 and 14 at 100. The red triangle marks the position of the south magnetic pole.

Download figure to PowerPoint

Many of the tracks to the south-east showed a high degree of spatial similarity. In one region, 1010 km from Macquarie Island (marked A in Fig. 1), the tracks of six seals (HM1, LF1, LF3, LM1, LM2, LM6) passed within 12 km of each other. Although 12 days separated the first and last passage though this convergence, two of these seals (LM1 and HM1) did coincide on the same day and their tracks had been within 40 km of each other for the previous 4 days. Although, in general, there was less spatial similarity within the west group of tracks, two seal tracks in particular converged in time and space. Seals HF1 and HF3 remained within 10 km of each other between 13 and 15 January 1996 (marked B in Fig. 1) having previously been hundreds of kilometres apart.

Daily travel rate was frequently in excess of 100 km day−1 and varied between day and seal. Over days 5–10 the mean of the mean daily travel rates for each seal was 88 km day−1 with a SD of 16·6 km day−1. The maximum of the 5–10 day means was 122 km day−1 (seal HM3). The mean path length of completed Phase 1s was 1252 km (SD = 444), and the mean distance of their terminal location from Macquarie Island was 1169 km (SD = 293).

All transition locations from Phase 1–2 in the eastern group were north-east of, but close to, the Pacific Antarctic Ridge (Fig. 1 and the solid circles in Fig. 3a). The tracks leading to these locations were further to the east of the ridge and did not appear to be related to it. The western tracks were more diverse, but all the transition locations of completed Phase 1s were close to the Indian Antarctic Ridge.

In Fig. 3d we show simulated tracks from Macquarie Island based on swimming speeds between 0 and 100 (in steps of 20) km day−1 at a constant course of magnetic east but influenced by modelled ocean currents at 100 m depth (see Materials and methods). Most of the tracks of the eastern group were aligned with, but to the north-east of, the simulated tracks over the first 500 km down to the southern tip of the Campbell Plateau. Thereafter the seal tracks took a more southerly course and the end locations of Phase 1 tended to the south-west of the simulated tracks.

The results of the nearest neighbour spatial tests are shown in Table 3. The two nominal variables of sex and year of deployment and the ordinal variable of weaning mass were examined for their influence on the nearest neighbour statistic (h) of the terminal locations of completed Phase 1s and completed Phase 2s. At the P = 0·05 confidence level, neither a seal’s sex, year, nor weaning mass predicted that of its nearest neighbour at the terminal locations of completed Phase 1.

Table 3.  The influence of sex and year of deployment and weaning mass on terminal locations of completed movement Phases 1 and 2 (shown as solid circles in Fig. 3a,b). The nearest neighbour test statistic used is described in Materials and methods. The values indicate the probability that H0 (the factor does not influence the nearest neighbour index) is true
Terminal locationsnSexYearWeaning mass
Phase 1190·4830·0950·277
Phase 2130·0840·2870·272

phase 2

The mean of the Phase 1–2 transition dates was 6 January, and they ranged from 25 December to 18 January. The average duration of completed Phase 2s was 67·1 days (n = 14, SD = 24·3). Travel rates were variable, but slower than in Phase 1, and frequent changes of direction were observed. Periods of slow movement were often interrupted by more rapid travel to a different location. However, there was no apparent overall temporal pattern to this behaviour, both within and between seals.

The direction of travel (Fig. 3b) was variable and meandering in western group. In contrast, travel in the eastern group was directed generally to the south-east, although there were periods of travel of varied direction. This south-east trend generally maintained the seals within a 500-km wide corridor north-east of and parallel with the Pacific Antarctic Ridge. The mean displacement between the start and the end of Phase 2 in this group was 393 km (SD = 113 km) and the mean path length was 530 km (SD = 182 km).

The distances travelled in Phase 2 by the western group were similar with a mean displacement of 420 km (SD = 180 km) and a mean path length of 474 km (SD = 226 km). Seal HM5 (western group) travelled much further than any other seal, with a displacement of 670 km and path length of 3325 km. Although the western group was more scattered, two seals in particular appeared to be associated with the Indian Antarctic Ridge. The tracks of HM5 and LM10 became more sinuous over this region and they spent a total of 79 days within a 200-km radius circle of the location marked C in Fig. 1.

At the P = 0·05 confidence level, neither a seal’s sex, year, nor weaning mass predicted that of its nearest neighbour at the terminal locations of completed Phase 2 (Table 3).

phase 3

The mean of the Phase 2–3 transition dates was 13 March and they ranged from 12 February to 9 May. The average duration of completed Phase 3s was 42·3 days (n = 7, SD = 11·0) and their mean path length was 2246 km (SD = 860). All seals except LM2 started moving back towards Macquarie Island (Fig. 3c). The movements were generally less directed than during Phase 1. Two seals (LF6 and LM10) separately approached within 200–300 km of Macquarie Island and then almost circumnavigated the island at roughly this distance for 3 weeks before making a final approach to the island from the south-east. Of the seven seals that were tracked all the way back to Macquarie Island, six approached (from 100 to 200 km) from the south-east. An eighth seal (LF2) that travelled eastwards from the west group, was tracked to an area 150 km south-east of Macquarie Island before contact was lost. HM3 passed within 20 km of Campbell Island on its approach from the east to Macquarie Island, but there was no evidence that it hauled out there.

A dramatic exception to this pattern of returning to Macquarie Island was seal LM2. From the south-east group, it moved 1500 km north directly towards to the Antipodes Islands and then, after a large loop, 750 km north-east to Chatham Island.

association of tracks with oceanographic features

In Figs 1 and 3 we include the positions of fronts and boundaries associated with the easterly Antarctic Circumpolar Current (ACC) (redrawn from Orsi et al. 1995). The southern limits of movements (in Phase 2) of the south-eastern group were aligned with the southern ACC front (SACCF). The modal distance of the mean daily locations of the Phase 2 eastern group from the SACCF was 90 km to the north-east, with a secondary mode at 250 km. There was no obvious association with the Subantarctic (SAF) or Polar (PF) Fronts in this phase.

The seals that moved south-easterly direction during phase 1 moved through water of decreasing sea surface temperature, from about 7 °C near Macquarie to about 2 °C at the end of phase 1. The seals that moved in a westerly direction showed a similar, but less pronounced trend. During Phase 2, most of the eastern group remained within or close to the 2–5 °C isotherm band (c. 250 km across). This band was more diffuse to the west of Macquarie Island (> 500 km across) and there was no obvious association with the tracks there. There was no obvious association between SST and the tracks in Phase 3 or between the sea colour (SeaWiFS) images and tracks in any phase.

Two seals visited the margin of the Antarctic pack ice. During the last 3 weeks of April, HM5 (west group) travelled south to the ice margin (D in Fig. 1) and tracked it north-east for the next 6 weeks (Phase 2) before departing north (Phase 3) towards Macquarie Island. LM7 (south-east group) spent the second week of March close to the ice margin (E in Fig. 1), although approximately 500 km to the east of HM5’s ice margin tracks.

estimated time to starvation

The mass loss rate during the post-weaning fast for the heavy weaning mass group was 0·93 (SD 0·15) kg day−1, and for the light group was 0·68 (SD 0·09) kg day−1. These two means were significantly different (t-test, t = 5·11, modified d.f. = 14·6, P < 0·001). Using these loss rates and our criteria, the mean estimated time to protein starvation was, for light and heavy animals, respectively, 70·2 (SD 9·0) and 81·1 (SD 8·7) days post-weaning and to fat starvation was 77·9 (SD 9·3) and 113·8 (SD 11·4) days post-weaning.


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References


The movements of southern elephant seal pups in this study fell into three phases. Phase 1, lasting an average of 30 days, consisted of rapid directed dispersal from Macquarie Island with a mean extent of 1169 km. Phase 2, lasting an average of 67 days, consisted of slower and less directed travel. Phase 3, lasting an average of 42 days, consisted of rapid, but less directed than in Phase 1, travel back to Macquarie Island (for six of the seven seals tracked to the end of Phase 3) or to Chatham Island (for seal LM2). We consider it reasonable to assume that Phase 2 primarily represents feeding. This supposition is supported by LeBoeuf et al. (2000), who showed that the proportion of days with reduced travel rate in northern elephant seal tracks was positively related to mass gain between departure and return to land.

The classification of movements into three phases appeared in most cases to be appropriate. However, there were potential difficulties when considering tracks of different durations. For example, in April HM5 increased its travel rate to almost 100 km day−1 for a period of 2 weeks. It then slowed down again and the definition of end of Phase 2 (5-day running mean of daily travel rates last rose above 20 km day−1) was not reached until 9 May. If the SRDL had failed in April the definition of end of Phase 2 would have been satisfied on c. 1 April. Thus, the end of Phase 2 as assigned may have been premature in seals with a shorter tracking duration. In addition, there was variable reduction in travel rate from seal to seal after their initial fast dispersal from Macquarie Island. HM3 decelerated abruptly while LF7 decelerated slowly. Thus, the date of Phase 1–2 transition was sensitive to the defined threshold of 20 km day−1 in LF7, but less so in HM3. In summary, we regard the three phases of movements to be useful and realistic groupings, while at the same time we regard the exact dates and durations with caution.

comparison with adult movements

Hindell et al. (1991) inferred the tracks of 14 southern adult elephant seals from Macquarie Island using sea temperature data and showed that they may forage up to 4000 km from Macquarie Island. The four males and five of the 10 females in that study seemed to travel to the Antarctic continental shelf, while the five remaining females travelled to the Antarctic Polar Front. None of these adult foraging areas matched well with the Phase 2 areas of the pups in this study. However, additional data provided by Slip et al. (1994) show that the area of our Phase 2 south-eastern group is also used by post-moult adult females. Recent tracking studies (SMRU, unpublished) have also suggested that post-moult females sometimes follow similar routes to the south-east group of pup tracks in this study.

The variability in travel rate during Phase 2 was similar to that described for adult elephant seals (McConnell & Fedak 1996; Campagna, Fedak & McConnell 1999; LeBoeuf et al. 2000) although the extreme pattern of some adults remaining almost stationary feeding near the seabed on or near the continental shelf was not observed.

influence of intrinsic factors on movement patterns

The nearest neighbour spatial test showed no evidence that sex, year, weaning mass or departure day, affected Phase 1–2 or Phase 2–3 transition locations. Sexual segregation of foraging areas has been demonstrated to varying degrees in both southern (Hindell et al. 1991; Campagna et al. 1995; McConnell & Fedak 1996; Campagna et al. 1999) and northern (Stewart & Delong 1990; LeBoeuf et al. 1993; LeBoeuf et al. 2000) elephant seal adults. Further, LeBoeuf et al. (1996) showed that pups start to exhibit sexual foraging segregation from their third to fourth trip to sea, while Stewart (1997) found segregation was established in males that were 2–4 years old. This segregation has been attributed to the differing energetic requirements of the highly dimorphic sexes in elephant seals (Stewart 1997). While sex may account for a certain degree of variation in choice foraging areas, it appears not to be the whole story. A localized foraging area on the continental shelf off the Falkland Islands used by an adult male from Patagonia (Campagna et al. 1999) was very close to an area used by a female from South Georgia (McConnell et al. 1996). Thus, sexual segregation may be more apparent within rather than between breeding colonies. Our failure, however, to observe sexual segregation in this study does not detract from the hypothesis that any sexual segregation is driven by differing energy requirements since Bell et al. (1997) showed that there was no difference in male and female growth rates of pups returning to Macquarie Island after their first trip to sea. Thus, under this hypothesis, any sexual segregation would not be expected until later in the pups’ development.

influence of environmental factors on movement patterns

The rapid, directed dispersal in Phase 1 is similar to that of post-breeding and post-moult adult southern elephant seals (Hindell et al. 1991; Hindell et al. 1992; McConnell et al. 1992; Campagna et al. 1995; McConnell et al. 1996; Campagna et al. 1999). McCann (1985) argued that dispersal from South Georgia was driven by insufficient local prey density. It is likely that a similar situation exists at Macquarie Island. The rapid nature of pup dispersal may also act to minimize predation by killer whales (Orcinus orca L.) (Guinet, Jouventin & Weimerskirch 1992).

The pattern of dispersal from Macquarie Island formed two groupings: a tight south-easterly group and a more diffuse group to the west. Bornemann et al. (2000) also found a close grouping of southern elephant seal pups as they dispersed to the west, avoiding pack and sea ice, from a breeding site at King George Island, off the Antarctic Peninsula. In contrast, most of the adult females in that study were associated with the ice edge. In our study only two pups travelled to the ice edge, and then only for a combined duration of 7 weeks.

The simplest hypothesis to explain the observed south-east pup dispersal from Macquarie Island is that the pups passively drifted in the ocean currents. In the vicinity of Macquarie Island the predominantly easterly Antarctic Circumpolar Current (ACC) is diverted to the south-east by the Campbell Plateau for approximately 700 km. In this region the current can reach speeds of 0·8 m s−1. The path taken by a passively drifting particle at 100 m depth is shown by the 0 m s−1 swimming speed simulated track in Fig. 3d, and it is clearly inconsistent with the seal track data. However, further inspection of the track data suggests that the addition of the simple rule ‘swim magnetic east’ may produce trajectories similar to the tracks of the south-eastern group. The resultant trajectories at a variety of swim speeds show a general similarity to the south-eastern tracks, but not sufficiently so to reject the hypothesis that swimming at a constant magnetic bearing plays no role in navigation. The gross role of ocean currents in dispersal thus remains uncertain in the south-east group, but it certainly appears to have no role in the movements of the western group. In another satellite telemetry study, Loughlin et al. (1999) hypothesized that the movements of male northern fur seals (Callorhinus ursinus L.) in the Bering Sea and North Pacific Ocean were influenced by surface currents. However they concluded that individual seal tracks were, for the most part, independent of surface currents.

The Phase 2 tracks of the south-eastern grouping were within the 2–5 °C sea surface temperature isotherm band. Otherwise, there was no evident correlation with the available remotely sensed sea surface temperature or colour data. However, these data sets were integrated over time and space and may thus have obscured any relationship with smaller scale or transient ocean surface features.

The return route during Phase 3 was generally less directed than the outward Phase 1. The Phase 3 track of seal LM2 was exceptional in that it travelled north in a directed fashion to the Antipodes Islands and then to Chatham Island. Since this seal had never previously been to either of these islands it could not have been making use of a spatial memory map. However, the directed nature of its approach suggests that the seal either sensed the bearing to these islands from many hundreds of kilometres away or that it followed another animal which had been there before.

Seven of the eight seals which were tracked back to, or close to, Macquarie Island approached the island from the south-east, including one animal that had travelled from the western group. This funnelled approach from the south-east was against the prevailing current of the ACC and contrasts with the wide spread of initial departure bearings. Such a pattern of behaviour is consistent with the hypothesis that final navigation back to Macquarie Island involves the detection of a down current, or down wind, chemical signature of Macquarie Island. The use of such olfactory cues has already been suggested in the migration of green turtles (Chelonia mydas L.) to Ascension Island (Koch, Carr & Ehrenfeld 1969) and is well documented in salmon (Oncorhynchus spp.; Dittman & Quinn 1996). The chemical plume hypothesis could be readily tested by using the techniques of Oliver et al. (1998) and translocating pups up and down stream from Macquarie Island.

These south-eastern group Phase 2 tracks were bounded to the south-west by the Pacific Antarctic Ridge. A similar association of elephant seal tracks with subocean ridges and seamounts has previously been observed by a number of workers (McConnell et al. 1996; Jonker & Bester 1998; Bornemann et al. 2000). They suggested that seals were attracted to increased prey density due to enhanced production caused by local upwelling. In this study we suggest that the mechanism connecting the Pacific Antarctic Ridge and foraging in Phase 2 is via the influence of the ridge on the eastwards flow of the Antarctic Circumpolar Current (ACC) (Gordon, Molinelli & Baker 1978). The boundary of the ACC, and the positions of the major frontal systems within it (Orsi et al. 1995) are shown in Figs 1 and 3, and the southern boundary of the south-east group Phase 2 tracks is clearly aligned close to the southern ACC front (SACCF). We should, however, be aware that Orsi mapped the positions of ACC and its frontal systems using historical records, and that the position of the fronts associated with the ACC can vary significantly through time (Moore, Abbott & Richman 1999; Pakhomov, Ansorge & Froneman 2000; Trathan et al. 2000). Thus, there is a degree of uncertainty in the actual position of the ACC fronts and boundaries during our study years. However, Nicol et al. (2000) have recently shown the importance of the area to the south of the Southern Boundary of the ACC (SB-ACC) on local productivity at all trophic levels. Tynan (1998) also documented concentrations of krill (Euphausia superba Dana) and sperm whale (Physeter macrocephalus L.) near the SB-ACC (as mapped by Orsi) and concluded that the SB-ACC ‘provides predictably productive foraging for many species, and is of critical importance to the function of the Southern Ocean ecosystem’. Our study suggests that the area around the southern extent of the ACC is also important as foraging grounds for a significant proportion of southern elephant seal pups.

The pattern of tracks we have observed is not random and is likely to be the result of a combination of intrinsic and extrinsic factors. It is difficult to know if the numerous coincidences of tracks that have occurred are the result of chance encounters or some combination of the use of environmental cues and/or communication links with conspecifics or other animals. However, the frequency of such encounters encourages further observation and offers hope that clues to the cues that animals use to locate foraging locations may be gained from them.

implications for maternal investment

We have made a preliminary attempt to use the behaviour of naïve pups at sea, in conjunction with estimates of the stored resources they have when they depart, to examine the consequences of maternal expenditure on survival to nutritional independence. We emphasize that this is currently based on a number of assumptions that need further study to refine and validate but we believe it remains a useful exercise. We did not measure body composition in our study animals, but assumed that their body composition at weaning and the composition of the mass they lost were similar to that reported for southern elephant seals elsewhere by Carlini et al. (2001). We make the conservative assumption that pups at sea will use materials at the same rate as they do while ashore. While we expect that energy requirements are likely to be higher at sea, it is possible that opportunistic feeding balances this to some degree. And finally, we assume that 10% body fat reserve and 30% protein loss represent critical levels for survival. It is important that all these assumptions are examined and we hope that their use here will draw attention to their importance.

Several of the implications of this exercise deserve special emphasis. Based on the above assumptions, the time taken for animals to enter Phase 2 (the assumed foraging phase) is very close to estimates of critical time for smaller pups whereas larger ones seem to have a greater margin of safety. The calculations also suggest that protein stores as well as blubber stores should be considered when examining the value of maternal expenditure. While animals adapted to prolonged fasting can reduce absolute and relative protein utilization, adequate protein supplies are nevertheless required during fasting (Dulloo & Jacquet 1999). The consequences of the fat–protein balance at weaning also extend to diving ability. In this same set of pups, Hindell et al. (1999) showed that larger pups displayed enhanced diving capabilities, possibly as a result of their greater lean body mass. Thus, the optimal balance of fat and protein resources at weaning may be a complex response to the need to avoid starvation before reaching distant foraging areas and the ability to dive adequately once there. Additional factors such as the role of fat in thermal insulation may also influence this balance. For these reasons and those listed in the paragraph above, detailed studies of body composition in the pup’s first year of life seem essential for understanding maternal expenditure strategies.

The function of the post-weaning fast, common in many species of phocids (Arnbom et al. 1993) is not clear but it seems likely that it has some important physiological function (Blackwell & Leboeuf 1993; Pattersonbuckendahl et al. 1994; Thorson & LeBoeuf 1994; Falabella, Lewis & Campagna 1999) or social (Arnbom et al. 1993; Modig, Engstrom & Arnbom 1997) function because it is always present and is expensive in terms of the amount of body stores consumed to support it. It also acts to isolate pups from their mothers and may deny them the opportunity to capitalize on the mothers foraging experience. Our results suggest that the pup’s decision when to terminate the fast is a particularly critical and complex one. Arnbom et al. (1993) showed that large pups tend to both remain on shore longer and depart heavier, presumably gaining advantage both from the fast and extended survival time at sea before finding food. Animals must leave anticipating a significant further period without food. Physiological signals initiating departure must therefore come in advance of the acute consequences of fasting, in some way taking into account an expectation of the time to successful foraging.

It seems likely that year-to-year variability in oceanographic conditions (Sharhage 1988) will influence the time it takes pups to find food and the rate at which it can be consumed. Thus, we would predict a significant variability in pup survival – body reserves that are adequate in one year may be inadequate or superfluous in others. Indeed, Hindell et al. (1991) have shown that first year survival at Macquarie has ranged from 42–46% to as little as 2% during a period of rapid population decline. In northern elephant seals, LeBoeuf et al. 1994b) found that first year survivorship ranged annually between 20% and 49%. However, the response of pup survivorship to oceanographic conditions will depend upon the extra level of maternal expenditure that is provided to insure pups against the consequences of occasional, extreme years. If mothers routinely provide superfluous resources to their pups, a decrease in survivorship would only be apparent in years when the oceanographic conditions were extremely unfavourable. The pattern of pup survivorship would be further complicated if the mothers’ expenditure was modified by one, or a series of many, unfavourable years. Such a hypothesis is testable with long-term parallel biological and oceanographic studies. Finally, we should be aware that the maternal cost would be reduced if the pup were capable of converting any superfluous resources into increased growth, or capacity for growth or subsequent fitness.

There could be a trade-off between the mother’s material expenditure on her pup and the information the pup has, either from the mother herself or other sources, to help it find food. If food sources were local, reliable and/or the pups were directed to them by information from their parents, then less reserves may be required to give a reasonable expectation of survival until finding food. In such a scenario mothers could give less, and the value of a large expenditure would be reduced. Thus, pups would not require as large a reserve to survive and an extended post-weaning fast would be less costly. However, if food were distant, patchy and unpredictable the value of a given maternal material expenditure may be greater. The availability of good information and cues to direct pups to food could influence the time and effort needed to find food and thus reduce the level of maternal expenditure required.

In summary, maternal expenditure strategy in southern elephant seals would appear to be a complex response to many factors. However, a necessary key to understanding the importance of these factors is an appreciation of the difficulties faced by naïve pups on their road to nutritional independence in a new and variable environment. The elephant seal population on Macquarie Island has declined markedly since the 1950s (Hindell 1991), and is now less than half what it was. In recent years there has been a steady decline of about 1·6% per year (Hindell, Slip & Burton 1994). A number of theories have been put forward to explain why the Macquarie and other southern Indian Ocean population are declining while those of the South Atlantic are stable or increasing (Hindell et al. 1994). We suggest that, whatever the cause for the decline, the complex relationship between maternal expenditure, pup condition at weaning and long-term trends in oceanic conditions needs to be understood before any convincing conclusions can be drawn. This basic biological information can only come from integrated, long-term studies of seal behaviour and oceanography.


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

This study was funded by the Netherlands Antarctica Program of NWO (Project 751 49 505), the Natural Environment Research Council Sea Mammal Research Unit and the Australian Antarctic Division (Human Impacts Project 1007 and Biological Sciences Project 2265). We are grateful for the essential support and advice from the Australian Antarctic Division at Macquarie Island, especially Dave Slip and Clive McMahon. Beverly A. de Cuevas of the Southampton Oceanography Centre made OCCAM data available to us. Alejandro Orsi kindly provided location data of the oceanographic feature associated with the Antarctic Circumpolar Front. We also acknowledge the helpful referees’ comments of Dan Costa and Joachim Plötz.


  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  • Anderson, S.S. & Fedak, M.A. (1987) Grey seal, Halichoerus grypus, energetics – females invest more in male offspring. Journal of Zoology, 211, 667679.
  • Argos (1989) Guide to the Argos System. CLS Argos, Toulouse, France.
  • Arnbom, T., Fedak, M.A. & Boyd, I.L. (1997) Factors affecting maternal expenditure in southern elephant seals during lactation. Ecology, 78, 471483.
  • Arnbom, T., Fedak, M.A., Boyd, I.L. & McConnell, B.J. (1993) Variation in weaning mass of pups in relation to maternal mass, post-weaning fast duration, and weaned pup behavior in southern elephant seals (Mirounga leonina) at South-Georgia. Canadian Journal of Zoology – Revue Canadienne de Zoologie, 71, 17721781.
  • Baker, J.R., Fedak, M.A., Anderson, S.S., Arnbom, T. & Baker, R. (1990) Use of a Tiletamine–Zolazepam mixture to immobilize wild gray seals and southern elephant seals. Veterinary Record, 126, 7577.
  • Barton, C.E. (1997) International geomagnetic reference field: The seventh generation. Journal of Geomagnetism and Geoelectricity, 49, 123148.
  • Bell, C.M., Burton, H.R. & Hindell, M.A. (1997) Growth of southern elephant seals, Mirounga leonina, during their first foraging trip. Australian Journal of Zoology, 45, 447458.
  • Blackwell, S.B. & Leboeuf, B.J. (1993) Developmental aspects of sleep-apnea in northern elephant seals, Mirounga angustirostris. Journal of Zoology, 231, 437447.
  • Bornemann, H., Kreyscher, M., Ramdohr, S., Martin, T., Carlini, A., Sellmann, L. & Plotz, J. (2000) Southern elephant seal movements and Antarctic sea ice. Antarctic Science, 12, 315.
  • Boyd, I., Arnbom, T. & Fedak, M. (1993) Water flux, body-composition, and metabolic-rate during molt in female southern elephant seals (Mirounga leonina). Physiological Zoology, 66, 4360.
  • Cahill, G.F., Marliss, E.B. & Aoki, T.T. (1979) Fat and nitrogen metabolism in fasting man. Hormone and Metabolic Research, 2, 181185.
  • Campagna, C., Fedak, M.A. & McConnell, B.J. (1999) Post-breeding distribution and diving behaviour of adult male southern elephant seals from Patagonia. Journal of Mammalogy, 80, 13411352.
  • Campagna, C., Leboeuf, B.J., Blackwell. S.B., Crocker, D.E. & Quintana, F. (1995) Diving behavior and foraging location of female southern elephant seals from Patagonia. Journal of Zoology, 236, 5571.
  • Carlini, A.R., Marquez, M.E.I., Ramdohr, S., Bornemann, H., Panarello, H.O. & Daneri, G.A. (2001) Post-weaning duration and body composition changes in southern elephant seal (Mirounga leonina) pups at King George Island. Physiological and Biochemical Zoology, 74, 531540.
  • Costa, D.P. (1993) The relationship between reproductive and foraging energetics and the evolution of the Pinnipedia. Symposium of the Zoological Society of London, 66, 293314.
  • Dittman, A.H. & Quinn, T.P. (1996) Homing in Pacific salmon: mechanisms and ecological basis. Journal of Experimental Biology, 199, 8391.
  • Dulloo, A.G. & Jacquet, J. (1999) The control of partitioning between protein and fat during human starvation: its internal determinants and biological significance. British Journal of Nutrition, 82, 339356.
  • Falabella, V., Lewis, M. & Campagna, C. (1999) Development of cardiorespiratory patterns associated with terrestrial apneas in free-ranging southern elephant seals. Physiological and Biochemical Zoology, 72, 6470.
  • Fedak, M.A. & Anderson, S.S. (1982) The energetics of lactation – accurate measurements from a large wild mammal, the grey seal (Halichoerus grypus). Journal of Zoology, 198, 473479.
  • Fedak, M.A., Anderson, S.S. & Curry, M.G. (1983) Attachment of a radio tag to the fur of seals. Journal of Zoology, 200, 298300.
  • Fedak, M.A., Arnbom, T. & Boyd, I.L. (1996) The relation between the size of southern elephant seal mothers, the growth of their pups, and the use of maternal energy, fat and protein during lactation. Physiological Zoology, 69, 887911.
  • Fedak, M.A., Lovell, P. & McConnell, B.J. (1996) MAMVIS: a marine mammal behaviour visualization system. Journal of Visualization and Computer Animation, 7, 141147.
  • Gordon, A., Molinelli, E. & Baker, T. (1978) Large-scale relative dynamic topography of the Southern Ocean. Journal of Geophysical Research, 83, 30233032.
  • Guinet, C., Jouventin, P. & Weimerskirch, H. (1992) Population changes, movements of southern elephant seals on Crozet and Kerguelen Archipelagos in the last decades. Polar Biology, 12, 349356.
  • Hindell, M.A. (1991) Some life-history parameters of a declining population of southern elephant seals, Mirounga leonina. Journal of Animal Ecology, 60, 119134.
  • Hindell, M.A., Burton, H.R. & Slip, D.J. (1991) Foraging areas of southern elephant seals, Mirounga leonina, as inferred from water temperature data. Australian Journal of Marine and Freshwater Research, 42, 115128.
  • Hindell, M.A., McConnell, B.J., Fedak, M.A., Slip, D.J., Burton, H.R., Reijnders, P.J.H. & McMahon, C.R. (1999) Environmental and physiological determinants of successful foraging by naive southern elephant seal pups during their first trip to sea. Canadian Journal of Zoology – Revue Canadienne de Zoologie, 77, 18071821.
  • Hindell, M., Slip, D. & Burton, H. (1994) Possible causes of the decline of southern elephant seals in the southern pacific and southern Indian Oceans. Elephant Seals: Population Ecology, Behavior, and Physiology (eds B.LeBoeuf & R.Laws), pp. 6684. University of California Press, Berkeley.
  • Hindell, M.A., Slip, D.J., Burton, H.R. & Bryden, M.M. (1992) Physiological implications of continuous, prolonged, and deep dives of the southern elephant seal (Mirounga leonina). Canadian Journal of Zoology – Revue Canadienne de Zoologie, 70, 370379.
  • Ihaka, R. & Gentleman, R. (1996) R: a language for data analysis and graphics. Journal of Computational and Graphical Statistics, 5, 299314.
  • Jonker, F.C. & Bester, M.N. (1998) Seasonal movements and foraging areas of adult southern female elephant seals, Mirounga leonina, from Marion Island. Antarctic Science, 10, 2130.
  • Koch, A.L., Carr, A. & Ehrenfeld, D.W. (1969) The problem of open sea navigation: the migration of the green turtle to Ascension Island. Journal of Theoretical Biology, 22, 163179.
  • Laws, R. (1994) History and present status of southern elephant seal populations. Elephant Seals: Population Ecology, Behavior, and Physiology (eds B.LeBoeuf & R.Laws), pp. 4965. University of California Press, Berkeley.
  • LeBoeuf, B.J., Crocker, D.E., Blackwell. S.B., Morris, P.A. & Thorson, P.H. (1993) Sex differences in diving and foraging behaviour of northern elephant seals. Symposium of the Zoological Society of London, 66, 149178.
  • LeBoeuf, B.J., Crocker, D.E., Costa, D.P., Blackwell. S.B., Webb, P.M. & Houser, D.S. (2000) Foraging ecology of northern elephant seals. Ecological Monographs, 70, 353382.
  • LeBoeuf, B. & Laws, R. (1994a) Elephant seals: an introduction to the genus. Elephant Seals: Population Ecology, Behavior, and Physiology (eds B.LeBoeuf & R.Laws), pp. 126. University of California Press, Berkeley.
  • LeBoeuf, B.J., Morris, P.A., Blackwell. S.B., Crocker, D.E. & Costa, D.P. (1996) Diving behavior of juvenile northern elephant seals. Canadian Journal of Zoology – Revue Canadienne De Zoologie, 74, 16321644.
  • LeBoeuf, B., Morris, P. & Reiter, J. (1994b) Juvenile survivorship of northern elephant seals. Elephant Seals: Population Ecology, Behavior, and Physiology (eds B.LeBoeuf & R.Laws), pp. 121136. University of California Press, Berkeley.
  • Loughlin, T.R., Ingraham, W.J., Baba, N. & Robson, B.W. (1999) Use of a surface-current model and satellite telemetry to assess marine mammal movements in the Bering Sea. Dynamics of the Bering Sea (eds T.R. Loughlin & K.Ohtani), pp. 615630. University of Alaska Sea Grant, AK-SG-99-03, Fairbanks.
  • McCann, T. (1985) Size, status and demography of southern elephant seal (Mirounga leonina) populations. Studies of Sea Mammals in South Latitudes (eds J.Ling & M.Bryden), pp. 117. South Australian Museum, Sydney.
  • McConnell, B.J., Chambers, C. & Fedak, M.A. (1992) Foraging ecology of southern elephant seals in relation to the bathymetry and productivity of the Southern-Ocean. Antarctic Science, 4, 393398.
  • McConnell, B.J. & Fedak, M.A. (1996) Movements of southern elephant seals. Canadian Journal of Zoology – Revue Canadienne de Zoologie, 74, 14851496.
  • McMahon, C.R., Burton, H.R. & Bester, M.N. (2000) Weaning mass and the future survival of juvenile southern elephant seals, Mirounga leonina, at Macquarie Island. Antarctic Science, 12, 149153.
  • McMahon, C., Hoff, J.V.D., Burton, H. & Davis, P. (1997) Evidence for precocious development in female pups of the southern elephant seal Mirounga leonina at Macquarie Island. Marine Mammal Research in the Southern Hemisphere. Vol. 1. Status, Ecology and Medicine (eds M.Hindell & C.Kemper), pp. 9296. Surrey Beaty & Sons, Chipping Norton.
  • Modig, A., Engstrom, H. & Arnbom, T. (1997) Post-weaning behaviour in pups of the southern elephant seal (Mirounga leonina) on South Georgia. Canadian Journal of Zoology – Revue Canadienne de Zoologie, 75, 582588.
  • Moore, J.K., Abbott, M.R. & Richman, J.G. (1999) Location and dynamics of the Antarctic Polar Front from satellite sea surface temperature data. Journal of Geophysical Research – Oceans, 104, 30593073.
  • Nicol, S., Pauly, T., Bindoff, N.L., Wright, S., Thiele, D., Hosie, G.W., Strutton, P.G. & Woehler, E. (2000) Ocean circulation off east Antarctica affects ecosystem structure and sea-ice extent. Nature, 406, 504507.
  • NOAA (1988) Data Announcement 88-MGG-02, Digital relief of the Surface of the Earth. National Geophysical Data Center, Boulder, Colorado.
  • Oftedal, O.T., Boness, D.J. & Tedman, R.A. (1987) The behaviour, physiology and anatomy of lactation in the pinnipedia. Current Mammalogy, 1, 175245.
  • Oliver, G.W., Morris, P.A., Thorson, P.H. & LeBoeuf, B.J. (1998) Homing behavior of juvenile northern elephant seals. Marine Mammal Science, 14, 245256.
  • Orsi, A.H., Whitworth, T. & Nowlin, W.D. (1995) On the meridional extent and fronts of the Antarctic Circumpolar Current. Deep-Sea Research Part I. Oceanographic Research Papers, 42, 641673.
  • Pakhomov, E.A., Ansorge, I.J. & Froneman, P.W. (2000) Variability in the inter-island environment of the Prince Edward Islands (Southern ocean). Polar Biology, 23, 593603.
  • Pattersonbuckendahl, P., Adams, S.H., Morales, R., Jee, W.S.S., Cann, C.E. & Ortiz, C.L. (1994) Skeletal development in newborn and weanling northern elephant seals. American Journal of Physiology, 267, R726R734.
  • Reilly, J.J. & Fedak, M.A. (1990) Measurement of the body composition of living gray seals by hydrogen isotope dilution. Journal of Applied Physiology, 69, 885891.
  • Saunders, P.M., Coward, A.C. & DeCuevas, B.A. (1999) Circulation of the Pacific Ocean seen in a global ocean model: Ocean Circulation and Climate Advanced Modelling project (OCCAM). Journal of Geophysical Research – Oceans, 104, 1828118299.
  • Sharhage, D. (ed.) (1988) Antarctic Ocean and Resources Variability. Springer Verlag, Berlin.
  • Slip, D., Hindell, M. & Burton, H. (1994) Diving behaviour of southern elephant seals from Macquarie Island: an overview. Elephant Seals: Population Ecology, Behavior, and Physiology (eds B.LeBoeuf & R.Laws), pp. 253270. University of California Press, Berkeley.
  • Stewart, B.S. (1997) Ontogeny of differential migration and sexual segregation in northern elephant seals. Journal of Mammalogy, 78, 11011116.
  • Stewart, B.S. & Delong, R.L. (1990) Sexual differences in migrations and foraging behavior of northern elephant seals. American Zoologist, 30, A44.
  • Thorson, P. & LeBoeuf, B. (1994) Developmental aspects of diving in northern elephant seal pups. Elephant Seals: Population Ecology, Behavior, and Physiology (eds B.LeBoeuf & R.Laws), pp. 271289. University of California Press, Berkeley.
  • Trathan, P.N., Brandon, M.A., Murphy, E.J. & Thorpe, S.E. (2000) Transport and structure within the Antarctic Circumpolar Current to the north of South Georgia. Geophysical Research Letters, 27, 17271730.
  • Trillmich, F. (1996) Parental investment in pinnipeds. Advances in the Study of Behavior. Vol. 25. Parental Care – Evolution, Mechanisms, and Adaptive Significance (eds J.Rosenblatt & C.Snowdon), pp. 533577. Academic Press, London.
  • Tynan, C.T. (1998) Ecological importance of the Southern Boundary of the Antarctic Circumpolar Current. Nature, 392, 708710.
  • Vincent, C., McConnell, B., Ridoux, V. & Fedak, M. (2002) Assessment of Argos location accuracy from satellite tags deployed on captive grey seals. Marine Mammal Science, 18, 301322.