The mating system of the Weddell seal, Leptonychotes weddelli

Brief description

Metadata record for data from ASAC Project 2184
See the link below for public details on this project.

The objectives of this project were:

To characterise the mating system of the Weddell seal by:
1) acoustically tracking males under the ice during the breeding season,
2) measuring changes in health and condition of individual males over the breeding season,
3) determining whether vocalisations are used as advertisements of individual quality to attract females, and/or in male-male competition,
4) develop and use a combination of microsatellite loci tests to assign paternity to newborn pups, and then use these results to determine whether the variance in male mating success is related to territory size, tenure and/or individual characteristics.

A large number of collected data files are available for download. Many files are in an unknown format, but will open with a standard text editor. See below for summaries of the two seasons of fieldwork.

1997/1998 Season:
In November/December 1997, we conducted a pilot study at the Turtle Rock colony (77.727S, 166.85E) in McMurdo Sound. All of the techniques outlined in the proposal were successfully trialled. Acoustic pingers were attached to seven males and five females for a total deployment of 104 seal days and mass and morphometrics obtained for each animal. Preliminary analysis of male movements indicate that males held adjacent yet non-overlapping territories on the southern side of Turtle Rock, along a major ice crack and where the congregation of females was highest. Both the size and shape of the males territories, and the evidence from the vocalisation data show that we captured the dominant males at the site.
Both males and females were immobilised using Ketamine/Diazepam with no loss of an animal, nor signs of respiratory depression. Vocalisations were recorded from all territory holding males, and both behavioural and vocal responses of both male and female seals to familiar and unfamiliar calls were observed. We bleach marked all animals to which we attached pingers and these markings were visible on our under-ice video - with which we also recorded behavioural responses to both animals and our under-ice speaker during playback experiments. We conducted a daily census of all animals at Turtle Rock and above-ice movements were recorded. Skin samples were taken from 24/25 males seen at the site and 43/45 mother-pup pairs (One male was only seen on a single occasion at the colony, though sighted elsewhere, and two females disappeared shortly after our arrival at the colony).

Significant findings
Dominant males hold under-ice territories which are adjacent yet non-overlapping - however territory boundaries change considerably over the course of the breeding season. Males respond to playbacks of their own and others calls as do females. Females towards the end of lactation will visit each males territories. Whether to assess individual males or not is yet to be determined.

1998/1999 Season
Between October 29 through December 10 1998, the behaviour of male and female weddell seals at the Turtle Rock colony (77.727S, 166.85E) were monitored both above and below the ice. This season, we switched from the seal sled method of capture and restraint (see K027 report 1997) to the use of a pole net and tripod. Seals were bagged by placing a seal hood over their head and then a 3m pole net (consisting of two, 3m long poles connected by a 2m wide, 2.5cm mesh, net , was placed over them and the poles tied tightly at both ends, leaving them constrained within the netting bag. The pole net was then hoisted under a tripod (built by Antarctica New Zealand) using a chain block suspended from the head of the tripod, and the animal weighed using electronic scales. For attachment of instruments, animals were immobilised with an intra-muscular injection of Ketamine/Diazepam at a dose rate of approximately 2.0mg/100 kg Ketamine, 0.4mg/100 kg Diazepam as was used successfully in 1997. Animals were only immobilised for attachment of instruments with HR electrodes (ie 3 males and 7 females). Animals were not immobilised for removal of instruments with the exception of one female who was particularly active. A small number of untagged animals were tagged in the rear flippers using tags provided by the University of Minnesota Weddell seal program as part of their long-term studies of the McMurdo Sound Weddell seal population. Maximum animal handling time including gluing of instruments and allowing for equilibration of isotopes (see below) was approximately 3 hours/seal. The mass of animals at first and last capture is shown in Table 1 below.

Animal Movements - Males: Movements under the ice were monitored using depth modulated acoustic transmitter (Vemco V16P). An array of three hydrophones, each approximately 500m apart, was placed around the colony on the southern side of Turtle Rock.. The position of each animal (x, y, z locations) was automatically logged when it was underwater at intervals of between 15 and 60 sec. The array was powered continuously using 12V dry-fit batteries connected in series. A VHF radio transmitter (Sirtrack) was glued to the dorsal surface of each male using a quick-dry Epoxy (Araldite). Time depth recorders (MkV1) Heart rate loggers, and an Acoustic Heart Transmitter were attached to three males. The VHF transmitter was used to assist in relocating animals that left the study site during the breeding season and to monitor time spent on the ice via a Televilt Scanning receiver mounted atop a Wannagan placed near the SW side of Turtle Rock. The position of males on the surface at the colony was also mapped approximately once every two days.

Females: Under ice movements and feeding behaviour of six females was monitored by attachment of acoustic pingers as outlined above. We attached Time depth recorders (MkV1) Heart rate loggers, and an Acoustic Heart Transmitter to each of five of these females, the sixth did not appear to transmit heart-rate. A seventh female was captured but no instruments fitted, as she did not respond to the immobilising agents.

Energetics -Body composition of 12 males was determined by measuring total body water using hydrogen isotope dilution on two separate occasions. At first capture, a blood sample (5ml) was drawn directly into Vacutainer collection tubes from the femoral vein at the base of the rear flippers using a 1 * inch, 18g needle and each animal was then injected with 5ml tritiated water (HTO) (specific activity 1 mCi per ml). The animal was then weighed as outlined above. Unless further instrument attachment was to occur, the animal was then released in order to allow the HTO to equilibrate with the body water pool (approximately three hours), and later recaptured for a second blood sample to be taken. Recapture and sampling usually took less than 10min. The blood samples were allowed to settle in the warmth of the Apple in the field and the serum fraction separated. Aliquots of serum were then held frozen for later analysis in Australia at the University of Tasmania. This procedure was repeated later in the season, and the changes in mass and TBW will be used to estimate energy expenditure (Reilly and Fedak 1991).

Mass changes are shown in Table 1.
Seal Tag Name Mass1 (kg) Mass2 (kg) Mass loss Seal Days Rate of mass lost/day
Purple 37 #1 Dudley 413.5 354.5 59 24 2.46
Purple 547 #2 Shed 369.5 319.5 50 20 2.50
Pink 928 #3 385.5 338.5 47 22 2.14
Red CT 283/965 #4 352.5 304.5 48 22 2.18
White 423 #5 King C 455 428.5 26.5 22 1.20
Pink 981 #6 Whiteboy 370.5 331.5 39 17 2.29
Y1339 #7 405.5 384.5 21 15 1.40
Pink CT 549 #8 Joe 362 325.5 36.5 15 2.43
Y1299 #9 Markboy 314.5 280.5 34 16 2.13
Orange CT 842 #10 344.5 293.5 51 14 3.64
Purple 808 #11 337.5 . .
Red 347 #12 313.5 . .

2) Function of Vocalisations

Method:
Hydrophones were used to obtain several recordings of five major call types from 8 of our captured males (pinger frequency allowed us to distinguish between individuals occupying the array). Following the 1999 field season, a correlational analysis will be used to determine if information on male characteristics (assessed using our physiological measures of their health or "quality") are revealed by vocalisations of the males we sampled over the three field seasons. Our current total sample size for this component of the research stands at 13 (1997 and 1998). It has become increasingly clear that the Long Trill calls, produced exclusively by males, may play important role in attracting females and challenging rivals. Two playback experiments were conducted to examine the function(s) of this important vocalisation, and other call types used by males. In the first experiment (initiated in 1997), the responses of 8 monitored males and a single female to the playback of each major call type and a control sound (walrus calls) were examined according to a systematic experimental schedule. For both males and females, we were able to record changes in position relative to the underwater speaker (using data from the pinger array), vocal behaviour (using a DAT recorder and a pair of hydrophones), activities near the playback speaker (using three underwater video cameras), swimming speed and heart rate of specific animals. Our current total sample size for this component of the research stands at 13 males and 2 females (1997 and 1998). The second experiment (also initiated in 1997) examined male-male competition and inter-sexual call function more directly. Our pilot study showed that males actively overlap the Long Trill songs of rivals with their own Trills, in a manner that is similar to territorial songbirds. We conducted "interactive" playback experiments to examine the consequences of overlapping the Long Trill calls of rivals. Five consecutive Long Trill calls of specific resident males (identified using a "real time" field spectrograph) were either (1) completely overlapped, (2) partially overlapped or (3) preceded by the recorded Long Trill calls of an unfamiliar male. A MiniDisc player was used to broadcast these calls to different resident males according to a systematic schedule. Underwater video cameras, the pinger array and hydrophones were then used to record the changes in patterns of under-ice movements and the vocal responses of 4 males and 5 females. Our current total sample size for this component of the research now stands at 7 males and 8 females (1997 and 1998). We also obtained continuous sound and video samples of male and female Weddell seals occurring along the main ice crack at Turtle Rock using a timelapse VCR connected to fixed video cameras and a hydrophone.

3) Paternity analysis: collection of samples

Method
The mating success of males at Turtle Rock will be determined by laboratory analysis of skin samples (6 mm diameter). These were collected from the edge of the interdigital webbing of the hind flipper using a leather punch, from all males, females and pups in 1997 and 1998, with further collections planned for 1999 and 2000. Samples were stored in eppendorf tubes filled with 100% ethanol. Sample degradation is minimal using this technique. Analysis has still to be conducted. This season we trialled a new technique for sampling using a small biopsy punch on the end of a pole but this technique proved unsatisfactory as biopsy heads became blunt after only 2-3 animals had been sampled. However, the clipping technique proved so successful that an experienced clipper could remove samples with such discretion that at times the animal being sampled did not wake.

Significant findings
Some of the results from the first year of this study were presented at the SCAR conference in Christchurch last August, and the abstract published in the NZ Natural Sciences series.
Harcourt, R.G., Hindell, M.A. and Waas, J.R. 1998. Under-ice movements and territory use in free-ranging Weddell seals during the breeding season. New Zealand Natural Sciences 23: 72-73
One of the most interesting findings relates to the interpretation of three dimensional dive profiles. One paper on three dimensional dive profiles in free-ranging Weddell seals is nearing completion. Other planned papers include measurement of heart-rate during diving, female foraging behaviour, communication and territorial behaviour, as well as the major reproduction papers.

Lineage

Progress Code: completed

Statement: Values provided in temporal and spatial coverage are approximate only.