Patterns of weight gain by Weddell seal pups · 2011-05-06 · 0 C CDa CD 0. CD 0 C CD a a V C1....
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>. 0 C CD a' CD 0. CD 0 C CD a' a' V C1. Patterns of weight gain by Weddell seal pups HILL, S. VACCA, S. BARTSII, R. RElcilli, J.W. TESTA, and D. SINIFF L)epartinent of Ecology and Behiwioral Biology University of Minnesota Minneapolis, Minnesota 55455 Over the past several years researchers from the University of Minnesota have investigated the long-term population dynam- ics of the Weddell seals of McMurdo Sound (Kaufman, Siniff, and Reichle 1975; Siniff et al. 1977; Testa 1986). Recently our efforts have been concentrated on aspects of reproductive ecol- ogy, especially parental investment. One area of interest has concerned patterns of weight gain by Weddell seal pups be- tween birth and weaning. Such patterns may affect the survival and the future reproductive patterns of both the pup and its mother. We were interested in how much and how quickly seal pups gained weight, and what factors led to differences among the pups. These questions were investigated during the 1985-1986 austral summer. Methods. A field camp was set up at the pupping/breeding colony at Hutton Cliffs on the western edge of Ross Island approximately 18 kilometers north of McMurdo Station. The camp was occupied continually between 15 October and 19 December 1985. We walked through the colony at approx- imately daily intervals during the pupping season (19 October to 14 November) and tagged new pups as they were encoun- tered. The pups were weighed as 500fl after birth as possible, but never before the umbilical cord had detached and the pup was dry, and at weekly intervals up to age 40 days. Mothers were weighed and their lengths and girths measured once near the birth of the pup and again as near as possible to day 40 following parturition. A total of 58 pups and 35 mothers was measured sufficient times to use in the following analyses. Activity patterns (on ice vs. in the water) of 12 pups were monitored continuously for periods between 15 and 31 days, over the time when weekly weights were being measured. Radio transmitters were attached to the dorsal fur of the pups, and the signal monitored by a scanning receiver. If the pup was on the surface of the ice, a mark was made on a strip-chart recorder. The total time a pup spent in the water as a proportion of the time it was being monitored was calculated, and this proportion used on the following analyses. Results. The 58 Weddell seal pups weighed 32.0 ± 4.7 kilo- grams (mean ± standard deviation) at birth and 110.9 ± 19.0 kilograms 40 days later. The average rate of weight gain was 2.04 ± 0.06 kilograms per day. Over the same period, the mothers of these pups were losing an average of 4.16 ± 0.15 kilograms per day. There were no significant differences between the weights of male and female pups at birth or at 40 days of age, nor in the rates of weight transfer. The birth weight of a pup did not significantly affect its rate of weight gain, but there was a signifi- cant correlation between birth weight and 40-day weight [(P:h = 0) = 0.003, r = 0.39]. Weight gain by pups was significantly correlated with the weight of their mothers SOOfl after parturi- tion [(P:b = 0) = 0.001, r = 0.63], and with the rate at which the mothers lost weight [(P:b = 0) 0.02, r = 0.40] (figure 1). Additionally, the level of activity, measured as the proportion of its time that a pup spent on the water, was in- versely correlated to its rate of weight gain [(P:b = 0) = 0.002, r = -0.80] (figure 2). Discussion. The lactation period is probably the most impor- tant time during the first year of a Weddell seal's life. During approximately 7 weeks, a pup makes the transition from a terrestrial mammal (thin, hairy, non-swimming) to a marine mammal (thick-blubbered, thin-haired, swimmer), and during the process may gain 5 times its birth weight. Over the same period a lactating female will lose twice as much weight as her pup gains. We found that male and female Weddell pups grow at the same rate, and do not differ in weight as weaning. This is in contrast to other species of seals wherein male pups grow much faster than females (Doidge, Croxall, and Ricketts 1984; Reiter, Stinson, and LeBoeuf 1978). Early growth patterns of Weddell seals probably reflect the lack of size difference in adults. Although birth weights were quite similar among all pups, growth rates and weaning weights did differ. Weight gain by a pup was positively correlated with the size and rate of weight loss of its mother, and negatively correlated with its own level of activity. Heavier mothers were able to provide more energy to their pups and provide it at faster rates, both of which increased the rate at which pups put on weight. It was not surprising to find that pups who spent more time in the water gained weight more slowly than those who spent less time swimming. Pup Weight Gain vs. Mother Weight Loss Mother weight loss (kg/day) Pup Weight Gain vs. Weight of Mother Weight of mother after parturition (kg) Figure 1. Relationship between Weddell seal (Leptonychotes wed- deli,) females' weight loss and weight just after parturition and pups' weight gain. Data are from Hutton Cliffs colony in eastern McMurdo Sound, Antarctica. ("kg" denotes "kilogram:') 1986 REVIEW 209
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Patterns of weight gain by Weddellseal pups
HILL, S. VACCA, S. BARTSII, R. RElcilli,J.W. TESTA, and D. SINIFF
L)epartinent of Ecology and Behiwioral BiologyUniversity of Minnesota
Minneapolis, Minnesota 55455
Over the past several years researchers from the University ofMinnesota have investigated the long-term population dynam-ics of the Weddell seals of McMurdo Sound (Kaufman, Siniff,and Reichle 1975; Siniff et al. 1977; Testa 1986). Recently ourefforts have been concentrated on aspects of reproductive ecol-ogy, especially parental investment. One area of interest hasconcerned patterns of weight gain by Weddell seal pups be-tween birth and weaning. Such patterns may affect the survivaland the future reproductive patterns of both the pup and itsmother. We were interested in how much and how quickly sealpups gained weight, and what factors led to differences amongthe pups. These questions were investigated during the1985-1986 austral summer.
Methods. A field camp was set up at the pupping/breedingcolony at Hutton Cliffs on the western edge of Ross Islandapproximately 18 kilometers north of McMurdo Station. Thecamp was occupied continually between 15 October and 19December 1985. We walked through the colony at approx-imately daily intervals during the pupping season (19 Octoberto 14 November) and tagged new pups as they were encoun-tered. The pups were weighed as 500fl after birth as possible,but never before the umbilical cord had detached and the pupwas dry, and at weekly intervals up to age 40 days. Motherswere weighed and their lengths and girths measured once nearthe birth of the pup and again as near as possible to day 40following parturition. A total of 58 pups and 35 mothers wasmeasured sufficient times to use in the following analyses.Activity patterns (on ice vs. in the water) of 12 pups weremonitored continuously for periods between 15 and 31 days,over the time when weekly weights were being measured.Radio transmitters were attached to the dorsal fur of the pups,and the signal monitored by a scanning receiver. If the pup wason the surface of the ice, a mark was made on a strip-chartrecorder. The total time a pup spent in the water as a proportionof the time it was being monitored was calculated, and thisproportion used on the following analyses.
Results. The 58 Weddell seal pups weighed 32.0 ± 4.7 kilo-grams (mean ± standard deviation) at birth and 110.9 ± 19.0kilograms 40 days later. The average rate of weight gain was 2.04± 0.06 kilograms per day. Over the same period, the mothers ofthese pups were losing an average of 4.16 ± 0.15 kilograms perday. There were no significant differences between the weightsof male and female pups at birth or at 40 days of age, nor in therates of weight transfer. The birth weight of a pup did notsignificantly affect its rate of weight gain, but there was a signifi-cant correlation between birth weight and 40-day weight [(P:h= 0) = 0.003, r = 0.39]. Weight gain by pups was significantlycorrelated with the weight of their mothers SOOfl after parturi-tion [(P:b = 0) = 0.001, r = 0.63], and with therate at which the mothers lost weight [(P:b = 0)0.02, r =
0.40] (figure 1). Additionally, the level of activity, measured asthe proportion of its time that a pup spent on the water, was in-versely correlated to its rate of weight gain [(P:b = 0) = 0.002,r = -0.80] (figure 2).
Discussion. The lactation period is probably the most impor-tant time during the first year of a Weddell seal's life. Duringapproximately 7 weeks, a pup makes the transition from aterrestrial mammal (thin, hairy, non-swimming) to a marinemammal (thick-blubbered, thin-haired, swimmer), and duringthe process may gain 5 times its birth weight. Over the sameperiod a lactating female will lose twice as much weight as herpup gains.
We found that male and female Weddell pups grow at thesame rate, and do not differ in weight as weaning. This is incontrast to other species of seals wherein male pups grow muchfaster than females (Doidge, Croxall, and Ricketts 1984; Reiter,Stinson, and LeBoeuf 1978). Early growth patterns of Weddellseals probably reflect the lack of size difference in adults.
Although birth weights were quite similar among all pups,growth rates and weaning weights did differ. Weight gain by apup was positively correlated with the size and rate of weightloss of its mother, and negatively correlated with its own level ofactivity. Heavier mothers were able to provide more energy totheir pups and provide it at faster rates, both of which increasedthe rate at which pups put on weight. It was not surprising tofind that pups who spent more time in the water gained weightmore slowly than those who spent less time swimming.
Pup Weight Gain vs. Mother Weight Loss
Mother weight loss (kg/day)
Pup Weight Gain vs. Weight of Mother
Weight of mother after parturition (kg)
Figure 1. Relationship between Weddell seal (Leptonychotes wed-deli,) females' weight loss and weight just after parturition and pups'weight gain. Data are from Hutton Cliffs colony in eastern McMurdoSound, Antarctica. ("kg" denotes "kilogram:')
1986 REVIEW 209
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Pup weight gain vs. time in water
Proportion of time spent in water
Figure 2. Relationship between Weddell seal (Leptonychotes wed-deli,) pup weight gain and proportion of time spent in the waterduring the period of nursing. Data are from Hutton Cliffs colony ineastern McMurdo Sound, Antarctica. ("kg" denotes "kilogram:')
The size of a seal pup at weaning is probably important indetermining it subsequent survival. At that stage, pups are lefton their own to find food, and a fat pup would have sufficient
reserves to survive for quite some time while perfecting itsfood-gathering and predator-avoidance abilities. Over evolu-tionary time, there has probably been strong selection for fastand large transfers in weight between mother and pup duringlactation. However, pups who learn to swim well while stillunder the protective influence of their mothers may have anadvantage over those who do so while on their own.
This research was supported by National Science Foundationgrant DPP 83-18473 to D. B. Siniff, and with the able and energet-ic assistance of D. Garron and K. Prentice.
References
Doidge, D.W., J.P. Croxall, and C. Ricketts. 1984. Growth rates ofAntarctic fur seal Arctocephalus gaze/la pups at South Georgia. Journalof the Zoological Society of London, 203, 87-93.
Kaufman, G.W., D.B. Siniff, and R. Reichle. 1975. Colony behavior ofWeddell seals, Leptonychotes weddelli, at Hutton Cliffs, Antarctica.Rapports et Procés-verhaux des Reunions, Conseil international pour l'Ex-p/oration de la Mer, 169, 228-246.
Reiter, J., N.L. Stinson, and B.J. LeBoeuf. 1978. Northern elephant sealdevelopment: The transition from weaning to nutritional independ-ence. Behavioral Ecology and Sociobiology, 3, 337-367.
Siniff, D.B., D.P. DeMaster, R.J. Hofman, and L.L. Eberhardt. 1977. Ananalysis of the dynamics of a Weddell seal population. EcologicalMonographs, 47. 319-335.
Testa, J.W. 1986. Long term patterns in life history characteristics and popula-tion dynamics of Weddell seals (Leptonychotes weddelli) in McMurdo Sound,Antarctica. Doctoral Thesis, University of Minnesota, Minneapolis,Minnesota.)
Second cetacean survey of easternTierra del Fuego
and Isla de los Estados
R.N.P. GOODALL
Prograrna Cetdceos AustralesCentro Austral de investigaciones CientIficas (cADic)
Tierra del Fuego, Argentina
As part of a U.S.-Argentinian program of cooperativeresearch organized by the National Science Foundation andCADIC, we took part in an expedition aboard the R/V Polar Dukefrom 12 May to 2 June 1986 to the Peninsula Mitre of easternTierra del Fuego and Isla de los Estados. This was the secondsuch project, the first being carried out aboard the tIv Hero in1981 (Goodall and Galeazzi in press-b). Very little work hadbeen done on the marine mammals of this rather inaccessibleand seldom-visited area (Pine, Angle, and Bridge 1978).
The objective was to further scientific understanding of thedistribution and biology of marine mammals in eastern Tierradel Fuego by surveys of beaches (on foot) for stranded material
and observation of living animals. Beaches checked in 1981would be resurveyed for new material, and we hoped to reachbeaches inaccessible at that time. Periodic beach surveys offerone of the best ways of accumulating data and specimens of thecetaceans of a given area, especially those that are least known(Geraci and St. Aubin 1979). Those participating in this studywere: Natalie Goodall, Alejandro R. Galeazzi, Margarita Godoy,and Gustavo MarfIa, all of Ushuaia. Adrian Schiavini assisted uson some beaches, and we accompanied him on seal surveys.
During the 22 days of the cruise, we were able to survey 33beaches in 18 bays and coves (figure), as well as checking othersvisually from a zodiac when conditions made landings impossi-ble. Table 1 lists the beaches surveyed. Extensive coastal sur-veys from the zodiac made in Bahia Aguirre, Bahias Franklin,Flinders, San Juan de Salvamento, York, and Blossom and thearea from Puerto Vancouver west to Cabo Webster, as well as theIslas Dampier and Menzies. Other members of the expedition(geologists Ian Dalziel and assistants) examined the shores ofIslas Elizalde, Zeballos, and Goff re and collected one specimen.Areas which were surveyed in 1981 but could not be reached in1986 for climatic or other reasons were: western Bahia Aguirre,Bahias Valentin, Capitán Cánepa and Puerto Cook.
Collections were made of 18 cetacean specimens. Incidentalto the cetacean work, we also collected specimens of 12 pin-nipeds, two otters, once guanaco; notes were taken on thepresence of marine birds and 47 collections were made of skel-etal material of dead birds.
210 ANTARCTIC JOURNAL
