Energetics of lactation in harp seals (Phoca groenlandica) from the gulf of St. Lawrence,Canada |
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Authors: | C Lydersen K M Kovacs |
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Institution: | 1. Norwegian Polar Institute, P.O. Box 399, N-9001, Troms?, Norway 2. Department of Biology, University of Waterloo, N2L 3G1, Waterloo, ON, Canada
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Abstract: | This study reports the findings of an integrated, comprehensive analysis of lactation energetics in harp seals conducted
using longitudinal measurements of mass, body composition and milk composition from mother-pup pairs in conjunction with water
flux measurements in pups. The nursing period of harp seals is a short, intense and relatively efficient period of energy
transfer from mothers to pups. The average daily milk intake for pups was 3.65±0.24 kg which is equivalent to 79.5 MJ of energy.
Eighty-one per cent of the energy received in the milk was metabolisable and 66% of the energy was stored by the pups as body
tissue. The field metabolic rate of pups was 3.9±0.4 time basal metabolic rate. The pups were growing at a rate of 2.2 kg
per day during the nursing period. The distribution of this mass gain varied in terms of tissue composition, depending on
the age of the pups, but over the whole nursing period approximately half of the tissue was stored as fat. Harp seal mothers
lost an average of 3.1 kg per day during lactation which was composed of 37% water, 50% fat, 11% protein and 2% ash. Mothers
spent half of their time during the lactation period actively diving and only one-third of their time on the surface of the
ice. Milk compositional changes followed the normal phocid pattern with increasing fat content and decreasing water content
as lactation progressed. The mean mass transfer efficiency was 73%. However, this value cannot be used without qualification
because female harp seals in this study fed to varying degrees, consuming an estimated 0–4.8 kg of fish per day. Feeding does
not appear to be required in order to achieve the energy requirements for lactation, given the energy stores possessed by
females, and some females do fast through the entire period so feeding may be considered opportunistic in nature.
Accepted: 25 April 1996 |
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Keywords: | Energetics Lactation Maternal investment Behaviour Harp seals Phoca groenlandica |
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