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Abstract NUTRITIONAL ECOLOGY OF REPRODUCTION IN THE WEDDELL SEAL (LEPTONYCHOTES WEDDELLII) Olav T. Oftedal and Regina Eisert Weddell seals, like many true seals (Phocidae), prepare for lactation
by storage of nutrients in body tissues. During lactation, about
40% of initial mass is expended to cover metabolic needs and milk
production. Nonetheless, most lactating Weddell seals begin active
diving to depths of 300 m or more by 3-4 weeks postpartum, and dietary
biomarker data indicate that at least 70% of Weddell seals may forage
in late lactation. We are striving to model the flux of nutrients
in mothers and pups via administration of isotope combinations,
including water labeled in both hydrogen (2H and 3H) and oxygen
(18O). By measuring maternal energy expenditure, milk production
and changes of nutrient stores of both mothers and pups, we are
examining the relative contribution of current foraging (“income”)
vs. reliance on stored nutrients (“capital expenditure”)
to pup rearing. One outcome will be to determine whether prey consumption
is opportunistic, necessary only in females with limited nutrient
stores relative to lactation costs, or essential to the lactation
strategy of this species. Recent trends in pup production in Erebus
Bay (McMurdo Sound, Ross Sea) include a 50% drop in the numbers
of pups born during years of unusually heavy ice accumulation due
to presence of icebergs, with recovery in 2006 following ice break-out.
We hypothesize that ice conditions affect Weddell seal foraging
opportunities via impacts on primary production and prey populations,
forcing changes in pupping locations. Further study is needed on
the effects of annual, cyclic or long-term changes in prey abundance
on Weddell seal reproduction.
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