b13C, 6I5N, and C/N were measured for each of 247 muscle tlssue samples from 12 blrd, 4 seal, and 4 fish species collected In the Weddell Sea primanly d u n n g March 1986 ht3C values ranged flom -31 3 to -22 O%o and, in the case of f~s h and seal san~ples, varied inversely with C/N T h~s ~m p l~e d that l~p i d concentratlon s~gn~ficantly influenced these vertebrate hI3C measurements No such relat~on-shlp was found between C/N and bI5N where the latter values ranged from + 4 4 to + l 1 2 % w~t h cons~derable overlap among many of the taxonomic groups measured Notable exceptions to thls were found in the Wilson s storm-petrel and the Kerguelan petrel, among whlch elevated bl'N values of some lndivlduals probably reflected feeding outslde of the Weddell Sea Significant feedlng on vertebrate biomass was ~n d~c a t e d by the 15N enrichment of the southern giant fulmar and several snow petrel ind~viduals Some d~e t separation among crabeater, Antarct~c fur, leopard, and Ross seals was also evldent Nevertheless, the overlap In hI5N among most Weddell Sea vertebrates, coupled with an observed range of vertebrate values that was considerably narrower than that of t h e~r potent~al pley supports the hypothesis that many of these h~g h e r consumers share a small number of common food resources and trophlc levels

The social and reproductive behaviors of crabeater seals (Lobodon carcinophagus) were studied from September through November, during 1975, 1976 and 1977. Seals were immobilized, or controlled with a canvas bag over the head, then tagged and measured. Behavioral observations were recorded on all seals encountered.Crabeater seals were classified into three groups: (1) family groups (2) mated pairs, and (3) fast ice concentrations. Family groups consisted of an adult female, her pup, and an adult male. After weaning, the male and female formed a mated pair, and remained together for 1 to 2 weeks or until copulation. Adult females without a pup were joined by a male as they came into estrus, forming the mated pair category. Fast ice concentrations, primarily composed of sexually immature animals ranged from 50 to over 1000 seals and inhabited bays where seasonal ice persisted.Data were obtained on the predatory behavior of leopard seals (Hydrugra leptonyx), which indicated intensive predation on crabeater pups just after weaning; the degree of predation probably declines through the 1st year of life. Crabeater seals older than 1 year are probably seldom attacked by leopard seals. Further studies to determine the impact of this predation on population parameters of the crabeater seal are suggested.