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.

A pod of seven killer whales (Orcinus orca) was seen to attack a lone crabeater seal (Lobodon carcinophagus) which was lying on an ice floe. The whale located the seal, moved away from the floating ice, then swam as a group close to the floe. This caused a wave which tipped up the ice floe and broke over it, causing the seal to be thrown into the water. The whales swam immediately to the vicinity of where the seal disappeared but it was not possible to ascertain if a kill was made.