Influence of storms and maternal size on mother-pup separations and fostering in the harbor seal, Phoca vitulina

Ten percent of a sample of 76 paint-marked female harbor seals fostered pups for some portion of the lactation period. Fostering appears to be associated with females having lost their own pup. In a subsample of 30 pairs followed closely, three of 16 females that lost their pups fostered, but none of the 14 females that maintained continuous association with their pups throughout lactation did so. Smaller, and presumably younger, females were significantly more likely to become separated from their pups than were larger, and presumably older, females (73 vs 33%). A high proportion (68%) of 35 separations observed occurred during the same day as, or within one day following, a storm. In seven of eight instances where the authors relocated pups after they were separated from their mothers during a storm, they found them in the direction of the surfae current, 4.9 km from their previous location. Storms were probably the primary cause of separation of harbor seal mothers from their pups, and younger mothers may be more likely to become separated from their pups. As fostering only occurs after a mother has lost her pup, fostering, too, may be more likely among younger females. -from Authors