The New England Aquarium welcomed the birth of a rare baby seal this week, officials announced Friday. A worker noticed blood on the floor of the seal holding area shortly before midnight Tuesday. She realized that a 14-year-old Northern fur seal, Ursula, might be in labor. After marine mammal trainers and veterinary staff arrived, they found Ursula in a corner with her 8-pound pup, the seal’s first. Ursula, originally from the New York Aquarium, and her partner, Isaac, from the Seattle Aquarium, were brought to New England to take part in a breeding program. This is the first birth of a Northern fur seal at the aquarium.