Shedd Aquarium welcomes a new sea otter pup. The orphaned southern sea otter pup, known so far as Pup 681, is just five weeks old and weighs less than six pounds. The small sea otter arrived at the aquarium on October 28 and continually receives constant care from the aquarium’s sea otter specialists and veterinarians.

State wildlife officials rescued the pup along the southern California coast. She was then taken to Monterey Bay Aquarium, a leader in sea otter rehabilitation. Shedd, which has 25 years of experience caring for fragile sea otter pups, rapidly accepted Monterey Bay’s call to give the small sea otter a permanent home.

The new pup is growing quickly and is achieving new milestones each day. Shedd employees are tracking the pup’s progress on a blog.

According to Defenders of Wildlife, sea otters are the heaviest members of the weasel family and are the second smallest marine mammals. Instead of an extra layer of blubber to keep them warm, as most marine mammals have, sea otters have the densest fur in the animal kingdom, ranging from 250,000 to a million hairs per square inch for insulation.

The source also states that California sea otters often grow to around four feet, and can weigh up to 45 pounds (females) and 65 pounds (males). Their lifespans are 10 to 15 years for males and 15 to 20 years for females.