Christmas came early at the Minnesota Zoo for two geriatric Hawaiian monk seals.

Discovery Bay residents Koa and Opua went under the knife just before the holidays to remove cataracts in hopes of improving their vision. The critically endangered mammals, each in their early 20s, are expected to recover over the next few weeks.

"The marine mammal staff have been monitoring the seals closely and are happy that both seals appear to be doing well and healing properly," said Melanie Oerter, the zoo's marine mammal curator.

"They are now both back in the water and may be seen swimming around their pools."

Veterinarians are particularly optimistic about Koa, who has given indications that she has regained some function. Zoo staff say she notices moving objects more than before. Meanwhile, Opua appears to be in less pain after having one malfunctioning eye removed.

The Apple Valley zoo inherited a group of five rehabilitated Hawaiian monk seals, all in their early 20s, in 2015. Four of the five have limited or no sight.

Dr. Carmen Colitz, a veterinary ophthalmologist who specializes in marine mammal eye procedures, flew in from Florida to evaluate all the seals and perform the hourlong surgeries.

One of the most endangered sea mammals in the world, the Hawaiian monk seal has been in steep decline since the 1950s. The National Oceanic and Atmospheric Administration estimates there are only about 1,000 left throughout the island chain. Their average life span is about 25 years.

"If we commit to housing animals here at the zoo, we must also commit to providing top-notch care so they can live their best lives," zoo spokesman Josh Le said.