Adoption at Sea Reveals the Secret Life of Otters

It began as a chance encounter on a January morning last year, when marine biologists heard the penetrating, distinctive screech of a baby sea otter somewhere in a kelp bed just offshore near Monterey.

By the time it ended about three weeks later, however, scientists from the Monterey Bay Aquarium had found evidence of something no one had previously suspected: Under certain circumstances, the California sea otter makes an excellent adoptive parent.

Of itself, this new observation--described by a research biologist in a scientific paper released by the aquarium this week--is unlikely to affect the future of the otter as a species or influence the political battle that has grown up around attempts to keep the otter from extinction.

There are now thought to be a little more than 1,500 adult otters and about 220 pups in California waters, with the population showing modest increases each year.

But to Marianne Riedman, the research biologist who reported the new findings, the facility of the sea otter for adoptive parenting is an observation of scientific note and emotional reassurance.

The Jan. 20 screeching in the kelp bed, Riedman said, was quickly investigated by aquarium personnel. Using binoculars and a telescope, they observed a pup--about 4 months old--swimming about in desperation and hunger.

The pup’s behavior quickly identified it as an orphan. It approached first one female otter and then another, only to be rejected with a snarl by each--what was then thought to be normal otter behavior, Riedman said. At first, the options appeared to be a human rescue or acceptance that the pup would die.

But then the pup swam up to an older female researchers had observed on and off for at least four years. She had been caught once and given a distinctive tag that identified her as Otter 203.

Otter 203 had given birth a few weeks earlier, the scientists thought, but apparently had lost her pup.

Adaptation to Mothering

This chance circumstance was to save the orphaned pup. Apparently because her hormonal system was still attuned to mothering, 203 quickly accepted her new charge and treated the little one as her own.

They swam together in the vicinity of Lover’s Point, near the aquarium on Cannery Row. The pup nursed and 203 dove to bring back prey, adjusting her own diet from mussels to kelp crabs and purple sea urchins--an apparently instinctive alteration of nutritional intake appropriate to nursing.

At one point, biologists netted both animals offshore to give each a health check and tag the newly discovered pup, which turned out to be female and somewhat underweight. She was given tag 555.

For three weeks, the observation continued. The last sighting, Riedman said, was on Feb. 4 of last year, when pup 555 was seen nursing just after 5 p.m.

Does This Happen Often?

Riedman, for one, thinks such adoptions occur more frequently than scientists have realized. “I think female otters are probably primed to take care of orphans after they’ve given birth and if they have lost their pups.”

Granted, the odds are long. An orphaned pup would have to be in a section of the open ocean, and would have to encounter a female otter who had recently lost her young, all in a period of days before the pup died of starvation.

Unfortunately, Riedman said, the bond between 203 and the pup 555 ended sadly. Four days after the two were last observed, the pup was found dead, washed up on Monterey State Beach. An autopsy was inconclusive, but Riedman speculated the pup may have gotten separated from 203 and been unable to find enough food.

Then, about four months later, 203 died--apparently the victim of the effects of old age. She was about 15--old enough in otter years to be her adoptive pup’s grandmother.