Monk Seal Mondays #159: Sleeping Seals

Sleep: It’s important for everyone. Including Hawaiian monk seals, and especially after multi-day foraging trips. Or when monk seals are molting. And, of course, when mothers are nursing. Some seals sleep smack in the middle of a sandy beach. But it’s not unusal for some to snuggle up with rocks and/or logs; or slip under vegetation. Or whatever happens to be on the beach.

According to National Geographic, “Monk seals spend most of their time at sea, but they come ashore to rest on beaches and use fringe vegetation as shelter from storms.”

But there may be more to it than that.

Dr. Mimi Olry has been observing Hawaiian Monk Seals for 16 years as the Kauai Marine Mammal Response Field Coordinator for the DLNR/Division of Aquatic Resources/Protected Species Program. “I don’t know for sure,” she says, “But the moms and pups, and specifically more vulnerable young animals and molting adults go up to the vegetation or objects on the beach (picnic table, chaise lounge, log) at night for protection, to not be out in the open. This may be because they are solitary, and also to avoid the reach of the high tide during the night, adverse weather, and terrestrial predators.”

It’s likely Hawaiian monk seals are also catching a few winks underwater. This behavior has been witnessed at Niihau.

“Hawaiian monk seals can hold their breath for up to 20 minutes and dive more than 1,800 feet; however, they usually dive an average of 6 minutes to depths of less than 200 feet to forage at the seafloor,” NOAA reports. “They usually sleep on beaches, sometimes for days at a time. They also occasionally sleep in small underwater caves.”

This behavior isn’t unique to Hawaiian monk seals. Mediterranean monk seals have been caught napping underwater, too. As well, other pinnipeds like fur seals, who spend months at a time at sea. But, yes, of course, all seals have to wake up frequently to surface and breathe. Harbor seals practice what’s called “bottling,” in which all but the seal’s face remains submerged, allowing the animal to breathe while resting and/or sleeping.

On narrow beaches or during times of high tides, this proclivity of Hawaiian monk seals to sleep under vegetation and/or manmade things can put them in precarious situations. Like these:

In most cases, it’s important to let sleeping seals lie. In some cases and with authorization, Dr. Olry and her team seek will displace these seals, so they find a safer place to sleep.

[All photos credit to NOAA and Kauai HMS Conservation Hui volunteers. Mahalo.]