Wild Neighbors: Seals of Approval

By Joe Eaton
Thursday September 03, 2009 - 11:05:00 AM
Lunchtime at Point Lobos: female harbor seal and pup.
Mila Zinkova
Lunchtime at Point Lobos: female harbor seal and pup.

Years ago at Point Reyes, I was taking a solo hike down Drake’s Beach in the direction of the lighthouse. Suddenly, a sleek gray head, like a bowling ball with big dark eyes, popped up just beyond the surfline: a harbor seal, checking me out. It kept pace with me for half a mile or so, tethered by curiosity, until I found a break in the cliffs and turned inland. 

I’ve seen a lot of harbor seals since that first encounter: hauled out on the Castro Rocks near the east end of the San Rafael Bridge or on the rocks along the San Mateo coast at low tide, riding the currents at the mouth of the Russian River, popping up among the boats at the Berkeley Marina. And they’ve improved with acquaintance. You couldn’t call them elegant: they’re chubby creatures, like flippered bratwursts. Captain Scammon, the 19th-century whaler-naturalist, said their proportions gave them “a bloated appearance, which seems ill adapted to much activity.” But they have a certain appeal. 

Part of it is behavioral: they’re not as rowdy or raucous as other pinnipeds. A sea lion or elephant seal rookery is like a frat party or a biker bar: constant jostling for space and status, threat displays, a din of barks and honks. Harbor seals have always seemed contrastingly mellow. They just hang out in companionable groups, often in what is technically called the banana or gravy-boat posture with head and tail above the horizontal (which may help dissipate heat). 

But that laid-back demeanor is deceptive. Male harbor seals bear bite marks from territorial battles. Unlike other bull seals, which guard harems of females on the beach, the harbor seal appears to patrol an offshore property through which females pass on their way to the land. Since courtship and mating take place in the water, much of their social behavior remains obscure.  

In our region, harbor seal pups are born around this time of year and between March and May. Most northern seals give birth on sea or lake ice, and their newborns have fine-haired white coats called lanugo, making them less visible to polar bears and other predators (although it doesn’t work with club-wielding Newfoundlanders). But harbor seals use sandy or rocky beaches as pupping grounds; their pups shed their white fur before they’re born. With maternity wards right at the tideline, pups have to be able to swim away with their mothers within minutes of birth. 

In their descent from otter-like ancestors in the North Atlantic some 25 million years ago, true seals have evolved an intricate set of adaptations to life in the sea. They’re more specialized than the eared seals (fur seals and sea lions), which can get around better on land. Harbor seals, with their short forelimbs and backward-projecting hind flippers, can only lurch along on their bellies. But they’re graceful enough in their true element. 

Other adaptations include an insulating layer of blubber, thin at birth but thickening rapidly as the pup feeds on its mother’s fat-rich milk. Scammon recognized harbor seal blubber as a source of high-grade oil. Perhaps because of their small size, though, these seals were never commercially exploited as elephant seals were, and their California population has remained stable—about 34,000 at the most recent estimate. 

Harbor seal physiology is fine-tuned for a foraging strategy based on diving. They can reach depths of 1,400 feet and stay down for 20 minutes or more. The seals exhale before they dive, and once underwater their lungs collapse, forcing oxygen into the blood and tissues. This allows them to surface rapidly without suffering the bends, the illness caused by nitrogen bubbles in the bloodstream. The downside of the seal’s anaerobic metabolism is a buildup of lactic acid, which has to be burned off after surfacing. 

The seal’s vibrissae, or whiskers, help it detect the motion of swimming fish at night or in murky water. A few years back, some ingenious German scientists trained harbor seals to follow a minisubmarine. Blindfolded and equipped with headphones to eliminate sonic input, they had no problem tracking the sub. But when their vibrissae were covered with a stocking mask, the seals were stumped. Each whisker can move independently as a seal scans for hydrodynamic cues by pushing its upper lip in and out. 

Harbor seals themselves may become prey to sharks and orcas. Pups are also vulnerable to eagles and sea lions and—ironically—to well-meaning humans. Don’t assume that a young seal alone on the beach is an orphan in need of rescuing. Mom may be just offshore, keeping a watchful eye on her offspring.