When you walk along a trail overlooking the numerous pocket beaches of Point Reyes, you may catch a glimpse of shy harbor seals (Phoca vitulina). They often haul out along the Pacific Coast from the Bering Sea to Baja California, sometimes in large numbers at established colony sites. Harbor seals are curious animals when in the water, and often lift their heads out of the water to look around. Sometimes when they see a person walking on the shore or kayaking, they follow at a distance of as close as 15–45 meters (50–150 feet) in the bays and estuaries of the park.
Harbor seals are residents of Point Reyes and so they may be sighted year-round both on land and in the nearshore waters. Some seals also migrate annually up to 800 km (500 miles) during the winter months to other foraging areas, and then return to Point Reyes to breed and molt their fur. Point Reyes has the largest population of harbor seals in California, excluding the Channel Islands, with twenty percent of state's harbor seals living or breeding within the park's boundaries. Select colonies at Point Reyes have been monitored since 1976, and have increased as the population has recovered with protection provided by the Marine Mammal Protection Act of 1972.
Harbor seals, and other pinnipeds, usually haul out in large groups onshore at traditional sites such as Point Reyes Headland. Their habit of hauling onto land to rest, give birth and nurse their young, and warm themselves in the sun provides nature enthusiasts a chance for an excellent wildlife sighting, but also makes the harbor seal vulnerable to disturbance. Harbor seals are shy animals whose habits are easily disrupted by the presence of humans on land. We recommend that visitors stay around 90 meters (300 feet) away from seals resting onshore.
How to Identify Harbor Seals
The harbor seal, northern fur seal, California sea lion, Steller sea lion and northern elephant seal are the five species of pinnipeds a visitor might see at Point Reyes. Harbor seals can usually be distinguished from elephant seals by size alone. The harbor seal is a rather small marine mammal, only getting up to 1.5 to 1.8 m (five to six feet) in length and 115 kg (250 pounds) in weight, whereas elephant seals are much larger. Bull elephant seals average about 1,360 to 2,500 kg (3,000 to 5,500 pounds), while females range in weight from 360 to 545 kg (800 to 1200 pounds). However, yearling and weaned pups weigh about 135 kg (300 pounds), so a young elephant seal could be mistaken for an adult harbor seal, if one attempts to identify the seal by its size. What color is the seal? While young elephant seals are a uniform gray, harbor seals are typically silver, white or gray, with black spots, although some harbor seals also are black or brown with white spots. Sometimes a harbor seal may have a reddish colored head or body, which is due to iron oxide deposits on the hair shafts.
Harbor seals and elephant seals are in the Family Phocidae (the earless seals) so unlike sea lions and fur seals, they do not have external ear flaps on the head, just a small hole where their ear is. Harbor seals and elephant seals also are unable to rotate their pelvis, and so they drag their body inchworm fashion around on land, on beaches, or other nearshore substrates that have a low slope. Sea lions, in contrast, can rotate their pelvis forward and walk on all four limbs, enabling them to use steep, rocky shoreline habitat unavailable to harbor seals. Harbor seals also differ from sea lions in their smaller size and lighter color. When in water, harbor seals propel themselves with their hind flippers in a sculling motion, and steer with their front flippers, whereas sea lions and fur seals propel themselves with their fore-flippers, like wings.
What Do Harbor Seals Eat?
Harbor seals are within the Order Carnivora, which means that they primarily eat meat. The meat they eat is fish in the nearshore waters of the park, such as herring, anchovies, sardines, hake, flounder, sole, salmon and sculpin. They also eat invertebrates such as octopus and squid and even crabs. The harbor seal is considered an "apex predator" because it feeds towards the top of the food chain. Apex predators are often used as an indication of the condition of their ecosystem because they can't do well unless all of the organisms within their habitat are doing well. Point Reyes has been using the harbor seal as one of the indicators of the condition of the area's marine systems. The population has grown and stabilized over the past decade and females give birth to pups around every year. During El Nino years, though, female seals often skip giving birth and the population counts onshore are lower, likely because seals are spending more time in the water looking for food.
What eats harbor seals?
White sharks are the primary marine predator of harbor seals, but occasionally other large sharks and killer whales eat them. Terrestrial predators such as coyotes and bobcats can also occasionally prey on harbor seals resting onshore, particularly pups that are very young.
Rarely, male elephant seals have been documented killing harbor seals in California at harbor seal colonies such as Jenner. This elephant seal behavior is very unusual, and the male seals do not appear to interact or haul out with other elephant seals. Instead, they haul out at harbor seal colonies.
Why Harbor Seals Haul Out
Harbor seals (and sea lions) haul out (come out of the water) almost daily to rest and to warm up. They cannot maintain their body temperature if they stay in cold water all the time because of their smaller size and thinner blubber layer. Northern elephant seals lose less heat than harbor seals because are much larger and have a thicker blubber layer that allows them to stay at sea for months at a time before coming onshore to rest and give birth.
All pinnipeds give birth on land, and that is one fact that distinguishes them from cetaceans, another group of marine mammals. Harbor seals give birth between March and June on tidal sandbars, rocky reefs and pocket beaches. They can give birth on areas which are inundated at high tide because harbor seal pups, unlike most pinniped species, can swim at birth. During the pupping season, mother seals will spend more time onshore nursing pups and resting, for an average of around 10–12 hours per day. The mother harbor seal stays with the pup almost continuously and rarely leaves the pup alone onshore. Mothers can take their pups with them when they go swimming and feeding because pups are adept swimmers.
A mother caresses and nuzzles its baby pup constantly, and for four to six weeks nurses it with her rich milk. The 48% fat content of milk makes the pup gain weight rapidly, and by around 30 days they are weaned. Pups weigh around 11 kg (25 lbs) at birth but when they are weaned they may weigh as much as 22 kg (50 lbs).
During the breeding season, male seals hold territories in the waters adjacent to where females haul out on shore, called maritory. Females are receptive to mating around when the pups are weaned and mating occurs in the water. Male seals will protect their maritory from other males and engage in stylized fighting during the breeding season.
Shortly after the pups are weaned, the seals begin their annual molt of their sea worn fur. The fur sheds much like a dog and the seals turn a luminous color with new fur. The molt period begins around mid-June and extends through July. During this time, seals will spend more time resting onshore because it is energetically taxing. Also, studies have shown that hair follicles grow faster in onshore than in the water. Seals can stay onshore resting for an average of 12 hours per day during the molt compared to around 7 hours per day during fall-winter months.
Harbor Seals Vulnerable to Disturbance
When seals and other pinnipeds haul out, they are extremely vulnerable to human disturbance. Often they will react when humans come within 90 m (300 ft). Their reactions can be anything from a head alert—lifting their head—to flushing—retreating into the water. Harbor seals leave their haul-out sites when harassed by people, dogs, boats, aircraft or other human actions. Even a temporary disruption stresses the animal by cutting into its time to warm up, rest, and nurture young. Harbor seals may also abandon a haul-out site permanently, as they did at historic sites in San Francisco Bay, due to high and chronic incidences of human disturbance.
March through July, the pupping and molting seasons, is an especially vulnerable time for harbor seals. While hiking along the shores of the Pacific during these months, you may come across a seal pup alone on the beach. It is most likely not abandoned. The mother is probably in the water nearby feeding. However, if a mother is repeatedly disturbed on a site with her pup, she may decide to abandon her pup for the safety of the water, so please be sure to stay well away from any seals you see.