With Pacific harbor seals love is in the air with mating and young seals being born along our shores. Harbor seal colonies arrive at rookery beaches in spring to give birth and nurture their young. These shy and playful marine mammals live over half their lives in the water, but birth brings them into aggregations onto remote shores or islands near shore.
Harbor seals reach five to six feet in length and can weigh up to 300 pounds. Males are slightly larger than females. The seal pups are born between February and April and weigh about 20 to 24 pounds at birth and are two feet long.
Pup cans swim immediately at birth and nurse for about one month before being weaned and fishing for themselves.
These seals are the least vocal among seals, but growl, snarl when threatened or at each other when competing for haul out space. Pups make a bleating noise that sounds like they are calling out for Maaaa.
Our local harbor seals mate in the water. Male seals compete for their mates by putting on acrobatic displays, slapping the water, making underwater vocalizations and sometimes fighting with rival males. Mature females usually mate and give birth every year. They can live as long as 25 to 30 years but average much less.
True seals have small flippers and must move on land by flopping along on their bellies like fat worms. As true seals, they are distinguished from sea lions by having ear holes without external ear flaps, and short flippers with long nails. With their long fore flippers and reversible hind flippers, sea lions have much better mobility of land than harbor seals. They favor near-shore coastal waters and are often seen on rocky islands, sandy beaches, mudflats, bays, and estuaries like the Elkhorn Slough and San Francisco Bay, and of course harbors!
Pacific harbor seals are commonly spotted or have rings with a range of fur coloration including white or silver-gray to black or dark brown. In San Francisco Bay, many harbor seals fur is fully or partially reddish in color in a condition called red pelage. This may be attributed iron oxide in the suspended sediments accumulate on the hair follicles.
Harbor seals are opportunistic feeders, primarily consuming bottom dwelling and schooling prey. Common prey species in harbors and bays include herring, flounder, and perch. They will also consume octopus, squid, and shrimp. Their diet varies seasonally and regionally with the availability of prey.
These seals are active swimmers and can dive to 1,500 feet for up to 35 minutes, although their average dive lasts under eight minutes and is typically shallower than a few hundred feet. Harbor seals can also sleep in the water by submerging their bodies and sticking their noses into the air like a snorkel--a behavior called "bottling."
Pacific harbor seals are found north of the equator in both the Atlantic and Pacific Oceans. In the northeast Pacific, they range from the Bering Sea to Baja California, Mexico.
Harbor seals do not migrate and in many areas such as the San Francisco Bay where they are present year-round. However, harbor seals are also capable of long-distance movements for breeding or following prey. They are usually found in small groups, but sometimes occur in numbers of up to 500. Natural predators of the Pacific harbor seal include orca (killer) whales and great white sharks.
The worldwide harbor seal population is estimated at 500,000 individuals. There are approximately 40,000 harbor seals in California waters.
Harbor seals are shy and easily disturbed by dogs or humans. Sometimes a pup and mother become separated due to disturbance by boaters or beachgoers, severely decreasing the pup’s chance of survival.
Easily frightened, they can also abandon their haul out spots if frequently disturbed. I frequently advise curious kayakers and stand up paddle boarders to keep a safe distance from the small colony I observe near my boat in Sausalito. This colony has been slowly growing and now numbers over 40 individuals. This year we have already observed over 6 new pups.
Harbor seal colonies in the Bay Area are vulnerable to other human impacts including loss of prey from overfishing, tangling in nets or fishing gear and pollution. Sick, injured or abandoned seals receive care at the Marin Marine Mammal Center. Like other marine mammals these seals are protected under the Marine Mammal Protection Act and should not be harassed or cause any noticeable change in behavior. Sick or dead marine mammals, or observed disturbance should be reported to the center at 415 289-SEAL.
Beachgoers and water enthusiasts should practice caution around our harbor seals, especially during the pupping season and give them a respectful distance.
Join me on a Bay Area Naturalist Adventure seeing seals, seabirds and other wonderful Bay Wildlife on a sea kayak tour. More information on our ecotours and ocean conservation is at SharkStewards.org.