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Harbor Seal Facts | Seal Conservancy

Harbor Seal Facts

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  • Harbor seals are pinnipeds. They are true seals; that is, they do not have visible ear flaps.
  • They inhabit the Northern Atlantic and Pacific Oceans and the Baltic and North Seas but generally stay close to the coast, hence their name.
  • Harbor seals are site faithful, which means that they stay with the same resting, haulout, and birthing site.  Thus, they will spend their entire lives along the same stretch of coastline.
  • They are generally 5-6 feet long and weigh up to 300 pounds, with males being slightly larger than females.
  • There are approximately 20,000 harbor seals along the California Coast — about 5,000 of which are in Southern California, most of these residing in the Channel Islands.
  • The La Jolla colony has about 200 seals who use the site at Casa Beach as a haul out location year-round.
  • They also use the beach during the winter and spring as their rookery.  A rookery is a specific area where seals gather each year to mate and raise young.
  • Over a million visitors come to La Jolla every year to view this unique harbor seal rookery, the only one of its kind in an urban setting, and the only mainland rookery in Southern California south of Ventura.
  • Harbor seals can vary widely in color − from white or silver-gray to black or dark brown. Almost all harbor seals have spots. Colors and spots are unique to the individual and can be used to identify individual seals.
  • They can dive down to depths of 1,500 feet and are capable of staying under water for up to 40 minutes.
  • The average dive of a harbor seal lasts between 3 and 7 minutes.
  • Harbor seals communicate with each other using body postures and are the most docile and least vocal of all pinnipeds.
  • Harbor seals must “haul out” (come out of the water) on land between 7 and 12 hours each day.
  • Hauling out is necessary to maintain their body temperature (thermal regulation).
  • This is because in cold water, blood vessels constrict, slowing the flow of blood to the skin and reducing heat loss. When hauled out, the process is reversed and blood vessels expand, allowing heat to be released to the environment.
  • Contrary to popular belief, the seals, when hauled out, are not simply “basking in the sun”. We know this because seals in temperate regions haul out regularly even on the coldest winter days, and seals in polar regions remain hauled out on the ice, even during the most ferocious storms.
  • Although they haul out in (sometimes quite large) groups, harbor seals do not like to touch each other. This is in direct contrast to sea lions, who are commonly seen piled on top of each other on the off-shore rocks at the La Jolla Cove. If you watch the harbor seals closely, it is interesting to observe how they go to great lengths to avoid touching each other. The exception to this rule is the bonding between a mother and her newborn pup, when they “nose” each other frequently.
  • Each year after the breeding season, Pacific harbor seals experience a “catastrophic molt” during which they lose their hair in sheets over a period of only one to two months. During this catastrophic molt, their ability to retain heat is greatly reduced. Thus, when they are molting, harbor seals will spend considerably less time in the relatively cold water and considerably more time hauled-out on land.
  • The seals who live at Casa Beach experience their annual “catastrophic molt” between late April and the first week in June each year. This is why both the number of seals hauled-out, as well as the duration of time hauled-out, increases dramatically during this time period.


  • Harbor seals are mammals — females bear a single pup which they care for alone.
  • Mating occurs under water.
  • The gestation period is 9 months.
  • Adult females typically give birth to one pup each year.
  • At the Casa Beach rookery, the official pupping season begins each December 15 and ends 5 months later on May 15.
  • Seal pups have been born every year at Casa Beach since the mid-1990’s.
  • At La Jolla’s latitude, pups are born in February and early March.
  • Each year, about 40 seal pups are born at the Casa Beach rookery.
  • Most pups are born on land.
  • Pup mortality is high: up to 50%.
  • The average weight of a newborn pup is 20 – 25 pounds.
  • Pups are well-developed when born and can swim and dive within hours.
  • Mothers typically nurse their pups for 4 to 6 weeks.
  • In their early weeks of life, a mother harbor seal may carry her pup on her back while swimming and diving.
  • The average lifespan of a harbor seal is 20 – 25 years.
  • Harbor seals are opportunistic feeders who tend to hunt for fish, cephalopods, and other invertebrates during high tide.
  • Harbor seals do not drink water; they metabolize water from their food.
  • Seals can rest underwater. Their lungs collapse when they dive, their heart rate slows dramatically, and blood flow to some organs is restricted. In this way their bodies conserve oxygen and prevent the “bends.”
  • Harbor seals are most vulnerable when out of the water and will quickly return to the ocean if a threat is perceived.
  • Harbor seals can be seen year round at Casa Beach and Seal Rock at the foot of Jenner St. and Coast Blvd. in La Jolla.  You are most likely to see the greatest number of seals between April 24 and June 6.  You are least likely to see any seals on the beach between 8am and 6pm during the months of July, August, and September.
  • It is very rare for harbor seals to choose a haul out site so close to humans, making the rookery at Casa Beach a rare natural treasure, indeed.