Harbor Seals

 

Harbor Seal Pup

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.

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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.

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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.

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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.

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Harbor Seals Are 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.

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How You Can Help

If you see a lone pup, do not touch, move or otherwise disturb it. It is extremely difficult to reunite a mother and her pup after the pup has been moved, and very difficult to raise a pup in captivity.

Please take care NOT to make your presence known—either visually or audibly—when you come across an individual or a group of harbor seals when you are on land or on the water. Seals may flee into the water immediately when they hear or see a human. This flight disrupts their resting, can cause mother-pup separations and may endanger their health. If you see the seals raise their heads in a startle response, immediately back away so that they do not feel threatened.

Maintain a minimum distance of 90 m (300 feet) from any marine mammal in the water or on the shore to prevent a disturbance.

Harbor Seal Pupping Season Closures

Avoid areas closed to visitors during the pupping season, from March 1 through June 30. Drakes Estero and the mouth to Drakes Estero are closed to boating, canoeing, and kayaking. Double Point and the western end of Limantour Spit are closed to all visitor access. Tomales Point is a harbor seal pupping area, but is not closed. Please use care not to disturb the animals at these places and keep a distance of 90 m (300 feet) away. Download the maps below indicating closed areas or ask for one at a visitor center.

Harbor Seal Pupping Season Closures Maps

• Map of Estero closures (2,952 KB PDF)
• Map of Hog Island closure (98 KB PDF)
• Map of Limantour Spit closure (148 KB PDF)

Reporting sick, injured, or abandoned marine mammals

If you see a harbor seal (adult or pup) that you think is in distress, do not touch or approach it. Contact a park ranger and give the exact location and a description of the animal, making note of its behavior, color, size (length and girth), and any particular markings or tags.

Contact the nearest National Seashore ranger first:

• Bear Valley Visitor Center - 415-464-5100
• Lighthouse Visitor Center - 415-669-1534
• Ken Patrick Visitor Center - 415-669-1250

If there is no answer at National Seashore numbers, call the Marine Mammal Center at 415-289-7325

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Volunteer

Become a Harbor Seal Monitoring Docent at Point Reyes National Seashore. Volunteers monitor the population of harbor seals in spring and summer. The data that they gather help scientists follow trends in the population, assess their health, identify disturbances to the harbor seals and protect, and preserve this valuable resource.

Learn More

Check out the San Francisco Bay Area Inventory & Monitoring Network's Harbor Seal Seasonal Monitoring Updates to learn the latest news.

Even more information can be found on Pacific Coast Science and Learning Center's Harbor Seals web pages.

Protecting Marine Mammals

The Marine Mammal Protection Act of 1972 provides federal protection not only to harbor seals, but also to northern elephant seals, California and Steller sea lions, whales, porpoises, sea otters and other marine mammals. This law prohibits killing or harassing these shy creatures in any manner.

Any human action that causes a change in the behavior of a marine mammal is considered harassment.

Multimedia

From 2007 to 2012, Pacific Coast Science and Learning Center Science Communication Interns produced a series of podcasts exploring science from Bay Area national parks. One of these The Natural Laboratory podcasts is focused on harbor seals. Listen to the podcast below. Visit our Multimedia Presentations: The Natural Laboratory Audio Podcasts page for additional podcasts.

 

• The Natural Laboratory Podcast: What’s in a Seal?

  
  

  A The Natural Laboratory podcast produced by the Pacific Coast Science and Learning Center in 2009 in which John Cannon interviews three marine biologists about the effects of agricultural and industrial contaminants on harbor seals, and how what we learn from these studies can be extrapolated to the contaminants' impact on humans.

  Credit / Author:

  John Cannon / Pacific Coast Science and Learning Center

  Date created:

  07/17/2009

  Audio Transcript

  The Natural Laboratory Podcast Transcript: What’s in a Seal?

  [Intro music]

  John Cannon: This is The Natural Laboratory, a podcast exploring science for San Francisco Bay Area national parks. I'm John Cannon.

  The round, mottled bodies and whiskered snouts of harbor seals are a common sight on beaches around Point Reyes and San Francisco Bay. As a species, they've done fairly well in most places, managing to adapt to living in undisturbed areas near humans. But a hazard lurks beneath the surface, a danger that's far more sinister than even the great white sharks that patrol these waters.

  Runoff from agriculture and industry, chemicals from streets and sewers, and bacteria and pathogens have found their way into the water and the food chain as a result of how we humans use our environment. In the long run, these contaminants have the potential to do a lot of damage to harbor seals and to other species, like us.

  Infiltrating the miniscule droplets of oil found in single-celled marine plants called phytoplankton, these particles work their way up the food ladder, first through the organisms that graze on phytoplankton, then to the carnivores. Each step along the way creates high contaminant concentrations.

  And studies have shown that these industrial chemicals can cause problems with immune function and the reproductive system in seals and humans. By the time a harbor seal gets a hold of a rockfish or a crab, those chemicals have accumulated in the prey animal's fat, sometimes to a dangerous level. Harbor seals, with their thick ribbon of blubber, serve as a repository for these contaminants.

  But if seals are eating crabs and rockfish and other things in San Francisco Bay that are dangerous to them, what about us? We humans eat a lot of the same foods. In a way, we are predator of fish and crabs. So, that describes our position on the food chain or, in scientist's terminology, our trophic level.

  [Interview with Denise Gregg] Denise Gregg So, on some levels, the harbor seal, as an animal that eats at the same trophic level as a human, might be able to tell us about some of these environmental impacts on us as well.

  JC: That's Denise Gregg. She's a marine biologist at the Marine Mammal Center in Sausalito, California. She's studying the effects of contaminants on harbor seals. Armed with this research, scientists might be able to someday better understand how those chemicals in the water affect not only sea life, but also us.

  DG: You know, the study is to look at animals in San Francisco Bay during their first year, 'cause that's when survival is toughest for these animals. So, it's our best chance to make any kind of correlation between something that's impacting them and their ability to survive it.

  JC: These chemicals are stored in the seals fat cells. Most of their fat ends up in blubber surrounding the seal's body, just below the skin. Blubber doesn't have many nerve endings, so rotund seals make excellent research subjects because scientists can easily take small samples for contaminant analysis without causing too much trouble for the animal.

  Gregg also study seals in Tomales Bay at Point Reyes National Seashore that haven't been exposed to such high levels of contaminants. Here, every spring, mother seals give birth to hundreds of pups. Gregg predicts that the Tomales Bay seals will show lower contaminant levels than those in San Francisco Bay. She will compare here findings at the two sites to see if differences in seal health exist.

  To learn more about the seals in Tomales Bay, Gregg and a team of researchers from all over North America round up young seals that have just been weaned. On a foggy morning, Jim Harvey, a scientist at Moss Landing Marine Laboratories, gives instructions to the biologists, veterinarians, and volunteers who have come to lend a hand. He explains the process: two boats approach the beach where the seals haul out. A crew member on one of the boats throws a buoy attached to a long net toward the shore. That boat then sweeps back away from the beach, stretching the net as it goes.

  Jim Harvey: The net boat then does an arc in front of the haul-out site.

  JC: The net has small floats on top and weights on the bottom to help it stink to the seafloor.

  JH: So [unintelligible] 15 feet or so deep, um, so it gets set around, presumably creating a curtain around the seals.

  JC: The wetsuit-clad crew jumps into the water at the prescribed time to secure the net. Small sub-teams of scientists and volunteers weigh each seal in a sling suspended from a tripod on the sand. The seal gets a mild sedative, making the process a little less stressful. Then, blood and blubber samples are taken using an anesthetic medication to numb the area, similar to having a mole removed.

  Erin Flynn: They’re doing the work-up right now. The most recent thing they did was they took...um...a hair sample from near the fin area so they can use that to test for certain types of contaminants.

  JC: That's Erin Flynn. She’s an AmeriCorps volunteer with the National Park Service. She spends most of her time observing seals from the cliffs above popular haul-outs. Greg and other scientists use the data she gathers to determine the best time to capture the weaned seals, tag them, and collect samples.

  EF: You do it too early, you disrupt the moms and the pups, which is a really critical time for the seals. But if you do it too late, all the weaned pups go off to exotic places, like Monterey Bay.

  JC: Once the teams have all the information they need to take back to the lab, they release the seal. It can be a little unsettling for the seal, like being poked and prodded at the doctor’s office. But, in the long run, the data the team gathers could provide valuable tools to understand how things we do every day--such as driving our cars--affect our environment.

  So far, Gregg is finding what she'd expected: the harbor seals in Tomales Bay carry lower contaminant levels in their bodies than the harbor seals near San Francisco. Her larger study on human-induced effects on seal is still ongoing, however, so she doesn't have her final results yet. Where the lives of humans and seals intersect is certainly a fascinating part of the research for Gregg but equally as captivating are the lives of these commonly seen but still mysterious animals in Tomales Bay.

  DG: The Tomales site is interesting as a control site for many of the contaminant tests, but it's also an area where we know very little about the harbor seals. So, it's really exciting to have a chance to work out here in the park. But we don't know where they go after they’re born. We basically don't know very much about them at all. So, they're interesting in their own right.

  And the more we know about the animals we share our planet with, the better we can take care of all the creatures that call it home.

  Gordon Shetler was our on-scene reporter for this podcast.

  For the Pacific Coast Science and Learning Center in Point Reyes National Seashore, I'm John Cannon.

  [Exit music]

 

Photo Gallery

 

 

 

Science & Research Project Summaries

From 2006 to 2018, Point Reyes National Seashore and Pacific Coast Science and Learning Center (PCSLC) staff and communication interns assisted scientists conducting research through the PCSLC and the San Francisco Bay Area Inventory & Monitoring Network to produce a series of Resource Project Summaries, five of which were about harbor seals. These one- to two-page summaries provide information about the questions that the researchers hoped to answer, details about the project and methods, and the results of the research projects in a way that is easy to understand.

• Harbor Seal Monitoring at Golden Gate National Recreation Area and Point Reyes National Seashore, by Jessica Weinburg McClosky, National Park Service, May 2014.
• Harbor Seal Monitoring at Point Reyes National Seashore and Golden Gate National Recreation Area, by San Francisco Bay Area Network Inventory and Monitoring Program, August 2010 (726 KB PDF)
• Harbor Seal Monitoring at Point Reyes National Seashore and Golden Gate National Recreation Area, National Park Service, May 2007 (158 KB PDF)
• Harbor Seals and Northern Elephant Seals: Indicators of Marine Ecosystem Condition, National Park Service, October 2006 (169 KB PDF)
• Mercury Concentrations in Harbor Seals, by Tiffini J. Brookens, Moss Landing Marine Laboratories, April 2006 (103 KB PDF)

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