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  • Pacific Harbor Seals

    Helping Marine Mammals

    The Marine Mammal Center, located in the Marine Headlands, offers programs, tours, exhibits, and public viewing areas where visitors can learn more about their marine mammal patients.

Pacific harbor seal


Harbor Seal, by Mike Baird

Pacific Harbor Seal, by Mike Baird, www.flickr.bairdphotos.com

Pacific harbor seal

Pacific harbor seals (Phoca vitulina) are the only marine mammal resident in San Francisco Bay year-round. (The California sea lion uses the Bay seasonally for foraging, and some individuals use the floating docks at Pier 39 as a haul-out site). Harbor seals have spotted fur that varies in color. Males and females are about the same size, reaching a maximum of 300 pounds (140 kg). They are true or crawling seals, having no external ear flaps. True seals have small flippers and must move on land by flopping along on their bellies. In San Francisco Bay, many harbor seals are fully or partially reddish in color. This may be caused by an accumulation of trace elements such as iron or selenium in the ocean or a change in the hair follicle.

Harbor seals pup March – May and molt June – July. A pup can swim at birth and will sometimes ride on its mother’s back when tired. Adult females usually mate and give birth every year. They may live 25 to 30 years.

Harbor seals tend to congregate on the same terrestrial sites, called “haul-out sites” year after year. Their numbers are highest during the pupping (March – May) and molting (June-July) seasons. Haul-out sites are usually located where there is ease of access to water, proximity to food, and minimal disturbance. Some haul-outs are used year-round, while some are used seasonally. Some sites may be particularly important to seals during pupping and molting as these areas provide shelter from storms. Studies show disturbance by humans has been shown to cause declines in numbers of seals using sites and if sufficiently disruptive, disturbance may cause seals to abandon traditional haul-out sites, and may affect reproductive activities during pupping season.

Disturbance to haul-out sites is often cited as one potential reason for the lack of overall population increase in San Francisco Bay, in contrast with increases seen on the outer coast. Disturbances from kayaks and canoes are comparable to or even greater than those observed for powered vessels. Motorboats tend to maintain constant speed and heading, whereas paddle boats tend to move closer to the shore, approach directly, and change speed and direction frequently. The image of a boat that is slow, quiet, and low to the water may appear more like a predator than other watercraft.

Harbor Seal, by Mike Baird

Pacific Harbor Seal, by Mike Baird, www.flickr.bairdphotos.com

Harbor seals are federally protected under the Marine Mammal Protection Act. The Marine Mammal Protection Act prohibits take, which is harassing, hunting, etc. of a marine mammal. Harassment is any act of pursuit, torment, or annoyance which has potential to injure a marine mammal in the wild, or potential to disturb by causing disruption of behavioral patterns, including migration, breathing, nursing, breeding, feeding or sheltering.

The following guidelines will help you protect Pacific harbor seals from disturbance:

  • Maintain minimum distance of 328 feet (100 meters) from haul-out at all times and at least 492 feet (150 meters) from March – July.
  • Maintain constant heading and speed while passing haul-out, avoid sudden stop or sudden changes in heading or speed, avoid paddling directly at resting seals.
  • If seals show signs of disturbance such as all seals are watching your group or seals begin to approach water, move farther from haul-out.

In the event that you do see an injured marine mammal (information from The Marine Mammal Center):

  • Do not touch, pick up, or feed the animal.
  • Observe the animal from a distance and keep people and dogs away.
  • Note physical characteristics such as size, presence of external ears, and fur color.
  • Note the animal’s condition.
  • Look for obvious identification tags or markings.
  • Determine the animal’s exact location for accurate reporting.
  • Call The Marine Mammal Center with as much information as you have.

To Report a Stranded Marine Mammal:
(415) 289-7325 or (415) 289-SEAL

Sources/Further Reading

San Francisco Bay Area Water Trail Final Environmental Impact Report

Marine Mammal Center