Pupping season for harbor seals in San Francisco Bay spans approximately March 15th through May 31st, with pup numbers generally peaking in late April or May.  There are two major harbor seal pupping sites in San Francisco Bay:  Mowry Slough, in the south bay, and Castro Rocks, in the north bay.  Pups are also seen in small numbers at Yerba Buena Island, in the central bay, and Corte Madera Marsh, in the north bay, although births have not been witnessed at these sites.

Maximum number of pups hauled out at Castro Rocks has ranged from 9 in 1998 (based only on one month of data collection:  May 1998) to 21 in 1999 and 27 in 2000.  The estimated total numbers of mother/pup pairs using Castro Rocks is higher, according to A. Bohorquez, a graduate student at SFSU and field biologist for the Richmond Bridge Harbor Seal Survey.  Based on photographs of mother/pup pairs, Borhorquez estimates that 35 mother/pup pairs used Castro Rocks in 1999, and 40 in 2000 (Bohorquez, pers. comm.).
 
 

Numbers of mother/pup pairs at Mowry Slough are higher; a maximum of 78 pups were onsite in 1999, and 90 in 2000.  Not enough surveys were conducted at Mowry during pupping 1998 to provide pup numbers for that year.  This project recorded 6 pups at Yerba Buena Island in 1998, 7 in 1999, and 8 in 2000.

Pupping season is a particularly sensitive time for harbor seals in San Francisco Bay.  Harbor seal mothers nurse their pups for approximately 28 days, and in that time pups must gain enough weight to carry them through the following month or so while they learn to catch food effectively on their own.   Pups separated from their mothers during the early stages of nursing (due to disturbance, etc.) may not be able to reunite with their mother, and young pups will almost certainly die without their mother's care.  It is therefore very important to minimize disturbance to harbor seals during the pupping season; Mowry Slough is closed to watercraft during the pupping season, and seismic retrofit work on the bridge piers closest to the Castro Rocks haul out site is not permitted during pupping season.
 
 
 

One note of caution regarding pups who appear to be alone:  harbor seal mothers will periodically leave their pups alone on the haul out while they forage for food, returning to the same area later on to reunite with their pup. If you see a harbor seal pup that appears to be alone and abandoned, please DO NOT approach or interfere with the animal in any way.  Mothers will often wait offshore until humans have left the area before returning to their pup, and may abandon the pup if harassed to a sufficient degree.  Seal pups that are "rescued" by well-meaning individuals sometimes die due to starvation or overheating, because their would-be rescuers are not trained in marine mammal care.  Other pups end up in a rehabilitation center unnecessarily.  According to the Marine Mammal Center in Sausalito, CA, a seal pup's best chance for survival is to remain with its mother, as the seal mother's milk contains important antibodies that no substitute formula can provide.
 
 
 

In the event that you see a seal that appears to be in trouble, immediately contact your local marine mammal rehabilitation center, who will send out trained staff to help the animal whenever possible or necessary. If you are in California, the following numbers may be helpful.  For the San Francisco Bay Area (including from San Luis Obispo to Mendocino), contact The Marine Mammal Center in Sausalito, at 415-289-SEAL.  For San Diego County, contact Sea World, at 800/541-7325.  In Orange County, Friends of the Sea Lion at 714/494-3050.  In Los Angeles County, call the Marine Mammal Care Center at 310/548-5677.  In Santa Barbara and Ventura Counties, Santa Barbara Marine Mammal Center at 805/687-3255.
 
 
 
 
 

There are things that we can all do to help protect and preserve the harbor seals that are found in S.F. Bay.  Harbor seals, unlike the male California sea lions seen at Pier 39 in San Francisco, are highly sensitive to disturbance by humans (noise, etc.).  If you use a boat in the Bay for fishing, sightseeing, etc., give the seals some room whenever you are near a haul out site such as Castro Rocks or Yerba Buena Island.  The minimum distance recommended by NMFS is 100 yards (a football field length); seals are more sensitive to disturbances within this 100 yard "comfort zone".  In addition, boats that travel parallel to the haul-out site, with a constant speed and heading, tend to cause fewer disturbances to the seals; avoid stopping near the haul out site, or approaching the haul out site directly.  Seals are particularly sensitive to jet skis and kayaks, which tend to approach haul out areas more closely than larger vessels.  Despite being quiet and relatively environmentally friendly, kayaks are one of the most common causes of seal 'flushes'. A 'flush' in harbor seals occurs when seals are disturbed to the point where they move rapidly off the haul out into the water.

The same minimum 100 yard "comfort zone" applies to pedestrians.  Distance is the key; please observe seals from a distance, using binoculars or a spotting scope.  If we observe these guidelines, seals will continue to be a part of the Bay community.  Harbor seals that are flushed off the haul out site by disturbance may not rehaul onto land during that tidal cycle; as seals need these resting times on land to "recharge their batteries" (so to speak), loss of time on the haul out site can be detrimental to their well-being.  With the limited number of haul out sites remaining for harbor seals in San Francisco Bay (as in other areas), protecting these sites is an important part of protecting harbor seal populations.  Harassment of marine mammals (such as causing seals to 'flush') is a violation of the Marine Mammal Protection Act of 1972, and is punishable by fines.
 
 

Good areas for viewing harbor seals in and around San Francisco Bay include Point Bonita (at low tide) and Alviso Slough, in the south bay.  Point Bonita is located in the Marin Headlands, and can be reached via an easy, paved walk from the trailhead parking lot.  Harbor seals at Point Bonita can be easily and safely viewed from the paved public trail above the haul-out site, located east of the light house.  Please DO NOT attempt to climb down the cliff to the beach to view the seals, as this will put you well within the seals' 100 yard "comfort zone". Alviso Slough requires more of a hike, but can be a great walk for anyone interested in wetlands, shorebirds and harbor seals:  the harbor seal site at Alviso can be observed from a trail that leaves from the Alviso Marina (the distance from the parking lot to the observation site is 3.3 miles; there are toilets, drinking water, parking and trailmaps at the Marina).  The trail heads along Alviso Slough for its entire length; the seal haul out site is located at the junction of Alviso Slough and Coyote Creek (N. Bell, pers. comm.).