Protecting Harbor Seals in San Francisco Bay

Pacific Harbor Seal Haul Out Sites in San Francisco Bay
A map showing Pacific harbor seal haul out sites in San Francisco Bay. Pupping may occur at any of these sites, though some locations may support only a few pups. Primary pupping sites are highlighted in red.

There is nothing cuter than a Pacific harbor seal pup.

And as it turns out, these adorable marine mammals can be heard crying “maaaa” right in our own backyard. From March to June, Pacific harbor seals pup at multiple sites along the shores of San Francisco Bay. But our lovable flippered neighbors are also highly sensitive to our presence in the Bay, and human activities both in the water and on land can have negative consequences for pupping seals.

According to National Park Service scientist Dr. Sarah Allen, Castro Rocks, Mowry Slough, and Newark Slough serve as the primary pupping sites in the Bay. Pupping in smaller numbers is also observed at other haul out locations, which include Redwood City’s Bair Island, home to an ambitious wetland restoration effort. (Click on the image above to see a map of harbor seal haul out and pupping sites in the Bay.) Mudflats, rocky intertidal zones, pocket sandy beaches, islands, and wetlands are some of the habitats used for pupping. Dr. Allen tells Save The Bay that if sufficiently deep water is located nearby and human disturbance is absent, future restored wetlands may become new pupping sites as well.

Just as we have the power to improve the condition of Bay wetlands for seals, human activity can also reduce the quality of pupping habitat. As Dr. Allen explained to Bay Nature in 2011, development can cause pupping site abandonment and contributes to the lower number of pups in the Bay compared to other coastal sites. The Marine Mammal Center, which cares for abandoned Pacific harbor seal pups, also notes that “harbor seal colonies in the Bay Area are vulnerable to human disturbance, climate change and human-produced pollutants.” The Center warns that seal moms may be frightened by humans, prompting them to desert pups or pupping sites.

According to the Marine Mammal Protection Act guidelines, a buffer equal to the length of one football field should be maintained to avoid disrupting these shy creatures. The National Park Service also advises that paddlers and people on land avoid alerting seals of their presence, move away if any behavioral disruption is observed, and refrain from trying to rescue seals. If a distressed seal is detected, contact the Marine Mammal Center at 415-289-SEAL.

In addition, we need to ensure that harbor seals and other Bay wildlife are not harmed by shoreline development. Of particular concern today is a proposed development in the South Bay city of Newark that would pave over wetlands and hundreds of acres of historic baylands in order to build an 18-hole golf course and nearly 500 houses. The shoreline area targeted for development, referred to as “Area 4,” is located directly adjacent to Mowry Slough. Pollutants originating from this development, such as pesticides from the proposed golf course, could negatively impact downstream water quality, threatening wildlife.

Harbor seals’ sensitivity to disturbance, coupled with ongoing attempts to develop the Bay shoreline, underscores the importance of supporting Bay restoration and continuing the fight to preserve wildlife habitat. Learn more about Save The Bay’s wetland restoration programs, pollution prevention efforts, and opposition to the fill of Newark’s baylands.