San Francisco Bay Seal Project

The harbor seal (Phoca vitulina) is the last resident marine mammal species in San Francisco Bay, breeding and feeding year-round in its waters. San Francisco Bay is actually not a bay, but the largest estuary on the West Coast, an enormous pool in which the waters of the Pacific Ocean mix with the nutrient-rich fresh waters from California's Central Valley and western Sierra Nevada mountains. An area of enormous biological productivity, the Bay was once home to harbor seals, sea otters, and other marine mammals, yet fur hunting in the 1700s and 1800s decimated local populations. In this century, shoreline development has further reduced the number of animals that could survive in the area. There has been no growth in seal numbers in the Bay since the first reliable counts were made in the early 1970s, despite a steady increase in harbor seal population along the California coast after the implementation of the 1972 Marine Mammal Protection Act. In 1991, there was a severe drop in seal numbers at the primary seal pupping site in south San Francisco Bay and seal numbers have yet to fully recover in this area.

The San Francisco Bay Seal Project (Seal Project), part of Earth Island Institute's International Marine Mammal Project, combines biological research with conservation advocacy to protect the Bay's last resident marine mammal population. In 1989, the Harbor Seal Project began a comprehensive study of San Francisco Bay's resident harbor seal population. Project work included detailed observations at all primary seal haul-out sites. Specifically, the project engaged in humane sampling of seal blood to determine both levels of toxic pollutants and the seals' general health, surveyed food preferences by identifying fish bones in seal scat, and used radiotelemetry to track seal movements, identify seal feeding areas and record haul-out patterns. The results of this study form the basis for the conservation activities of the San Francisco Bay Seal Project. The Seal Project's work includes the following:

Regular ground or aerial monitoring of seal activities and numbers at all San Francisco Bay haul-out sites;
Protection of existing Bay haul-out sites from development or other human disturbance; public education on the presence of harbor seals in the Bay and their role in the estuarine ecosystem; and
Ongoing collection of data on the level and significance of environmental contaminants found in the resident seals; dissemination of this information among regulatory agencies and non-profit groups advocating a reduction in the discharge of environmental contaminants to the Bay.

Natural History of Harbor Seals

Distribution and Threats

Harbor seals are found throughout the northern hemisphere in the nearshore waters of the Atlantic and Pacific Oceans. Their need to regularly haul out on land to rest and nurse pups ties them to coastal feeding areas, which are often contaminated with industrial and municipal pollution. Studies have indicated a host of harmful effects on the health of harbor seals living in the Waden Sea, north of the Netherlands. The Wadden Sea is polluted by Rhine River discharge containing a variety of toxic contaminants, including PCBs, dioxins, and furans. The effect of toxic pollution on harbor seal health is a primary focus of the Seal Project.

Haul-Out Sites

Harbor seals use a variety of "haul-out" sites for resting or pupping. A haul-out site is a shoreline region where seals congregate, primarily to rest or to nurse their pups. Haul-out sites may be mudflats, sandflats, rocky outcroppings exposed only at low tide, or marshland covered with wetland vegetation, but they all share two key characteristics: isolation from predators or humans and easy access to water.

If left undisturbed, generation after generation of harbor seals uses the same haul-out site. The Mowry Slough area, in the extreme southern tip of San Francisco Bay, has been a pupping site for at least the last 100 years, as far back as records are available. Many other Bay haul-out areas used in the past have been lost to shoreline development.

Today there are seven primary haul-out or pupping sites along the Bay shoreline. An additional six sites are used irregularly or by fewer than 10 seals at a time.

Locomotion

Harbor seals are very graceful and swift in the water, propelling themselves forward by sweeping their powerful hind flippers back and forth in a sculling motion. At low speeds, the foreflippers steer the seal through the water; at high speeds, they are held close to the body, reducing drag. Harbor seals may dive to depths of 1,500 feet (300 meters) when foraging. They may leap completely out of the water (porpoising) or hold their upper body above the water for a better look across the waves (spy-hopping).

On land, harbor seals are quite awkward. While their flippers are the vestigial limbs of ancestral land mammals, they are of limited use outside of the water. The long bones of terrestrial mammals limbs are greatly shortened in pinnipeds and retained almost completely inside the seal's body. The harbor seal's foreflippers emerge from the body at the equivalent of the human elbow or knee, preventing the seal from lifting its body off the ground. To move on land, seals lunge their upper body forward. Sea lions, by contrast, are much more agile on land, using their longer and more flexible limbs to raise their bodies off the ground and waddle along the shore.

Harbor seals' cumbersome movements on land contribute to their extreme sensitivity to disturbance by impeding their escape from predators and humans. When humans or other threats are sighted, the seals quickly respond by flushing into the safety of the water. Hauling out in herds provides them greater protection since one individual can warn the entire group of danger.

Movements

Unlike many other pinnipeds*, harbor seals do not migrate with the seasons. Their numbers appear to increase during the spring breeding season and summer molt when seals haul out more frequently and for longer periods of time, increasing the land count. Seasonal movement between preferred haul-out sites has been observed, with protected bays and estuaries used more for pupping than are other areas. As the largest estuary on the West Coast, San Francisco Bay has the resources to support a year-round resident population which lives, feeds and pups within the Bay's waters.

Harbor seals are aptly named, given their requirement to regularly seek a "harbor" in order to haul out on land. In general, seals take advantage of the warmer daylight hours to come ashore. The relatively warm air temperatures on land allow increased blood flow to the skin, speeding healing of cuts and wounds, and nourishing hair growth during the seals' annual summer molt.

[*There are three orders of marine mammals: cetaceans (whales and dolphins), pinnipeds (from the Greek meaning "feather foot") including seals, sea lions and walruses, and sirenians (manatees and the now-extinct sea-cows). Sea otters belong to the order Carnivora.]

Feeding and Predation

Harbor seals are primarily bottom feeders, eating a variety of fish and mollusks that live near the ocean floor. Food preferences may vary among regions because they depend on what fish and invertebrates are available and the foraging preferences of the seals' competitors. The study found that the seals in San Francisco Bay feed primarily on plainfin midshipmen, yellowfin goby, white croaker, Pacific staghorn sculpin and northern anchovy.

Just as seals eat fish and squid in order to grow and raise their young, seals themselves are food to other animals. Along the California coast, great white sharks feed on harbor seals and other pinnipeds. In more northern areas, orcas rival the sharks as primary harbor seal predators.

Breeding

In San Francisco Bay and along the central California coast, harbor seals pup from mid-March through May. Females usually give birth to a single pup which they nurse for three to five weeks. Nursing is only possible when the seals are hauled out on land. Lactation ends roughly one month after birth. The month-old pup must begin to catch fish and other prey on its own, guided only by previous observations of its mother's foraging behavior. The seal pup must live off blubber reserves during this learning period. The nursing period, during which pups gain almost a pound a day, is therefore crucial. Disturbance by humans or wild predators can disrupt feeding, thereby reducing the milk intake and subsequent weight gain of the pup, ultimately threatening the pup's chances of survival after weaning.

Pups are able to swim within minutes after birth. They follow their mothers into the water when the rising tide floods haul-out sites or when the females feed. Mothers are often spotted carrying pups on their backs between foraging dives. When their mothers dive, the pups generally remain on the surface of the water.

Harbor seal mothers are not adapted to defend their offspring from land-based dangers. When threatened, they flush into the safety of the water, sometimes leaving the slower pups onshore. The females remain in the water watching the stranded pups until the danger passes. Females may also leave defenseless pups onshore during brief feeding trips to nearby waters. Humans often mistake solitary pups for abandonees because they do not understand that the mothers will return. Interference in these situations can cause more harm than good. Never approach a pup or remove it from a beach unless professionals have confirmed the pup is abandoned. If you suspect a seal is injured or abandoned in northern California, please call The Marine Mammal Center at (415) 289-7325.)

Females breed immediately after their pups are weaned. Through delayed implantation of the embryo, the fetus does not begin to develop for several months, ensuring that birth occurs during the regular pupping season. Females mature and begin to breed successfully at 4-5 years of age, males at 6-7 years. Harbor seal lifespan ranges from 20 to 30 years in the wild.

Environmental Risk Factors

Environmental Contaminants

Harmful levels of certain toxic pollutants have been found in San Francisco Bay harbor seals. Polychlorinated biphenyls (PCBs), industrial organic chemicals with a variety of uses, most notably as insulators in electrical transformers, were found at extremely high levels in San Francisco Bay harbor seals. The levels of PCBs found in the blood of resident seals actually exceed those found in the highly contaminated seal population living along the north coast of Europe. Seals from that area suffer reduced reproductive rates attributable to PCBs and related toxic organic contaminants. Recent studies have also shown the same compounds responsible for damage to the seals' immune systems. This chemical-induced suppression of the seals' ability to fight off disease and infection has been implicated in the great seal epidemic that devastated the seal population in the Wadden Sea and parts of the North Sea along the north coast of Europe in 1988, killing over 18,000 harbor seals.

The research study also examined blood concentrations of selenium and toxic heavy metals in addition to its analysis of organochlorine contaminants. Selenium and mercury were found at potentially harmful levels in San Francisco Bay harbor seals.

Insulation and Oil Spills

Harbor seal fur is not useful in insulating the harbor seal from cold ocean waters. Though the fur is thick, it lacks the soft underfur which traps an insulating layer of air next to the skin of sea otters and fur seals. Instead, harbor seals retain their body heat with a thick layer of blubber and restricted blood flow to the skin and flippers. The insulating blubber renders harbor seals less prone to hypothermia should oil coat their fur, but, like all mammals, they are susceptible to the toxic effects of ingesting oil while feeding. Pups nursing from oil-coated mothers are subject to amplified risk due to ingestion of oil on the mother's body. Seals also suffer the toxic effects of oil spills by inhaling the fumes from slicks.

Redcoats

Up to 40%of San Francisco Bay's resident seals develop red-colored fur on their head, shoulders or entire body. Many of these "redcoat" seals, often those with the deepest red color, develop abnormally short vibrissae (whiskers). Vibrissae are sensory organs used in feeding; they guide seals to food by detecting the the waves created by passing fish. In studies of captive seals, shortened vibrissae made it harder for seals to catch fish. The potential link between the redcoat phenomenon and environmental contaminants is currently under study.

SF Bay Seal Project:
What You Can Do

We must act aggressively to reduce toxic contamination of the harbor seals in San Francisco Bay. Here is what you can do to help:

Write the San Francisco Bay Regional Water Control Board. Urge them to enforce current discharge regulations, especially as related to selenium and dioxin discharges into the Bay.

Executive Officer Loretta Barsamian
S. F. Bay Regional Water Control Board
2101 Webster St., #500
Oakland, CA 94612
Write UNOCAL to urge them to change their production process to reduce discharge of selenium and dioxin into the Bay.

Roger Beach, C.E.O.
UNOCAL 76
P.O. Box 7600
Los Angeles, CA 90051
Write or call Pacific Gas & Electric to ask that they step up their replacement of electrical transformers containing PCBs.

Use the local address on your PG&E bill,
Attention Division Manager of Electrical Department
or call (800) 743-5000.
Write to California Governor Pete Wilson to oppose any weakening of laws that currently protect the Bay habitat.

Governor's Office
55 California St., Suite 2929
San Francisco, CA 94104

The Marine Mammal Protection Act provides broad-based protection for marine mammals. A key component of this protection is minimization of habitat loss due to development and toxic contamination. An important harbor seal haul-out site at Blair Island, near Redwood City, CA, is currently threatened by development.

To ask that all of Blair Island be included in S.F. Bay National Wildlife Refuge, please write to:

Michael Spear, Regional Director
U.S. Fish & Wildlife
911 NE 11th Ave.
Portland, OR 97232-4181
To oppose Redwood Shores' proposed development of Blair Island, please write to:

Mr. Don Warren
Redwood Shores Properties
1875 S. Grant St., Suite 1000
San Mateo, CA 94472

You can support the SF Bay Seal Project's research and conservation advocacy

by mailing donations, by check, to: