By Diana Dunn
Deep greens envelop hillsides and wildflowers splash vibrant colors across the blooming Bay Area landscape. The revitalizing powers of spring are not limited to dry land, however. Dramatic transformations are occurring in our local marine environment as well; just consider the harbor seals. March is a hectic month for these captivating pinnipeds. It marks the beginning of pupping season in the Bay Area, which is when female harbor seals give birth.
Body Structure and Locomotion
Harbor seals are often confused with their thunderous cousin, the sea lion. One distinguishing characteristic between these two marine mammals is that harbor seals lack ear flaps, making them truly part of the seal family. Underwater, harbor seals are sleek and agile. Their fusiform bodies are tapered at both ends, and they utilize their front flippers for steering and their hind flippers for propulsion. On land, however, harbor seals become awkward bananas. They move like caterpillars and, unlike sea lions, do not have the ability to rotate their hind flippers.
Most harbor seal coats are spotted, varying in color from grey, to brown, to black. Oddly, harbor seals that inhabit the San Francisco Bay have a reddish tint to their coat. This red coloration is thought to be caused by a buildup of trace elements in the water, the most common of which is iron.
Range and Habitat
Unlike some other marine mammals, harbor seals have a considerably sedentary lifestyle. Traditionally, the seals in the San Francisco Bay watershed are non-migratory and spend their whole lives along the same expanse of coastline. Harbor seals can be found as far north as Alaska on the Pribilof Islands and as far south as Baja, Mexico. These special creatures enjoy sandy beach, bay, mudflat and estuary habitats.
Harbor seals are not picky eaters. They are considered opportunistic feeders because they’ll prey on a variety of aquatic species, including crustaceans, squid, herring, salmon, rockfish, flounder and mollusks.
Mating and Lifespan
Even though Harbor Seals return to the same breeding grounds annually, they do not form breeding colonies. Breeding season starts in the spring, typically six weeks after female seals give birth to their pups, and continues into the summer months in California. The gestational period of female harbor seals lasts for nine to eleven months. Weighing up to 30 pounds, harbor seal pups are already able to swim at birth. They have the capacity to live to 25 to 30 years of age, and males typically have a shorter life expectancy than females.
The Marine Mammal Protection Act that was passed in 1972 has enabled harbor seal populations along the California coast to recover from prior hunting and harassment by humans. Current records estimate that the harbor seal populations from the Pribilof Islands to Baja is in the range of 120,000 – 150,000 individuals.
Photo credits (top to bottom): NOAA, Abe Kleinfeld, Paul Chinn.