Harbor Seals Adapt to New Home Float

Richard Bangert  Two harbor seals sleep on the new float provided by the Water Emergency Transportation Authority. The metal grab hooks on the float were installed so that the fabricator could lower the float into the water. Once the float is anchored at its permanent location, the hooks will be removed and the voids grouted, although the seals like using them as pillows. One side of the float has a ramp for easy access.

Harbor Seals Adapt to New Home Float


A new cement float for harbor seals was delivered to Alameda Point on June 22. It is the first-of-its-kind on the West Coast. With seals starting to use the new platform, a milestone has been reached culminating two-and-a-half years of citizen advocacy to maintain a resting site for harbor seals at Alameda Point. A ferry maintenance facility is slated to begin construction this summer where the seals have been finding solitude for more than a decade. The new float will be anchored 100 yards from the facility.

In an effort to acclimate the seals to their new float and surroundings, the float is being moved in stages to its permanent location. It will be anchored a hundred yards offshore from the Bay Trail near the soccer field on West Hornet Avenue.

The old wooden dock that the seals had been using for a decade was demolished on July 11 in order to prompt the seals to start using the new float. On July 28, the float underwent its first move, followed by a second move last Tuesday, Aug. 9. Two more moves are scheduled in the next four weeks.

The number of seals in the harbor in mid-summer is typically in the single digits, with seal monitors recording a high of seven in recent weeks. During the winter, two dozen or more seals have regularly made use of the old wooden dock. The new cement float appears small, but it can comfortably hold up to 30 seals. 

The design and location of the new harbor seal float was selected with the assistance of marine mammal expert Dr. Jim Harvey, director of the Moss Landing Marine Laboratories. Dr. Harvey recommended a location near the old wooden dock in order to stay within the seals’ known comfort zone. He said that ferries moving about nearby would not alarm the seals. Kayaks and canoes approaching too closely, on the other hand, will arouse the seals.

During the winter months at Alameda Point, it was not uncommon to see two dozen seals hauled out on the old wooden dock and some odd planks tied to the dock pilings. The inner harbor at Alameda Point is the only harbor seal haul-out site in the East Bay between Yerba Buena Island and Fremont. The sheltered harbor with good food foraging makes the area ideal for seals. 

The floating structure provides a benefit beyond that of traditional land-based resting areas — it is available for use throughout the tide cycle. Harbor seals need to come out of the water periodically to warm up and also to shed their coat, called molting. Unlike their marine mammal cousins, sea lions, harbor seals become worried when people get too close. Repeatedly rousting seals from a resting site could lead to abandonment of the area. It is a violation of the federal Marine Mammal Protection Act to harass or disturb resting harbor seals. Fines can be in the 10s of thousands of dollars.

The new float is 20 feet by 25 feet. One side is sloped to make it easier for the seals to haul out. The float is made of reinforced concrete. Styrofoam enclosed within the concrete keeps the platform afloat. This custom-designed structure was built by Kie Con Inc. in Antioch, based on a patent held by International Marine Flotation Systems of Vancouver, British Columbia, at a cost to WETA of $68,000. 

Local harbor seal advocates have established a Facebook page called Alameda Point Harbor Seal Monitors. Community members interested in contributing their observations of the harbor seals are invited to contact the group at alamedaharborseals@gmail.com. The agency that issued the permit, the San Francisco Bay Conservation and Development Commission, is interested in knowing whether the float is being used for its intended purpose. They will rely on citizen science. More than a year of data has already been recorded by volunteers on the behavior of the harbor seals at Alameda Point.


Richard Bangert posts stories and photos on his blog Alameda Point Environmental Report.