Castro Rocks are located directly next to the
Richmond-San Rafael Bridge, ranging from 50 ft to more than 240 ft from
the bridge itself. The rocks are available to the seals during most
mid to low tides. The largest rock is approximately fifty feet
in diameter, and the rocks span approximately 825 ft in a southwesterly direction.
Castro Rocks are of particular importance to the ecosystem of San Francisco
Bay because of their use as a haul out and breeding site by Bay harbor seals
-- Castro Rocks is the largest rookery site in the north San Francisco Bay,
and the second largest in the entire Bay. The retrofitting of the Richmond-San
Rafael Bridge was underway from 2001-2005. Biologists from San Francisco
State collected data on the seals throughout the retrofit project, in order
to assess seal responses to construction work, and to recommend ways to minimize
disturbance to this important seal colony.
Two SFSU field biologists observe the harbor seals
from the observation platform, located roughly 30 meters above the seal haul
out. Biologists get a bird's eye view of the seals using a spotting
scope and 10X50 field binoculars. In addition to disturbance studies
of the seals, data collected during this study will provide additional information
on population size, haul out patterns, movement patterns, pup production and
more.
Caltrans has worked with NMFS and marine mammal
researchers in the design of a construction schedule that will minimize disturbance
of the seals during the pupping and molting seasons. During the pupping
season, mothers with pups may abandon their young if subjected to heavy human
disturbance. During the molt (when seals shed their old coats to make
way for new ones), seals must spend more time on the haul out in order to
adequately maintain their internal body temperature. During these two periods,
which combined extend from mid-February through late August, construction
work will only be done in areas away from the seal haul outs; during other
times of the year (when the haul outs tend to be used by fewer seals, and
young pups are not present), construction will be done on the sections of
the bridge nearest Castro Rocks. In this way, disturbance of the seals
may be minimized while still allowing construction on the bridge to continue
in a timely manner.
If you've driven across the Richmond Bridge lately,
you may have noticed the white buoys which mark the boat exclusion zone, designed
to keep boats and other watercraft at a safe distance from the seals.
Harbor seals are the only marine mammals resident
in the Bay year round, and are an important and attractive part of the Bay
wildlife community. Please do your part to keep the seals in S.F. Bay!
Boats, jet skis and kayaks should be kept a minimum of 100 yards (roughly
the length of a football field) from the haul out area, to avoid disturbing
the seals (a violation of the Marine Mammal Protection Act).
Please note that stopping/parking unauthorized vehicles on the Richmond-San
Rafael Bridge is not permitted.
For more on harbor seals at Castro Rocks, see the Project Summary Page with references.
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