To view this page ensure that Adobe Flash Player version 11.1.0 or greater is installed.

WILDLIFE CONTEXT Bay Area residents sometimes glimpse harbor seals, with their spotted, pudgy bodies and soulful eyes, lounging on the rocks near the Richmond-San Rafael Bridge, at Alameda Point, the Richardson Bay shoreline, or Sausalito. Harbor seals sit at the top of the food web within the Estuary and along the nearshore outer coast, preying on many differ- ent fishes, octopuses, squid, and crustaceans. They rest, molt, and nurse their pups on land at traditional haul-out sites but forage at sea, often close to their haul-out sites. Harbor seals are the only year-round, resident marine mam- mal in the Estuary. As opportunistic predators of seasonally abundant fish and invertebrates, harbor seals respond quickly to changes in regional environmental conditions. During El Niño years when many prey species moved away from warmer than usual waters, the STATUS & TRENDS There is no clear trend to the data between 1998 and 2014. Adult harbor seal numbers decreased in 2011, but pup numbers were not as depressed. Anal- ysis suggests the status of the harbor seal pop- ulation is fair: there has not been a substantial drop in numbers. While harbor seal numbers along the adjacent coast have improved since the Marine Mammal Protection Act passed in 1972, Estuary harbor seal numbers have not. THREATS & CHALLENGES Seals are vulnerable to disturbances from boats, habitat loss, human-related pollutants (oil, mercury, pesticides, and other contaminants), and prey availability, as well as the cumulative effects of 300 200 100 0 Poor HARBOR SEALS 400 BAY 2014 2012 2010 2008 2006 2004 2002 2000 1998 cator provides an index of harbor seal abundance. Pro- tocols for monitoring harbor seals are well established and have been implemented in the Estuary since 1998 at two prime locations for breeding harbor Photo: Bob Wick, BLM seals: Yerba Buena Island and Castro Rocks. Harbor seal abun- dance, excluding pups, was used to gauge the health of the Estu- ary, based on a series of timed counts of harbor seals during the breeding season. The benchmark is based on the mean — 328 seals — of the annual maximum number of seals counted at the two locations from 2000-2010. 500 Fair INDICATOR This indi- HARBOR SEALS Good number of total seals surveyed at colony sites in central California declined. 45 HARBOR SEALS B AY . . S TAT U S . . Fair . . . .T R E N D . . . . No change .....BENCHMARK..... Derived from historical average 2000-2010 all of these threats. Seals in the Bay also re- spond to the ecological condition of the coastal ocean, and its biological diversity (see also The Ocean Connection p. 61). Unusual warm ocean conditions, such as the El Niño conditions of 2015, are often associated with a breakdown in food webs, with less prey such as anchovies — prey for seals — in nearshore coastal waters. But since resident seals within the Estuary for- age more on resident prey species, El Niño may have less of an impact on them. The intensity and frequency of El Niño events is predicted to increase in the future in response to changes in climate, and seal monitoring could provide opportunities to react to these new types of events as they unfold.