Harbor seal, Phoca vitualina richardii, population trends in the San Francisco Bay Estuary, 1970-2002.
Grigg EK, Allen SG, Green DE, Markowitz H. 2004. Harbor seal, Phoca vitualina richardii, population trends in the San Francisco Bay Estuary, 1970-2002.. California Fish and Game. 90(2):51-70
Pacific harbor seals, Phoca vitulina richardii, have used the San Francisco Bay estuary in California as a nursery area and foraging site for thousands of years. Like other pinniped species, harbor seals in California were intensively hunted in the late 1800's and early 1900's, resulting in population declines obvious in the San Francisco Bay (SFB) by the 1920's. In 1972, the Marine Mammal Protection Act was passed, providing protection and management of harbor seal populations. We examined historical data (1970-1997) and our own ground counts at three primary SFB haulout sites (1998-2002) in order to understand the degree of recovery of the SFB harbor seal population. One of the largest estuaries on the west coast of the United States, SFB today is highly urbanized and heavily impacted by human activity. We documented a mixed response and recovery of harbor seals in SFB, likely due to a combination of factors, including habitat alteration, disturbance, pollution, and survey techniques. From 1970-2002, seal numbers at all three sites increased slightly during the fall/winter season, and increased at two sites during the pupping/molting season. At the largest SFB rookery site, however, no change was seen in seal numbers during the pupping molting season.
- Type
- Journal Article
- Authors
- Grigg, Emma; Allen, Sarah; Green, Deborah; Markowitz, Hal
- Units
- SFAN
- Keywords
- Phoca vitulina richardii, San Francisco Bay