Using seabird long term data for monitoring the state of the San Francisco Bay Estuary Sara Acosta 1, Meredith L. Elliott 1, and Susan Euing 2 1PRBO Conservation Science/Marine Ecology Division, 3820 Cypress Drive, #11, Petaluma, CA 94954 2U. S. Fish and Wildlife Service, Alameda Point, P.O. Box 159, Alameda, CA 94501
Brandt’s Cormorants at Least Terns at Alcatraz Island Alameda Point
Photo by Sara Acosta 8 Background Aric Crabb ,Bay Area News Group 7
6 • 7 5 Colony located on the former Naval Air Station, 6 4 y = 0.1965x - 388.17 Alameda. R² = 0.21 Background 5 3 • Has been monitored by GGAS (1979-1999), PRBO 2 4 (2000-2001), and USFWS (2002-present). y = 0.0922x - 178.92 • pairs) breeding (# ln 1 3 R² = 0.701
Located in Golden Gate National Recreation Area, 1.6 pairs) breeding
• (# 0 Largest colony north of San Luis Obispo County; one of 2 ln km from San Francisco. 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 • Sandstone island severely modified by humans; has a high the most successful colonies in the state. 1 Year 0 level of human disturbance. 1975 1980 1985 1990 1995 2000 2005 Figure 1. Population trends of the Alcatraz Island Brandt’s Year • One of the few known estuarine breeding sites for Cormorant colony, 1991-2009. Population and productivity trends Figure 3. Population trends of the Alameda Point Brandt’s Cormorants (BRAC). Least Tern colony, 1976-2009.
2 • y = 0.0003x 3 - 1.5237x 2 + 3042.2x - 2E+06 Population and productivity trends Population has been increasing at an average of 9.7% 1.8 R² = 0.3086 Alcatraz Island 1.6 3 per year (Figure 3). Año Nuevo Island 1.4 Southeast Farallon Island • 1.2 • 2.5 Breeding success increased in the 1980s, declined in the Farallon Island population of BRAC: declining for 20 1 years at time of inception of the Alcatraz colony in 2 1990s, and has increased in recent years (Figure 4). 1991. 1.5 • Despite their absence in 2009, population of BRAC has 1 BreedingBreedingsuccesssuccess
Diet trends pair) pair) fledglings/breeding fledglings/breeding successsuccess(# (# Breeding Breeding 1975 1980 1985 1990 1995 2000 2005 2010 been increasing an average 22% a year (Figure 1); faster 0.5 (#(#fledglings/breedingfledglings/breeding pair) pair) Year than either Año Nuevo or Farallon Islands. 0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 • • Dropped fish have been collected since 1981. Figure 4. Least Tern breeding success at Alameda Point, Mean productivity is higher compared to coastal (Año 1976-2009. Year • Atherinopsid have been the dominant dropped Nuevo) and offshore (Farallon) islands (Figure 2). prey in most years. Since the 1990s, northern anchovy ( Engraulis mordax) and surfperches have Atherinopsidae (silversides) Diet habits of Brandt’s Cormorants and prey Figure 2. Productivity trends of Alcatraz Island, Año Engraulidae (anchovies) declined while Clupeids have increased (Figure 5). Clupeidae (herrings) Nuevo Island, and Southeast Farallon Island, 1999-2009. Salmonidae (salmon) availability in the SF Bay Embiotocidae (surfperches) Gobiidae (gobies) Osmeridae (smelts) Others • Diet from 2000-2002 show that BRAC at Alcatraz eat No data No % of collected prey (by number) (by prey ofcollected % Importance of diet data No mostly northern anchovy ( Engraulis mordax) and a 10% 0%
variety of benthic fishes (Yakich 2005). • 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 The percentage of northern anchovy collected in a Year • Productive waters and shallow, benthic habitat of central year and the breeding success of the tern colony Figure 5. Family composition of dropped prey collected SF Bay provide foraging opportunities that differ from from the Alameda Point Least Tern colony, 1981-2009. are related (Figure 6). oceanic waters and likely contributed to success of the 2 • Increased abundance of the energy-rich anchovy in y = 0.6373x + 1.5401 R² = 0.2054 Alcatraz colony (Saenz et al. 2006). 1.8 the Bay could positively influence Least Tern 92 • 1.6 93 The 2009 breeding population crash of BRAC at 81 86 87 breeding success (Elliott et al. 2007). 1.4 94 88 08 Alcatraz suggest the Bay is changing and warrants 91 • 1.2 01 89 The small proportions of dropped anchovy over 09 90 further studies to compare Bay conditions, diet, and prey 1 85
the past 10 years could indicate a declining 0.8 02 00 availability. 04 03 anchovy population in Central and South Bay. 0.6 07 05 95 • 0.4 More studies on reproductive success and diet are 84*
Breeding success (# fledglings pair) per breeding fledglings success(# Breeding 0.2 06 82 necessary to better understand changing Bay 0 -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 conditions and its effects on wildlife. Log -transformed proportion of northern anchovy in dropped prey Figure 6. Northern anchovy proportion of dropped prey Photo by Sara Acosta versus Least Tern breeding success, 1981-2009.
Literature Cited Elliott, M. L. R. Hurt, and W. J. Sydeman. 2007. Breeding biology and status of the California Least Tern Sterna antillarum browni at Alameda Point, San Francisco Bay, California. Waterbirds 30(3): 317-325. Acknowledgments Saenz, B. L., J. A. Thayer, W. J. Sydeman, and D. A. Hatch. 2006. An urban success story: breeding seabirds on Alcatraz Island, California, 1990-2002. Marine Ornithology 34: 43-49. We acknowledge our partner, the National Park Service, for collaborating with us on Alcatraz seabird monitoring. We also acknowledge Golden Gate Yakich, J. D. 2005. A dietary analysis of Brandt’s Cormorants ( Phalacrocorax penicillatus ) breeding in Central San Francisco Bay. Master’s thesis, San Francisco State University, California. Audubon Society (GGAS) for their many years of monitoring the Least Tern colony in Alameda.