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| Long-term Studies of Seabirds on Año Nuevo Island and Mainland |
Principal Investigator(s)
William Sydeman (PRBO Conservation Science)
Julie Thayer (PRBO Conservation Science)
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Start Date
1992-01-01
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Funding
SIMoN
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Overview
Several new seabird colonies have been established in the last decade in central coastal California.
Año Nuevo Island (ANI) is the largest and most diverse seabird breeding colony in the Monterey Bay
National Marine Sanctuary (MBNMS), hosting breeding populations of Rhinoceros Auklets
(Cerorhinca monocerata), Cassin's Auklets (Ptychoramphus aleuticus), Brandt’s Cormorants
(Phalacrocorax penicillatus), Pelagic Cormorants (P. pelagicus), Western Gulls (Larus occidentalis),
Pigeon Guillemots (Cepphus columba) and Black Oystercatchers (Haematopus bachmani).
Additionally, ANI is an important roosting site for Heerman's Gulls (Larus heermani) and the
endangered Brown Pelican (Pelicanus occidentalis). Other species that have occurred on ANI include
state-listed Ashy Storm-Petrels (Oceanodromo homochroa) and Fork-tailed Storm-Petrels (O. furcata).
There are several threats to marine bird populations of the MBNMS. Environmental variability (e.g.,
climate change) and a variety of human factors (e.g., bycatch and indirect effects from commercial
fisheries, oil and pesticide pollution) affect seabird populations in this region. We have initiated what
we hope will be long-term (i.e., multi-decadal) studies of breeding seabird population dynamics,
demography and prey use in the MBNMS, with an emphasis on ANI. Such information will provide
valuable insights into changes of these upper-trophic level predators in central California and help
marine wildlife managers develop appropriate conservation strategies. This project is funded by SIMoN, the Bella Vista Foundation, Oracle Corporation, and Exxon/Mobil Corporation.
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Summary to Date
The year 2003 represents the 11th year of monitoring seabirds on Año Nuevo Island (ANI). Rhinoceros
Auklet, Brandt’s Cormorant, and Western Gull populations increased from 2002 to 2003, to the highest
levels yet recorded for ANI. Reproductive success, however, has been variable. Rhinoceros Auklets
banded as chicks in nest boxes earlier in our project are now recruiting into the ANI breeding
population, providing novel information on age-at-first-breeding, immigration and recruitment rates for
this species worldwide. Auklet diet reveals a shift from an anchovy-based diet in the 1990s to rockfishbased
diet in recent years, corresponding to a shift in ocean climate in 1998-1999.
We continue to
provide scientific advice to the California Department of Fish and Game (CDFG) on how to manage
fisheries from an ecosystem perspective. Most recently, we reviewed the draft Market Squid Fishery
Management Plan and provided recommendations to protect squid as one of the primary prey resources
for marine birds and mammals in the MBNMS. Future monitoring should include analyses of food
habits of other seabirds of the MBNMS. For more information download the full PDF report below.
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Monitoring Trends
- Rhinoceros Auklets totaled approximately 270 breeding birds in 2003. Brandt’s Cormorant
and Western Gull populations on the island numbered ~ 1740 and ~2370 birds, respectively.
- Productivity (chicks fledged per pair) in 2003 was lower than in 2002 for all species except Pelagic
Cormorants breeding on the mainland.
- We collected and archived diet samples Rhinoceros Auklets, Pelagic Cormorants, and Brandt’s
Cormorants in 2003, adding to our long-term databases of marine bird food habits. See Figure 2 below.
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Discussion
In the past 5 years, marine bird populations have increased on ANI yet reproductive success has been
variable. Through these studies, we have gained valuable new information on survival, recruitment and
immigration, demographic processes that are important to better understand seabird population
dynamics. Prey is also key to population dynamics, but highly variable due to climate change and at
risk from certain fisheries. Sustained time-series of marine bird population trends, productivity and
prey use are valuable for tracking long-term changes in community and ecosystem health.
Future work should involve analysis of cormorant diet. Analyses of ANI seabird population dynamics,
reproductive success and prey use in relation to other colonies would also be beneficial to understand
how populations of these species in the MBNMS compare to the dynamics of these populations
elsewhere.
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Study Parameters
Click here to view the parameters measured in this study. |
Study Methods
Click here to view the methods and materials used in this study. |
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Images and Documents
Aerial view of Ano Nuevo Island and mainland. Photo: PRBO Conservation Science
Figure 1. Population dynamics of Pelagic Cormorants, Pigeon Guillemots and Cassin’s Auklets on Ano Nuevo Island, 1976-2003.
Figure 2. Percent number of prey species in Rhinoceros Auklet chick diet on Año Nuevo Island over 11 years, 1993-2003.
Long-term Studies of Seabirds on Año Nuevo Island and Mainland, 2003
Final Report to the Monterey Bay National Marine Sanctuary –
Sanctuary Integrated Monitoring Network
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