Water Resource Collections and Archives

Diving Ducks in San Francisco Bay

Organization: Oikonos Ecosystem Knowledge
2008 Grant Recipient - San Francisco Bay Region

Purpose

Diving Ducks in San Francisco Bay - Understanding estuarine subtidal habitat quality for wildlife: carrying capacity of diving ducks in the San Francisco Bay estuary.

This grant was to conduct a study to develop a carrying capacity model for diving ducks to evaluate impacts of contaminants and use these models to predict effects of future subtidal habitat changes on waterfowl populations.

Diving ducks are in decline and their management historically has been overlooked in San Francisco Bay due to the difficulty of determining their habitat requirements. The primary goal was to estimate the total number of wintering diving ducks that can be supported in the San Francisco Bay estuary based on their daily food requirements and the availability of quality underwater habitat.

In the future, the models may also assist managers predict changes in diving duck population size under different scenarios of human-related changes including sea level rise, geomorphologic change, increased disturbance, and habitat restoration.

2012 Update

New prey database completed:

Project partners completed an online atlas of invertebrate prey datasets that benefited this research and is publically available for other studies. Before this grant most of the invertebrate prey information from San Francisco Bay was not accessible because it was spread throughout many entities and not standardized to share electronically.

Seaduck habitat modeling results:

During winter in subtidal San Pablo Bay, California, the three main diving duck species are lesser scaup (LESC, Aythya affinis), greater scaup (GRSC, A. marila), and surf scoter (SUSC, Melanitta perspicillata), which all feed almost entirely on the bivalve Corbula amurensis. Although decreased body mass, increased foraging effort, and major departures of these birds from San Pablo Bay appeared to result from food limitation, we found no consistent niche partitioning by prey size, water depth, or location. However, an energetics model we developed that accounts for differing body size, locomotor mode, and dive behavior indicated that each species will become limited at different stages of prey depletion. Depending on year, 35 to 65% of Corbula standing stocks were below estimated threshold densities for profitable foraging by these birds. Ectothermic predators, especially flounders and sturgeons, could reduce excess carrying capacity for different duck species by 4 to 10%. As reported for a range of predators elsewhere, a substantial quantity of prey above profitability thresholds was not exploited before most ducks left San Pablo Bay. Such pre-depletion departure has been attributed in other taxa to foraging aggression. However, in diving ducks that showed no overt aggression, this pattern may result from high costs of locating all adequate prey patches, resulting reliance on existing flocks to find food, and propensity to stay near dense flocks to avoid avian predation. For interacting species assemblages, modeling profitability thresholds can indicate the species most vulnerable to food declines. However, estimates of total habitat needed require improved understanding of factors affecting the amount of prey above thresholds that is not depleted before the predators move elsewhere.

Documents

• San Francisco Bay Benthic Macroinvertebrate Atlas - USGS Webpage
  Information on benthic macroinvertebrate populations is provided on this page to pull together information currently available from numerous agencies in disparate databases. To maximize the value of these data, San Francisco State University and the U. S. Geological Survey have combined data from several of these sources into a single comprehensive database.
   
• Spatial database for the distribution and abundance of benthic macroinvertebrates in the San Francisco Bay. Rowan, A., K.B. Gustafson, W.M. Perry, S.W. De la Cruz, J.K. Thompson, and J.Y. Takekawa. 2011. San Francisco State University, San Francisco, CA; U.S. Geological Survey, Western Ecological Research Center, Dixon and Vallejo; and U.S. Geological Survey, National Research Program, Menlo Park, CA.

Contacts for the Project

Susan Wainwright-De la Cruz
US Geological Survey and Oikonos – Ecosystem Knowledge
Western Ecological Research Center
Phone: (707) 562-2004
Email: SDelaCruz@usgs.gov