Understanding the link between waterbirds and Pacific herring in San Francisco Bay

Surveys verify that the small fish are an important food resource to a wide array of wintering waterbirds.

A variety of gulls enjoy the herring run at Pt. Orient in San Francisco Bay.

In an effort to better understand the relationship between waterbirds wintering in San Francisco Bay and Pacific herring, surveyors from Audubon California and the Golden Gate Audubon Society recently documented a number of feeding frenzies coinciding with herring runs at Point Richmond.

In one of these surveys at Point Orient last week, the group spotted an assortment of 330 gulls (mostly Mew with some Glaucous-winged, Herring, California, and Ring-billed mixed in). The gulls were feeding on herring roe attached to eelgrass near the shoreline.

The survey was one of the first of a new kind of Bay waterbird survey, one specifically targeted toward the herring feeding frenzies. Because our regular bi-monthly surveys at Richardson Bay and Point Richmond do not necessarily overlap with herring spawn events, these kinds of surveys are needed to truly capture the connection between spawn events and waterbird species that use herring fish and eggs for food.

The week before the Point Orient event, volunteer Tony Brake noticed around 3,000 surf scoters (Melanitta perspicillata) and hundreds if not thousands of Greater/Lesser Scaup (Aythya marila/affinis) off the Pt. San Pablo shoreline. These estimates were confirmed by Audubon staff on Feb. 22 and 23, and to our knowledge, the scoters have not left the area yet. We are excited to discover such high numbers of surf scoters because research suggests that these long-lived sea ducks have declined considerably over the past six decades.

The Sea Duck Joint Venture has designated surf scoters a high conservation priority. Surf scoters winter in shallow coastal waters and estuaries and are cryptic breeders in remote locations of the North American taiga, so estimating population size is challenging.  Therefore, we want to gather as much information on this species as possible.  In addition to the surf scoters and Greater/Lesser scaup, Brake sighted four Long-tailed ducks amidst the raft, which are rare visitors to the Bay. Eelgrass and herring roe can be an important food item of Long-tailed ducks.

In partnership with Golden Gate Audubon volunteers, the Richardson Bay Audubon Center & Sanctuary has been surveying waterbirds along the Pt. Richmond shoreline since 2016 in an effort to document bird use of the shoreline and surrounding waters. Pt. Richmond supports high bird species diversity and abundance during the winter and our bi-monthly surveys will be used to help protect this area.

Pacific herring (Clupea pallasii) is a major reason migratory birds spend the winter in San Francisco Bay. These fish are distributed throughout the North Pacific Ocean and enter estuaries to breed once a year. Spawn events provide an energy dense food source for tens of thousands of wintering birds in the Bay. (Learn more about Audubon California’s conservation plan for Pacific herring here.) Already, about a handful of herring spawn events have taken place at Pt. Richmond during winter 2018 - more than any other location in the SF Bay this year.

Modeled after our Richardson Bay Sanctuary surveys, the Pt. Richmond surveys are conducted at an even finer spatial resolution. Volunteer observers use a scope to count the birds and record their behavior within 250 square meter grid cells.  Audubon staff are working with five key volunteers from Golden Gate Audubon - Brake, Yvonne McHugh, Elizabeth Sojourner, Judith Dunham, Ralph Pericoli, and Anne Ardillo – who are dedicated to this challenging survey methodology. The grid cells allow us to compare avian habitat use with other spatial data such as Pacific herring spawn biomass and location of eelgrass beds. After each survey, our SF Bay Conservation Manager analyzes the results and creates abundance maps, which are circulated to the volunteers.

This project is supported with funds from the Gordon and Betty Moore Foundation.

If you’re interested in getting involved in the surveys, contact Julia Kelly.

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