Monday was the first big day of the year for Pacific herring in California, centered in San Francisco Bay. The Sausalito waterfront teemed with grebes, cormorants, gulls, pelicans, sea lions and harbor seals feeding on herring as they moved to spawning beds in Richardson Bay. A cluster of about 20 fishing boats doled out gill nets and hauled in fat, wriggling fish. Enraptured bystanders watched and snapped photos of this unique scene for an urban estuary.

Further into the bay, rafts of Scoters, Scaup and Bufflehead aggregated where fish were in the act of depositing energy-rich eggs on eelgrass (Zostera) and algae (Grasilaria), and other substrates such as pilings and submerged rocks. All were exploiting this ephemeral yet vitally important winter food source for waterbirds in San Francisco Bay and the west coast.

A number of times each winter, Pacific herring move en masse with the high winter tides from the ocean into west coast estuaries to spawn. The vast majority of California’s herring now occur in San Francisco Bay, with a much smaller number returning to Tomales Bay. Both sites are Important Bird Areas due to their hemispheric importance to waterbirds. Up to 60 species rely on these estuaries for food and rest in the winter months.

A 2007 study conducted by Wesley Weathers of U.C. Davis and John Kelly of Audubon Canyon Ranch  shows that wintering waterbirds in Tomales Bay switch to herring or roe when it is available, and that well over 50% of roe deposited by herring is consumed by waterbirds.  Scoters (Surf and White-winged) are particularly dependent on roe. These Watch List species have suffered major declines since at least the 1970’s.

At the Richardson Bay Audubon Center and Sanctuary, staff and volunteers on Monday reported a record 12,000+ waterbirds within Sanctuary boundaries alone. This large concentration of waterbirds during the herring run may be no coincidence - greater Richardson Bay is the hotspot of herring spawning in San Francisco Bay. This suggests that Richardson Bay Sanctuary, closed to vessels in these months, may be a critically important feeding and resting area for waterbirds relative to the rest of San Francisco and Tomales bays.

The importance of herring for estuarine and coastal invertebrate, fish, mammals and waterbird species begs the question: how are these fish doing?

Spawning herring have been fished for 150 years in California, and is the last remaining commercial fishery in San Francisco and Tomales Bays. (There were at least 20 boats clustered around Sausalito on Monday, crisscrossing the water with gill nets.) There is currently little demand for the meat, however nutritious and tasty; the value is in the roe which is extracted and sold mainly to Japan.

The California Department of Fish and Game manages the fishery, generating annual stock assessments and quotas. We took a look at the data, and the picture is not pretty.

Since 1978, total spawning biomass – the number of fish returning to spawn – in California has decreased dramatically:

Further, there is a coastwide trend in decreasing length-at-age, meaning fish are getting smaller.  Most worrisome of all, every year since 2003 there is a larger proportion of younger fish, and a smaller proportion of older fish, in the population. This is known as age class truncation, and can be the death knell for a fishery, because younger fish produce fewer and less healthy eggs than older fish. Herring can spawn numerous times, and taking out bigger, older fish year after year may be the root of the problem.

In the next several years, the State will tackle these issues as it develops a Management Plan. By law this plan must consider the energetic needs of birds and other predators when setting fisheries quotas. That may mean closing the fishery until these needs are better understood and accounted for. As the Plan develops, we will urge the State to take a precautionary approach in protecting this vital resource for waterbirds and the entire marine and estuarine ecosystem.