When Pacific herring spawn here in the San Francisco Bay, sea lions, seals, pelicans, and tens of thousands of cormorants, gulls, and migratory ducks are in a feeding frenzy. It occurs primarily in December and January.
The herring are known as a keystone species, a species that has a large and critical effect on the surrounding ecological environment.
If all the contingency factors are in place, in the late fall the Pacific herring come into the San Francisco Bay, especially Richardson Bay.
They wait for water temperature, salinity, and other conditions to be just right, then they head to the shallow shorelines to begin their reproductive process. Males release sperm, females release eggs.
She releases thousands of eggs at a time, up to 20,000.
The Pacific herring prefer a sea grass known as eelgrass (Zostera marina) for depositing their eggs and protecting their young. The eggs are adhesive, and are also sprayed onto rocks, pilings, and other underwater structures. Eelgrass info here.
A typical herring adult is about 4-8 inches long (10-20 cm). And being at the low end of the food chain, they have numerous predators, including humans. The juvenile survival rate is about one adult per 10,000 eggs.
It is easy to see when a “spawning event” is occurring. I’ve been watching them for weeks. Although it’s impossible to see what’s going on underwater, above water there is a flurry of activity. I find the spectacle endlessly fascinating.
Gulls, cormorants, pelicans, ducks, and sea lions congregate near the shoreline. They eat the fish and the eggs. Sea lions are diving and snorting, thick flocks of birds are everywhere, there’s splashing and squawking.
After the eggs are released, the surviving embryos turn into larvae, then juvenile fish. In fall they swim out to sea, riding California currents.
There have been years when the herring were overfished; populations declined. Some years the herring population fell so low that fishing was prohibited. See graph at end.
When herring fishing had to be curtailed, people were forced to cooperate and manage the situation before the herring were forever lost. And they have.
Herring fisherman, conservationists, naturalists, scientists, and residents have joined together in an ongoing effort to host the herring. Dredging, boat activity, global warming, algae, oil spills and other pollution have all been important topics.
It is impressive to see what humans can do when they work together, and that spawning miracle is pretty amazing too.
Photo credit: Athena Alexander unless otherwise specified.