San Francisco Bay Herring Spawn Potential Map

by Dan Chase


Pacific herring and eggs

Pacific herring and eggs

Pacific herring (Clupea pallasii) are found in large schools throughout the California’s coastal zone and are an important forage species that sustains a valuable commercial and recreational fishing industry in San Francisco Bay.  While primarily found off shore, the species moves into bays and estuaries in the winter to lay their eggs. These large spawning events can last several days, and attract large numbers of birds, marine mammals, and predatory fish.

To maintain and protect the fishery, the California Department of Fish and Wildlife (CDFW) oversees in-water activities that have the potential to interfere or negatively affect herring spawning.  Within the San Francisco Bay, Pacific herring spawning typically occurs November through April.  All in-water projects in the San Francisco Bay west of the Carquinez Bridge that occur during the herring spawning window are required to consult with CDFW, and are at risk of project delays of two weeks to a month or more if herring spawns occur in areas where in water dredging or construction is being performed.

WRA herring spawn potential viewer

WRA herring spawn potential viewer

WRA’s GIS and Fisheries experts have developed an online interactive map to help evaluate the potential for Pacific herring spawning in the San Francisco Bay Estuary. The map viewer is available for public use to help evaluate the risks of performing in water work during the herring spawning season. The information presented in the viewer is based on recent Pacific herring spawning data provided by CDFW as well geospatial data representing known spawning substrate for Pacific herring in the area.

The information in this map viewer is intended to be used as a reference tool for projects that will involve in-water work during the Pacific herring spawning window and would require CDFW approval to proceed.  During the spawning window, any in-water project within San Francisco Bay is required to fill out a waiver with CDFW prior to November 15, 2015.  WRA can assist with this process in addition to providing consultation or biological monitoring expertise.

For further information about Pacific herring spawning in the Bay, or this tool in general, please contact Justin Semion or Dan Chase.  For more information about our capabilities, please see our Fisheries and GIS services pages.