Biomass estimates of Pacific herring, Clupea pallasi, in California from the 1990-91 spawning-ground surveys

Abstract

The spawning biomass of Pacific herring, Clupea pallasi, estimated from spawning-ground surveys in San Francisco Bay declined to 45,850 tons this season, following a peak of 71,000 tons in the 1989-90 season. This is the first major decline since the 1983-84 El Nino. In Tomales Bay the 1990-91 spawning biomass more than doubled to 779 tons. The spawning biomass has increased the past two seasons, while the fishery has been closed. There was no biomass estimate for Bodega Bay, but an additional 95 tons of herring were caught in Bodega Bay this season. The total herring biomass for the Tomales- Bodega area is a minimum of 874 tons. Humboldt Bay was surveyed by the Department for the first time this season, and spawning biomass was estimated to be 400 tons. January was the month of peak spawning activity in all spawning areas surveyed. In San Francisco Bay, 62% of all spawning occurred alonq the San Francisco waterfront; for the first time there was no significant spawninq in the northern part of the bay. Nearly 70% of the spawning activity in San Francisco Bay occurred on January 3-6, 1991. A total of 3.5 million m2 of eelgrass, Zostera marina, was measured in Tomales Bay this season. The change in eelgrass density this season varied from bed to bed, however the overall density of eelgrass in Tomales Bay declined. (44pp.