Pacific herring, Clupea harengus pallasi, studies in San Francisco Bay, Monterey Bay, and the Gulf of the Farallones, July 1982 to March 1983

Abstract

Herring stocks were hydroacoustically surveyed and sampled in San Francisco Bay from November 1982 to March 1983. Twelve discrete herring schools were identified, all of which spawned between November 7 and February 23. One additional school was found in the Bay in March but showed no evidence of spawning. Total biomass estimate from hydroacoustic surveys was 67,040 tons. Based on MRR biomass estimates from spawned egg counts, an additional 10,000 tons may have spawned in November and December without being detected hydroacoustically. The largest schools occurred in January and February. Hydroacoustic estimates of biomass for individual schools during the season ranged from 270 to 22,300 tons. Sixty-seven samples, containing a total of 12,232 herring, were collected with variable mesh gill net and midwater trawl or obtained from the commercial roundhaul and gill net fisheries. In general, a trend was observed of decreasing mean size and age as the season progressed. Schools spawning in November and December consisted primarily of 4-, 5-, 6-, and 7-yr-old fish. Schools sampled from January to March were predominantly 2-, 3-, 4-, and 5-yr-old herring. The 1978, 1979, and 1980 yr classes (ages 5, 4, and 3 yr) were strong, comprising up to 90% of the samples. The 1981 yr class (2-yr olds) was relatively weak. Abundant rainfall and resultant low salinity in San Francisco Bay surface waters apparently delayed or prevented herring from spawning in February and March. A relationship may exist between relative abundance of young-of-the-year fish, as noted from midwater trawl samples collected by the Department's Bay-Delta Study, and the resultant year class strength of newly recruited 2-yr-old herring in San Francisco Bay's spawning stocks. (57pp.