Pacific herring, Clupea harengus pallasi, studies in San Francisco Bay and the Gulf of the Farallones, June 1984 to March 1985

Herring stocks were surveyed hydroacoustically and sampled in San Francisco Bay from November 1984 to March 1985. A maximum of 13 schools entered the Bay and spawned between November 1 and March 10, although large schools (greater than 1000 tons) occurred only from mid-December to March. Total biomass estimate from hydroacoustic surveys was approximately 29 500 tons, and it was determined that at least 5500 additional tons were not detected. This is an increase from last season's adjusted total of approximately 25 000 tons. Although different from MRR's biomass estimate from spawn escapement plus commercial landings(40 000 tons in 1983-84 and 46 000 tons in 1984-85), hydroacoustic estimates showed a similar trend of recovering stock biomass.Sixty-six samples, containing a total of 8031 herring, were collected with variable-mesh gill net and midwater trawl or obtained from the roundhaul and gill net fisheries. The usual pattern of decreasing mean length and age of herring as the season progressed was observed.Small schools that spawned in November and December consisted primarily of 3- to 6-yr-old herring. Two-yr olds became a significant part of spawning schools beginning in mid-January. The 1982 and 1983 yr classes(3- and 2-yr olds) comprised 81-94% by number of schools spawning from mid-January to March, with the 1982 yr class being particularly strong.Recovery from poor growth conditions during the 1982-83 El Nino event was evidenced by age-length and age-weight relationships, particularly for younger fish. Mean body length for 2-, 3-, and 4-yr-old herring averaged 8 mm greater than in 1983-84. Weight at age was 24 to 41%higher for ages 2 to 6 yr and 15 to 16% higher for 7- and 8-yr olds.Average fecundity was estimated from egg counts from 94 unripe herring. Mean value was 227.1 eggs/g with a 95% confidence interval of 5.1 eggs/g.Survival of young-of-the-year (YOY) herring from 1983-84 spawns was greater than from the previous season. The positive correlation previously observed between relative abundance of YOY herring from the Department's Bay-Delta Project samples and the resultant year class strength of newly recruited herring in San Francisco Bay's spawningstocks was not evident this season; the contribution of the 1983 yr class (2-yr olds hatched during the 1982-83 season) was better than expected. (84pp.)