Pacific herring, Clupea harengus pallasi, studies in San Francisco Bay, central and northern California, and Washington; March 1985 to May 1986 | Marine Resources Administrative Report No. 86-6

Herring schools were surveyed hydroacoustically and sampledin San Francisco Bay from late October 1985 to March 1986.Nine schools entered the bay and spawned between October 30and March 5; large schools (greater than 1000 tons) occurred only from December to March. Total biomass estimate from hydroacoustic surveys was 36,600 tons, and it was determined from spawn escapement and catch that an additional 5600 tons were not detected. This is an increase from last season's total of approximately 35,000 tons. Heavy rainfall and depressed salinities in the bay inhibited spawning for 3 wk in February and March. Eighty- five samples, containing a total of 13,260 herring, were collected with variable-mesh gill net and midwater trawl or obtained from the roundhaul and gill net fisheries. Mean length of herring decreased only during the early part of the season; the strong showing of the 1982 and 1983 yr classes resulted in more uniform length composition of samples from December to March.Age composition for the entire spawning season consisted of90% by number and 85% by weight 2-, 3-, and 4-yr olds (1984, 1983, and 1982 yr classes). The 1981 yr class again was relatively weak. The 1982 yr class has had the highest mean length and weight as 3- and 4-yr olds that we have seen in 5 yr.Fecundity estimates from the past three seasons averaged 222.8 eggs/g and showed no significant difference amongseasons.Survival of herring from 1984-85 spawns was greater than the previous year and indicates that the 1985 yr class may be above average in relative strength.A morphometric analysis of herring from Humboldt Bay, FortBragg, Tomales Bay, and San Francisco Bay indicated that northern stocks could be separated from southern stocks with an 85-87% success rate, but morphometric differences were not great enough to separate herring from Tomales and San Francisco Bays. Growth differences, expressed as mean age per BL interval, were apparent in the four groups and show a gradual increase in growth rate with increasing latitude. Herring from Washington, aged by scales and otoliths, also fit this trend. (102pp.)