Publication Date:
2021-06-28
Description:
Herring schools were surveyed hydroacoustically and sampled in San Francisco Bay from late October 1986 to March 1987. Eight large schools (greater than 1000 tons each) spawned from December to February and seven smaller schools were detected throughout the spawning season. Total acoustic biomass estimate using a "visual integration" technique was 40,930 tons, and it was determined from spawn escapement and commercial landings that an additional 2240 tons were not detected. This is a slight increase from last season's total of approximately 42,200 tons. For the first time, biomass was also estimated using echo integration equipment. A total biomass was obtained of 33,050 tons, including herring not detected acoustically. This estimate must be considered preliminary and subject to revision after target strength of San Francisco Bay herring is determined.Eighty-seven samples, containing a total of 13,125 herring, were collected with variable-mesh gill net and midwater trawl or obtained from the roundhaul and gill net fisheries. Mean body length (BL) of sampled herring decreased by about 20 mm from the beginning to the end of the spawning season. A combination of variable-mesh gill net and midwater trawl samples for a particular school closely approximates mean BL and age composition data from unbiased roundhaul samples.Age-weight and age-length relationships were average to above average compared with those of the previous two seasons. The 1982 year class exhibited unusually good growth, with a mean BL of 202.8 mm for herring aged from stratified random samples.The 1982 through 1985 year classes (5- through 2-yr olds)contributed 97% by number and 95% by weight to the total 1986-87 spawning biomass in San Francisco Bay. Good recruitment has occurred during the past four seasons. The weak 1981 year class contributed little to the total biomass as 6-yr olds.Average catch per tow of young-of-the-year (YOY) herring is a potential index of abundance for recruitment 18 months later as 2-yr olds. Estimated recruitment has only varied by 15% during the past three seasons and does not reflect the magnitude or trend in YOY catches in the bay. (85pp.)
Keywords:
Management
;
Fisheries
;
Biology
;
Pacific herring
;
Clupea harengus pallasi
;
San Francisco Bay
;
California
Repository Name:
AquaDocs
Type:
monograph
Format:
application/pdf
Format:
application/pdf
