Pacific herring, Clupea pallasi, studies in San Francisco Bay, April 1990 to March 1992
Reductions in project staffing required modification of hydroacoustic survey protocol for the 1990-91 and 1991-92 field seasons. Echo integration surveys were discontinued and hydroacoustic biomass estimates were generated solely from visual integration data. Hydroacoustic surveys were discontinued in the middle of the 1990-91 field season due to further reductions in staff. Visual integration surveys were continued the following season.Herring schools were surveyed hydroacoustically in San Francisco Bay from mid-November 1990 to early January 1991. Two spawning waves were surveyed prior to the truncation of the field season. Biomass estimates for these waves from visual integration methods totaled 39,900 tons. The largest herring school ever surveyed in San Francisco Bay spawned in early January 1991. An estimated 38,600 tons of herring was observed from Sausalito to Hunters Point in the south bay.Hydroacoustic surveys were continued in the 1991-92 field season. A total of six distinct spawning waves were detected and estimated using visual-integration methods. The biomass estimate for the season totaled 36,900 tons; however, a significant portion of one wave may have been missed hydroacoustically but was accounted for by spawning ground surveys. It was speculated that this component was ripeningoutside of the Golden Gate Bridge, beyond our normal survey area.During the incomplete 1990-91 field season, 13 samples containing 2,830 herring were collected by midwater trawl. Older fish dominated both waves and sex ratiosfavored males. Sixty-two samples comprised of 3,961 herring were sampled by midwater trawl and the round-haul fishery during the 1991-92 field season. Unlike previous seasons, mean body length of herring did not decline significantly until late January, due to a lack of returning 2-year-olds. The 1990 year-class appears to be extremely weak, but recruitment will not be complete until this year-class returns as 3-year-olds in the 1992-93 season.Recruitment strength of the 1989 year-class could not be evaluated in the shortened 1990-91 field season. However, as 3-year-olds the 1989 year-class is below average. The 1990 year-class was forecasted by the herring young-of-the-year (YOY) index to be weak. This year-class as 2-year-olds is the weakest on record. The 1991 year-class appears to be stronger than the 1990 year-class based on results of the YOY surveys, but is projected to be weak also. A final assessment for both year-classes cannot be made until they return as 3-year-old herring and recruitment into the fishery is complete. The YOY index for the 1992 year-class suggests that it will be slightly below average but much stronger than the previous two year-classes. (40pp.)
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| Format: | monograph biblioteca |
| Language: | English |
| Published: |
California Department of Fish and Game, Marine Resources Division
1994
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| Subjects: | Management, Fisheries, Biology, Pacific Herring, Clupea pallasi, San Franciso Bay, California, age groups, |
| Online Access: | http://hdl.handle.net/1834/18332 |
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