NORTHERN ANCHOVY, ENGRAULIS MORDAX, SPAWNING IN 



SAN FRANCISCO BAY, CALIFORNIA, 1978-79, RELATIVE TO 



HYDROGRAPHY AND ZOOPLANKTON PREY OF ADULTS AND LARVAE 



Michael F. McGowan 1 



ABSTRACT 



Eggs and larvae of Engraulis mordax were sampled by nets monthly for one year. Either eggs or larvae 

 were caught every month. Both were most abundant when water temperature was high. Mean egg abun- 

 dance did not differ among stations but larvae were more abundant within the San Francisco Bay at 

 high and low salinity than near the ocean entrance to the Bay. Larvae longer than 15 mm were collected 

 over the shoals in spring and autumn but were in the channel during winter. Zooplankton and 

 microzooplankton were abundant relative to mean California Current densities. Adult spawning biomass 

 in the Bay was 767 tons in July 1978, based on egg abundance and fecundity parameters of oceanic animals. 

 San Francisco Bay was a good spawning area for northern anchovy because food for adults and larvae 

 was abundant and because advective losses of larvae would have been lower in the Bay than in coastal 

 waters at the same latitude. 



The northern anchovy, Engraulis mordax, is the 

 most abundant fish in San Francisco Bay (Aplin 

 1967), but little is known about the seasonal dura- 

 tion or areal extent of northern anchovy spawning 

 there (Eldridge 1977; Sitts and Knight 1979; Wang 

 1981). In the California Current, spawning is 

 thought to be related to abundance of food for adults 

 (Brewer 1978) or to seasonal patterns of abundance 

 of food for larvae (Lasker 1978). Dense patches of 

 appropriate food for larvae are believed to be neces- 

 sary for survival of larvae (Lasker 1975; Scura and 

 Jerde 1977). Zooplankton are generally more abun- 

 dant in estuaries than in coastal and oceanic waters. 

 Therefore, San Francisco Bay, the largest estuary 

 on the west coast of North America, could be a 

 favorable habitat for spawning northern anchovy 

 and their developing larvae. 



The northern anchovy could affect plankton 

 dynamics in the San Francisco Bay (the Bay) by 

 preying on zooplankton and by excreting concen- 

 trated nutrients for phytoplankton. It is the target 

 of a seasonal bait fishery (Smith and Kato 1979), and 

 it is an important forage fish for many other species 

 (Recksiek and Frey 1978). Quantitative estimates 

 of the adult stock size and numbers of eggs and lar- 

 vae are needed to understand the ecology of this 

 anchovy in the Bay. 



This paper reports the results of a 1-yr survey of 



Cooperative Institute for Marine and Atmospheric Studies, 

 Rosenstiel School of Marine and Atmospheric Science, University 

 of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149. 



the northern anchovy eggs and larvae, zooplankton, 

 and microzooplankton in San Francisco Bay. Dis- 

 tribution and abundance of eggs and larvae were 

 related to water temperature, salinity, turbidity, 

 stratification, abundances of potential adult prey, 

 and potential larvae prey. The suitability of the Bay 

 for spawning and development of larvae was as- 

 sessed. An estimate of spawning stock abundance 

 within the Bay was calculated from egg abundance, 

 and the impact of this biomass of anchovies on the 

 zooplankton was estimated. 



MATERIALS AND METHODS 



Study Site 



San Francisco Bay consists of three major parts 

 (Fig. 1): 1) Central Bay opens to the Pacific Ocean 

 through the Golden Gate at lat. 37°49'N, long. 

 112°29'W; 2) North Bay receives the drainage from 

 the Sacramento and San Joaquin Rivers and in- 

 cludes Suisun, San Pablo, and Richardson Bays; 

 3) South Bay is the largest single embayment, ex- 

 tending some 27 nmi from Coyote Creek in the south 

 to the Oakland-San Francisco Bay Bridge in the 

 north. The following description of San Francisco 

 Bay was taken from Conomos and Peterson (1977). 

 Mean depth is 6 m at mean lower low water, or 2 

 m if the large expanses of mudflats are included. 

 There is a 10 m deep dredged ship channel in the 

 northern part. Tides are mixed semidiurnal ranging 

 from 1.7 m at the Golden Gate to 2.7 m at the south- 



Manuscript accepted July 1986. 



FISHERY BULLETIN: VOL. 84, NO. 4, 1986. 



879 



