134 



Fishery Bulletin 103(1 



dard deviation of the length distribution within the 

 40-50 mm bin for each sampling event is provided in 

 Table 2. Thus, the amount of time (measured by otolith 

 increments) needed for fish to grow to the 40 mm-50 

 mm size group was used to compare growth. Differences 

 in age at length were evaluated and compared with 

 observed variation in juvenile abundance. 



distributed throughout the bay (Fig. 3). Peak abun- 

 dances occurred in May for both 1999 and 2000, and 

 juveniles were caught throughout the study area. By 

 June, abundances decreased and herring became more 

 concentrated in the central Bay region, presumably ag- 

 gregating in this area prior to exiting San Francisco 

 Bay for the coastal ocean (Fig. 3). 



Results 



Egg and juvenile abundance 



Both the magnitude and timing of estimated egg deposi- 

 tion differed little between the 1998-99 and 1999-2000 

 spawning seasons (Fig. 2). Total egg deposition was esti- 

 mated to be 9.66 x 10 11 eggs for 1998-1999 and 8.59 x 10 11 

 eggs for 1999-2000 (Watters 2 ). Peak egg deposition in 

 both spawning years occurred in January (Fig. 2). 



Abundance of juvenile herring resulting from these 

 two spawning seasons differed greatly. The cumula- 

 tive estimated relative recruitment (ICPUE) of juve- 

 nile herring was 7.75 times greater in 2000 than 1999 

 (Table 1). 



General patterns of juvenile herring distribution were 

 similar in 1999 and 2000. Juvenile herring recruited to 

 the sampling gear in March and April and were widely 



Watters, D. 2000. Unpubl. data. Calif. Dep of Fish and 

 Game, 411 Burgess Dr., Menlo Park, CA 94025. 



7x10" 

 6x10" 



■a 5x10 



CD 



cd 4x10 



"D 

 cfl 



lu 3x10 

 2x10" 



1x10" 



1998-1999 

 1999-2000 



Nov 



Dec Jan Feb Mar 

 Spawning month 



Figure 2 



Total egg deposition by Pacific herring [Clupea pal- 

 lasi), summed by spawning month for the 1998-99 and 

 1999-2000 spawning seasons. Data provided by the Cali- 

 fornia Department of Fish and Game, Menlo Park. 



Spawning-date distributions 



The temporal distribution of successful spawning-dates 

 differed between the 1999 and 2000 year classes (Fig. 4, 

 A and B). In 1999, the earliest spawning-date that 

 resulted in juvenile recruitment was 30 November 1998. 

 The greatest numbers of juvenile recruits were a product 

 of the middle of the spawning season, from approxi- 

 mately early January 1999 though early February 1999, 

 and the highest recruitment occurred from spawnings 

 between 10 January and 14 January 1999 (Fig. 4A). 

 An additional spike of recruitment was observed from 

 spawning events at the end of the season (early March). 

 The period of highest recruitment came at the same time 

 as the highest spawning intensity. Spawning events 

 early in the spawning season (November-December) 

 appeared to produce few juveniles (Fig. 4A). 



In 2000, juveniles recruited from much earlier spawn- 

 ing events. Back-calculated spawning dates indicated 

 that spawning may have occurred as early as 13 Octo- 

 ber 1999 (Fig. 4B). Both the March 2000 and April 2000 

 juvenile surveys contained herring with back-calculated 

 spawning dates that ranged from mid to late October, 

 indicating that a spawning event occurred extremely 

 early in the spawning season and was undetected by 

 the spawn-deposition survey (which commences in No- 

 vember). Although early spawnings appeared to produce 

 some recruitment success, a near lack of success was 

 noted for many of the mid-season spawnings that oc- 

 curred from mid-November through mid-January 2000 

 (Fig. 4B). This period of poor survival was then followed 

 by the period of highest recruitment; spawning dates 

 ranged from mid-January to early March and peak re- 

 cruitment resulted from February spawning (Fig. 4B). 



Juvenile mortality corrections superimposed upon 

 the spawning-date distributions had little effect on 

 the general results. An instantaneous juvenile mortal- 

 ity rate of 0.016/d produced minor adjustments on the 

 percent recruitment resulting from particular spawning 

 periods in both years (Fig. 4, A and B). This mortality 

 correction did not alter the general spawning periods 

 that resulted in juvenile recruitment. Increasing the in- 

 stantaneous juvenile mortality rate to 0.05/d (O'Farrell. 

 unpubl. data) also had negligible effects on the general 

 results of the spawning-date distributions. 



Data for both 1999 and 2000 are not totally complete. 

 The spawning-date distribution for 1999 was based on a 

 total of 380 herring, whereas 558 herring were caught 

 between the months of March and June. Similarly, the 

 2000 spawning-date distribution was based on a total 

 of 3861 herring, whereas 4069 herring were caught dur- 

 ing the same months (Table 1). Fish were omitted from 



