RICHARDSON: SPAWNING BIOMASS AND EARLY LIFE OF NORTHERN ANCHOVY 



At an estimated spawning biomass of 3,631,200 t 

 (MacCall et al. 1976) the harvest quota would be 

 635,400 t or approximately 17% of the total spawn- 

 ing biomass. At the recent reduced biomass level of 

 1,564,100 in 1979, the optimum yield established 

 for the 1979-80 season in the U.S. Fishery Conser- 

 vation Zone was 153,100 t (Stauffer 1980), equiv- 

 alent to only 10% of the total spawning biomass. 



Thus the actual realizable yield and in turn the 

 feasibility of establishing a fishery on this north- 

 ern stock of northern anchovy is difficult to assess. 

 Northern anchovy are considered to be important 

 forage items for fishes such as salmon and albacore 

 off Oregon and Washington but northern anchovy 

 biomass actually consumed by these species has 

 not been adequately estimated. Northern anchovy 

 are also important items in the diet of marine 

 birds. Weins and Scott (1975) estimated that four 

 species of marine birds consume 28,000 t of north- 

 ern anchovy annually off Oregon. 



If the northern anchovy stock off Oregon and 

 Washington could support a harvest of 10% of the 

 total biomass, as in the recent quotas on the re- 

 duced biomass for the central subpopulation, a 

 yield of about 14,465-100,526 1 might result. If this 

 is reasonable, the feasibility of establishing such a 

 fishery still remains to be determined. Feasibility 

 partly depends on distribution patterns and habits 

 of the stock and on economic considerations, the 

 latter of which is beyond the scope of this paper. 

 Seasonal patterns of distribution were discussed 

 by Laroche and Richardson (1981). The most com- 

 pact aggregations appear to occur during the 

 spawning season in the offshore spawning center. 

 However, school sizes appear to be small. Smith 

 (footnote 3) estimated that half of the northern 

 anchovy schools counted during the acoustic sur- 

 vey in July 1977 were <4 1 and only 1.1% were over 

 64 t. Small school size could be a deterrent to 

 fishery development. 



COMPARISON OF NORTHERN AND 

 CENTRAL SUBPOPULATIONS 



Important ecological differences exist between 

 the northern and central subpcpulations of E. 

 mordax with respect to spawning times and loca- 

 tions and associated environmental parameters. 

 Off California, spawning takes place throughout 

 the year (Figure 7) with a peak occurring between 

 January and April (Smith and Richardson 1977). 

 Off Oregon, spawning takes place over a 2-mo 

 period (Figure 7) with a peak in July, based on the 



15 



% 10 - 



5 - 



CALIFORNIA 



1951 - 60 



II I I I I I I 1 I I 



J FMAMJJ ASOND 

 100r 



OREGON 



1971-72 



% 50 



10- 



1 



J FMAMJ J ASOND 



FIGLT^E 7. — Spawning cycle o{ Engraulis mordax off California 

 and Oregon. Upper graph is after Smith and Richardson (1977). 

 Lower graph is based on catches of northern anchovy larvae 

 given by Richardson (text footnote 5). 



collection of small larvae (Richardson 1973, foot- 

 note 5). These differences in peak spawning times 

 certainly contribute to reproductive isolation. 



Off California (Figure 8), at the initiation of 

 peak spawning southward flow of the California 

 Current is minimal (Saur 1972) with resulting 

 minimal larval transport south away from the 

 spawning area; temperature at 10 m depth ( Lasker 

 and Smith 1977) is reaching minimum values in 

 the annual cycle; upwelling is minimal but in- 

 creasing (Bakun 1973); day length is beginning to 

 increase after the shortest day in December. In 

 contrast, off Oregon (Figure 9), at the time of peak 

 spawning, current flow to the south is at a 

 maximum (Huyer 1977); surface temperatures 

 (Johnson 1961) are reaching maximum values in 

 the yearly cycle ( excluding the colder waters of the 

 nearshore upwelling zone); upwelling activity is at 

 a maximum (Bakun 1973); day length is beginning 

 to decrease after the longest day in June. 



Off California (Figure 10), spawning takes place 

 closer to the coast (Smith and Duke'^) than off 



"Smith, P E., and S. Duke. 1975. Nearshore distribution of 

 northern anchovy eggs and larvae i Engraulis mordax). NOAA 

 NMFS, Southwest Fish. Cent., Admin. Rep. No. LJ-75-58, 15 p. 



871 



