RICH.^DSON: SPAWNING BIOMASS AND EARLY LIFE OF NORTHERN ANCHOVY 



Also, based on egg distribution the spawning 

 aggregation appeared more widely distributed in 

 a north-south distance. Mean temperature and sa- 

 linity at 3 m depth at positive stations in 1975 and 

 1976 were 15.66° and 15.96° C and 31.07 and 

 31.281., respectively. Distribution of larvae did not 

 correlate with high surface chlorophyll levels and 

 abundance was generally highest in regions of low 

 plankton volume. During the acoustic survey in 

 1977, northern anchovy larvae were collected 

 (Methot footnote 12) on each transect in concentra- 

 tions up to 5,606 under 10 m^ sea surface (Figure 

 5). No larvae were found in samples taken within 

 46 km of the coast. Mean length of larvae on each 

 transect again showed an increasing trend toward 

 the south. 



125°30' W) between 56 and 130 km offshore (Fig- 

 ure 5). No adult northern anchovy were collected 

 at trawl stations on the southern two transects. No 

 trawls were made on the transects off Cascade 

 Head or Cape Perpetua. 



School concentrations, recorded by sonar, were 

 presented by Smith (footnotes 10, 3). Based on 

 sonar traces and results of the pelagic trawl 

 catches, he concluded schools of spawning adult 

 northern anchovy were centered 83 km offshore in 

 the surveyed area and 37 km south of the Colum- 

 bia River mouth with the inner edge about 37 km 

 offshore and the western edge between 102 km. and 

 130 km offshore. The northern edge was not de- 

 fined above lat. 47 ° N and the southern edge was at 

 lat. 44°N. 



Adults 



During the acoustic survey in 1977, running ripe 

 adult northern anchovy were collected on the 

 three northern transects (lat. 47°02' N, long. 

 124°56' W; lat. 46°60' N, long. 126°33' W; lat. 

 46°19' N, long. 124°54' W; lat. 45°40' N, long. 



EGG AND 

 LARVA CENSUS ESTIMATES 



The total area represented by the survey in 1975 

 and 1976, was 148.81 x 10» m^. Census estimates of 

 the total number of northern anchovy eggs and 

 larvae in that area for each cruise are in Table 3. 



Table 3. — Egg and larva census estimates (Q, and C^^) and spawning biomass estimates (B) of Engraulis mordax in the survey area 

 off Oregon and Washington in 1975 and 1976. Values of parameters used in the biomass estimating procedures are presented except 

 those for K (proportion females) and F (mean fecundity) which are constants, 0.5 and 720. See Methods section for description of 

 procedures and equations. 



Sette and Ahlstrom Egg Method 

 [Equations (4) and (5)] 



Simpson Egg Method 

 [Equations (4) and (7)] 



Saville Egg Method 

 [Equations (4) and (8)] 



Smith Larva Method 

 [Equations (10) and (11)] 



'Equation (2). 

 2Equations(12),(l3). 

 3Equation(6). 

 "Equation (7). 



^Based on Sette and Ahlstrom Census. 



"Equation (3). 



'Based on Smith Census. 



603,094 

 307,022 



294,933 

 170,694 



262,506 



144,654 



696,479 

 723,705 

 894.074 

 920,001 



867 



