FISHERY BULLETIN: VOL. 70, NO. 3 



k - 



= 



1 for night samples 



2 for day samples 



1 for anchovy 



2 for sardine 



I.Of- 



The corrected and uncorrected curves plotted on 

 a semilogarithmic scale are shown with nmo 

 and n'ljko expressed in percent of total in Fig- 

 ures 3-6. The corrected curve for anchovy 

 larvae caught at night shows a slight increase 

 in the rate of decline with size. The corrected 

 curve for anchovy caught during the day is 

 essentially linear as is the corrected catch curve 

 for sardine larvae caught during the night. The 

 corrected catch curve for sardine larvae caught 

 during the day shows a decreasing rate of de- 

 cline with size. In all cases the corrected curves 

 show little indication of undersampling of small 

 larvae. 



The following equation was used to estimate 

 the portion of larvae not collected by the type 1 

 net because of passage through the mesh: 



(6) 



l.4|- 



1.2- 



nn 



1.0 



08 



06 



0,4 



02 



& 



A 

 O 



A 



O 



10 



Lj (mm) 



Figure 1. — Scatter diagram of estimates of mesh re- 

 tention by type 1 (0.55-mm mesh) net using equation 

 (2) (Sij(2) ), mesh retention using equation (3) (sij(3)), 

 and standard length (Lj) for northern anchovy larvae. 



08 



-.0.6 - 



W 



04 



02 



(2) 



(3) 



(2) 



(3) 



NORTHERN ANCHOVY 

 PACIFIC SARDINE 



4 

 (mm) 



Figure 2. — Estimates of mesh retention by type 1 (0.55- 

 mm mesh) net (Sij) against standard length (Lj) for 

 larvae of northern anchovy and Pacific sardine using 

 equations (2) and (3). 



where 1 — Pio = portion of larvae of species o 

 not sampled by type i net be- 

 cause of passage through 

 meshes. 



Equation (6) implies that an equal number of 

 night and day samples are taken. This is ap- 

 proximately correct. The estimate of Pio for 

 anchovy is 0.60. The estimate of P\o for sardine 

 is 0.67. Thus anchovy larvae are undersampled 

 by about 12% relative to sardine larvae because 

 of differences in mesh retention and size com- 

 position. 



CATCH CURVE OF TYPE 3 

 (0.505-MM MESH) NET 



Figure 7 shows the catch curve plotted on a 

 semilogarithmic scale of anchovy larvae caught 

 by the type 3 net during 1969 by the CalCOFI. 

 This data is preliminary (P. E. Smith, personal 

 communication) and catches have not been sep- 

 arated by day and night. The interesting fea- 

 ture of this curve is that it is essentially linear 



844 



