LENARZ: MESH RETENTION OF LARVAE 



lOOf- 



100 



CC 10 



01 



001 



UNCORRECTED (n^^jj) 



CORRECTED (nj:jj 



J L 



J \ L 



2 5 375 575 775 975 1175 1375 15 75 



475 6.75 8.75 1075 12.75 1475 



Lj (mm) 



lOOi- 



- o 



10.0 



O 1.0 



cr 



UJ 



a. 



a I 



0,01 



UNCORRECTED (n^jgi' 



CORRECTED (n'^jgi 



J L 



25 375 5.75 7.75 9.75 1175 13 75 1575 



4.75 6.75 8.75 10.75 12.75 14 75 



Lj (mm) 



Figure 3. — Corrected (n'ljn) and uncorrected (nun) 

 catches by standard length (Lj) of northern anchovy 

 taken at night with type 1 (0.55-mm mesh) net. Catches 

 are expressed in percent of total. 



with size. This indicates that few if any small 

 anchovy larvae escape capture by passing 

 through the meshes. Thus a 10% decrease in 

 mesh size and a large decrease in the variance 

 of mesh size changed Pn from 0.60 to about 1. 

 The difference in Pn between the type 1 and 

 type 3 nets means that total catches of anchovy 

 larvae by the type 1 net should be multiplied by 

 1.7 to be comparable to catches of anchovy larvae 

 by the type 3 net. 



DISCUSSION 



The similarity of the catch curves of anchovy 

 larvae caught by the type 3 net and the corrected 

 catch curve for the type 1 net suggests that the 

 estimates of su are reasonably accurate. It 



Figure 4. — Corrected (n'jj2i) and uncorrected (mij2i) 

 catches by standard length (Lj) of northern anchovy 

 taken during day with type 1 (0.55-mm mesh) net. 

 Catches are expressed in percent of total. 



would be a remarkable coincidence otherwise as 

 the data are independent. 



It is interesting that the type 3 (0.505-mm 

 mesh width) net apparently retains most if not 

 all anchovy larvae, for the body depth at the in- 

 sertion of the pectoral fin of 3.75-mm an- 

 chovy larvae is about 0.35 mm (P. E. Smith, 

 personal communication) which is considerably 

 less than the mesh width. Smith, Counts, and 

 Clutter (1968) summarized the results of Saville 

 (1958) by concluding that an organism must be 

 wider than the mesh diagonal to be completely 

 retained. A conclusion of this study is that the 

 "diagonal rule" is too conservative for slowly 

 towed nylon nets. Heron (1968) concluded that 

 mesh variability is a very important factor in- 



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