< 



O 









k 







30 



- 





1 







25 



— 





' 1' 

 >f 31 







20 



- 





f 1 



1 ll 

 1 ll 







15 







1 







10 



- 



•7 

 I 



;/' 



■7' 









5 





.... .7/ 











I 



/■' ' 



1 



: 1\ 

 a* 

 V 

 \> 



V 





26 32 38 44 50 56 62 68 74 80 CM 



_l I I I I 1 



10 



15 



20 25 

 LENGTH 



30 



IN 



Figure 7. — Catch distributions — haddock. Solid line = cod ends + covers; 

 dash line = 138 mm cod ends; dot line = 107 mm cod ends. 







A . 





V 







/ 



/ 



/ 



/ 



/ 





,•8 



A 







"\ 



// 















11 14 17 20 23 26 29 32 35 38 41 44 47 50 CM 

 I I I I I 



Figure 8. — Selection curves — yellowtail flounder. Solid circles = 133 mm 

 covered; open circles = 102 mm covered; open triangles = 133 mm uncovered. 



Table 12. — Yellowtail flounder selection factor sum- 

 mary. 





Total 



no. of 



Fish 





Selection factor 



Experiment 



Small 

 mesh 



Large 

 mesh 



Alternate 

 tow 



One 



Two 

 Four 



Combined 1 



3,581 



8,881 



321 



12,783 



2.07 

 2.08 



2.16 



2.16 

 2.09 



2.18 



2.37 

 2.30 



2.29 



Yellowtail Flounder 



'Combined also contains data from Experiment Four. 



These results are based on catch data from Experiments 

 One, Two, and Four. The selection factors determined during 

 this series of experiments (Table 12) show the alternate tow 

 selection factors are in close agreement with those found by 

 Lux (1968). Assuming the real selectivity lies between the two 

 methods used, 2.25 is a fair choice for the selection factor. The 

 selection curves determined from the combined data (Fig. 8, 

 Tables 13 to 15) indicate the 25-75% selection ranges 

 found throughout the experiment varied from 3 to 6 cm. 

 Again, as with the Atlantic cod data, the selection factors for 

 the small covered mesh are lower than those determined for 

 the larger mesh. 



It should be noted that a comparison of the two large-mesh 

 selection curves determined by the two methods used is not 

 strictly valid. This is due to the fact that the uncovered selec- 

 tion curve was derived by comparing the large-mesh uncovered 

 cod ends with the small-mesh uncovered cod ends and the 

 covered selection curve was derived by comparing the large- 

 mesh covered cod ends with the 50 mm covers. In the first case 

 the retention percentages will be affected by the selectivity of 

 the small-mesh cod ends, this occurring where the selection 

 process overlaps (in this case about 17 to 27 cm). The degree of 

 inaccuracy introduced was checked by adjusting the large- 



Table 13. — Yellowtail flounder length frequency 

 distributions and percent retained for the small- 

 mesh (102 mm overall average) covered tows — six 

 vessels. 



Length 



Numbers caught 





interval 





102 mm 



Percent 



(cm) 



102 linn 



plus covers 



retained 



10-12 







2 



0.0 



13-15 







36 



0.0 



16-18 



14 



185 



7.6 



19-21 



78 



335 



23.3 



22-24 



242 



333 



72.7 



25-27 



274 



286 



95.8 



28-30 



216 



216 



100.0 



31-33 



491 



496 



99.0 



34-36 



715 



720 



99.3 



37-39 



523 



524 



99.8 



40-42 



282 



284 



99.3 



43-45 



182 



182 



100.0 



46-48 



52 



52 



100.0 



49-51 



9 



9 



100.0 



52-54 



4 



4 



100.0 



55-57 



2 



2 



100.0 



Totals 



3,084 



3,666 





12 



