120 



100 



sS 60 



A 



Ai 



26 32 38 44 50 56 62 68 74 80 86 CM 



10 



15 



20 25 



LENGTH 



30 



Figure 3. — Selection curves — cod. Solid line = 105 mm covered; dash line 

 135 mm covered; dot line = 135 mm uncovered. 



Selection data for the 107 mm covered cod end tows are 

 given in Table 8 and the corresponding selection curve, drawn 

 by eye, is shown in Figure 6. The 50% retention length of ap- 

 proximately 34 cm (13.4 in) gives a selection factor of 3.17. 

 Selection data for the 138 mm covered cod end tows are given 

 in Table 9, and the corresponding selection curve is shown in 

 Figure 6. The 50% retention length of approximately 42 cm 

 (16.5 in) gives a selection factor of 3.04. Selection data for the 

 107 mm and 138 mm uncovered tows are given in Table 10. 

 (For a detailed explanation of the methodology, refer to Pope 

 et al. 1975.) From this method, a 50% retention length of 48 

 cm (18.9 in) is obtained for the 138 mm cod end which gives a 

 selection factor of 3.47. 



The portion of the available population, represented by the 

 cod-ends-plus-covers curve, that each cod end selects is shown 

 in Figure 7. Very few fish were present below the selection 

 range of the 107 mm cod ends. As expected, the larger cod end 

 caught fewer of the smaller fish. A review of the length fre- 

 quency distributions shows that the larger cod end caught 

 more of the larger size fish than the small cod end. Table 11 

 shows the effect of this increased efficiency in higher landings 

 of the large cod end. 





















~ 



















• 





- 















o 







- 













• ^~ 





■::■. :.--■-.: : 

 KRTH MEAN 









° 



■ 



•■' 



;§5rv 













^^^ 



















50 60 



so so cm 



35 if J 



Figure 4. — Cod girth to length relationships. Solid circles = Scituate; open 

 circles = Gloucester. 



Table 6. — Atlantic cod landings. 



Length 













interval 





Small 



uncovered 



Large 



uncovered 



(cm) 



Kg/fish 



No. 



Kg 



No. 



Kg 



10-12 



0.03 











13-15 



0.04 











16-18 



0.04 











19-21 



0.04 



1 



0.04 







22-24 



0.09 



1 



0.09 







25-27 



0.13 



5 



0.7 







28-30 



0.22 



16 



3.5 



1 



0.2 



31-33 



0.34 



31 



10.5 



2 



0.7 



34-36 



0.45 



64 



28.8 



4 



1.8 



37-39 



0.58 



83 



48.1 



12 



7.0 



40-42 



0.67 



124 



83.1 



14 



9.4 



43-45 



0.85 



99 



84.2 



22 



18.7 



46-48 



1.03 



59 



60.8 



30 



30.9 



49-51 



1.21 



60 



72.6 



33 



39.9 



52-54 



1.44 



61 



87.8 



55 



79.2 



55-57 



1.71 



51 



87.2 



60 



102.6 



58-60 



2.07 



61 



126.3 



80 



165.6 



61-63 



2.30 



58 



133.4 



88 



202.4 



64-66 



2.66 



50 



133.0 



106 



282.0 



67-69 



3.02 



58 



175.2 



108 



326.2 



70-72 



3.38 



63 



212.9 



109 



368.4 



73-75 



4.10 



55 



225.5 



106 



434.6 



76-78 



4.50 



44 



198.0 



60 



270.0 



79-81 



5.40 



33 



178.2 



49 



264.6 



82-84 



5.90 



15 



88.5 



23 



135.7 



85-87 



6.30 



17 



107.1 



12 



75.6 



88-90 



7.20 



7 



50.4 



12 



86.4 



91-93 



7.70 



8 



61.6 



8 



61.6 



94-96 



8.60 



8 



68.8 



7 



60.2 



97-99 



9.90 



5 



49.5 



1 



9.9 



100-102 



10.80 



1 



10.8 



5 



54.0 



103-105 



11.70 



3 



35.1 



1 



11.7 



106-108 



12.60 



2 



25.2 



5 



63.0 



109-111 



13.50 



2 



27.0 



2 



27.0 



112-114 



14.40 



1 



14.4 



1 



14.4 



121-123 



19.40 



1 



19.11 







135 



29.70 



1 



29.7 







Totals 1,148 2,537.4 



Landings (discard <42 cm) 2,362.6 



Landings (discard <52 cm) 2,145.0 



1,016 



3,203.7 



3,184.6 

 3,095.1 



