Figure 3 gives the impression that the selectivity is lessened by 

 enlarging the mesh widtho This does not appear to be true iq any of 

 the other curves and it is likely that the flat curve of the 8 3/4 

 centimeter cod end was caused by faulty testing. The much steeper 

 10 centimeter curve supports this opiniono 



It is very difficult to make regulations to encourage the selec- 

 tivity of the netSo It is hardly possible to order the fishermen to 

 use single-knitted meshes in the cod end when this would weaken the 

 constructioji of the nete Nor can a maximim towing speed be seto One 

 can only try to convince the fishermen that it is not necessary to 

 tow as Tast as possible, by pointing out that the British and German 

 ships have the habit of turning their engine over at slow speed dur= 

 ing the towingo 



I* is practical, however, to order a larger minimum mesh widtho 

 Elaborate English tests have shown the effects of this in practio«o 



The English fishery biologist, Davis (1934 a,c) had two indenti-= 

 cal trawlers fish for two months on a normal commercial basis as near 

 as possible to one another© One had a cod end with 7 l/2 centimeter 

 meshes and the other had meshes of 10 centimetero The principal 

 catch was haddocko The results of this test, given in weight, appear 

 in figure 6o Fewer small and more large fish were caught with the 

 large=meshed cod endo Moreover, the smaller-meshed cod end brought 

 up more trasho The total returns were approximately alike for both 

 ships o Therefore, undersized fish, labor and material were saved 

 without financial loss© 



A similar test was made with two trawlers fishing for "heek" out 

 of Cardiff (Fishery notice, 1934) » Cod ends with meshes of about 10 

 centimeters were compared with cod ends with meshes of about 12 l/2 

 centimeters o The large-meshed net caught only half as much undersized 

 "heek* as the small=meshed one© The returns per-10-»hours fishing for 

 the larger-mesh net averaged 27 guilders, with the small meshes, 25 

 guilders/7 schillings « It was clearly more economical to fish with 

 the larger-«ieshed cod end© 



The above tests were made by order of the British Government, 

 but similar tests were made by a shipping concern on their own 

 initiative in Grimsby during 1945© Nine trawlers were employed 

 for these tests© They fished in the West and mid-North Sea, 

 chiefly for medium sized cod, plaice and fine fish© The large«= 

 meshed net produced about one basket of undersized fish each haul, 

 while the small-meshed net produced 37 baskets each haul© The large- 

 meshed net hauled about 42 baskets of trash against 105 for the 

 small=meshed one© 



48 



