Therefore, in more recent years, the oatch-per-day at sea for 

 steam trawlers will make the density appear somewhat higher than 

 it actually is. The catch-per-travel-day of the sailing trawlers 

 will give the appearance that the density had declined more than 

 actually is the case., Both graphs show that during the years 

 1927-35, the density of the stock sustained a regular yearly decline. 

 Figure 4 shows a part of curve I of Figure lo ME is the average annual 

 total catch for the period ig27-.29 (422 million kilograms) and W 

 is the same total during the period 1933-35 (404 million kilograms) o 

 During the first period, the amount CE is reduced annually, while 

 DF is reduced during the second period. The two periods are 6 years 

 apart and if we assume that the amount of the decline has increased 

 regularly and if we take the curve over the trajectory CD as a 

 straight line, then we can represent the amounts during these 6 

 years by C^ E. , Cp Ep, and so forth» The total decrease between 

 both periods is thus s 



EC •»- E, C, + E„ C„ + E C + E C + E C 



11 2 2 3 3 4 4 5 5j 



or 



6EC + EP + EP +EP + EP +EP 



11 22 33 44 5 5o 



E, P., E„P-,, and so forth are to be represented as TF; together they 



11 2 2 

 are 2o5 W» The amount of the reduction is then; 



6 EC + 2.5 PF. 



The average density during the period 1933-35 coincides with the 

 point B in curve II of figure 1. If we look at the catch-per-day at 

 sea in figure 3, it is noticeable that the average level of the period 



1903-13 was passed for the last time in 1929i^ for the steam trawlers 

 and in 1927 for the sailing ship^yit has already been stated that 

 the post-war steam trawler statistics will make the density seem to 

 appear too high and the sail trawler statistics too lowo We assiwie, 

 therefore, that the density level of the period 1903-13 (that is point 

 A in curve I) was reached in 1928. It is also known, however, that the 

 amount of the reduction between the periods 1927-29 and 1933-35 is equal 

 to the difference between the density level in A and in B, thus it is 

 equal to 30 relative units (30a) . We have then the equation; 



6 EC - 2.5 PF = 30a (l) 



la/ Editor's note; Apparently an error in these dates. Possibly 

 slTould read •*.,.. in 1927 for the steam trawlers and in 1922 for the 

 sailing ship." 



2/ That the level 1903-13 was reached temporarily can probably be 

 "accounted for by the influence of weak year classes. 



3i 



