catch- per=unit-"Of -time also must have increasedo However, the 

 catch-per-day at sea has declinedo This is somewhat clearer when 

 (as was done in table 6) a correction is made for the working of 

 the Vi gne ron-Dahl net (by multiplying the values for the years 

 1925=27 when the V"=D net first came in use by 5/6 for haddock and 

 codj and by 7/8 for plaiceo The values of later years were multi= 

 plied respectively by 2/3 and 3/4) <, The values in table 6 are a 

 combination of Germanj English;, Dutch and Scottish observations o 



It is clear that since 1918j, the density of the haddock stock 

 has declined steadily o The recession of the total landings can 

 never be blamed on a possibly decreased fisheryo We must conclude 

 that after 1918 a state of overfishing of haddock has appeared, 

 probably beginning about 1925o 



An increase of fishing intensity is shown always by the gradual 

 disappearance of older individuals » During a state of overfishing, 

 the older fish alone account for a trifling percentage of the catches o 

 Since it is principally these older individuals which spawn^ there 

 is danger that the breeding production will become too small© However, 

 since one female lays so many eggs, a fairly small nximber of older 

 fish is often sufficient to keep the stock up to paro The overfishing 

 first manifests itself because the production capacity of the fish 

 stock diminishes, but if the overfishing continues it can also happen 

 that the egg production becomes too smallo The overfishing of 

 plaice in the Baltic has taught us how soon this may have fatal results o 



The size of a year class at the end of the first year is especially 

 dependent on (besides the number of eggs laid) a number of environ- 

 mental factors which may fluctuate greatly from year to year, and 

 thereby bring about the well-known fluctuations in the strength of 

 the various year classes o Consequently, a decline of egg production 

 may not be noti cable if it is coupled with a favorable influence of 

 •nvironmental factors o Eventually such a decline becomes clear, 

 however, because the average strength of the year classes diminishes o 

 Although it cannot be said with certainty, it appears that this was 

 the case with haddockj therefore, this would show that the haddock 

 were very seriously threatenedo 



bbo Cod 



The total catches in table 5 show an increase during the period 

 1903=14 parallel with an increase of the fishing intensityo During 

 the war period the returns decreased, only to increase to the pre- 

 war value during the period 1919-22© Thereafter, a decline is shown, 

 but is not as pronounced as the decline of the haddocko 



There was no overfishing of the cod stock before 1914, but after 

 1918, we see a small decline of the total catches from the North 

 Sea, together with an increase of the fishing intensityo Table 6 

 shows that the density of the cod stock had declined far less than 



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