244 R. J- H. BEVERTON 



The total annual landings of the above five species since 1906 are shown in 

 Fig. I. They fall broadly into two groups, the landings of plaice, haddock 

 and cod being some ten to twenty times greater than those of sole and turbot. 

 Although the relation between landings and population size is certainly not 

 the same in all five species, there is no doubt that this difference in landings 

 reflects a corresponding difference in order of magnitude of population size. 

 It is also possible to see from Fig. i that in certain species, notably haddock, 



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 O 

 P 120 



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1900 05 10 15 20 25 30 35 40 A5 50 55 60 



Year 



Fig. I. — Total international landings of certain species from the North Sea, 1906-57. 



there is evidence of a downward trend; whereas in others, such as plaice, the 

 landings have remained at a roughly constant level throughout. 



Long-term trends within each population can, however, be examined 

 better by calculating the landings in each year as a ratio of the average 

 landings of the species over the whole period, and plotting these ratios on a 

 logarithmic scale, as shown in Fig. 2. It is now apparent that the most 

 marked trend, an upward one, is in fact shown by sole (at the top of the 

 diagram), the landings of which have increased by some eight times since 

 the beginning of the century. This may be, in some degree, an exaggeration 

 of recent trends in the true population size of sole because fishing for sole 

 has become more specialized in the last decade ; but this increased fishing has 



