SOME RESULTS OF THE INTERNATIONAL FISHERY INVESTIGATIONS. 461 



14 inches in total length. This is tlie average size, for the male fish 

 when they first become sexually mature are smaller (one inch or more) 

 than the females. Such fish spawn in the spring. It was formerly 

 believed that during the spawning season plaice became crowded 

 together on certain " spawning grounds." The trawling experiments 

 of the Huxlci/ lent little support to this belief, though there are certain 

 indications that spawning migrations do occur. Such mature fish are 

 not distributed everywhere over the fishing grounds. The ITuxley found 

 that they did not occur, or only very exceptionally, in the shallow 

 waters within the 10-fathom line. On tlie other hand, they were 

 relatively abundant on the Dogger Bank, and here and there in the 

 deeper parts of the North Sea well off the shore. 



All fishery experiments made by the International naturalists agree 

 in this respect, that on the eastern side of the North Sea, off the coasts 

 of Holland and Denmark, in what has been called the Heligoland 

 Bight, we have a predominant small plaice population. There is further 

 agreement as to a general law of the distribution of this fish : that the 

 deeper the water the larger the fish. This, of course, only applies to 

 fishing grounds where the water is less than 50 fathoms in depth. It is 

 safe to say that plaice are absent altogether, or at least very scarce, on 

 sea bottoms of this depth. Indeed, outside the 20-fathom line the fish 

 is very scarce. It is most abundant near the shore, and becomes less 

 abundant as the water gets deeper. The general law that the plaice in- 

 creases in size as the water becomes deeper is nowhere stated so clearly as 

 by Eedeke.* This naturalist has analysed the results of the fishing ex- 

 periments of the Dutch exploring steamer Wodan, made off' the coast of 

 Holland from the Hook to the Zuider-Zee. The distribution of the plaice 

 of different sizes so constantly depends on the depth that Eedeke has 

 drawn lines on the chart which lie terms " isomegalins." Each 

 isomegalin is a line drawn approximately parallel to the coast. The 

 isomegalin I bounds a narrow strip of sea in which only plaice of one 

 to two years in age, and less than 10 centimetres (4 inches) in length, 

 are to be found. Outside this, and parallel to it, is the isomegalin II, 

 between which and the line I are only plaice of over two and less than 

 three years of age, and from 10 to 15 centimetres (4 to six inches) in 

 length. Outside isomegalin II is the line III, which again forms the 

 outer limit of plaice of from three to four years of age and from 6 to 8 

 inches in length. The general law of distribution is stated by Bedeke 

 in these words: "Tlic distribution of the plaice thus appears to be a 

 function of its size, and is so uniform that one can almost say the 

 plaice are so many centimetres long when tlie depth in which they arc 

 taken is so many metres." 



* liappts. d Vroc-vcrh, vol. iii., i;t05. Distrilmtion of tlip plaice on tlic Dutch coast.- 



