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THE DISAPPEARANCE OF THE PLAICE. 



Pkok. W. GAKSTANG, M.A.. D.Sc. 



In 1875 the plaice caught in the North Sea was 549 cwts., 

 and in 1892 it was 168 cwts. ; in the same period haddock 

 dropped from 837 cwts. to 436 cwts., prime fish from 63 cwts. 

 to 29 cwts., and rough fish increased from 30 to 49 cwts., and 

 the total was 1565 cwts. in 1875 as against 638 cwts. in 1892. 

 In 1867 the total was 2012 cwts. Official statistics since 1892 

 told very much the same tale. 



One of the methods of tracing the migration of the fish in 

 the North Sea is by means of labels or tallies, and inducing 

 to the fishermen to return them, and then' mapping them 

 out. Plaice marked and put into the sea between the Thames 

 and Belgium, that is in the southern part of the North Sea, 

 in the Spring, migrate northward, travelling great distances. 

 Fish marked and placed in the sea off the Danish coast make 

 out towards the open as the summer advances, and partly 

 return in the following winter. The summary of these and 

 other experiments shows that the fish tend seawards and 

 northwards in the summer time. Fish marked and placed in 

 the water in the north of the North Sea, are practically caught 

 in the south in the winter months, but found to be return- 

 ing northwards in the summer. These fish are apparently 

 coming to spawn, and it was a curious fact that in the first year 

 ■of these experiments all the fish caught coming south were 

 males. Later, when the females were found coming south, 

 the females were of a larger size. As a matter of fact, the fish 

 put in in the first year had been rather a small lot, and the male 

 plaice spawned when smaller than the female. All the fish 

 migrating to the south in the winter time were mature fish, 

 and the reason we had no females in the first year of the experi- 

 ment was that the females caught and marked had not reached 

 maturity. Plaice spawned from January to March, but chiefly 

 in February, and to prove whether the southern part of the 

 North Sea really was the spawning ground of the plaice, a special 

 net was made for dredging up the minute eggs of the plaice, 

 and dredgings made all over the North Sea proved the truth 

 of the theory ; the eggs were in far greater numbers in the 

 southern part of the sea than in the northern part. 



If one looks at the section of the backbone of any fish, he 



apog Dec. i. 



