332 REPORT OF THE COUNCIL. 



spawning plaice, have been continued. The results show that, on an 

 average, female plaice are first mature when at the end of their sixth 

 year on the grounds around the Dogger Bank, at the end of their fifth 

 year in the southern part of the North Sea, and at the end of their 

 fourth year in the western part of the Channel. Males, on an average, 

 mature a year earlier than the females. 



There is evidence to show that spawning takes place particularly in 

 the deep water off the Yorkshire coast and at the southern end of the 

 North Sea, but not in the region of the Leman Banks or on the Dogger 

 Bank. Spawning off Yorkshire appears to occur later than on the 

 southern spawning ground. 



The examination of 123 otoliths suggests that local and sexual 

 differences are reflected in the otolith, owing to a diminution of growth 

 at maturity. The data are not however considered to be as yet suffi- 

 cient for the satisfactory substantiation of this conclusion. 



The material for this research consists in observations on the size and 

 maturity of 13,247 plaice, in 4,106 of which the age was determined 

 from the otoliths. 



Observations on Plaice in the Barents Sea. — By the kindness 

 of Messrs. Hellyer, a member of the staff was enabled to make a 

 voyage to the Barents Sea in a Hull trawler, in August last. In the 

 course of this voyage 2,146 male and 2,365 female plaice were 

 measured. 



The "average size at first maturity," i.e. the length at which 50 % 

 are mature, was found to be about 40 cm. for female plaice from the 

 Barents Sea ; which is the same as for those from the central grounds of 

 the North Sea. Whereas, however, in the Barents Sea the great 

 majority of the plaice caught on the voyage were considerably above 

 this " average size at first maturity," and had therefore spawned once at 

 least, the majority of plaice examined in the North Sea were below it, 

 most of them not having spawned at all before being caught. The 

 North Sea thus is in the condition which theoretically should result 

 from the overfishing of such a plaice population as that of the Barents 

 Sea. 



The rate of growth of the Barents Sea plaice appears to be slow, 

 possibly owing to the low temperature (about 2° F. above freezing 

 point) which prevails. 



There is some evidence that the plaice migrate towards Atlantic 

 water for spawning purposes, as do those of Iceland. 



An account of this voyage appears in the Journal of the Associa- 

 tion, vol. viii., p. 71. 



Vitality of Trawl-caught Plaice. — A report has been prepared 



