60 



It is necessary to realise to some extent tho wealth of the 

 annual contributions, tho death rate at different stages, and the 

 sampling done by fishing as that by experimental work. 



1915. Buchanan Wollaston. Report on the Spawning Grounds of the Plaice in the 

 North Sea. Fish. Invest., Ser. II., v. 2. 



Rosa M. Lee. Review of Commercial Trawler Statistics. Fish. Invest., Ser. II., 

 v. 2. 



1915. Wallace. Report on tho Age, Growth and Sexual Maturity of the Plaice in 

 certain parts of the North Sea. Fish. Invest., Ser. II., v. 2. 



6.— MARKING EXPERIMENTS. 



The preceding presentation of the facts has served to state 

 the nature of the seasonal migrations and their effects in deter- 

 mining tho location of the inshore fishes and their relationship 

 to the distribution in general in the North Sea. The variations 

 produced by tides and the variation brought about by the con- 

 ditions of successive seasons have also been indicated. But our 

 knowledge of the movements of these fish has been greatly extended 

 by marking experiments. During a number of yeais samples 

 of the fish captured in the trawl net were retained and marked and 

 liberated. The fish were measured, usually weighed as well, 

 and when they were recaptured we obtained not merely informa- 

 tion as to migration but as to growth, and the experiments enabled 

 an estimate being made as to the effect of fishing on the total 

 population of marketable fish. 



Flounder. — The accompanying chart (figure 5) exhibits in 

 a graphic manner the results of the marking experiments with 

 respect to flounders. The basal line marks the time from that 

 of marking to recapture, and the vertical lines tho size. Tho 

 flounders were marked and liberated during the summers 1904-07. 

 It will be observed that the flounders caj)tured not long after 

 marking in' the first quarter showed, as we should expect, little 

 or no migration. What little migration was exhibited was to the 

 south for a short distance, but in winter and spring the recaptures 

 were somewhat to the north of the place of liberation. This goes 

 to indicate that the inward movement is to the south as well as 

 inshore, and tho winter offshore movement is to the north. But 

 from February to Juno, and especially in March and April, which 

 is the season of spawning, tho flounders were captured for the 



