Indices representative of the age composition should be used with great caution, since the 

 drift net, which is the principal gear for herring fishing, is a selective device. Moreover, we 

 wish to point out that the size composition of a drift net catch is also conditioned by the net selectiv- 

 ity and natural selection of fishes during the formation of a school . 



For a long time, the tagging of herring was not considered advisable because of the harm- 

 ful effects this rather drastic operation has on the fish. In Alaska, the first experimental tagging 

 of herring was done by Rounsefell and Dahlgren (64) . They used a tag inserted into the body cav- 

 ity of the fish. The tags were subsequently detected by special magnetic instruments installed in 

 the conveyer through which the herring travelled from the boats to the processing factories . This 

 method proved to be quite effective, but its application is limited because the herring must be de- 

 livered by a conveyer system. During recent years, this method has been widely used in Norway 

 and Iceland. 



After the end of the war, Wood (81), a Scottish biologist began using small external tags, 

 which were attached to the body of fish by means of a wire near the dorsal fin. 



The number of tagged herring subsequently found in catches was relatively hlg^ . This 

 proved that the use of external tags is effective . 



The Polar Institute imdertook experimental herring tagging early in 1952. White Sea herring 

 moving towards the shores for spawning were observed. We used red celluloid tags fastened with 

 a nickel wire anterior to the dorsal fin . The high percentage of tagged fish found in catches showed 

 that this marking method can yield good results . As an experiment in 1953-1955, the Polar Institute 

 released approximately 12, 500 herring bearing such tags. 



Studying fish migrations by tags is quite effective . However, the movement of tiie tagged 

 fish can only be followed within the regular fishing grounds . When tagging fish to study their 

 migrations and at the same time to determine the fishing intensity, the important factors are the 

 nimiber of fish that survive the test and the maximum possible tag returns . If, however, the only 

 purpose is to establish migration paths, it is important that the mortality rate of tagged fishes 

 should not be excessively hig^. 



Effective detection of tagged fishes in catches depends primarily on the tag's consplcuous- 

 ness and the methods of processing the fish. Internal tags and the tag-detection methods, there- 

 fore offer considerable advantages in places where great quantities of fresh herring are landed 

 directly from the fishing boat. This method could not be used at all, however, where the herring 

 are processed directly on board the fishing boat, since the magnetic instrmnents would have to be 

 installed on board each herring- fishing vessel, and this would considerably complicate processing 

 operations. We, therefore, believe that in our fishing industry, external tags should be used. 

 Herring bore satisfactorily Polar Institute tags . The tag labels are readily noticeable ensuring 

 that a great number of tagged fish can be subsequently detected in catches . 



Herrtng fishing as developed by the Soviet Union during the last few years leads us to expect 

 favorable results from mass tagging. However, this should not be the only method used. The 

 modem organization of fisheries, the extensive application of detecting instnmients used to reveal 

 concentrations of herring, and the large-scale fishing all suggest that the new method for tiie study 

 of migrations consists briefly of the following: Modem underwater detection instruments built on 

 the principle of supersonic wave reflection enable scientists quickly and accurately to locate and 

 follow movements of herring concentrations. At present, we are able to estimate the schools of 

 herring, their distribution and density only on the basis of test catches . Detailed study of abiotic 

 and biotic conditions in which the movement and concentration of herring schools occur is a hig^y 



