CONSIDERATION OF INDIVIDUAL FISH 97 



cessive spawning periods. The Scandinavian^ and Danish writers 

 believe that a period of eighteeA months elapses between the 

 spawn,ing periods, in which case the spring herring of one year would 

 become the autumn herring of the next, and so on. Heincke contests 

 this view. He argues that if the interval between two successive 

 spawning periods exceeded one year then we should get an equal 

 distribution of spawning herring in all months of the year. This 

 argument loses much of its force if the interval were approximately 

 eighteen months, since there would then be two principal spawning 

 periods, spring andautumn. 



Since the capture of the mature herring is the occasion of an 

 enormous fishery, we possess a great deal of information of the 

 appearance of the mature fish on our coasts (see p. 47). It is, 

 therefore, a matter for some surprise that the spawning grounds 

 are not well known and have not been determined with any exacti- 

 tude. In certain cases limited areas have been explored, the eggs 

 of the herring collected and the development of the young studied. 

 The first investigation of this kind was that undertaken by AUman.^ 

 who was deputed by the Scottish Fishery Board to investigate the 

 herring of the Firth of Forth. He found the spawn of the herring 

 on rough rocky ground near the Isle of May, at depths from 14 

 to 20 fathoms. .These eggs were attached to stones, shingle, shells 

 and other objects on the sea bottorri. Since then the spawn of 

 the herring has been obtained from other localities, notably from 

 the Ballantrae Bank in the Firth of Clyde,* where large numbers 

 of herring eggs have been dredged up from a gravelly bottoni in 

 comparatively shallow water. A still more striking instance is 

 that of the Baltic herring which spawn off the Danish island of 

 Langeland in depths of from i to 4 fathoms, or even enter the 

 mouth of the River Schlei,* where the writer has observed them 

 spawning in brackish water at depths of only a few feet. The eggs 

 of the herring have been collected in this locality attached to the 

 submer::3d portions of a fresh water plant {Potamogeton pettinatus). 

 It is a remarkable fact that the herring can maintain itself in arms 

 of the sea which have been permanently shut off from the main 

 ocean and in which the water has become practically fresh.^ 



^Nti^!%t^ar.8^8.ST?" ''*■ ^'^'- '^-'^'^«.- B*nd" M.n7nv. 



^ Royal Commission on Herring Trailing, 1863 

 S.;.l.!p;bUshe?l8fr^ "' *^^ "^™"^'" ^y J- ^"^^^"^ E-^-^' -'^ ^-- ^^^'• 

 Commhsion?i:SS.''^ """P^" ^''^''' ""' ^^^^^ ^'^^S) in the Jahresbericht der K. 



' S^^ Jt"^«?; " Altersbestimmung durch otolithen bei den Clupeiden " Wiss 

 Meeres. Abt. Keil., N.F. Bd. 6, 1902, p. no. "i-ciuen, wiss. 



H 



