of the Fishery Board for Scotland, 



63 



moment know next to nothing, either of the extent or of the causes of 

 migration. 



Before the migration of the herring can be understood, it will be neces- 

 sary (1) to make an exhaustive examination of their food, and to discover 

 what physical conditions influence the movements of the shoals of Crus- 

 tacea and other forms which serve as food ; (2) to determine how the 

 various varieties of herring (should any exist) may be distinguished from 

 each other; (3) to study further the influences which guide the herring 

 in selecting a spawning ground ; and (4) to ascertain how far the move- 

 ments of the herring are modified by storms, temperature, currents, and 

 other physical conditions. 



We may, in the meantime, suppose that herring are regulated in their 

 movements during the greater part of the year by the supply of food, and 

 that during the rest of the year they are under the influence of what may 

 be known as their spawning instinct. 



If we take as an example the Ballantrae herring, we may suppose that 

 after the spawning is over they leave the coast and begin to feed, and 

 that, though directly influenced to a certain extent by the temperature, 

 storms, and other physical changes, their movements are almost en- 

 tirely determined by the movements of the Crustacea and other minute 

 creatures on which they feed. Storms and increased surface temperature 

 will probably only lead them to seek stiller and deeper water, for it is believed 

 that they not only avoid the light, but also that they prefer a low to a 

 high temperature, while the currents which sweep along the shoals of 

 mysis and other crustacca may lead the herring at one time towards the 

 west coast of Ireland, at another towards the Outer Hebrides, or it may 

 be into the upper waters of the Firth of Clyde. There is, however, no 

 evidence that the herring which spawn on the Ballantrae Bank in spring 

 frequent Lochfyne and its neighbourhood during the rest of the year. 

 While moving hither and thither in the wake of their food supply, we 

 know that their condition rapidly improves, and that they soon begin to 

 store up fat in their muscles along the sides of the intestine and in the 

 lobes of the liver. During all this time their movements are naturally 

 very inconstant, so that when the fishing of any district depends on the 

 arrival of herring in search of food, it is likely to be subject to great 

 fluctuation. In course of time, some nine or ten months apparently after 

 the last spawning period, a sufficient supply of nourishment having been 

 stored up, the influence of the spawning instinct begins to assert itself, 

 and to a great extent to overcome all other tendencies. 



The spawning instinct seems to imply several things, but it specially 

 leads the herring to select ground suitable for the deposit of the eggs and 

 waters having a suitable depth and temperature, which will provide an 

 abundant supply of food for the young fry. 



Lj ungman found that herring when under the influence of the spawning 

 instinct (which one may suppose has been elaborated through the influence 

 of natural selection) moved towards the inshore banks on the coast of 

 Sweden along valleys at the bottom of the sea. If this is so, we may 

 suppose that, unless there is a very strong instinctive desire to return to 

 their birthplace as the coast is approached, the - main shoal breaks 

 up into divisions which select all the available inshore banks. It is 

 conceivable that, while nearing the coast in this way, a great storm might 

 break up and scatter the shoal, and carry the herring to other parts of the 

 coast, and thus lead to the desertion of the usual spawning ground, or 

 that, even although the eggs were safely deposited, owing to the appear- 

 ance of cold Arctic currents, the temperature might be reduced below the 

 point suitable for their development. Further, overcrowding on the bank, 

 or the great destruction of spawn or of spawning herring, might also lead 



