DISTRIBUTION AND MIGRATIONS 263 



the movements of the food supply, for as has been already 

 mentioned, spawning takes place in the open sea, well away 

 from land. The Scad or Horse Mackerel {Trachurus) feeds 

 almost entirely on the fry of Herring, Pilchard, and other fishes, 

 and sometimes appears quitesuddenly off our coasts in incredible 

 numbers at certain seasons, and then equally suddenly dis- 

 appears. Mr. Yarrell has described a shoal of these fishes seen 

 on the coast of Glamorganshire in 1834, which passed the 

 particular locality for a whole week in such vast numbers 

 that the sea, looked on from above, appeared "one dark mass 

 of fish." They were pursuing the fry of the Herring, and 

 feeding-time was observed to be morning and evening. 



On account of its great economic importance, and because 

 of its sporadic occurrence, the migrations of the Herring {Clupea) 

 are of special interest. The seasonal movements of the shoals 

 have been studied extensively by the scientific men of several 

 European countries, but although our knowledge of this 

 intricate problem has been enormously increased, much has 

 still to be learned. At some seasons Herrings may be found 

 in huge numbers in a given locality, at others they will disappear 

 almost entirely; in other places they may be caught all the 

 year round, but the numbers captured on a given ground may 

 exhibit an immense amount of variation from one season to 

 another. These annual fluctuations in the yield of Herrings 

 have attracted the attention of naturalists for many years, 

 and amusing explanations were advanced by some of the earlier 

 writers to account for them. That of Mr. Pennant, for example, 

 smacks rather of extreme piety than of scientific reasoning. 

 "Were we to consider this partial migration of the herring in 

 a moral light," he writes, "we might reflect with veneration 

 and awe on the mighty power which originally impressed on 

 this most useful body of his creatures, the instinct that directs 

 and points out the course, that blesses and enriches these 

 islands, which causes them at certain and invariable times to 

 quit the vast polar deeps, and oflfer themselves to our expecting 

 fleets. That benevolent Being has never, from the earliest 

 records, been once known to withdraw this blessing from the 

 whole, though He often thinks proper to deny it to particulars ; 

 yet this partial failure (for which we see no natural reason) 

 should fill us with the most exalted and grateful sense of His 

 providence, for impressing so invariable and general instinct 

 on these fish towards a southward migration, when the whole 

 is to be benefited, and to withdraw it when only a minute part 



