THE SOLES 73 



Life-History of the Soles 



The Influence of Temperature. The soles — like the hake — 

 are essentially ' southern ' fishes. Hjort {Depths of Oceayi, 

 p. 452) notes that on the shallow coast banks and on the 

 Dogger down to 20 fathoms the bottom temperature of the 

 North Sea rises to 54° F. at least ; on the other hand, below 

 21 fathoms the summer and winter temperature is very much 

 the same — about 43° F. He suggests that down to 21 fathoms 

 the sole maij find in the North Sea shallows water of approxi- 

 mately the same temperature as it is accustomed to in deeper 

 waters off the Atlantic coast of Europe. If that is so, and if 

 temperature is the deciding factor, it is clear that any circum- 

 stance which prevented the water on a particular bank from 

 rising in summer to 54° F., or which postponed the rise of 

 temperature, might either prevent the soles from frequenting 

 that shallow altogether or might make their visit abnormally 

 late. Conversely an exceptionally early summer at the bottom 

 might produce unusually large congregations of soles. And if 

 soles frequent these shallows for spawning purposes the effect 

 on the brood of the year might be very great. By far the 

 most prolific grounds in the North Sea are situated at from 

 10 to 20 fathoms.^ But the French deep sea expeditions have 

 caught soles at 130 fathoms off the Atlantic coast of Europe. 



The Spawning Grounds. The eggs in the North Sea have 

 generally been found in depths between 8 to 20 fathoms near 

 Norderney from April to August, May being the principal 

 month. Spawning also takes place in the Channel ; off 

 Plymouth soles spawn in the earlier months ^ of the year ; 

 and in the Irish Sea from May to July. It has long"^been 

 beheved by fishermen — and is apparently now believed by 

 Science — that the main spawning-grounds are very mucJEi 

 farther to the south ; and the spawners in our home waters 

 are doubtless wanderers. It is important to notice that when 

 500 soles were placed in St. Andrews Bay in 1897 they appar- 

 ently spawned in due course.^ Eggs ^ have been found off 

 Marseille as earlv as February and off the east coast of Scotland 



- Journ. M. B. A., vol. xii, part 2, p. 197. 

 ^ British Marine Food Fishes, p. 9. 



* The eggs measure from -045 to -051 inch in diameter, i, e. about 700,000 to 

 the quart. 



