12 



Part III, — Fifteenth Annual Report 



the East coast of Scotland and England to the neighbourhood of the 

 Wash ; (2) that it then travels in an easterly direction towards the 

 coast of Denmark, and then northwards to the Skagerak, which it 

 may or may not enter, and finally passes northwards along the 

 west coast of Norway, at least as far as the Loffoden Islands. 



Drift bottles were found scattered along a stretch of about 1700 

 miles of coast, in Scotland, England, Holland, Germany, Denmark, 

 Sweden, and Norway, between 53° and 69° N. latitude. 



A detailed study of the winds prevailing during the time the 

 experiments were in progress, based upon over 12,000 observations, 

 appears to show that this circulation of the surface water in the 

 North Sea is principally due to the preponderance of south-westerly 

 and westerly winds, which tend to heap up the surface water on the 

 western, or continental coasts, when, as it cannot escape southwards 

 owing to the shallows and the narrow orifice of the Channel, it 

 passes to the north ; but subsidiary influences may aid the move- 

 ment. For some weeks last winter, owing to prolonged gales and 

 strong winds, first from a south-easterly and then from a north- 

 easterly direction, the circulation was reversed, the surface water 

 passing rapidly northwards along our east coast, from Norfolk to the 

 Shetlands. 



The main object of the experiments was to determine the part 

 taken by the surface currents in transporting the floating eggs and 

 larvae of the food fishes from the great spawning areas lying oft the 

 coast to the territorial waters and inshore grounds. It is shown 

 that as the normal current moves along our east coast in a southerly 

 direction at a mean rate of about two or three geographical miles 

 a day, and as the floating eggs, according to the species and the 

 season, take from about a week to over three weeks to hatch, and 

 the larva? are exposed for some weeks additional to the action of 

 the current, they may be carried for very considerable distances 

 from the place where they are spawned. 



From a study of the mean temperature of the surface waters off 

 the east coast of Scotland in each month throughout the spawning 

 season, namely, from January to August, and of the duration of 

 the development of the embryonic fishes within the eggs of the 

 various species at such temperature, it is shown that the spawning 

 grounds of early spawners, as the cod, haddock, and especially the 

 plaice, may be normally situated more than fifty or sixty miles to 

 the north of the locality where the young fishes are found. 

 With summer spawners, on the other hand, whose eggs develop 

 with much greater rapidity, owing to the higher temperature of 

 the surface waters, the distance between the spawning area and 

 the ' nurseries ' of the young fishes is much less. The spawning 

 areas off a particular part of the coast do not normally supply the 

 inshore waters opposite to them, but those situated further south ; 

 thus, for example, the breeding grounds off the coasts of Forfar- 

 shire and Kincardine stand in relation to St Andrews Bay and 

 the Firth of Forth, while the breeding grounds situated to the 

 east of the latter stand in relation to the coasts of Berwickshire 

 and Northumberland. 



It is shown that the southward drift of the floating eggs and 

 larvae of the plaice is in agreement with the migratory movement 



