RAPPORTS. XIV: MASTERMAN — 16 — 



there is a mean value of over 60 fish on the Sylt grounds, and the figures for area A t 

 also suggest similar large numbers there. A northern limit for soles can be taken along 

 a line from the north-west corner of area B 5 , south-east and south of the Dogger to 

 Flamborough Head. They are fairly abundant on the grounds in the neighbourhood of 

 the Leman Banks and Botney Gut. 



These results confirm those obtained from a study of general statistics (vide ist. 

 Report on Pleuronectidae). 



The medium soles are predominant amongst the size groups. This species manifests 

 the same law of bathymétrie distribution as has been determined for plaice viz. an in- 

 crease in size, the deeper the water and the more offshore the ground. The "medium" fish 

 are more prevalent on the inshore grounds than they were found to be for plaice. 

 "Large" fish are present too, but only during the spawning season. 



The difference arises from the fact that soles are inshore shallow water summer 

 spawners, and the larger sizes migrate inshore to spawn. While plaice on the other hand 

 spawn in deeper water in the winter and only a very few go back into quite shallow 

 water after spawning. 



Yearly fluctuations. In these is found no continuous decrease or increase but an 

 extraordinary abnormality the occurrence oi which coincides with certain abnormal con- 

 ditions of temperatures and salinity. All experience shows the extreme sensitiveness of 

 soles to changes of temperature and it is therefore most probable that the high tempera- 

 tures of 1906 and the low temperatures of 1907 may in part account for the great abun- 

 dance of soles in the eastern area and their scarcity in the northern areas in 1906 with 

 the reverse fluctuations in 1907. 



Seasonal fluctuations. Here again there is definite evidence of the response of soles 

 to temperature changes. The inshore grounds are abundant in this species, a rapid immi- 

 gration beginning about April and culminating in the summer. Complementary variations 

 to those inshore areas are found in the offshore areas where a minimum in spring and 

 summer is followed by a maximum in autumn and winter. Soles appear to move into 

 deeper water at the approach of the colder weather. 



These changes may be compared with those given above derived from a study of 

 general statistics and are also confirmed by the Report of Redeke and Tesch, referred to 

 elsewhere. 



In the winter they are discovered in extraordinary large numbers in the deep small 

 pits such as the Sole Pit and North East Hole which are found in area B 2 . In the shal- 

 lower waters around these holes they are but a small fraction of the numbers inside. 



One particular case is noted. During October to December 1905 there was a sudden 

 cooling of the surface waters of the North Sea, and at the same time the fish disappeared 

 very rapidly from the inshore Danish waters. In the adjacent area C 2 (over 20 fathoms) 

 the winter maximum appeared as early as November. In the winter of 1906 to 1907 the 

 sea temperatures continued higher than usual up to December and then fell suddenly 

 in the early months of 1907 to very low values. Simultaneously the migration from A 3 

 and B 4 was delayed in 1906, the averages being fairly high up to December. The winter 

 maximum in area C 2 was late and protracted beyond the usual time. 



Spawning. April, May and June are the chief months for the spawning of soles. At 

 this period the fish are congregated in shallow waters, mainly under 15 fathoms. In the 



