94 SECTIONAL ADDRESSES 



You will, I think, have noticed that in this outline of recent events I 

 have made no reference to other hydrographical data, such as salinity 

 and temperature, and I must needs do so now lest you suspect me of 

 suppressing evidence which is not in accord with the story I have told 

 you. For the plain fact is that the observations we have of salinity and 

 temperature do not fit into the picture. 



For many years past Dr. H. W. Harvey has followed the temperature 

 and salinity changes at the western end of the Channel, ^^ and during the 

 period since 1924 he has found that the most conspicuous movements 

 were large incursions of low salinity water in May 1928 and in March 

 and April 1936, while in 1932, 1933 and 1934 (especially in 1933) patches 

 of water with unusually high salinity moved eastwards up the Channel. 

 So far as can be seen these movements show no correspondence with the 

 marked biological changes which have occurred : it is in the phosphate 

 data only that a correlation can be found. 



In the year 1921 there was an exceptional influx of Atlantic water, 

 which filled the Channel ^^ and flooded into the North Sea. Salinity 

 and temperature were much above normal and numbers of unusual 

 planktonic organisms of Atlantic origin were found in the North Sea.^' 

 Recent experience at Plymouth might lead one to think that such an 

 influx as this would bring benefit to the herring fisheries, but actually 

 it was just the reverse, for at Plymouth and in the North Sea, at Lowestoft, 

 Yarmouth, Grimsby and North Shields, the herring fishery was much 

 below normal.^* 



In recent years also a number of unusual planktonic forms have 

 entered the Channel, brought apparently by incursions of low salinity 

 water flowing round Ushant ; but these movements have had no effect 

 on the depleted phosphate supply. 



It thus appears that incursions of Atlantic water into the Channel 

 may bring advantage to the biology of the area or may be detrimental, 

 that no obvious connection between the biological data and temperature 

 and salinity is noticeable, and that so far as we can at present see the 

 only correlation that can be established is with phosphate. The ex- 

 planation lies, I believe, in our very considerable ignorance of the 

 constitution and origin of the water-masses which from time to time 

 enter the Channel. 



There is evidently more than one way in which an influx of Atlantic 

 water may be advantageous. It may, in the first place, bring water with 

 a high content of phosphate and other nutrient salts which will subse- 



11 H. W. Harvey, ' Hydrography of the Mouth of the EngUsh Channel, 1925-28 

 and 1929-32,' Journ. Marine Biol. Assoc, XVI, p. 791 (1930) ; XIX, p. 737 



(1934)- 



1* J. R. Lumby, ' The Sahnity and Temperature of the Southern North Sea 

 and Enghsh Channel during the period 1920-21,' Publications de Circonstance, 

 no. 80 (1923). 



1* A. C. Hardy, ' Notes on the Atlantic Plankton taken off the east coast of , 

 England in 1921 and 1922,' ibid., no. 78 (1923). 



1* J. R. Lumby, ' Salinity and Water Movements in the English Channel 

 during 1920-23,' Min. Agric. Fisheries, Fish. Invest., ser. 2, VII, no. 7, p. 18, 

 fig. ix (1925). H. W. Harvey, ' Hydrography of the English Channel,' Conseil 

 Internal. Rapp. et Proc.-Verb. des Riunions, XXXVII, Rapp. Atlantique, 1924, 

 pp. 82-84 (1925). 



