GEiNERAL BIOLOGY 



715 



(on the west coast of Sweden), and are captured in the 

 deep channel of the Kattegat, or in the fjords of Bohuslan. 

 Pettersson discovered that the regular occurrence of these 

 herrings in several cases coincided with certain large sub- 

 marine waves which he could register in the Gullmar fjord, 

 and he sets up the hypothesis that there is a certain connec- 

 tion between these two phenomena. Fig. 513 shows curves 

 denoting different salinities in the Gullmar fjord in November 

 and December 19 10, and it is seen that the deep salt layers 

 rose several times during November, like huge waves, up 

 towards the surface. Extensive investigations off the coast 

 in the Kattegat proved the occurrence of similar deep-sea waves 



Bomo. 



Kov Dec, 7910, 



17 19 Z1 Z3 Z5 17 19 



10 



100 ? 2'tOOO 30000 HL. 



Fig. 513. — Submarine Waves in the Gullmar Fjord in November and 

 December 1910. (From Pettersson.) 



in the latter locality. These waves, according to Pettersson, 

 carried the water of the Jutland coast banks (bank-water with 

 a salinity of 32 to 34 per thousand) like a torrent into the 

 Kattegat and its fjords, forcing the fresh surface water out. 

 The herring shoals dwelling on the Jutland coast banks were 

 literally, Pettersson says, sucked into the fjords of the Swedish 

 west coast as by an enormous vacuum pump. This inflow, 

 Pettersson points out, takes place periodically and coincides 

 with the phases of the moon (see Fig. 513). One wave, on 

 the 15th of November, occurred at full moon, when the moon 

 was nearest to the earth (perigee), another wave on the 28th 

 of November occurred at new moon, when the moon was 

 farthest from the earth (apogee). Coinciding with the last 

 wave the herring shoals appeared, and between the 23rd and 

 24th of November 24,000 barrels of herring were taken. 



