70 HJOliT's UYDKOGUAI'IIIC-BIOLOGICAL STUDIES 



tempeniture of the bank water on the Norwegian coast is high in 

 summer, and gradually diminishes through the autumn and winter. 



If this be admitted, we see that the presence of herrings in the 

 eastern part of the Cattegat from August to March is associated with 

 the presence of bank water, and that this bank water, while retaining a 

 fairly constant salinity, undergoes a considerable reduction of temperature 

 during the successive autumn and winter months — from 14° or 15° C. 

 to 4° C. The iluctuations which determine the movements of the herring 

 are probably, therefore, in this case not so much changes of temperature 

 as changes of salinity. The herrings arrive with the bank water and 

 disappear with it. 



The relation of these herrings to the spring herrings of the west 

 coast of Norway is not quite clear. The herrings present in the autumn 

 (November) are regarded by Hjort as immature herrings undergoing 

 their " feeding migration." Whether they spawn on the west coast 

 of Sweden in the following January is not stated, although Pettersson's 

 statement that the winter herring are, as a rule, inferior in quality to the 

 autumn herring tends to support such a view. 



Eeference to Gerhard von Yhlen's Report of the Sea Fisheries of the 

 Ldn of Gotehorg and Bohns for 1877 (translated in U. S. Fish. Com. Rep. 

 for 1877, p. 741), however, shows that in that famous herring year the 

 fish arrived in November, 1877, and remained until March, 1878. The 

 herrings were of different sizes and in different conditions, many being 

 immature, both " year-old " and nearly full-grown, and many being 

 mature breeding herring (12 inches long) and many spent. From 

 November to January lOtli the two last classes were most abundant ; 

 after January 10th the larger class of immature herrings were the most 

 abundant ; while before, and at the end of the season, the immature 

 " year-old " fish were alone. The mature fish spawned in November 

 and December, and in February great quantities of herring-fry, two 

 inches in length, appeared in the district of Fjellbacka, on the eastern 

 shore of the Skagerack. 



3. Growth of Herring. — Hjort concludes his work with an examina- 

 tion of the question as to the rate of growth of the herring. During 

 the spring fishery fish of two sizes are met with simultaneously, one of 

 250 mm. length, the other of 300 mm. These presumably represent 

 two " yearly classes," i.e., lish hatched in different years. 



In the fjords herring of three different sizes live together. 



In summer the three classes are distinguishable by the following sizes : 



(1) 50- CO niiij. (2| ins.) = (presumably) ^ year old (Musseii). 



(2) 120-140 rniu. (5 ins.) = (presumably) 1| year did (Hladsilden). 



(3) 160-185 mm. (6^ to 7 ins.) = (pre3um ibly) 2^ year < kl (Five-p-int 



herring). 



