1 895- ^O- 9- HYDR.-BIOL. STUDIES OF THE NORW. FISHERIES. 59 



ments of the temperature have proved tliat changes in the temj>erature take 

 place to a surprising extent, and, according to what hasbeen previously 

 mentioned. therefore also in the currents, as in a year, such as^obser\ed 

 b\- myself ( 1 894), the temperature may be ven.' high (5 ") and therefore 

 North Sea Water on the coast, whilst in other \ears a cold^ layer — 

 from 100 to 150 mètres in thickness — a fresher current, may be 

 found on the coast. 



In what here follows I shall give some instances of how the fisher)' 

 got on under these changing conditions. 



Curator 0. S. yensm reports concerning the year 1881 : »In 188 1 the 

 herrings were observed in swarms throughout the whole of Januar\". in the 

 same manner as in 1880; but, in Februar}-, when ready to spawn, they did 

 not go in to land, but continued to wander about in shoals until the be- 

 ginning of March when the fisher\- terminated. There was, consequently, 

 ver}- Uttle night netting, that which, through its regulant}-, was always the 

 most paying method of fishing, and the fishermen were obliged to, con- 

 stantl}-, venture upon the unsafe and difficult capture of herrings out in 

 the open sea isee Chart of Depths II). The numerous parties of fisher- 

 men which had assembled there, waited in vain for a good haul of the 

 nets. The minor hauls of herrings which were made were not due to 

 the regular landward migration for the purpose of spawning, but to the 

 whales which occasionally chased a few shoals to the shore. 



As is known, the Herring is ven,- sensitive to the temperature, and 

 prefers to keep to the deep where a certain temperature is met with.* 

 It is also an old experience that in a mild Winter it goes in to the 

 land, whilst in cold and calm Winters it keeps out in the deep.« ^The 

 average temperature,, says Jensen, jwas somewhat low from the 7th of 

 Februar}-; on the surface 2.3"; at a depth of 38 mètres 2,7'; at 75 

 mètres 3,3° and at 113 mètres 4.8 degrees.« As then ^the Herring, in 

 1 89 1, did not come under the land to spawn, it spawned in the open 

 sea. On the 9th Februar}- the sea, off Brandesund, was obser\ed to be 

 whitish from the spawning, and on the I7tli Februar}-, the same thing 

 was noticed 4 miles West of Rovaer.« v On the ist March Herring roe 

 was perceived on the fishing lines which were set at a depth of 70 to 

 80 fathoms.« 



During that year, too, tlie temperature was low, the Baltic layers 

 deep along the land, and the Herring spawned beyond the shallows in 

 the deep water. 



The year 1883 ^^s ver}- different. Buck's tables shew a tempera- 

 ture of 5" on the surface. On the 19th Februar}, r he says, :»the 



