THE SALT-WATER FISHERIES OF BOHUSLAX. 179 



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 that the herrings occasionally go under the ice which has formed for some 



time/^ and that there is good fishing when the ice has broken. 



28. Regarding the intluence of the depth of the water and the pressure 

 of the icater on the herrings we do not possess snfficient observations 

 to form a definite scientific opinion. The scientific authors who have 

 recently treated the biology of the herring have arrived at essentially 

 different views regarding the question whether the herring must be con- 

 sidered as a fish specially fitted for a life near the bottom of the sea in 

 the deep basins outside the coast, or whether its nature fits it better for 

 a life near the banks in the open sea or comparatively nearer the surface. 

 It is clear that the migrations of the herrings nuist in the latter case go 

 on near tlie surface, whilst in the former case the herrings would, both 

 in coming and going, seek deep waters. 



The Dutch fishermen who use floating nets have observed that the 

 herrings often change very suddenly from one depth to another, but it 

 is not known whether these changes only extend to a few fathoms or to 

 a greater depth ; nor do we know whether these changes are made on 

 account of the greater or less pressure of the water, though the last- 

 mentioned hypothesis is certainly highly improbable. 



A French naturalist, Carbonnier, has expressed the oi^inion that the her- 

 rings, like other fish, are, immediately after having done spawning, com- 

 pelled to seek deeper waters to obtain the greater pressure "which has 

 become necessary on account of their empty belly " ; but although we cer- 

 tainly possess a number of observations all tending to show that the 

 "empty" herrings go into deeper waters than the "full" herrings, we do 

 not know enough on this point to justify us in embracing Carhonnier^s 

 opinion ; for herrings have been known to come to the surface immedi- 

 ately after spawning, and data are not even wanting which go to show 

 that "empty" herrings lived nearer the siu'face than "full" ones. 



29. We must also take into consideration the influence exercised on 

 the herrings by the character of the bottom, both as regards its formation 

 and composition and its vegetation. Concerning its orography, we know, 

 from observations made during the Scandinavian herring-fisheries, that 

 the herrings, when approaching the coast, often follow the valleys of the 

 bottom, probably because there they find calmer and more sheltered 

 waters and a more even temperature, not excessively cold in winter nor 

 very warm in summer. Thus the herrings seem, during the last great 

 herring-fisheries, and even several times since, to have approached the 

 southern coast of Bohuslan by way of the so-called "great furrow" or 

 valley ; and the depression of the bottom, which, from its northern end, 

 extends towards the Marstrand fiord, has evidently something to do with 

 the circumstance that the great fisheries generally commenced near the 

 islands at the mouth of this fiord. Similar easily distinguished valleys 



*6 This phenomenon naiglit possibly be explained by the supposition that a layer of 

 ice prevents the sea-water underneath from getting any colder, as the soil keeps 

 warmer under a cover of snow. 



