XVII.-IS SAWDUST AS SERIOUS AN OBSTACLE TO THE ASCENT 

 OF SALMON IN OUR RIVERS AS IS GENERALLY MAINTAINED ? 



By Prof. H. Easch.* 

 [Translated by Tarleton H. Beau.] 



That the rivers on which there is considerable cutting of timber grad* 

 nally become more and more destitute of salmon is an undeniable factj 

 but while it is asserted that the sawdust introduced into the river from 

 the saw-mills causes the salmon coming from the sea either to forsake 

 its foster stream because of meeting the sawdust, to seek another river 

 not polluted, or else, when the fish attempts to pass through the areas 

 quite filled with sawdust, then this, by fixing itself in the gill-openings 

 or between the gills, causes its death, yet later experience seems to en- 

 title us to the assumption that sawdust neither causes the salmon to 

 forsake its native stream nor produces any great mortality among the 

 ascending fishes. The hurtfulness of the sawdust to the reproduction 

 of the salmon is not so du^ect, but is exceedingly great in this, that it 

 partly limits and partly destroys the spawning-grounds of the river. 



The river Dranmien, below Hellefos, has for many years been greatly pol- 

 luted by sawdust, and the abundance of salmon decreased constantly until 

 the fishermen at Hellefos adopted the so-called artificial method of hatch- 

 ing, whereby they supplied the river each year with a considerable number 

 of fry, which, after wandering to sea, returned to the cataract, although 

 the quantity of sawdust is the same as heretofore ; and one cannot see 

 that the ascending fish is in any marked degree aifected thereby. The 

 case is different when it reaches a cataract where many saw-mills are 

 situated, and there meets an insurmountable obstacle to its further 

 advancement. Its desperate leap is in vain, and as it is driven down 

 exhausted in the water filled up with sawdust, it will undeniably be 

 liable to get some of it so tightly wedged in the gills that it cannot get 

 rid of it, and death will then sooner or later be the result. To this dan- 

 ger the male salmon will be especially exposed near and at the spawning 

 time, since the increased length of the so-called notches of the lower jaw 

 prevent it from completely closing its mouth. The salmon which are 

 not seldom found dead after the spawning time are nearly always males. 

 That, at the same time, most of the deaths result from violent struggles 



*Meddelelser Ira norsk Jseger-og Fisker-Forening, Sden Aargaug, Kristiania, 1873, 



p. 56. 



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