

The Influence of Light on the Migrations of the Eel. 



By C. G. Joh. Petersen. 



That the eel is a night-animal is well known by every one; most know 

 also that eel-speariug is carried on at night by means of lights (flares). It is indeed 

 the general impression everywhere, though not amongst fishermen, that these 

 lights are used to attrået the eels, whereas the truth is, that the eels flee from 

 them; but without the lights the fishermen would uever be able to see the eels at 

 night-time. By their means a glimpse of the eel is got and then the spear is 

 quickly brought into operation. It need not be thought that the day-time would 

 be better for eel-spearing, because then, as a matter of faet, the eels are generally 

 hidden under the plantgrowths or at the bottom and would as a rule never be seen. 



There are however exceptions to this as to every rule; an owl even may 

 show itself in the day-time; but it is a rule that the eels mostly travel by night. 

 The eels that are speared are usually the yellow, not the adult eels, and the eels 

 which migrate in greatest quantity are the silver eels. To capture as many as 

 possible of these latter whilst migrating from the Baltic through our Belts is the 

 great task before us. Whether the light (artificial light) had any influence on the 

 silver eels I did not know with certainty when I begau these investigations in 

 1904; almost all I knew was only that they also shunned the flare lights and that 

 in North Italy, in the great silver-eel fisheries, fires were sometimes lit alongside 

 the canals in order to stop the eels migrating. 



It was further known also, that the silver-eels migrate almost entirely by 

 night and nearly always only during the nights when the moon was not shining 

 in the evenings, that is to say, from a few days after full moon till about new 

 moon in the so-called moonless nights.*) 



I then got the desire to test whether it really was the case that the mi- 

 grations of the silver-eel could be stopped by artificial light, and therefore sent the 

 assistant of the Biologicai Station, cand. mag. A. Otterstrøm, to Kilen near Struer 

 in order to make experiments. These were made in the autumu of 1904 and the 

 result was, that a couple of petroleum lanterns set up on posts in the narrow 

 outlet from this brackish-water fjord, could stop the whole migration of the eels 

 so that none were taken in a trap-net fixed across the outlet. 



*) Of the many exceptions to this rule there need onl.v be mentioned ; that the eel has 

 been seen to migrate in the day-time, that it could migrate when clouds covered the moon and 

 that on tho whole it was influenced by various atmospheric conditions; but that it greatly prefers 

 dark to light for its migrations, no one can doubt. 



