A STUDY ON TROUT AND YOUNG SALMON. 307 



The fixing of the size limit at 20 cm. will however in my 

 opinion be dependant on the form of regulation by means of 

 which, protection of the young trout is to be effected. 



If we are going to protect sea trout under 20 cm., by a 

 prohibition against killing such fish, no inconvenience worth 

 mentioning will be incurred in the case of the larger rivers, 

 because the capture of small fish is here of small importance. If 

 however we consider the large number of small rivers or brooks, 

 which in our country fall into the sea, such a prohibition would 

 be unjust. A very large proportion indeed of these rivers is 

 inhabited not only by sea trout but by large numbers of fresh- 

 water trout, mainly brook trout and this latter form, in nume- 

 rous rivers, rarely exceeds 20 cm. in length. 



As an example of such a rivulet may be mentioned the 

 little 0re-elv in the Sheidsdal in the Batten-fiord, which river 

 has been specially investigated. It heads from a small tarn 

 about 7 kilometers from the sea. The whole of its length is 

 inhabited by a freshwater trout-form which only in rare excep- 

 tions exceeds 20 cm. in length. Of this fact I was convinced 

 after I had measured specimens caught in all parts of the river. 

 They attained sexual maturity at a length of 15 cm. Graphically 

 represented, their measurements run thus: 



Each dot represents a fish, 

 cm. 



10 o o 



11 o o o o o 



12 000000000 



13 000000000000 



14 00000000000000000 



15 o o o o o o 



16 00000000 



17 o o o o o 



18 o o o ( s^^ually mature 



19 



20 o 



