PROPAGATION AND PROTECTION OF THE RHINE SALMON. 821 



that the salmon that remain in the river for a second year or longer are to a 

 very large extent males. 



Regarding these latter males, another suggestion has been made by myself, 

 viz, that they will never descend to the sea, but will die after once, others twice, 

 perhaps, having taken part in the propagation of the species. This suggestion 

 is based on the fact that no descent of larger young salmon hitherto has been 

 observed, though the means of making such observations have not been wanting. 

 I have not been able, however, to prove in a direct way the exactness of my 

 hypothesis. 



Another point to which I may be permitted to call your attention is that 

 when I said that "grown-up" fish return from the sea and enter the river, if 

 possible to reach the spawning places, the age and in consequence the size of 

 these fishes, and their state of maturity as well, are extremely different. It is 

 of course easy enough to determine the size of the salmon entering the river. 

 Miescher-Ruesch, who did the same (in 1878 and 1879) for salmon caught near 

 Basel and who for the first time applied the graphical method afterwards intro- 

 duced into science for other fishes as the "Petersen method," found that the 

 curve of the sizes of the salmon of the Basel market is one with three tops or 

 maxima, making it clear at once that three different ages were represented, and 

 showing with great evidence at the same time that the difference in age between 

 the youngest and middle-aged salmon was about the same as that between the 

 latter and the oldest fish caught. 



To check the results arrived at by the Basel professor, I ordered to be 

 measured for me (1893) a large number of salmon caught near the mouth of 

 the Rhine and offered for sale at the Kralingsche Veer market. From March to 

 December 4,653 salmon were measured, and the curve constructed with these 

 figures corresponds in the main with that given by Miescher-Ruesch for the 

 Basel salmon. The salmon of the Rhine (fig. i) present themselves in three 

 sizes: Smallest, 54 to 74 centimeters, mean 64 centimeters (2 to 4 kilograms); 

 middle size, 74 to 98 centimeters, mean 88 centimeters (6 to 10 kilograms); 

 largest, 98 to 134 centimeters, mean 106 centimeters (12 to 25 kilograms). 



The fishes of dift'erent sizes do not enter the river together or in a haphazard 

 way. The different sizes present themselves in different seasons, but they do 

 in one year exactly as in any other (fig. 2). 



The smallest fish (grilse) are called vSt. Jacob salmon in Holland. They 

 ascend the Rhine in July and August, exceptionally few coming in June; they 

 continue to ascend in September, though in smaller numbers than in the forego- 

 ing months, and even in October and November a few may still be taken. They 

 are most of them males and they are all of them in so far advanced a state of 

 maturity that they will be able to take an active part in the propagation of the 

 species a few months or weeks or days after their arrival. This holds good 



