RECENT RESEARCH UPON SALMON 



243 



The Scottish Fishery Board have, as yet, no returns to 

 show from marked smolts ; but their list of fish marked as 

 kelts and recaptured clean is full of interest. The longest 

 interval between such marking and recapture has been 5 1 5 

 days, in which case a kelt taken in the Spey in March, 1897, 

 weighing 7 lb., was recaptured in the same river in August, 

 1898, weighing 19 lb. The stages of this fish may be 

 reckoned as follows : — 



Spawn deposited . 

 Went to sea as smolt 

 Returned as grilse . 

 Returned as salmon (8 lb. ?) 

 Descended as kelt (7 lb.) 

 Returned as summer fish (19 lb.) 



Autumn, 1891 or 1892. 

 Spring, 1894. 

 Summer, 1895. 

 Spring or summer, 1896. 

 March, 1897. 

 August, 1898. 



Its age, therefore, was five or six years, according to 

 whether it left the river as a smolt in its second or third 

 spring. But it must not be assumed that all fish of 19 lb. 

 weight are necessarily only five or six years old, for the returns 

 of twenty-two kelts recaptured as clean fish seem to show a 

 remarkable variation in the rate of increase, estimated by 

 Mr. Calderwood to range from as low as 77*2 per cent, per 

 annum to as high as 813-9 P^'* z^nt. per annum. This 

 estimate, however, appears to be fallacious in one important 

 respect, for it is based on the assumption that the rate of 

 increase throughout the year is the same as that between the 

 dates of capture and recapture. Some kelts travel rapidly to 

 the sea, where they will put on flesh at a great rate ; whereas 



