of the Fishery Board for Scotland. 



2o 



representing the actual proportion of smolts that come back towards the 

 end of their third year in the sea. Probably a repetition of the marking 

 experiment would bring out a larger proportion of spring fish, although 

 many of them may enter the river before the netting season commences 

 and so escape notice. 



Parr and Smolts. 



In previous papers I have stated that the age at which most of the 

 smolts leave the Tay is a little over two years, with the reservation that a 

 few may go when one or three years. Statistics and photographs of scales 

 with ridges in three divisions, taken from young fish of doubtful age, will 

 be found in the Twenty-fifth Report (pp. 57 and 66), which, with some 

 doubt, I was then inclined to put down as not over two years old. Further 

 investigation now causes me to regard each series of their ridges as 

 representing a whole year or part of that period, so that the July parr 

 referred to would be in their third summer, and the April-May smolts at 

 the end of their third year. So far, however, I have found comparatively 

 few of such examples. 



In the early part of the present year (1910) I have received pamphlets, 

 kindly sent by Dr. Knut Dahl (Norway) * and Dr. Hoek (Holland) f , 

 in both of which reference is made to the scales of salmon. Dr. Dahl 

 states he has a more extensive paper in preparation, and meantime it can 

 only be inferred from a diagram he gives, that he considers 3| years to 

 be the average time that the Norwegian parr remains in the river. Until 

 his promised contribution to the literature on the subject is published, one 

 is not able to know on what, grounds his conclusions are based. I have 

 examined too few Norwegian scales to hazard a definite opinion, but those 

 that have passed through my hands have the appearance of a two year 

 old migration, and in one or two exceptional specimens a younger age 

 might doubtfully be read. 



Dr. Hoek limits his observations to salmon from the Rhine, and seems 

 to think that the smolts generally leave that river for the sea after the 

 completion of their first or second year, but that a few may delay migration 

 until the end of the third year. From the measurements he gives, the 

 young fish must be of larger size than those of the Tay. 



I may mention that scales from the Hampshire Avon sent me by Dr. 

 Kingston Barton rather suggest that warm water and good feeding may 

 accelerate the smolt stage, and that some at least of the young fish in that 

 river possibly migrate when less than eighteen months old, and yet be 

 * quite as well developed as Tay smolts that have completed their second 

 year. This is a point that might be better studied by some one in the 

 Avon district who could procure and compare specimens of parr and smolts 

 at different seasons of the year. 



It is satisfactory to find that the study of scales is not only assuming- 

 larger proportions in this country, but has also been taken up abroad, as 

 by a comparison of results it is hoped that more light will be thrown on 

 the life-history of the fish. Mr. J. Arthur Hutton,J in a very clear and 

 instructive pamphlet, has done much to make known the value of scale 

 indications, and has carefully studied the fish of the Wye and other rivers 

 both in England and Norway. Dr. Turnbull,§ of the London Hospital, is 

 one of several investigators who has done good work in the same field. 



* " The Assessment of Age and Growth in Fish," by Knut Dahl (Bergen). 

 Leipsig, 1909. 



f " On the Age of the Salmon to be derived from the Structure of the Scales," by 

 Di. P. P. C. Hoek. Amsterdam, 1909-10. 



% " Salmon Scales as indicative of the Life-history of the Fish," by J. Arthur 

 Hutton. 1909. 



§ " The Scales oi Salmon," by Hubert M. Turnbull, M.D. {The Field, Deer. 11th, 

 18th, and 25th, 1909). 



