104 DEPARTMENT OF THE NAVAL SERTICE 



the length of the fish at the times the different winter rings were formed. This entire- 

 ly graphical method of measuring the growth of each individual specimen will natur- 

 ally not give such accurate figures as those obtained by the more exact, but less rapid, 

 methods of measurement and calculation; both the use of the mirror and the subse- 

 quent graphical multiplication involve the occurrence of errors which can of course, 

 be diminished by the application of more exact methods. For most purposes, how- 

 ever, the method will be found sufficiently accurate. 



VIII. DEFINITIONS AND ABBREVIATIONS ADOPTED. 



Various expressions and signs employed in the following pages will need to be 

 defined. 



1. Age. — Age is expressed by the number of annual rings which have been found 

 on the scales of the specimen in question, the relation of time of capture to season of 

 birth being, however, here taken into consideration whenever possible. Thus a herr- 

 ing taken at Newfoundland in the spring will, if its scales show, say, ten summer belts 

 be reckoned as 10 years old, whereas one from the same place, but taken in the autumn, 

 and with ten summer belts, will be regarded as about 9J years eld, having regard ti) 

 the spawning season at Newfoundland. 



2. Age-group. — In assigning a specimen, say, to age-group 10, this is to be under- 

 stood as meaning that its scales showed ten summer belts, ignoring the fact, when 

 nothing is stated, as to whether it was taken in early spring or late autunm. The 

 term is therefore used without regard to season of birth or time of commencing new 

 summer growth. 



3. Year-group. — When a fish is assigned, say, to year-group 1910, this means, 

 that the specimen in question probably formed its first summer belt in that year. For 

 all fish spawned in the spring, the date of the year-group will be identical with that 

 of the year of birth ; in the case of those spawned later, however, towards the autumn, 

 it will remain open as to whether or not they formed any summer belt during the 

 remainder of the year in which born. Fish taken during the period of transition to 

 new summer growth may be difficult to class correctly in their proper year-group, and 

 personal judgment will here be brought into i)lay iridp \). 113). 



4. Growth-dimensions. — On the basis of growth measurements, we obtain for each 

 specimen figures indicating its calculated length at the time of forming first winter 

 ring. This calculated fir^t winter length is noted as I,, while similarly, the calculated 

 lengths or time of formation of second, third, and subsequent winter rings, will be 

 designated by ?^, I., etc. Subtracting Z, from L, we obtain the calculated increment 

 of growth during the time falling between the formation of the first and second winter 

 rings, this increment being denoted by i, and similarly, /,=?, — L t^^^l^-^l„, etc. 



f). Length. — By the length of a herring is understood the distance from the point 

 of the snout to midway between the extreme points of the tail-fin when naturally 

 extended. The length may be measured in millimetres or centimetres, and a fish is 

 assigned to its nearest length-group; thus all fish, between the limits 29-5 and 30-5 cm. 

 length, will belong to the 30 cm. group. 



IX. COLLECTING OF MATERIAL. 



The methods of individual age-determination and growth-measurement naturally 

 suggest themselves as aids to the statistical investigation of the biology of the herring. 

 If, however, they are to be used for this purpose, it will be necessary to formulate pro- 



