CANADIAN FISHERIES EXPEDITION, lOl.'i-lo 99 



could ever have been brought to exhibit pecularities so inarked, if the number of 

 erroneous determinations, a neutralizing influence, had been considerable. As will 

 be shown later on, the Canadian material furnishes several excellent instances of 

 consistency in the results arrived at. For the present, it will sutKce to point out that 

 the material from the Canadian investigations presents, in the case of some localities, 

 no particular points of difficulty, whereas samples taken elsewhere have included fish 

 with scales by no means easy to decipher. On the whole it may be said that the 

 Newfoundland material from the gulf of St. Lawrence is to be regarded as well suited 

 for the purpose of age determinations, whereas some part of that from the open coast 

 presents many difficulties. It is of great importance, however, in such investigations, 

 to familiarize oneself, by long-continued observation, with the peculiarities of the 

 particular herrings to be dealt with. Valuable aid is also furnished where oppor- 

 tunity occurs of following the progress of a single age-group from year to year. There 

 is probably no single circumstance which has so largely contributed to tlie firmness of 

 conviction, now i)revailing among Norwegian investigators, than the fact of their 

 having been in a fortunate position to watch the growth of a single rich year-class 

 throushout an extended period of time. 



The greater or less probability of error, or uncertainty, may depend upon various 

 factors. The sources of error may be divided into two categories : — 



1. Circumstances of a purely technical nature. The technical methods 

 employed in dealing with the material are of considerable importance, and will 

 therefore be described at greater length later on. 



2. Conditions independent of the technical treatment, i. e., such as will 

 make themsdlves apparent even when the most adequate technical methods are 

 employed. In this case, it is generally a question of fish whose scales have the 

 winter rings indistinctly marked, or which exhibit fainter intermediate mark- 

 ings between those normally legible, or again, as with older specimens, the 

 outermost rings so close together as to render them difficult to distinguish. 



Where the winter rings are not sharply defined, they frequently present the 

 appearance of several very thin lines, one outside the other, in the form of a faint 

 band. Such double or manifold rings would seem to be of most frequent occurrence 

 among those earliest formed; a type of scale very commonly met with is that where 

 the outermost rings are rather clearly mai'ked and easily distinguishable, while the 

 inner one, and possibly the next few, will be vague and double. How far this may be 

 connected with the spawning, as tending to render the rings more sharply defined, 

 cannot be stated with icertainty,, but it is not unlikely that such is the case. 



The fainter rings occasionally found between the true ones have been termed by 

 Dahl (I) " secondary rings ", and are so distinguished in the present report, albeit 

 the term might well be taken to embrace various kinds of rings. I was at first of the 

 opinion that the position of all kinds of these '* secondary rings " varied from scale 

 to scale, and that their disturbing influence might therefore be eliminated by examin- 

 ing a sufficiently large number of scales from each fish. Objections to this have, 

 however, been raised by Hellevaara (IV), who considers that secondary rings may be 

 found, the position of which corresponds on the different scales of a fish — being, how- 

 ever, in some scales almost indistinguishable. 



As to the origin of the secondary rings, nothing ean be said with certainty. The 

 dislocated scales described on p. 93 show, however, that a slight shifting of the scale 

 from its normal position may occasion the formation of secondary rings. In other 

 cases, faint shadows, produced by the inner fibrillar plates, may be seen. Plate VI, 

 fig. 23, reproduces a photograph of a scale exhibiting such shadows. Where the winter 

 rings are faint or doubled, it may be conceived that these shadows may become of 

 some importance as sources of errors. 



With regard to the close-set outer rings in older fish, there is little to be said, 

 save that as the rings lie closer and closer with increasing age, we have here a limit 



