242 



Part III. — Seventeenth Annual Report 



the sum of several hauls made in that place, would at once prove or 

 disprove the possibility of pointing out the successive annual groups, and 

 would also show their numerical relation to one another, with an accuracy 

 proportionate to the number of fishes captured. But as the size of the 

 growing fishes must be in some proportion to their age, and as it has been 

 well established that the plaice, under normal conditions, increases in 

 size from shallow to deeper water, it follows that the mass of the 

 older fishes must live at a greater depth than the mass of the younger ones. 

 This, again, means that the annual series of plaice, whether distinguish- 

 able or not, in principle must follow one another in succession from the 

 shallow to the deeper water, and though perhaps overlapping one another 

 at the margins, still claim for themselves areas of their own, each of 

 which being inhabited — not solely, but principally — by the greater bulk 

 of one particular series. 



Thus the size of the plaice captured very much depends upon what 

 depth of water has been examined. A haul made about the centre of any 

 area which was the special habitat of a particular series would principally 

 contain fishes belonging to that series, and would only show more or less 

 indistinct indications of the neighbouring ones. And hauls made at any 

 place where such areas merged into one another would not contain fishes 

 belonging only to one series, but to the two adjoining series ; and these in 

 most cases would become well intermingled, and would have the appear- 

 ance of one very much extended group. When, therefore, Petersen 

 conducted fishing operations at four or five different places within an area 

 extending from the shore to about six miles at sea, and had a depth 

 ranging from nothing to eight fathoms, it is clear that the result is of 

 doubtful value as regards the demonstration of the true annual series of 

 plaice. His choice of fishing-places, however carefully considered in 

 regard to other purposes, must have been to a large extent a matter of 

 guess as regards the location of the various series, and their representation 

 is therefore often erroneous. It must be remembered, liowever, that Dr. 

 Petersen's elaborate work was not carried on solely nor principally for 

 the purpose of studying the growth rate of the plaice. 



Another, and I think better, method by which the natural series or 

 groups could be well shown would be to capture all the fishes living on a 

 strip of ground, say 10 to 15 yards wide, and extending from the shore 

 to the greatest depth within the locality that he examined. Such a 

 collection ought to show the distinction of all the groups living within 

 the area, and in their approximate numerical proportions to one auother. 

 To realise such an ideal method in its entirety would be difficult, or 

 perhaps impossible; but a fair approach may be made if the fishing is 

 conducted on lines at right angles to the shore instead of along it. In 

 the former case all depths and areas could be examined without trouble, 

 while this in the latter case is almost impossible. 



1 shall now examine some of the groups shown in Petersen's Tables, 

 and when possible single out what fishes appear to me to belong to the 

 various annual series. Most information regarding the smallest fishes is 

 contained in the records for 1893 (Tables III., IV., and V., second part). 

 I snail aiso confine my examination to the northern portion of the Katte- 

 gat, and principally to the coast line north of Hals. 



The small plaice not yet one year old (Petersen's "0" group) are only found 

 to inhabit the very shallow water along the shores, and, owing to their 

 comparatively small range in size, they are always marked off distinctly. 

 This group was principally studied from May to October 1893, when 

 fishing with a "prawn-catcher" was conducted near Fredrikshavn. The 

 results are recorded in Petersen's Table III., which I have here repro- 

 duced (Table VI.) The "0" group is distinctly shown for May, June, 



