APPENDIX K: KYLE ^20 — 



Evidence from marking experiments. A second method of investigating the 

 amount of fishing and abundance of fish on an area, is by means of marking experiments. 

 When a large number of fish are marked, the percentage returned has been taken to 

 indicate the intensity of fishing. It has to be noted, however, that this method has also 

 a certain amount of unreliability. For example, if the numbers returned are small, this 

 may be due to irregularities in marking, to the fishermen not returning the fish, and so on ; 

 if the numbers returned are large, this may be due to the fish having been replaced on 

 grounds particularly well-fished, so that the percentage returned would not be representative 

 of the whole area. 



The results of the plaice marking experiments in the Kattegat are not yet published 

 in their entirety. From Trybom's experiments,^ it appears, that 13,7% of the plaice marked 

 in July 1903 and 17"5% of those marked in September 1903, were recovered up to June 

 1904. These were marked on the Swedish side, and many of them were retaken on the 

 Danish side of the Kattegat, especially at the Skaw. According to Petersen^, 80% of 

 the plaice marked in the north-western portion of the Kattegat were returned within four 

 months. 



Without further information, it is obviously somewhat difficult to say, which of these 

 percentages best represents the intensity of the fishing in the Kattegat as a whole. 



4. Summary and conclusions with regard to the Kattegat plaice fishery 



When the matter is regarded from a broad point of view, the main conclusion which 

 the Danish and Swedish statistics show, regarding the plaice fishery of the Kattegat, is, 

 that the total quantities of plaice taken annually from that region have not decreased 

 over the period 1890 — 1902, in spite of the fact that the fishing power has greatly 

 increased. 



An endeavour must be made to reconcile this conclusion with the observations of 

 Petersen in 1894, that the Kattegat plaice had reached its "culmination" about 1890 and 

 thereafter or even earlier had begun to decline. It is necessary to attempt this recon- 

 ciliation, as many may think the two conclusions quite opposed to another, whereas the 

 opposition is more apparent than real. 



In the first place, it has to be remarked that Petersen laid more stress on the 

 overfishing aspect, and only put forward the view, that a decrease in the stock of plaice 

 had occurred, somewhat hesitatingly. As explained in the beginning, the two problems 

 are here separated, because this enables us to concentrate our attention upon the biological 

 or scientific aspects of the matter. 



From the scientific standpoint, the most important question is, how can we, on biolog- 

 ical grounds, explain the persistence of the plaice fishery in the Kattegat, in a condition 

 not far from its maximum productivity, for a period sufficiently long to display its exhaustion ? 



Of the phenomena described by Petersen: the decrease in the average catch per 

 boat can be readily explained by the largely increased number of boats, and the decrease 

 in the quantities of large plaice is a phenomenon similar to that exemplified by Hjort 



1 Biologiska Undersökninger, 1901 — 1904. Ur Svenska Hydrografisk biologiska Konimissionens 

 Skrifter. Haftet II. 



2 See Appendix G, p. 17. 



