— 5 — APPENDIX H; GARSTANÜ 



smaller fishes. There is other evidence also that the labels tend to di'op off the smaller fishes 

 after a certain lapse of time. 



Experiments have been made by the German investigators with the object of discovering 

 another form of label which might expedite tlie process of marking at sea, which, by Peter sen's 

 method, naturally requires a considerable amount of time when large numbers of fishes 

 are being dealt with. In the German experiments two forms of label have been tried in 

 succession, namely (1) an aluminium ring piercing the flesh shortly in front of the tail, and 

 (2) a sliarp vulcanite stud stabbed through the fish in the same region. Interesting as these 

 experiments have been, I gather from Dr. Heincke' that he is inclined in part to attribute 

 the low percentage of recoveries in the case of the German experiments to the relative 

 unsuitability of the labels employed, especially in the case of the smaller fish. The slovver 

 rate of growth of the German marked fishes tends to support this opinion. For the present, 

 therefore, it seems desirable to exclude the smaller German fish from any consideration of 

 the problems of rate of growth and intensity of fishing as shown by the marking experiments. 



The still lower percentage of recoveries in the case of the Dutch experiments cannot be 

 attributed to the method of marking, since the same methods were employed as in the case 

 of the Danish and English experiments. In this case the paucity of the recaptures appears 

 attributable to two causes, firstly, to the high percentage of very small plaice marked in 

 several of the Dutch experiments, and, secondly, but chiefly, to the vitality of the fishes dealt 

 with having been impaired by the great weight of the total catch of fish on those occasions. 

 The highest percentage of plaice recovered has been attained by tlie Danish experiments, which 

 have been carried out by means of a small trawl (50 ft. otter) usually dragged for a short 

 time only (half-hour to two hours). Under these circumstances, the plaice in the Danish ex- 

 periments would be received on deck in a healthy condition. In the English experiments, 

 although the trawl used was the full-size commercial trawl (either beam or otter), it was kept 

 down as a rule for a short time, about one hour, the total catch of fish on those occasions 

 rarely exceeding 60 kilos. The Dutch experiments were made usually after two-hour-hauls of 

 the large otter trawl, and tlie weight of the total catch rarely fell below 100 kilos., exceeding 

 200 kilos, in several cases, and attaining nearly 400 kilos, in experiment no. 17. In view of these 

 facts it appears fairly certain that the low percentage of Dutch recoveries is attributable in 

 the main* to injuries sustained by the fish in the act of hauling the trawl, which lead ultimately 

 to a high mortality. 



After these preliminary remarks I may proceed to describe the general results of the 

 marking experiments. The latter fall naturally into two groups, according to the season of 

 the year in which they were carried out. All the Danish experiments and some of tlie Swedish, 

 German and English experiments were cari'ied out in the spring, from March to May. These 

 show the summer migrations of tlie fish. The remaining experiments were carried out in the 

 second half of the year, from July to December. These throw light chiefly upon the winter 

 movements. Two charts (PI. I and II) have therefore been prepared on which the general 

 features of the plaice migrations observed have been grapliically represented. 



■ Rapporta et procès-vorbaux des Roiuiions. Vol. II. Report of the mooting of Committee ß at Amster- 

 dam, p. 34. 



