APPENDIX H: ÜARSTANG _ 16 — 



compared with those of the Dutch investigators in tlie same region, can only be attributed to 

 the fact that the English experiments were carried out in the winter months, when the abun- 

 dance of fish in this region is at its minimum, while the Dutch experiments were carried out 

 in July, when the abundance of flsh was practically at it's maximum — since the nets employed, 

 the duration of the hauls, and the methods of marking and liberation were practically identical 

 in the two cases. 



A certain number of experiments especially directed to an investigation of this point have 

 been carried out by the English steamer. On the Texel Ground in April the "Huxley" trawled 

 for three hours, making a total catch of 84 kilos., chiefly T^laice {P. platessa), AaJos {P. limanda), 

 grey gui'nard {Trigla gurnardus), and whiting {Gadus merlangus). The total number of plaice 

 caught was 496. Upon hauling the trawl the fish appeared to be perfectly healthy. The sea 

 was smooth; the sunshine was continuous but not hot, the air temperature being 13-6° C. 

 After three hours' exposure on deck the vitality of 215 of the plaice was determined by 

 placing them in tanks of running water. The total mortality was 95 per cent., all the small 

 fish below 20 cm. being dead. The fish were left two hours in the tanks. 



In May on the Sylt Grounds the "Huxley" again trawled for three hours, the total weight 

 of the catch being 152 kilos. The plaice numbered 708. The plaice immediately after hauling 

 appeared to be ç[uite healthy, the vitality of 63 being tested in the tanks. After an hour's 

 exposure on deck 29 per cent, of the small plaice below 20 cm. were dead, and 16 per 

 cent, of the total catch were dead. Next morning, after lying on deck for seven hours, all 

 the plaice were dead, the vitality of 165 being tested as before. This was a night haul, the 

 trawl being hauled at 1,30 a. m., and the deck was wet with showers of rain and some spray. 

 Dr. Petersen accompanied the English naturalists on this occasion. 



Off Ymuiden in August another experiment was made, the trawl being kept down for 

 four hours, resulting in a total catch of only 35 kilos. On hauling, a great mass of jelly- 

 fish (Chrysaora, Cyaneaj was found to be mixed with the fish. The total catch of plaice was 

 307, and, upon testing their vitality ten minutes after hauling, 77 per cent, were found to be 

 dead. After twenty minutes' exposure on deck 153 plaice were tested, and of these 151 were 

 dead and the other two moribund. In this case the mortality of the fish was mainly attri- 

 butable to the injuries caused by the stinging of the jelly-fish. 



Again, on the Broad Fourteens in August a seven-hour-haul of the trawl resulted in a 

 total catch of 84 kilos. The plaice numbered 364; the other kinds present were soles {Solea 

 vulgaris), gurnards, dabs, viea,\ers {Trachinus/, and thornback r&js (Baja clavata). Immediately 

 after hauling, the vitality of 73 plaice was tested and of these 21 (29 per cent.) were dead 

 and 17 moribund. After exposure of one hour on deck 92 per cent, of the plaice were dead. 

 The air temperature was 25.5° C; sunshine was regular throughout, but weak, owing to 

 hazy weather. 



Although these experiments are few in number, they tend to show that under the ordinary 

 conditions of steam trawling few of the small plaice could be returned alive to the sea by the 

 fishermen, since the men would rarely attend to this point immediately after the hauling of 

 the trawl, even wlien the fish were received on board in a fairly healthy condition. 



