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Part III. — T irei it \j -first Annual Report 



much scarcer on the deep-water grounds than inshore. The 

 absence or great rarity of the young forms of some other species, 

 as the saithe or coal-fish, the hake,pollack,andhng, in the latter area, 

 while they are known to be common in many cases near land, also 

 indicates an extensive wandering. An inshore winter migration of 

 cat-fish was also established. The results generally tend to show 

 that the extent of the migratory movements of even such relatively 

 sedentary forms as flat-fishes is much greater than has been 

 commonly supposed, and that the predatory round-fishes may 

 traverse great distances. They suggest, moreover, that by extended 

 observations of the kind, whether on board fishing vessels or the 

 steamers engaged in the International Survey, it would be possible 

 within a limited time to prepare charts showing with considerable 

 accuracy the extent of the distribution and of the wanderings of 

 all the bottom fishes in the North Sea and adjoining areas, as well 

 as the facts relating to the place and period of spawning. 



The Hatching and Rearing of Food Fishes. 



During the hatching season in 1902 the number of fertilised eggs 

 of the plaice obtained from the spawning pond was 72,410,000, or 

 about seven millions more than in the previous year, and 29,120^000 

 more than in 1900. The number of fry which were hatched and 

 retained in the apparatus until approaching the post-larval stage 

 amounted to 55,700,000, and these were liberated off the coast of 

 Aberdeenshire and in Loch Fyne. At the end of the previous 

 season the number of adult plaice in the pond in good condition 

 was 767, most of which continued to thrive during the summer and 

 autumn. To these, others, obtained from the vessels engaged in the 

 trawling investigations, were added later, bringing the breeding- 

 stock up to about one thousand plaice of both sexes. 



In the latter part of January the temperature of the water in 

 the spawning-pond was rather lower than usual, and few eggs were 

 observed to have been shed until the early part of February. The 

 first collection was made on the 8th of that month, and after a 

 check in the spawning due to a severe frost, when the temperature 

 of the water sank to freezing-point, the number of eggs gradually 

 increased until in the first half of March more than two millions, 

 and occasionally nearly three millions, were taken from the pond 

 daily. Thereafter the number diminished, and the last collection 

 was made on the 25th April. 



The considerable increase in the productiveness of the hatchery 

 in recent years is due to the more ample and suitable arrange- 

 ments existing at the Bay of Nigg, and particularly the provision 

 of a large tidal spawning pond, in which a good breeding stock can 

 be maintained throughout the year. The natural conditions and 

 facilities for the work, and the abundant supply of sea-water of 

 good density and purity, have also assisted in the result. At the 

 same time the expense has been reduced, largely owing to the 

 supply of water to the tank being tidal, whereby the need of 

 pumping is greatly diminished, and the combination of the hatchery 



