Ixiv 



Twenty ninth Annual Report 



Traniing Investigations. 



These were made in the months of April, June, July, September, 

 October, and November, the vessel in the other months being chiefly 

 engaged in the hydrographic observations, or laid up for repairs and 

 overhaul. The total number of hauls of the trav^^l was 128, of which 

 71 were hauls with the large otter-trawl, generally with a small- 

 meshed net covering the cod-end, and 57 were hauls with a smaller 

 beam-trawl. The aggregate number of fishes obtained was 168,000, all 

 but a small number of which were measured and the sizes recorded, 

 while a large proportion were opened and the condition of the repro- 

 ductive organs determined and noted. In some instances, also, a 

 proportion of the stomachs were removed and forwarded to the 

 Marine Laboratory, where the nature of the food upon which the 

 fishes had been living was ascertained by Dr. Thomas Scott, 



The trawling with the large otter-trawl was made on various 

 grounds, including the Fisher Bank, the Witch Grounds, the grounds 

 off Aberdeen and the Firth of Forth, and the Moray Firth. The 

 trawling with the beam-trawl was confined to the old trawling 

 stations of the " Garland " in the Moray Firth, and the Firth of Forth. 

 These hauls were made with the same trawl-net as was used by the 

 " Garland," and as the investigations of that vessel were begun as long 

 ago as 1886 in the Firth of Forth, and are being repeated on the same 

 stations, and as nearly as possible at corresponding dates, comparison 

 of the results with reference to the relative abundance of the various 

 species of food-fishes at the different periods will be of interest and 

 value. 



Ex2^eriments on the Relation between the Size of the Mesh of Trawl 

 Nets and the Fishes Captured. 



Former investigations have shown that even comparatively small 

 changes in the dimensions of the mesh of trawl nets, especially in the 

 cod-end, materially affect the numbers and the sizes of the fishes 

 caught in it. In order to determine with precision the relation 

 between the size of the mesh and the number and sizes of the various 

 species of fish taken, several cod-ends have been used, each with a 

 different mesh, the whole of the cod-end being enveloped in a loose 

 bag of small-meshed netting to retain the fishes which pass through 

 the meshes of the trawl. The various fishes caught in the cod-end 

 and in the small-meshed netting respectively are then counted, 

 measured, and recorded. These experiments have been made on 

 various grounds, in different depths of water, near the shore and far 

 from the coast, and at various seasons, and similar experiments have 

 been made with the ordinary commercial trawl-net for comparison. 

 It will be possible, when the investigation is completed, to determine 

 whether it would be practicable to fix a limit of the dimensions of the 

 mesh, on certain grounds or at certain seasons, to enable the immature 

 or small fishes to escape capture, without unduly interfering with a 

 profitable fishery. The experiments also furnish important informa- 

 tion as to the abundance of small fishes on the grounds, which 

 normally escape being caught by the trawl net. In almost all cases 

 the fishes which pass through the meshes of the commercial cod-end 



