SEA-FISHERIES LABORATORY. 213 



have had any experience of plankton work — the marked 

 effect of the size and mesh of the net upon the resulting 

 catch, we give here from Form 47 the hauls of two surface 

 nets and a shear net taken off Bradda Head on April 

 23rd; and we add also another shear-net haul taken later 

 the same day a couple of miles off, between Bradda Head 

 and the Calf Island. It will be noticed that the two 

 surface hauls are very much alike in quantity and 

 constitution, and the two shear-net hauls are like one 

 another and very different from the surface hauls. The 

 shear-net has retained no Diatoms and no Dinonagellates, 

 but has caught far larger quantities of the larger 

 organisms, such as Medusoids (Hyhocodon prolifer) 4,500 

 against 10 and 100 taken in the surface nets at the same 

 time, Sagitta 200 against 2, young Shrimps 1,800 asrainst 

 5 and 8, and young Norway Lobsters 1,600 against 1. In 

 the case of the Copepoda the shear-nets have large hauls 

 of a large form such as Calanus, but much smaller hauls 

 of the smaller forms such as Acartia and Oithona. 

 Similarly the shear-nets have not retained the larval and 

 young Copepods, but have most of the fish eggs and all 

 the young fishes. Some of the differences in further 

 detail may be due to the depth at which the shear-net 

 was towed, but the broad lines of difference are clearly 

 seen to be caused by the nature of the nets. 



In order to determine more definitely, without any 

 disturbing influence due to depth, the difference in 

 catching power between the large open-meshed shear-net 

 and the much smaller ordinary tow-net made of fine- 

 meshed silk, we tied a tow-net to the frame of the shear- 

 net so that the two would work together side by side, and 

 we show here in Form 105 the results of two such double 

 hauls. 



In the first place, it will be noticed that the shear-net 



