o/ the Fislierij Board for Scotland. 



6^ 



On the Effectiveness of a Seine-frawl in a Small Pond. 



On June 16th, some years ago, when the pond at the Laboratory was 

 about to be cleaned, it was necessary to remove the plaice. This was done 

 by means of a seine-trawl about 57 feet long. The pond measures 90 feet 

 by 35 feet, but the whole of this area was not worked over. Eighteen feet 

 of the shallow portion of the pond was not netted (shown shaded in fig. 53), 

 The deep end harboured most of the fish, which were large plaice. 



The seine {ne., fig. 53) was run out and dropped down the front of the wall 

 at the deep end. The ground-rope Avas allowed to sink and then each end of 

 the net was drawn along one of the long sides. One end was taken across 

 the pond near the shallow end and the two ends of the net hauled together in 

 the corner. When the work was started, there was a depth of about 5| feet at 

 the deep end and 2i feet at the shallow end, while at the intermediate portion, 

 where the net was taken ashore on one set of drags, there Avere 3 feet of water. 

 For the next haul the net was taken in the opposite direction, and hauled 

 at the deep end. It was then worked to the deep and shallow ends alter- 

 nately. During the experiment, the water was flowing gradually out of the 

 pond, and after a time the men were able to take the net ashore on the 

 dried shallow end. The trawling was continued as long as it was 

 effective, that is, until about half of the bottom of the pond was dry. The 

 water remaining then was very dirty with fine mud. There would be about 

 18 inches of water left at the deep end. 



Seventeen drags were made, and the number of fish captured in each 

 was recorded. The direction in whish the haul was made is indicated in 

 the following table by the letters "D" and "S." "D " indicates that the 

 haul was made towards the deep end, " S " that the haul was made towards 

 the shallow end. 



There were actually 282 large plaice in the pond. Of these 222 were 

 taken by the net. 60 plaice were left in the pond. 

 One of the plaice had not yet got rid of its ripe eggs. 



LETTERS USED. 



a. — Anus. 



f a. — Second anal fin. 



ar. — Artery. 



at. — Attached edge. 



6/.— Bladder. 



hr. — Bram, 



ln\ - -Blood-vessel. 



c. — (Jentral I'egion. 



d. — Derma. 

 di. — Blasto disc. 

 hpx. — Blood plexus. 

 cl. — Clavicle. 



d. ^.— Dead tis.sue. 

 ce. — Cerebrum. 



e. m. — Eye muscles, 

 J. — Fascia. 



