156 



NOTE on MID-WINTEK SUKFACE and DEEP 



TOW-NETTINGS in the IEISH SEA. 



By Isaac C. Thompson, F.L.S. 



[Read March 17th, 1899.] 



Taking advantage of a fine day and smooth sea, after a 

 month of abnormally boisterous weather round our coasts , 

 on January 29th, 1899, I accompanied Mr. Dawson, 

 Superintendent of the Lancashire Fisheries, and Prof. 

 Herdman, on an inspection of the spawning grounds off 

 the west of the Isle of Man, in the fishery steamer " John 

 Fell." In addition to the apparatus and trawls used on 

 board the steamer, we were provided with dredges and 

 tow-nets belonging to the Port Erin Biological Station, 

 our point of departure. 



Gradually steaming up the western side of the Island, 

 when several hauls of the tow-nets and dredge were made, 

 it was thought by our scientific expert to be an excellent 

 opportunity for noting, on a typical winter's day, both 

 the quantity and comparative character of the plankton 

 collected, under similar conditions, at the surface and at 

 the sea bottom. 



The vertical, no less than the horizontal and seasonal 

 distribution of the Copepoda, must be of considerable 

 importance in connection with their value as fish food. 

 Some species, such as Temora longicomis, appear to live 

 only at or near the surface, while others, like Euchceta 

 norvegica, are seldom found in less than 100 fathoms in 

 depth. Some species evidently have a vertical migration, 

 though what is the positive reason for this it would be 

 difficult to answer. Light appears, in some cases, to act 



