46G SOME RESULTS OF THE INTERNATIONAL FISHERY INVESTIGATIONS. 



larviil to the post-larval stages, and arc little larger than one's thumb- 

 nail. As they grow they gradually move further out into deeper water, 

 but for this first year of their life and the next one they do not travel 

 very far from the shore on which they may first be found. After they 

 have entered on the third year of life, however, their more lengthy 

 migrations begin. These are iniluenced to a very great extent by the 

 nature of the sea area in which they find themselves. Thus the results 

 obtained by the Danish naturalists* show that the plaice marked and 

 liberated off the coast of JJenmark travelled for the most part along 

 the shallow water adjacent to the coast (Chart X) or, when liberated, 

 migrated inwards toward the shore. But other fishes travelled out- 

 wards into deep water. There is little doubt that these movements 

 depend to some extent on the season. Off the Danish North Sea coast 

 there is a distinct tendency for plaice to move from deep water towards 

 the shore during April, May, and June, but later in the summer they 

 appear to move off-shore again into deeper water and to spread over a 

 somewhat wide area. 



In the case of the English experiments carried out in the southern 

 part of the North Sea, the change of the migration path according to 

 the season is also displayed. In the charts giving synoptic representa- 

 tions of the experimentsf this is well shown. South of latitude 

 53° 30' in the North Sea, it may be said that plaice for the most part 

 travel to the south during the winter and to the north during the 

 summer. This applies to the larger fishes dealt with. The smaller 

 fishes hardly travel at all. Sometimes, in the case of the larger fishes, 

 the distance travelled is very considerable. Thus one plaice of 13 

 inches in length, liberated in December, 1903, in tlie middle of the 

 North Sea, nearly in the latitude of Grimsby, was found about three 

 months later in the English Channel, having travelled in the interval a 

 minimum distance of 175 miles. Other instances are recorded of lona 

 migrations made by marked plaice, and generally it may be said tliat 

 the larger fishes travel further and more rapidly than the smaller ones, 

 and in addition frequent deeper water. I'ut we meet with puzzling 

 exceptions to this general rule. Thus a medium-sized plaice liberated 

 by the Lancashire naturalists in the preserved waters of the south coast 

 of Scotland was found in the same place nearly two years afterwards, 

 having in the interval probably not left the bay in which it was first 

 found. 



To deduce the rate of growth from marking experiments is a simple 

 matter. The fish being marked and measured is again measured when 



* See charts X-XII, Meddelelsen Komm. Tfavundersog. , Fiskeri, Bd. i. Nr. 2, 1905. 

 t Garstaiig and Borley, Fishery aiid Hydrographical Invcsligalions in the North Sea, etc., 

 Southern Area (cd. 2670), 1905. 



