July, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



151 



The MigroLtion of 

 Flact-Fish. 



By J. Travis Jenkins, D.Sc, Ph.D. 



At the present time when so much is heard of over- 

 fishing and the consequent depletion of the fishing 

 grounds, the question of the movements of sea-fish is 

 one of considerable practical importance. 



The majority of scientific experts agree that round 

 fish, i.e., fish of the herring and cod type, perform 

 migratory movements of considerable magnitude, but 

 as regards flat fish, i.e., plaice, soles, and flounders, the 

 consensus of opinion is by no means so unanimous. 



The International Committee for Investigation of 

 the Seas, which has quite recently been established, has 

 taken up, among other problems, the question of the 



any given area can be determined by the proportion of 

 fish recaptured to the total number of marked fish re- 

 turned to the sea. Since each marked fish is carefully 

 measured both when it is returned to the sea and when 

 re-captured, the rate of growth can also be determined. 

 Plaice seem to withstand the marking operation wonder- 

 fully well, but soles are far more difficult to deal 

 with successfully. No doubt other results will be 

 arrived at, notably the efficacy of closed grounds in 

 maintaining a reserve of fish and the effect of the 

 density of fish population on the rate of growth. 



The interest and co-operation of the fishermen is 

 secured by means of a system of rewards payable for 

 marked fish, the amount depending on the amount of 

 information as to the locality of re-capture. It is sur- 

 prising to find how many hands a marked fish will 

 occasionally pass through before the label is detected. 

 In one instance a label which was returned showed 

 unmistakable signs of having been in the frying-pan. 



Marked Plaice which travelled 40 miles in 20 days and was then recaptured. 



migration of members of the flat fish family or 

 Pleuronectidae. 



This international committee consists of scientific 

 experts nominated by the Governments of England, 

 Norway, Sweden, Germany, and Holland, and is sub- 

 sidised by grants from the respective Governments. 



Batches of marked Pleuronectids, chiefly plaice, have 

 been marked from time to time and then liberated at 

 various points in the North Sea. The mark used con- 

 sists of a silver wire, which is threaded through the 

 body of the fish in the position indicated in the diagram. 

 To this wire are attached on the under side a bone 

 button (shown to the left beneatTi the tail of the fish), 

 and on the upper side a numbered brass label, in the 

 present instance L. 169. Each fish is carefully 

 measured and labelled, the whole operation from the 

 time the fish is removed from the tank to the time it is 

 replaced taking less than one minute. 



It is hoped that by these experiments the amount and 

 nature of the migration of flat fish will be determined; 

 and attempts will be made to show the influence of the 

 environment on migration. The intensity of fishing in 



It is yet somewhat premature to discuss the results in 

 detail, but it may be said that the idea of plaice and 

 soles being sedentary fish is now exploded. Plaice 

 have been returned which have travelled iio, 130, and 

 210 miles respectively. As to rate of growth, an eight- 

 inch plaice grows on the average from two-and-a-half 

 to three inches per annum. More detailed reports will 

 shortly be issued and are awaited by practical fisher- 

 men and biologists with equal interest. 



Scientific Agriculture. 



We have received from the Committee of the Lawes 

 Agricultural Trust a copy of the Directors' report on the 

 work done at the Rothamsted Experimental Station for 

 the year ending March 31st, 1905. The well-known 

 experimental fields are still continued without any 

 essential change; in addition a new field has been laid 

 out to test the residual value of various manures in the 



