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SCTENCE-GOSSIP. 



THE NORTH SEA TRAWL FISHERY. 

 By Johx T. Carrington. 



OCIEXCE and commerce are now so closely 

 allied that it seems in no way out of place for 

 the Marine Biological Association of the United 

 Kingdom to investigate the destruction by trawlers 

 of immature fish. A special number of the journal 

 of the Association was issued at the end of June, 

 which is occupied with "An Examination of the 

 present state of the Grimsby Trawl Fishery with 

 especial reference to the destruction of immature 

 fish ; by Ernest W. L. Holt." 



It will be remembered by our scientific readers 

 that Mr. Holt was, until recently, connected with 

 the Marine Biological Association as one of its 

 professional naturalists, and has devoted much 

 attention to the North Sea fisheries on its behalf, the 

 Association having had its base for this purpose at 

 Grimsby. In the introduction, Mr. Holt explains 

 that he was appointed by the council of the Marine 

 Biological Association to investigate the causes, 

 from their scientific aspects, of the acknowledged 

 deterioration of the North Sea trawl fishery. 

 During three years, Mr. Holt has laboured to collect 

 whatever information he could obtain on this ques- 

 tion. His headquarters were at Grimsby, where, the 

 Association, by arrangement with a local society, se- 

 cured the use of a small laboratory fitted with tanks 

 and other conveniences. The " question " requiring 

 investigation shortly resolved itself into a state- 

 ment, " that large numbers of immature fish were 

 destroyed by trawling." This especially referred to 

 flat fish, as little round, fish are not largelv affected 

 by capture in the trawl, readily escaping through the 

 mesh. Mr. Holt early came to the conclusion that the 

 North Sea fisheries are in a diminishing condition. 



It is not in accordance with the objects of this 

 magazine to deal with the commercial side of Mr. 

 Holt's report, which, however, contains in addition 

 a good deal of valuable information for ichthv- 

 ologists. Part ii. of the report is devoted largely to 

 immature fish ; that is to say, those which have not 

 reached the age for reproduction. To Dr. Wemyss 

 Fulton belongs the credit of having been the first 

 to endeavour to ascertain the size at which fish of 

 different kinds begin to breed. His investigation 

 appeared in the Eighth Annual Report of the 

 Scotch Fishery Board, being based on material 

 obtained from the East Coast of Scotland. Mr. 

 Holt followed with further results from the records 

 of the Royal Dublin Society's Fishery Survey, in 

 the Scientific Proceedings of that society, Part 

 vii., Vol. 9. These investigations made it evident 

 that even in one sex all fish of the same species did 

 not become mature at exactly the same size. This 

 applies especially with regard to locality. Still it 



is possible to arrive at a fair average standard in 

 any one locality. The table given by Mr. Holt of 

 sexual maturity in North Sea fish indicates in 

 inches in length : turbot, 18 ; brill, 15 ; common 

 sole, 12 ; plaice, 17 ; lemon sole, 12 ; common dab, 

 7 ; cod, 25 ; haddock, 13 ; whiting, 9 inches. 



It will be observed that the standard for North 

 Sea plaice is 17 inches, but Mr. Holt draws 

 attention to a dwarf variety of this fish which 

 appears to have its headquarters in the Baltic. 

 After examining several consignments of these fish 

 from German fish merchants to the Grimsby 

 pontoon, it was found that the largest measured 

 only 13J inches, which, with some females no 

 longer than 9J inches, were all full of ripe roe or 

 milt. The plaice of our south-west coast are 

 considerably smaller than the North Sea forms. 

 Their lengths of maturity varying from 11 to 15 

 inches. As another instance of variation of size of 

 maturity, the common soles of the south-west of 

 England, which are larger than those of the North 

 Sea, mature only at over 13 inches in length. 



Many people wanting in knowledge of the life- 

 history of our food fishes are too apt to recommend 

 artificial breeding as a means of replenishment. 

 Mr. Holt devotes considerable attention to this 

 subject. With the exception of skate, herring and 

 cat-fish, all our food fish propagate by means of 

 eggs which float singly on the surface of the 

 water for some considerable period of time, 

 during which the embryo is developing. In 

 most of the more valuable kinds the eggs 

 float until they are hatched, excepting those of 

 turbot, which seem to sink some days before 

 hatching. It will be seen that the difficulties in 

 the way of artificial propagation are almost 

 insuperable. It is necessary to have a continuous 

 change of water in the tanks where the eggs are 

 placed in captivity after being spawned. As they 

 float they naturally drift towards the overflow 

 from the tank, and to have any strainer sufficiently 

 fine to stop these eggs means that the eggs 

 immediately choke the strainer, thus not only 

 preventing the refreshing of the water, but causing 

 injury and disease among the eggs themselves from 

 overcrowding. This, of course, could be overcome 

 by having large spaces of water instead of labora- 

 tory tanks, but even then it is not probable that 

 an}- great percentage would ever reach the size 

 where reproduction commences, if it were con- 

 sidered desirable to keep them so long. The flat 

 fish generally frequent sandy beaches close inshore 

 until they are large enough to migrate to the shallow 

 banks in the main ocean. They have at this period 



