6 TllK LMPOVEKISHMENT OF THE SEA. 



(turbot, brill) ; but the latter may be neglected, since they themselves 

 Ibrm an important item in the produce of the same fishery, and their 

 numbers naturally bear a fairly constant proportion to the numbers of 

 the less predatory lishes (by no means limited to flat fishes) upon 

 which they prey. Professor Mcintosh concludes that the destruction 

 of immature ilat-fish by trawls and other drag-nets may be disregarded, 

 since immature tish of all kinds are destroyed in every mode of fishery 

 without injuriously affecting the supplies. Probably the most consider- 

 able destruction of immature fish, other than flat-fish, occurs in the 

 whitebait fisheries on our own coasts, and in the sardine fisheries of 

 France. But there are three excellent reasons why this destruction 

 should have less effect upon the abundance of herrings, sprats, and 

 pilchards than upon the stock of flat-fish — firstly, because the destruc- 

 tion of the former fishes in any given locality is necessarily limited to 

 a small portion of the year, owing to the periodicity in their surface 

 migrations, while the common types of flat-fish, whether young or old, 

 are never removed from the influence of the fisherman's implements of 

 capture ; secondly, because first-year herrings and sprats are sought so 

 eagerly by shoals of mackerel, etc., that the destruction wrought by 

 man at this stage can scarcely exceed a small fraction of the total 

 mortality ; and thirdly, because the larvae of plaice, and probably soles, 

 in consequeuce of their specialised habits, must undergo a heavy pre- 

 liminary mortality * at the time of metamorphosis, from which herrings, 

 at any rate, are probably exempt. Nature may thus be said to have 

 made ])rovision for a heavy death-toll of young herrings, but not of 

 young flat fish. 



The important question, in fact, is not whether some immature 

 fishes may be destroyed with impunity by all classes of fishermen, but 

 whether in any iishery the destruction of immature fish of any particu- 

 lar species is sufficiently great to sensibly increase the death-rate due to 

 natural {i.e. non-human) causes. For evidence upon this point I may 

 refer especially to the investigations of my colleague, Mr. Holt, and 

 of Mr. Cunningham, upon the destruction of immature plaice in the 

 North Sea (this Journal, vol. iii. pp. 339-448, vol. iv. pp. 410-4 ; and 

 vol. iv. pp. 97-143). 



In the present paper, however, I do not pretend to do more than 

 analyse the evidence as to whether the bottom fisheries are, or are 

 not, in a stable condition ; and, if they are undergoing the process of 

 exhaustion which Professor Huxley regarded as within the bounds of 

 possibility, to attempt to determine at what rate the process of de- 

 pletion is going on. 



Professor Mcintosh bases his conclusions upon the alleged failure of 

 the Scottish Fishery Board to demonstrate by their trawling experiments 

 • Cf. Petersen, licp. Danish Biol. Station, IV., 1894, p. 15. 



