182 THE MACKEREL 



have very much less vitahty than those of fish stripped before 

 they have been thus weakened. 



The larvae are about one-tenth of an inch on hatching. In 

 about four to six days the mouth appears and is open. By the 

 ninth day the fish is about one-fifth of an inch long and the yolk 

 is absorbed — and these five days or so probably constitute the 

 critical period when the baby food begins to be supplemented 

 by floating food of some kind. Dr. Lebour, in July, this year, 

 found quite a number of mackerel fry, at a stage a little later 

 than this, about one-fifth of an inch long, and a very large 

 number of these contained no visible food at all. It is not clear 

 whether they could or could not have been feeding on single- 

 celled ^ animals. Larger fry, apparently about three weeks old 

 and measuring about two-fifths of an inch, have been taken off 

 Plymouth in May 1914 ; and Atkinson has caught mackerel fry 

 on the night of the 13th August 1913 over the Great Fisher 

 Bank which measured nearly two inches. It is not known but is 

 assumed that the spawning period in the North Sea is May to 

 August, so these fish were not more than three months old. 

 R. S. Clark obtained young mackerel 3f to 4 inches long 

 inside the stomachs of haddock and whiting trawled off the 

 Tyne in October 1918 — and these, he calculated, were probably 

 fourteen months old. Clark concludes that the fry grow nearly 

 two-fifths of an inch a month on the average. During the fry 

 stage, Dr. Lebour finds, the mackerel live principally on the 

 eggs and larvae of copepods (like Temora and Calanus) and 

 ' water-fleas ' (like Podon and Evadne), and from the time they 

 reach three-tenths of an inch in length they start their career of 

 depredations on other fishes by feeding on young gobies and 

 blennies. One of half an inch contained a blenny more than 

 half his own size. 



Fluctuations in the Catch 



The best account of the ' caprices ' of the mackerel on 

 a particular coast is that given by Mr. A. H. Patterson.^ In 

 Yarmouth a big mackerel fishery was carried on, not without 

 vicissitude, in May and June, till the ' sixties ', when it suddenly 

 ceased. Needless to say the sailing trawlers were blamed. 

 They had ' invaded the feeding-grounds of the mackerel ' and 

 the mackerel had disappeared ; the case was clear. Then, 



^ Dr. Lebour has suggested to the writer that undigested food in the intestine 

 of a transparent larva renders it less transparent, and therefore more con- 

 spicuous to its enemies, and that Nature may have endowed little fishes with 

 the power of very rapid digestion in order to counteract this danger 



- Man and Xature in Tidal Waters (Methuen, 1909). 



