116 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



dealt with and the results are smoothed in much the same way 

 as in the case of the data of Fig. 1. It will be seen that the 

 curves are individual ones, the differences between one year 

 and another being greater than any errors due to sampling that 

 might reasonably be assumed. Generally, the percentage of oil 

 increases to a maximum which occurs sometime just before 

 spawning, that is about August or September, but the values 

 may rise towards this maximum at different rates, as the 

 graphs show, and there may be quite considerable differences 

 in the time of occurrence of the maximum, as the curve for 

 1914 shows. It does not seem possible to account for these 

 differences except on physical grounds, and it is very reasonable 

 to suppose that they are due to accelerations or retardations of 

 the process of fat formation by changes in the sea temperature. 

 I have already* suggested how this temperature factor may 

 operate, but no other data than those mentioned have since 

 been obtained. 



West Goast Mackerel. 



A few samples of mackerel were obtained in 1919 and 

 were examined in the same way as the Manx herrings. The 

 season off the coasts of Lancashire and Wales is a variable 

 one, beginning usually in June or July and ending in August or 

 September. The migration appears to be one which is con- 

 ditioned by the sea temperature, but it has not been investigated 

 and little is known as to the spawning and feeding habits of the 

 fish while in local waters. The mackerel is a highly suitable 

 fish for canning, but so far it has not, or hardly at all, been 

 utilised for this purpose in Great Britain. Obviously the very 

 short season and the difficulty of obtaining regular supplies on a 

 fairly large scale are great obstacles from the factory point of 

 view, and these can only be overcome, it would appear, by 

 recourse to the method of brine-freezing the fish as they can be 

 obtained, and then by cold-storing until a sufficient quantity 

 is obtained fully to employ a factory for some time. 

 * Ann. Rept. Lancashire Sea-Fish. Laby. for 1917, p. 56. 



