1899] THE MACKEREL AND ITS VARIATIONS 97 



The Mackerel and its Variations. 



Number 3 of volume v. of the new series of the Journal of the 

 Marine Biological Association was published at Plymouth towards the 

 end of November. It contains an important article on the " Variation, 

 Eaces, and Migrations of the Mackerel (Scomber scomber)" by Walter 

 Garstang. 



This is an attempt to determine whether there are any racial 

 peculiarities in groups of mackerel taken in different localities. Such 

 peculiarities have not hitherto been recognised, even as between 

 American and British representatives of the species ; but it is clear 

 that the establishment of such peculiarities would affect to a consider- 

 able degree our ideas concerning the migrations of this fish. 



Mr. Garstang has determined the peculiarities of more than 1600 

 mackerel from various localities, in regard to ten chosen characters of 

 which the following are the chief: — 



A. The number of black transverse bars or stripes on one side (the 

 left) of the fish. B. The number of transverse bars on one side (the 

 left) which cross or meet the lateral line. C. The presence or absence 

 of round black spots (" intermediate spots ") between the bars of series 

 A. The variation of this character is tabulated under two heads : — 

 (1) The number of fish per centum which possess one or more of these 

 intermediate spots, and (2) the total number of such spots per hundred 

 fish (the left side only of each fish being considered). D. The number 

 of rays in the first dorsal fin. E. The number of rays in the second 

 dorsal fin, including any incipient finlets which are still partially 

 connected with the fin by a low web or ridge, or which are merely 

 closely approximated to the fin and erectile with it. F. The number 

 of dorsal finlets, including all incipient finlets described under E. 



The American mean values for several of the characters, especially 

 A, B, C, and F, differ to such an extent from the British means, that 

 there can be no further doubt as to the existence of racial peculiarities 

 which distinguish American from British specimens of the mackerel. 

 As compared with the British mackerel, the American fish possesses 

 the following racial characteristics 2 — (1) A higher number of transverse 

 bars, (2) much greater spottiness, (3) a smaller number of fin-rays in 

 the second dorsal fin, and (4) a greater number of dorsal finlets. 

 These characteristics are average distinctions, and do not suffice to 

 distinguish every individual. 



With regard to the Britisli fish, the range of variation is very 

 limited, especially in the case of the second dorsal fin, the greatest 

 deviation from the general mean value of which does not amount to 

 T L of a fin-ray in any sample of 100 fish. The total number of fish 

 from the various localities is seen to be insufficient in this case to 

 afford a basis for the establishment of racial differences. In the case 



