of the Fishery Board for Scotland. 



303 



Table 11a. — Average Sizes op the Mackerel of the 

 Three Districts. 









Average 

 Size. 



Cm. 



6 



$ 



Total. 





Sex. 



No. 



No. 



Average 

 Size. 

 Cm. 



No. 



Average 

 Size. 

 Cm. 



Aberdeen, 



cJ 



112 



33 



207 



33*2 







2 



95 



33-4 







Clyde, 





91 



33-5 



183* 



33-6 



478 



33.4 



$ 



90 



34 



Barra and 



6 



35 



33 



88* 



33-6 







Stornoway, 



$ 



42 



35 









* Mackerel of undetermined sex included. 



It will be noticed that the fishes are grouped mainly about the sizes 

 32-35cm., the numbers tapering off above and below these limits. On 

 reference to Table IIa., which gives the average size of the fishes from 

 each district, it will be seen that their averages range from 33-35cm., a 

 space of less than one inch. In instituting a comparison between 

 the characters of two or more groups of fishes, it is necessary that they 

 be as near as possible of the same stage, which is conveniently determined 

 by their size. This is important in order to eliminate variations which 

 may be due to growth. All the mackerel here recorded, with three excep- 

 tions, are of mature size ; that is to say, their sizes do not fall below the 

 sizes of the smallest mature forms. The smallest mackerel was an unripe 

 female of a length of 26*8cm. The smallest ripe male was 27'7cm. 

 Two unripe specimens of 27 and 27 '5 were obtained from Barra. Their 

 sex was not determined. The smallest ripe female was 28*9cm. ; a male 

 of this size was also ripe. The smallest ripe female observed by Cunning- 

 ham* was 29'5cm., while the smallet ripe male was 30'3cm. He 

 considered a mackerel of that size to be two years old. 



In a total of 236 mackerel obtained from Loch Fyne and Barra, 

 measuring from 26-43cm., only 13 examples were not ripe; four females, 

 measuring 26 - 8, 28*4, 30, and 32 '3cm., were unripe ; four specimens of 27, 

 27*5, 28'5, and 28*6cm. (sex undetermined) were unripe; five males of 

 from 32-37cm. were not ripe, but may have been spent. It is thus 

 evident that the mackerel examined were of mature size. None of the 

 Aberdeen mackerel were less than 29 '4cm., and the fish at this size, a. 

 female, was spent. One specimen from Kilbrennan Sound was 27 •6cm., 

 and the ovary had the appearance of being spent. It is, then, obvious 

 that a fair comparison may be drawn between the groups, so far as the 

 stage of development is concerned. 



There is still sex-variability, which Heincke, however, found to be of 

 very little moment in the herring. I have, however, kept the averages 

 of the males and the females separate. When combining them to get the 

 average for the group I have included those mackerel which appear in 

 the Tables as of undetermined sex. 



* Journal Marine Biological Association, N.S. Vol. II., p. 232. 



