224 



Part III. — Twenty-fourth Annual Report 



At the " Doghole," off Aberdeen, on 30th July, 26 measured from 

 293cm. to 46cm. (ll r 9 ^- 18J inches) ; on 21st August, 12 ranged from 

 36*4cm. to 48*7cm. (14J-19g inches) ; on 3rd September, 8 taken at the 

 "Doghole" were from 39-4cm. to 45cm. (15|-17j inches); 5 on 31st 

 October measured from 39-5cm. to 535cm. (15|-21| inches); 5 on 5th 

 November were from 46*4cm. to 52cm. (18|-20^ inches) ; and on 28th 

 and 29th November, 33 measured from 39'2cm7 to 57*3cm. (15^-22$ 

 inches). On 12th December, 35 measured from 437cm. to 61 '6cm. 

 (17|-24| inches), the mean size being calculated at 49* 5cm., or 19^ 

 inches, and the age at 32 or 33 months. 



Comparatively few were taken in the Moray Firth. On 12th November 

 16 ranged from 44*8cm. to 61cm. (17§-24 inches) ; on 19th December, 

 15 were from 46cm. to 60cm. (18-23| inches); on 20th to 25th 

 December, 40 measured from 40*3 to 59'8cm. (15§-23| inches) ; on 17th 

 January, off Dunbeath, 41 measured from 41 "9cm. to 62'5cm. (16J-24§ 

 inches). 



In May, off the Shetlands, when they had begun their fourth year, 141 

 measured from 41-8cm. to 61'6cm. (16-24| inches). The mean in this 

 case is about 50cm., and the arithmetical average 50*9cm., or exactly 20 

 inches. 



The average size of the cod on the east coast of Scotland when three 

 years old may be placed at from between 19 and 20 inches, and the 

 probable range of sizes from about 16 to about 24 inches. 



The number of cod older than this in the collections was very small, 

 and their distinction into groups problematical. In the haul on 12th 

 November, in the Dornoch Firth, I have placed ten, measuring from 

 66"4cm. to 76cm. (25|-30 inches), as approaching their fourth year. 

 And on 20-25th December, in Burghead Bay, six measured from 61 "2cm. 

 to 73-4cm. (24-28J inches), which are assumed to be about the same age. 



It is now desirable to compare the differences in the average length of 

 the different groups, which represents the extent of the growth in a year 

 from one annual series to the next. Considering first the means of the 

 first and second series, as given in the Table, there are twelve cases in 

 which this comparison can be made. The difference between ths means 

 varies in different collections from 14*5cm. to 19cm., and the average 

 amounts to 16*57cm., or 6 J inches. Some are better than others, and if 

 we select the nine cases in which the number of fishes in either of the 

 series does not fall below 20, we find that the variation is from 145cm. 

 to 18 - 5cm., and the average of the lot is 16*2cm., or 6| inches. If the 

 comparison is limited to the cases in which more than 70 fishes are 

 represented in each series, and the numbers are fairly equal — and these 

 cases are three in number — the differences are respectively 15cm., Ib'bcm., 

 and 15cm., the average being 15" 2cm., or almost exactly 6 inches. 



There is another method by which comparison of the differences between 

 the groups can be made, viz., by comparing the difference between the sizes 

 at which the maximum numbers of fishes occur — between the maximum 

 ordinates, "modes," or apex, of each curve. As might be expected from 

 these collections, which contain only moderate numbers of fishes, the 

 members of any given group are not duly represented throughout; in some 

 instances the larger fishes predominate in numbers, in others the smaller, 

 and so on ; and thus in a single collection of this kind comparison of the modes 

 or maximum ordinates of two groups may be far from showing the true 

 differences between these groups. Thus, in the fourteen cases in which 

 such comparison can be made between the cod in their first year and those 

 in their second year, the distance between the maximum ordinates varies 

 from 11cm. to 22cm, or exactly double. The mean of these numbers, 



