of the Fisher 1/ Board for Scotland. 399 



average size of 279 5 mm., or 10^ inches. In the Firth of Forth the 

 series was scantily represented, and the limits are sometimes difficult to 

 determine. On 23rd July thirty-three ranged from 253 to 340 mm., 

 having a mean size of 280'4 mm., or eleven inches. On 22nd August the 

 average size of seven, ranging from 276 to 304 mm., was 289 mm. 



The observations show that the rate of growth of the whiting varies in 

 different regions (see PI. XX., XXI.). It is most markedly rhythmic in such 

 places as the Firth of Forth, where the summer and winter temperatures 

 have the greatest range. In winter growth is greatly retarded there, or 

 almost quite arrested, while in May, June, July, and August it is very 

 rapid, about three-quarters of the total increase in the year taking place in 

 these months. 



In an open bay, such as Aberdeen Bay, with deep water ofl' the shore, 

 the growth, while still markedly cyclical, is less so than in the former 

 case. In winter growth is slower, but it continues. The most rapid 

 increase also takes place here in May, June, July, and August. 



In the deep water towards the middle of the northern part of the North 

 Sea, it may be said that, although the observations on the whiting, except 

 with regard to the first series, are imperfect, growth loses much of its 

 cyclical character. It seems to take place almost as quickly in the winter as 

 in the summer, and is thus more uniform. The phenomenon is consistent 

 with the comparatively slight seasonal change of temperature that occurs 

 in these depths, and the later period when the minimum temperature is 

 reached. There is evidence that the growth at some part of the period 

 between December and May is a little slower, but further observations are 

 required. 



Moreover, it will be noticed from the curves that the young 

 whitings in their first summer are largest in the Firth of Forth and 

 smallest in the deep northern waters, while those at Aberdeen are of 

 intermediate size. This might be partly due toajjossible difference in the 

 spawning season ; but it is, no doubt, also due to the fact that in such 

 places as the Forth the larval fishes, on issuing from the egg, begin their 

 life in a rapidly rising temperature and grow quickly, while in the deep 

 water off the Shetlands at the same time they encounter a temperature 

 just beginning to rise, and which rises sluggishly. In August, for 

 example, the young whitings are as large in the Forth as they are in 

 Aberdeen Bay in September, and considerably larger than they are in the 

 northern waters, but in the following January they are rather smaller, and 

 they are considerably smaller when one year old. 



Another deduction from the curves is that the whitings of an area do 

 not appear to migrate far from it — i.e., the curves show the same features 

 for fish one, two, and three years old. 



With regard to the age of the whiting when it first attains maturity, 

 the observations which have Ijeen hitherto made as to the averao-e size 

 Avhen maturity is reached are not very extensive, and the areas in which 

 the fish were taken were not always sufficiently well determined, a point, 

 as will be seen from the Table given below, of some importance. 



In the Firth of Forth and neighbourhood both females and males were 

 found mature when nine inches in length.* On the west coast of 

 Ireland Holt examined a number of whiting, all the males being over nine 

 inches and all the females over eleven inches, and all were mature ;t and 

 the same observer, from the examination of fish at Grimsby, has fixed 

 nine inches as the size at which the majority of females first become 

 mature in the North Sea.J While the average size of the female and 



" TeiilJi Ann. Rep. Fisfuri/ Jinardfor Sa,//and, Part iii., j). iSda. 



t Rep. Council Ry. bub. Soc, 1891. App. C, p. 277. 



X-Tmnn. MuroK. Biol. A^sm:, iii., p. .377. 



