228 Part III. — Seventeenth Annual Report 





'J 1 n n h DC 



u iiuer 



o i.ncnes 





ann nnrlov 



ft 11 LI UUU.C1. 



• 



ctuu. uiiuer. 



ApnJ, - 



2*5 



i.n 

 10 



0 04 



May, 



24-7 



15-4 



34 



June, - 



21-2 



15*2 



1-4 



July, 



15-5 



12-0 



5-6 



August, - 



10-6 



70 



2-5 



September, 



12-2 



9-9 



6-0 



October, - 



43 



3-5 



1-2 



November, 



0-4 



0-4 



0-2 



The food of the gurnard consists for the most part of Crustacea, especi- 

 ally Crangon, Pandalus, arcd Portunus, and also to a considerable extent 

 of other fishes ;* but whether the supply of food is more abundant on the 

 inshore than the offshore grounds when the immature gurnards begin to 

 come in, and forms a factor in inducing the migration, is not clear. It 

 may be that the younger forms are specially susceptible to the changes in 

 the temperature of the bottom water. It may be seen from Table IV. 

 that from April to the end of September and October the mean tempera- 

 ture of the bottom water is higher within the Firth than it is outside 

 (VIII.-IX.), and the great bulk of the gurnards are always to be found 

 in the warmest water. 



The Bate of Growth. 



Owing to the prolonged spawning period of the gurnard, the difficulty 

 of determining the rate of growth from the collation of the measurements 

 at different seasons is very great. It is clear that individuals hatched 

 in April or May, and those hatched in August or September of the same 

 year, will be of very different sizes in the spring of the following year. 

 It is not only that the period of hatching is separated by an interval of 

 four or five months ; even more important is the circumstance that those 

 which are hatched in the spring pass their post-larval and young stages in 

 the warm water of the summer months when growth is most rapid, while 

 those hatched at the end of August or the beginning of September meet 

 at once with a falling temperature. It is well known that the growth of 

 fishes during the winter months is very slight; and thus, for the 

 two reasons indicated, the size of the young gurnards hatched in one 

 season may show considerable range of size even early in the next 

 season. There is a further cause of difficulty not always borne in mind — 

 viz., that the sizes of the sexes differ — the females being usually somewhat 

 larger, as in the gurnard ;t and there is little doubt that the rate of 

 growth of the female is somewhat more rapid. The rate of growth of 

 different individuals of the same sex also varies. It would therefore 

 require a large series of minute and detailed measurements of both sexes 

 to determine accurately the rate of growth. 



The very young gurnards are not, of course, caught in the ordinary 

 trawl-net of the "Garland" ; most of them under five inches, and almost 

 all at or under three inches, escape through the meshes. J But the majority 

 of these small forms are captured by the "shrimp " trawl-net, in which 



* W. ft. Smith, Tenth Annual Report Fishery Board for Scotland, Part III. pp. 215-218. 

 r Tenth Annual Report, Part III., p. 239. 

 % Twelfth Annual Report, Part ITT., p. 312. 



