BULLETIN OF THE UNITED STATES FISH COMMISSION. 223 



One great difference in the migration of gulls in 1884-'S5 from that in 

 1872-'73 is that in 18S-i-'S5 there were very few glaueus gulls (Lartis 

 glaucus) or Iceland gulls (L. islandicus), but in 1872-'73 both these spe- 

 cies were in vast numbers, comparatively speaking. It seems to me 

 possible that the l$72-'73 migration indicated by those arctic gulls 

 was of even wider and more extensive influence than that of 1884 and 

 1885 ; but, of course, there is room here for further study. 



Again, while the Tay usually is visited by sprats in great sprat sea- 

 sons, equally or nearly so with the Forth, and was so visited in 1872-'73, 

 though not to the extent that the Forth was, in 1884-'S5 it appears to 

 have been almost utterly deserted by fish and bird alike. The cause 

 was, no doubt, comparative scarcity of entomostracan life, dependent, 

 most likely, upon certain undefined conditions of sea temperature, af- 

 fected, posssibly from the river basin of Tay and its tributaries. If 

 light can be thrown upon these not-difficult-to-be-ascertained data, in a 

 few years, at most, much of our uncertainty as to the causes and effects 

 of the migrations of Entomostraca, sea fish, and even salmon and migra- 

 tory Salmonida?, will be removed. 



Temperature of the Firth of Forth, June, 1884, to January, 1885. 



Month. 



June (1884) 



July 



August 



September 



October 



November 



December 



January (1885) 



Kauge of surface temperature of the water. 



Near 

 Alloa. 



58 

 fCO] 

 [C5] 



58 



51 



45 

 [3S] 



35 



30° 



The figures In brackets were not observed, Wit are entered hypothetical^. 



Mr. Milne, in writing to me, adds " I believe that in hot summer days 

 the temperature at Alloa would be 70° or inpre * * * and during 

 severe winter weather would certainly be down to 32°." My belief is 

 that in October and April the temperature is uniform all over the Firth, 

 and from April till October it is higher at Alloa than at the Isle of May, 

 the difference attaining a maximum between July and August. From 

 October to April it is lower at Alloa than at the May, the difference 

 attaining a maximum about the end of the year. The maximum differ- 

 ence between the two places will be about 10° or 12°, giving a rate of 

 change of 0° 2' per mile. Suspended matter taken in ten samples at 

 Kincardine-on-Forth varied from 5 to 20 grains per gallon, averaging 

 about 10 grains.* 



I personally risited Kincardine several times, both in lS72-'73 and in 

 1884-'85, and witnessed the extraordinary congregation of gulls and the. 



*It was at Kincardine-on-Forth, the narrowest part of the Forth, between Alloa 

 and Borrowstounness [== Boness] that the greatest quantities of sprats were taken. 



