Mr. Hugh R. Milne, of the Marine Station at Granton, sends me some temperatures taken from the Firth of Forth, extending over June, 1884, to January, 1885, taken at three points, viz., Isle of May, Queensferry, and near Alloa. These data, in connection with the vast swarms of sprats or garvies (Clupea sprattus) and the attendant thousands of Gulls, are useful for future comparisons, and I append them here. It would be interesting to know similarly taken temperatures of the Tay Estuary, which was completely deserted this season by these migratory fish, and consequently by the birds also. If we had also means of knowing the temperatures of the Firth of Forth in 1872-73, when a similar vast migration of Sprats and Gulls was witnessed, such data would assuredly lead to most interesting, useful, and scientific results.
One great difference in the migration of Gulls in 1884-5 from that of 1872-3 is that in 1884-5 there were very few Glaucous Gulls (Larus glaucus) or Iceland Gulls (L. islandicus), but in 1872-3 both these species were in vast numbers, comparatively speaking. It seems to me possible that the 1872-3 migration indicated by these Arctic Gulls was of even wider and more extensive influence than that of 1884-5. But of course there is room here for still further elucidation and collection of statistics.
Again, while the Tay usually is visited by sprats in great sprat seasons, equally, or nearly so, with the Forth, and was so visited in 1872-3 though not to the extent that the Forth was, in 1884-5 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-temperatures, affected, possibly, from the river-basin of Tay and its tributaries. If light can be thrown upon these not-difficult-to-ascertain data, in a few years, at most, much of our uncertainty as to causes and effects of migration of Entomostraca, Sea-fish, and even Salmon and migratory Salmonidæ will be removed.
Temperatures of the Firth of Forth, June, 1884 to January, 1885.
| Isle of May. | Queensferry. | Near Alloa. | ||
| June (1884) | 51 | 53 | 58 | |
| July | (52) | 58 | (60) | |
| August | 54 | (59) | (65) | |
| September | (53) | 54 | 58 | |
| October | 53 | 52 | 51 | |
| November | 49 | 47 | 45 | |
| December | 44 | 41 | (38) | |
| January (1885) | (43) | 39 | 35 | |
| Range of surface temperature of the water | } | 10° | 20° | 30° |
Note.—The figures in brackets were not observed, but are entered hypothetically.
Mr. Milne, in writing to me, adds, "I believe that in hot summer days the temperature at Alloa would be 70° or more, 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 difference 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.
Note.—It was at Kincardine on Forth, the narrowest part of the Firth, between Alloa and Borrowstoness, that the greatest quantities of sprats were taken.
I personally visited Kincardine several times both in 1872-3 and 1884-5, and witnessed the extraordinary congregation of Gulls and the myriads of sprats. In 1884-5 one smack anchored off the pier at Kincardine took 16 tons of garvies (or sprats) during one tide. There were, in all, some twenty smacks all lying anchored at this narrow part of the Firth, but all of these were not fishing with the small meshed nets; some for herrings only. Hundreds of tons were sold at from 14s. to, latterly, 8s. a ton, and were spread over the adjoining farm lands for manure. Hundreds of tons more were sold for making up a compost manure—being in themselves considered too rich in phosphates—to a firm in Alloa. Hundreds of tons more besprinkled the mud-flats at low tide, or hung by their gills in festoons along the tangle covered timbers of the piers. The water itself was alive with them, and every wave that broke on the lower piers left the piers covered with glittering garvies. A man with a minnow landing-net could have caught an indefinite number by sweeping each wave as it came in.
Mr. J. T. Cunninghame, of the Scottish Marine Zoological Station, Granton, in reply to inquiries, tells me that "his notes dating 28th Nov. show that Copepods were very numerous and varied in the Firth of Forth, as were also Molluscan larvæ." The temperatures of the water, as will be seen by Mr. Milne's notes in December and January, 1885, were lower than at any other time of the year being (38) and 35 near Alloa (and Kincardine) as compared with 41 and 39 at Queensferry, and 44 and 43 at Isle of May. By the 17th Nov., as is recorded in our Migration Report, garvies are reported as very abundant around the Isle of May, at which time the temperature at that point was 49° against 47° at Queensferry and 45° at Alloa. These shoals were accompanied by great numbers of Gulls at Isle of May.