166 Part III —Twenty-fourth Annual Report 
Again, with regard to the tides, I am still of opinion that spring tides 
have no more influence in bringing the fish into the estuary than neap 
tides have. This opinion is against that of many of the fishermen, but I 
found that in 1904-1905 as many large catches of fish were made during 
neap tides as during spring tides, and that during the past winter, 
1905-1906, the largest catches of the season were made during the lowest 
phases of the neap tides. Here we must bear in mind, however, that 
the greater strength of the spring tides undoubtedly adds to the capturing 
power of the bag-net. 
Slight variations in the temperature of the air, I also find, have no 
marked influence on the movements of the fish, but prolonged frosts and 
subsequent colder waters of spates may drive at least the younger forms 
out into the sea again. Neither of these, however, account for the 
principal fluctuations in the number of fish in our estuaries. 
Spawning may, of course, be left out of account altogether, as the 
sprats do not spawn in the estuary proper, and spawning does not take 
place until the spring and early summer months. 
Storms, and especially south-easterly gales, on the other hand, are 
undoubtedly important factors to be taken into account; but that south- 
easterly gales do not always drive the fish into the Tay estuary may be 
easily seen by referring to the weather statistics of the two past sprat 
fishing seasons. I may point out, however, that a series of westerly 
gales sometimes drive many of the fish from the upper parts of the 
estuary, and may give rise to large catches of young herring. 
It was after a week of storms and south-easterly gales when the largest 
shoal of sprats of the past season made its appearance in the Tay estuary; 
but a greater storm of wind and rain a few days afterwards made little or 
no difference in the numbers of fish in the estuary. The same remarks 
hold good for the sprat-fishing season of J904—1905. 
There only remains now the question of the constant persecution by 
numerous and varied enemies and the consequent inherent restlessness 
and timidity of both fish. As is well known, large shoals of cod, ling, 
whiting, dogfishes, mackerel, and other fishes feed upon the sprat and 
herring, and shoals of haddock devour the spawn of the herring in large 
quantities. Seals, porpoises, and dolphins and many sea birds are also 
well known to be formidable enemies; add to all these, then, the cannibal- 
istic habits of the two fish themselves, and the great destruction made 
upon them by the sprat fishermen, and one cannot wonder at the great 
and constant fluctuations in the numbers of both fish in our estuaries. 
A sudden shoal of cod, whiting, or dogfish, or an increase in the 
numbers of seals and porpoises, or even the occasional presence of a whale 
in the vincity, will doubtless drive large shoals of sprats into our estuaries. 
Here I may mention that only a few years ago a large whale made its 
appearance in the Tay estuary, and during the same time the water was 
simply teeming with sprats, young herring, and young whiting. I may 
also mention that both porpoises and dolphins are not uncommon just 
outside the river, and seals are sometimes very plentiful even in the 
estuary. 
This incessant persecution, then, by numerous and varied enemies, may 
well explain the presence of the sprat, at any rate in such large and 
varying numbers, in our estuaries. 
From the preceding remarks one could naturally conclude that a 
diminution in the number of enemies would result in an increase in the 
numbers of sprats and herring, and that both fish, especially the sprat, 
would. in consequence remain further and longer away from our estuaries. 
Again, during other seasons, when perhaps cod, whiting, dogfishes, and 
