CERTAIN INFLUENCES ON THE MIGRATION OF FISHES. ( J5 



ones, and at the end of two or three years their sizes would be altogether dispropor- 

 tioned, some weighing only 2 or 3 ounces, others as many pounds. I have known 

 cases of trout (S.fario and 8. Jevenensis) reaching the weight of 4 pounds in two years, 

 whereas it usually takes three years for a trout to reach a pound. 



A smolt weighing a few ounces let off at Stormontfield on the Tay in the month 

 of May returned in July of the same year weighing 3 pounds. On the other hand, a 

 smolt which His Grace the Duke of Eoxburghe let off ou May 14 did not return 

 until July of the year following, and it had then attained a weight of only 6i pounds, 

 having, in fourteen months, only just doubled the weight gained by the other fish in 

 less than three months. 



These and many other observations tend to prove that fish spending a long time 

 in the sea do not continue to grow at the same rate as during the first few months. 

 There is little doubt but food supply is the great incentive which drives salmon to the 

 sea. They feed, and feed voraciously, in our rivers at times. But sometimes they take 

 but little food — as, for instance, when spawning, when the temperature is very low, 

 and when on migration. It is quite possible, for these reasons, to get plenty of salmon 

 with nothing in their stomachs; and, as their digestion is very rapid, even after a good 

 meal little trace of it might be found in a few hours. 



The idea seems to exist in many minds that the huge bodies of the salmon are 

 developed by a very indefinite something which the fish manage somehow or other to 

 obtain by a process which they call suction; and this, as a recent writer very aptly 

 remarked, points to something rather like microscopic supplies. 



There is, however, no doubt that the food of the salmon, when in the sea, consists 

 largely of herrings, young and old, sand eels, Crustacea, etc. They follow the young 

 herrings in shoals closely, and in many cases are found gorged with these fish. So 

 much is this the case that when, a few years ago, the herrings failed to visit a part 

 of the Scotch coast at the accustomed time, the salmon also failed to turn up in any- 

 thing approaching their usual numbers ; indeed, hardly any salmon were to be got at 

 all, although they were usually very plentiful during the herring season. In the sum- 

 mer there are a good many young herrings in the Solway Firth, as I have frequently 

 found when dredging, etc. It is a curious fact that the herring, which formerly was 

 excessively abundant as a mature fish in the Solway, should have left it entirely, 

 although immense quantities are still found in the sea just outside the Firth. 



A great many reasons have been given for the desertion of the Solway by the 

 herring. It took place about thirty years ago, and people blamed steamboats, trawl- 

 ing, railways, and many other things, but no really satisfactory reason could be given, 

 and I am not aware that anyone has ever yet explained the mystery. But knowing 

 as we do now what a great influence temperature has on the movements of fishes, 

 and putting other facts together, I dare say if we could put the question to the her- 

 rings and get an answer from them it would be that we had rendered the water of our 

 Firth unsuitable, and therefore they prefer keeping out of it. About the time the fish 

 left, or just before it, there was a great rage for hill drainage, and the result of this 

 hill drainage was that an amount of rainfall that formerly took several weeks to run 

 off.came down in about three days, during which time the rivers draining the water- 

 shed were in a state of high flood. Now when we take into consideration that the 

 watershed of the Solway Firth is about ten times as big as the Solway itself, it will 

 be seen that the effect of this hill drainage on the water of the Firth must be very 



