70 SALMONID^ OF BRITAIN. 



short, they could not do so without another visit to the sea ; consequently these 

 early ascending salmon, until they have again descended to the salt water, cannot 

 be those fish from which we have to expect ova for replenishing the stock in our 

 rivers. Knox, in 1854, observed that a smolt, after first descending to the ocean 

 and tasting its marine food, never again resorts to its infantile food as a constant 

 mode of nourishment. 



This brings me to the question of how it is possible to prove that insufficient 

 nourishment can impede or prevent spawning among the Salmonidee, or, in fact, 

 render a fish temporarily sterile. An instance will be adduced further on to show 

 how fungus among the American char was checked by decreasing their food, but 

 as one result these fish at Howietoun became sterile for the season. 



Deficiency of food may, therefore, occasion sterility by an entire arrest of 

 development in the ova, or, should the eggs be formed in the ovaries, it may stop 

 (possibly not entirely) their further augmentation in size, as cold will retard the 

 development of the embryo in eggs that have been deposited, as has been 

 abundantly proved by transmitting them to distant countries by the assistance of 

 ice. Possibly in some few instances these early-ascending fish may find a locality 

 where food from some cause is unusually abundant, allowing the ova to augment 

 in size, and that this is the explanation of occasionally a female salmon with large 

 eggs being captured at the end of the summer ; but normally these fish will be 

 sterile during the year of their ascent in the condition described, at least until 

 after they have revisited the sea. 



But it may be advanced, if this is so, how do land-locked salmon breed ? 

 Here we have an entirely different set of circumstances to deal with. The fish 

 have never been to the sea-feeding grounds, but have been compelled to adapt 

 themselves to local conditions. Thus, in large lakes, as Wenern and other 

 suitable places, where food abounds, they breed, or else they become " demoralized 

 salmon," as Agassiz remarked ; or, finally, they may die out, due to sterility, the 

 nourishment which they are able to obtain being insufficient or unsuited to allow 

 them to perpetuate their race. 



There is hardly a month in the year when fresh-run salmon may not be found 

 in our rivers, but the main run for spawning purposes occurs as a rule from 

 October to January, or even later. Some of the December and January fish, 

 however, are in that condition, as I have shown, that they could not spawn for 

 many months to come; and I am disposed to think that it is only autumn and 

 winter ascending ones that breed, but experiments are much needed to test this. 



The various runs of salmon which ascend our rivers,* do not appear to be 

 quite the same in each, but still there is a general resemblance, as will be seen 



* Mr. Willis-Bund, in his account of the Severn {Salmon Problems), shows at least eight 

 distinct runs during the year. They may be summarized as follows : — (1) End of December or 

 January, the largest run of the season, and spawning fish. (2) End of January or February, or 

 later ; spawning fish fewer in number, but generally large in size. (3) A run in February of 

 large clean fish, but at the end of the month of gillings. (4) February and March, a spring run 

 of giOings, which press up to the head- waters of the river, and are the early spawners for the 

 next season. (5) A small run of grilse, and some small salmon, during April. (6) June and 

 July, the main run of grilse. (7) Autumn run of Michaelmas giUings. (8) Great run of spawn- 

 ing fish, in October and November. But it must be noted that all the foregoing do not take 

 place invariably every year — thus grilse or gillings may be absent ; but there are, as a rule, 

 three distinct runs of spawning fish, and five runs of clean fish, and, irrespective of the fore- 

 going, there are individuals moving about. Fish which are ascending alone do not appear to be 

 so eager to press up, but stop at the foot of weirs in the pools ; while the largest run of sahnon is 

 on a spring tide. Possibly male fish pass up sooner than do the females, for at certain times in 

 the Usk the higher up the river the netting takes place, the greater is the percentage of males 

 to females which are caught. 



Mr. Anderson writes to me respecting the Forth, and the migration of sahnon and grilse 

 therein, remarking that his observations extend over a period of fifty years. (1) The first run of 

 salmon, the beginning of December till nearly the end of February, should there be a fresh in 

 the river ; they are coarse-looking fish, from 16 lb. to 30 lb. (2) About the middle or second 

 spring tide in February, clean spring-run fiah ; the fish 3 lb. or 4 lb. in weight, increasing in 

 weight every week until the end of April, when some are from 8 lb. to 10 lb. (3) The summer 

 salmon enters with the first spring tide in May, or earUer should the river be in flood ; they are from 

 12 lb. to 20 lb. (4) The first run of grilse, from 1 J lb. to 3 lb., enters the rivers in May ; in 1881, the 



