26 F. DAY: EARLY AND LATE SALMON RIVERS. 



the sea, are worthy of study. Jardine, Yarrell, and others have 

 remarked that the temperature of the river-water exercises some 

 influence in the time of the ascent of these fish, they usually first 

 selecting those that are warmest (of course in moderation), while in 

 most streams the eggs would be more rapidly hatched ; thus, other 

 things being equal, the young fish would be hatched earlier in the 

 warmer than in the colder streams. The Salmon Commissioners of 

 the Tweed remarked in 1867 that it was stated by several witnesses that 

 ' salmon do not enter the river freely when full of ice or snow-water, 

 while on the other hand, a high temperature of the river-water equally 

 deters them from entering it.' Mr. A. Young also remarked that as 

 a general rule such Scottish rivers as fall into the German Ocean and 

 Portland Firth are 1 early,' while those emptying themselves into the 

 Atlantic are 'late.' And it is suggested that as the German Ocean 

 is a cold sea, so the slight difference between the temperature of its 

 waters and those of the rivers induces salmon to ascend early. 

 Whereas rivers on the west coast mostly descend from snow-fed 

 sources, and are therefore cold, much colder than the Atlantic, 

 consequently the salmon wait until the snow floods have ceased. It 

 is also evident that the same comprehensive rule extends to the 

 English and Welsh rivers, and those on the east coast falling into the 

 German Ocean are earlier than those on the west, or of the south 

 coast of Devonshire and Cornwall, where the warmer Atlantic or 

 the English Channel would have the same influence as pointed out 

 by Mr. Young in Scotland. 



But there are also differences in degrees in the temperature of 

 the waters of rivers to be considered, and which may be influenced 

 by the extent of their course, the nature of the country through 

 which they pass, as well as the amount of rainfall. Thus rivers 

 which have their rise in mountains, and after a short and rapid course 

 fall into the ocean, would be colder than such as are longer and 

 more sluggish, and as Sir W. Jardine's and others' observations 

 pointed out, that in the cold months salmon naturally select the 

 warmer streams as well as their most sunny sides. Rainfall has been 

 observed to afford an index to the temperature of rivers, for its 

 distribution is dependent on the level of the land, the result being 

 that such as pass through districts with the heaviest rainfall, would, 

 as observed by Professor Huxley, be late rivers, while those 

 traversing lowlands where the rainfall is less, would be early rivers. 

 According to this view the waters of the Severn should be warmer 

 than those of the Wye, which latter should be of a higher temperature 

 than those of the Usk, and the salmon would ascend these rivers in 

 the foregoing order, which is the order in which they are tabulated 



Naturalist, 



