174 



NA TURE 



[December 26, 1907 



to show that this period is normally spent in offshore 

 waters, as occasional captures in mackerel nets would 

 suggest. The marking of Tay smolts and control 

 observations of the rings upon the scales of grilse 

 have now shown that the first fish re-appear in the estu- 

 aries as grilse twelve to fifteen months after leaving 

 the river as smolts, and that some fish may spend a 

 further summer in the sea before seeking fresh water, 

 then to re-appear as small spring fish. It would, 

 however, be premature to assume that no fish re- 

 ascend in the year of their descent as smolts. 



This observation leads us naturally to the second 

 essential fact of a salmon's life-history, that of the 

 distinction between the " short migration " and the 

 "long migration"; that is between the fish which 

 return to fresh water in the summer or as spawners 

 in the autumn or winter of the year of descent as 

 kelts, and those which spend a longer period in the 

 sea and return as clean fish early in the following 

 spring. The difference may be well illustrated by the 



admit? The unfortunate sacrifice of the Lismore 

 Weir marking experiments to the objections of cer- 

 tain anglers has undoubtedly deprived us of an oppor- 

 tunity of reaching some conclusion upon this most 

 important point; so far as the experiment went it 

 certainly pointed to such fish not remaining in the 

 Blackwater until the following spawning season, but 

 dropping back to the estuary before ascending to the 

 redds. Mr. Calderwood, in former papers, has 

 adduced evidence of what he terms a " pausing habit " 

 of winter clean fish in the lower waters of the Spey, 

 but he now states that " in Scotland we have not 

 evidence that clean fish arc in any sense temporary 

 visitors to fresh water or habitually drop back into 

 the sea " He moreover notes that the spring fish enter- 

 ing the Ness have already reached the Garry by early 

 in February, while the Tay fish are not found above 

 Loch Tay until May or later. This question is closely 

 connected with the further one, why are some rivers 

 early rivers and some late rivers ? To the latter ques- 



, fresh from the 

 :r Tay at 



cases of two Irish fish of the same sex (female), 

 weight (5 lb.) and length (2 feet i inch), marked as 

 slats on the same day, January 18, 1902, and at the 

 same place, one of which was re-captured on July 22, 

 1902, weighing 11 lb. and 2 feet 5 inches long, while 

 the other was re-captured on June 16, 1903, weighing 

 18 lb. and 2 feet 11 inches long. It is possible that 

 in some cases the " long migration " period may 

 extend over two years, and it by no means follows 

 that any individual fish is either always a short- 

 period fish or always a long-period fish. A remark- 

 able fact shown by results published up to date is the 

 preponderance of short-period fish in Ireland and of 

 long-period fish in Scotland. 



Another problem is raised by the winter and spring 

 fish of some rivers ; do such fish merely ascend a 

 short distance and then drop back again to the tide- 

 way for further feeding before finally running to 

 spawn, or do they ascend to the head-waters of the 

 river they enter so soon as the physical conditions 



NO. I 99 I, VOL. ■]']'\ 



tion Mr. Calderwood devotes considerable space, and 

 his remarks, whether accepted as providing an answer 

 or not, are well worthy of attention. 



We can but briefly allude to many other points of 

 interest touched upon by this book, such as the causes 

 prompting a salmon to seek fresh water, the effects 

 of temperature on a run of fish, and the question of 

 fish "changing rivers." 



Of the salmon's life in the sea until it comes coast- 

 ward we can but assume at present that it is spent 

 in pursuit of the shoals of herring or mackerel, while 

 noting that the drift-net fishery for salmon off the 

 west and north-west coasts of Ireland is conducted in 

 late spring and early summer, sometimes as much as 

 ten miles from the coast. 



We reproduce an illustration showing a November 

 fresh-run male salmon in full spawning livery, photo- 

 graphed before its return to the Tay after marking ; 

 the silver marking plate is seen on the dorsal fin. 

 The Irish marks are similar in form and similarly 



