32 RESULTS OF THE ATTEMPTS TO ACCLIMATISE SALMO SALAR- 



high range of surface or shallow water, is opeu to several 

 objections. 



1st. AVe have positive evidence to the contrary, gained from 

 the close observation of many years of the progeny of Salino 

 salar in confinement in the shallow artificial ponds connected 

 ■with the Hatchery at the Kiver Plenty. 



It is reasonable to infer that the water of these shallow 

 ponds arc more subject to extremes of temperature than our 

 open rivers and seas, where the fish are at liberty to seek for 

 the more congenial temjierature in the deeper waters. AVheu 

 we find, however, that under the most luifavourable conditions 

 foranadromusfishes — viz., confinement permanently in shallow 

 fresh water ponds — the undoubted progeny of Salmo salar 

 not only survive for very many years, but even breed there, 

 we have the best of reasons for being dissatisfied with the 

 temjierature argument. 



Apart from this: the idea that the tcmiJeratiu-e of our open 

 waters of rivers and seas varies to any material degree from 

 that of the southerly portions of Ireland and England where 

 the salmon exists is based upon very imperfect reasoning. 

 The vertical isotherms of our estuai'ies and seas have never 

 been properly investigated, and so far I am aware we ai'e not 

 providing Tasmania as yet with appliances for conducting 

 investigations of this kind. 



It is true we have perfect records of fresh water shallows, 

 as at the Plenty, and of sandy flats, as at Mr. Saville Kent's 

 late salt water enclosures at Sandy Bay, but these are utterly 

 deceptive as affording an index of the variations or mean 

 temjierature of neighbouring depths of the estuary, far less 

 of the submarine depths of the various sea-basins lying 

 beyond and hidden to ordinary observation. It must be borne 

 in mind that the sandy flats at the old Fisheries Establish- 

 ment at Sandy Bay arc exposed in summer, and especially 

 in January, to the direct rays of the sun at low water, and at 

 high water stage the sands are only covered for a very brief 

 period liy one to two feet of water. It would be absurd, 

 therefore, upon such evidence, to gauge the varying isotherms, 

 even at a distance of 400 yards from the shore lino. In 

 shallows laid bare to the sun's rays for many liours at each 

 tide, it is natural to expect that the surface layer of 

 shallow water would indicate a very high range in January, 

 but similar shallows in Great liritain and England might bo 

 selected showing a nearly equal higli range in the heiglit of 

 summer. The proper way to ascertain the temperature of 

 our waters is to follow the scientific method as carried out 

 recently by Dr. Uugh Robert Mill* in the investigation of 

 ** The temperature of the Clyde sea area." In Dr. Mill's 



f Nature, May, pp. 37-39 ; W-58. 



