FISHES—PHENOMENAL AND ECONOMICAL. 183 
Since the date of the earliest successful consignment of salmon ova to 
Tasmania, by the ship “Norfolk” in the year 1864, literally millions of salmon ova 
have been similarly imported, their fry being hatched out at the Salmon Ponds, near 
New Norfolk, and subsequently liberated in the Derwent and other apparently 
suitable rivers. Sometimes these young salmon were turned loose into the rivers in 
the earlier or parr form, and at other times in the silvery “smolt” condition when 
they were ready to make their first migration to salt water. In ‘no instances, 
however, have these salmon smolts been authentically known to return to the rivers 
the following year as “grilse” or in subsequent years as full grown salmon. Some 
have suggested that the young salmon on arriving at the sea were invariably devoured 
by sharks, barracouta, or other predatory fish. In that case, however, the salmon- 
trout that descended as smolts with them at the same time would have shared their 
fate. That, however, by no means happened, numbers returning to the rivers. It 
may be added that the active young salmon were far better qualified to take care of 
themselves in the salt water than many of the species of fish indigenous to Tasmania. 
It occurred to the writer that possibly the question of temperature was an 
essential element in the refusal of the salmon to adapt themselves to their new 
environments, and a series of thermometrical observations was inaugurated. From these 
experiments it was ascertained that the sea water on the Tasmanian coast averaged 
some ten degrees higher than that of the British seas, and corresponded more nearly 
with that of the Mediterranean on the South Coast of France. 
This fact was in itself a sufficient explanation of the disappointing results so 
repeatedly obtained. The salmon, unlike its hardier relation the trout, is known to 
be particularly sensitive to any changes of external conditions, and more especially 
to those of temperature. Consequently, the millions of young salmon fry and smolts 
that have been liberated in the rivers of Tasmania and made their way to the ocean, 
finding the temperature of the sea water in the vicinity of Tasmania too warm for 
their comfort, have, it may be predicted, wandered away, presumably in the direction 
of the Antarctic Ocean, in search of colder water. Interesting evidence in support 
of the correctness of this interpretation is afforded by the fact that precisely similar 
results have attended the attempts to establish salmon in rivers of the South of 
France which debouch upon the correspondingly warm waters of the Mediterranean. 
The young salmon have thriven as fry, parr, and smolts in the French rivers, but, 
on migrating to the sea, they wandered away and did not return to their native 
streams to spawn, as they would have done under their normal conditions. 
