62 



ON THE NATURAL ENEMIES OF THE SALMON IN 



TASMANIA. 



[By Morton Allport.] 



Having so far succeeded in the great work of the introduction of the 

 salmon to Australia, it now becomes necessary to consider what difficulties we 

 may have to encounter from the presence of creatures in our Tasmanian waters, 

 likely to prey upon the ova, the fry in their early stages, or the full grown 

 fish. 



Many persons imagine that enemies will be more numerous here than 

 in Great Britain ; I do not think so, and have endeavored to make a list 

 of our indigenous animals likely to prove injurious. And first as to those 

 found in the fresh waters ; — pre-eminent amongst which stands the beast with 

 a bill, the platypus ( Ornithorynchus anatinus). This sleek creature will 

 prove the chief scourge to the natural spawning beds in our rivers, for he is 

 not only well fitted l>y nature with rapid powers of locomotion in water, and 

 to hold his own in strong ripples, but he can remain under water for 

 several minutes at a time, and whilst there can burrow to the bottom of the 

 deepest spawning rids and avail himself of the beautiful spoon with which he 

 was furnished at his birth, for the very purpose, one would think, of scooping 

 up ova. 



When the large fresh water lobsters found in the northern rivers are 

 depositing their spawn (each ovum of which closely resembles in size 

 and appearance the ovum of the salmon) the platyj^us is generally very 

 busy in the neighborhood, and if caught and opened at this time, many of 

 these creatures will be found to contain upwards of a pint of spawn each. I 

 have little doubt that the young fish in its first helpless state would be taken 

 just as greedily, though I have uot yet been able to test this fact. When the 

 Tasmanian grayling, the sole representative of the salmonidse in our waters 

 (erroneously called the fresh water mullet or herring) are spawning, I have 

 repeatedly seen the shoals driven away by the unwelcome appearance of a 

 platypus, pi'obably on the look out for a supply of ova. It is in the quiet 

 waters of our most secluded lakes that the platypus is now found in the 

 greatest abundance, and it is in such places that he will, for some time, delay 

 the natural increase of the trout which must before long be established there. 

 The last time I visited Lake St. Clair the day was so bright, and the water 

 so still, that the noble beech trees, which clothe the eastern slopes of Mount 

 Olympus, seemed to be continued far down into the lake, and it was next to 

 impossible to say where the trees ended and their reflections began ; the result 

 was that the slightest disturbance on the placid surface of the water, caused 

 a ripple and was instantly detected. On approaching some of these ripples in a 

 boat, I discovered that each was caused by a platypus rising to breathe. Once 

 there were five of them on the surface together within a radius of a few hun- 

 dred yards, and one dived immediately under the boat, from which I could 

 see him most distinctly in the brilliantly clear water. On timing them I 

 ascertained that they frequently remained under water more than two minutes 

 when undisturbed, and, if alarmed, I have no doubt they could increase the 

 time of immersion considerably. 



The only other mammal likely to be destructive, and which is common to 

 both fresh and brackish water is, the yellow bellied beaver-iat or musk-rat 

 {Hydromys chrysoq aster). This creature, one of the few placental mammals 

 indigenous to Tasmania, is nocturnal and piscivorous, and must be care- 

 fully excluded from all fish-breeding establishments. When the ponds in 

 my father's garden were stocked with a small species of carp introduced here, 

 many years ago,from the Mauritius, the beaver-rats made great havoc amongst 

 the fish till 1 shot and trapped several, some of them in the very act of 

 dragging their pi-ey from the water. Though still numerous, these creatures 

 seem, like our carnivorous marsupials, to retire rapidly before civilization. 

 The presence of a few good terriers on the river banks will effectually clear 

 them. On the rocky shores of the Derwent, between Risdon and Bridgewater, 

 I have frequently tracked these animals to their shelter amongst loose stocesi 

 by the peculiar and powerful scent from which they derive their name of 

 musk-rats, and have sometimes killed three and four in a day ; their muscular 

 hind legs and webbed feet enable them to swim and dive with great rapidity. 

 Since writing this account of the beaver-rat. Mi'. Ramsbottom has shown me 

 a letter from Mr. Heniy Button, of Launcestoc, warning him to beware of 

 the same creature, and giving a very conclusive instance of their piscivorous 



