276 The N.Z. Journal of Science and Technology. [Jan. 
It would not be overestimating the depredation caused by the trout 
amongst the caddis fauna of the Hot Springs region if the loss were put 
at 90 per cent, of the orignial fauna. 
JThe State of the Insect Food-supply. 
My survey of the insects of the Hot Springs region quickly convinced 
me that the balance of nature has been completely upset by the intro¬ 
duction of the trout. By comparison with the state of affairs in most 
parts of the South Island, where the fauna, though seriously reduced in 
many places, is usually found to be more abundant than it is in this 
region, it appears certain that the rainbow trout has had a greater share 
in the eating-out of the insect fauna than has the slower and less greedy 
brown trout. The history of the trout-fisheries of the region may be 
briefly stated as follows :— 
(i.) Before the introduction of the trout the rivers of New Zealand 
swarmed with an aquatic insect fauna as abundant as that to 
be found in any part of the world. The lakes carried a less 
abundant fauna of fewer species. 
(ii.) The great majority of these insects, having evolved to their present 
state without the stimulus of the predatory action of any rapa¬ 
cious fish, possessed no means of defence against the trout when 
they were introduced. 
(iii.) The introduced trout, and especially the rainbow, gorged them¬ 
selves at leisure upon the rich food ; so that, in the course of 
a few years, trout of record size were being caught, and the 
fisheries obtained a world-wide reputation. 
(iv.) No scientific attempts have been made to conserve or renew the 
food-supply. On the contrary, the only idea seemed to be to 
put in more and more fry. 
(v.) As soon as the food-supply began to fail some of the trout became 
weakened, “ slabbiness ” became noticeable, and disease in the 
form of thread-worm and fungoid growths appeared. There is 
also considerable evidence of actual starvation of trout in certain 
streams. 
(vi.) Some attempts have been made of late years to reduce the number 
of trout by netting and trawling. These efforts may be said to 
have brought about some slight improvement in the condition 
of the fish. At the same time, the destruction of shags has 
diminished the prevalence of the thread-worm (of which the 
shag is said to be the intermediate host). But the disease is 
by no means stamped out, and most certainly requires further 
careful study. 
The present position of the trout-fisheries of the Hot Springs region is 
that there is, throughout most of the region, not enough food for the trout 
present. Many of the streams, especially those in which the fish spawn 
regularly, are almost totally “ eaten out,” and the amount of food in the 
lakes is woefully deficient. The only part of the region in which the state 
of affairs can be described as at all hopeful, so far as my investigations go, 
is the Tongariro River and its tributaries, where the supply of food is 
still fairly abundant. 
One might sum up the position, somewhat caustically, by comparing it 
with that of a grazier who put 10,000 head of cattle into a very rich 
1,000-acre paddock, left the animals to feed, and, when the food-supply 
