1921.] Tillyard.—Neuropteroid Insects as Trout-food. 
277 
began to fail, prepared to remedy it by putting in a fresh supply of calves 
every year, without making any attempt to improve the impoverished 
food-supply! 
Recommendations. 
It is clear that improvements in the trout-fisheries of the Hot Springs 
region can be effected along two distinct lines'—viz., improvement of the food- 
supply and reduction in the number of trout. No considerations of the 
attractions to tourists or anglers, from a superabundant supply of trout, 
should be allowed to cloud the main issue, which is this : that, unless a 
natural balance can be brought about between the introduced trout and the 
food-supply , the fisheries are sooner or later doomed to failure. 
With regard to the improvement of the food-supply, the position is at 
present a very serious one, in so far that the balance has been so greatly 
upset that no measures for the introduction of fresh types of food can be 
expected to succeed unless such food is most carefully protected until 
it becomes well established. It is therefore necessary to adopt at once 
measures which will not only help to conserve the remnant of the food-supply 
still existing, but will also give the aquatic fauna a chance of multiplying 
and approximating towards its original abundance. To bring this about 
I would make the following recommendations :— 
1. A badly impoverished stream should be selected, and should be 
completely blocked by means of specially designed trap-nets, so as to 
prevent any trout passing up it to spawn ; also, any trout at present in it 
should be taken out. Aquatic insects should then be introduced from neigh¬ 
bouring small streams where no trout exist ( e.g ., such parts of streams as lie 
above high waterfalls), and a careful record kept, by means of annual or 
biennial visits, upon the process of the aquatic insect-life in the stream. 
I estimate that it will take at least three years , possibly five, for such an 
impoverished stream to return to its original condition. If at the end of 
two or three years it becomes evident that the aquatic fauna is increasing, 
steps should then be taken to block off in the same way each spawning- 
stream in turn ; so that, in any given year, there will be only certain 
streams open to the trout for spawning, while the rest will be given a 
chance of recuperation.^ 
For this purpose I would recommend either of the following two 
streams :— 
(a.) Te Wairoa Stream, from the waterfall to the outlet of Lake 
Tarawera. (There is an abundant supply of aquatic insects in 
the small creek on the left-hand side of the road leading down 
to the wharf, about a mile from Te Wairoa Stream.) 
(b.) Tokaanu Stream. (Aquatic insects are abundant in the small 
streams around Waihi, two miles away.) 
In both cases the nature of the river-bed (pumice) and frequency of 
flood water make it impossible to block the stream by means of stake or 
pile nets. I would therefore recommend that the nets be strung on strong 
supports driven into the banks, and that their lower ends should hang 
freely into the stream, and carry lead weights at short intervals. The 
accompanying diagrams show the type of net to be used. 
If at the end of three years there is no sign of the native aquatic insect 
fauna reasserting itself I would recommend that an attempt be made 
to introduce the English “ green drake ” may-flv (Ephemera danica), or 
such other species as are known to be of great value aj food for trout. 
19—Science. 
