Art. XVI.— On the Absence of the Eel from the Upper Waters of the Waiau-ua and its Tributaries.
[Read before the Wellington Philosophical Society, November 12, 1870.]
During one of my earliest visits to a cattle station which I hold in the Valley of the Upper Waiau, a large river rising in and flowing along the eastern base of the Spencer Mountains, in the Nelson Province, I was informed by my manager that no Eels were to be found, either in the main river or in any of its tributaries, above a line of rapids which occurs some thirty miles below its source. Considering the almost universal distribution of the Eel in New Zealand, I was much struck by this statement, which at the time I was inclined to doubt, but which has since received at least negative proof, from the circumstance that although we have frequently fished for Eels in various parts of the main river and of its tributaries, and Lake Guyon, the outlet of which falls into it, we have never found any trace of them.
The absence of Eels in the Lower Danube (a fact apparently well attested) has been attempted to be accounted for, in part by the increased coldness of the water received below Ulm, from the great tributaries which rise in the Alps, but, as I shall hereafter show, this alleged cause is open to doubt; even if this opinion were well founded however, it would not account for their absence from the Waiau, for although all its waters above the line of rapids referred to are derived from mountains of great altitude, and snow-capped throughout the hottest seasons of the year, and its waters are necessarily very cold, yet they do not differ in these respects from adjacent rivers in which Eels are abundant. For example, the River Clarence, flowing to the eastward of, and parallel to, the Waiau, and within a distance of only four or five miles, and rising in the same chain of mountains; and the River Maruia, a large tributary of the Buller, also rising in the same chain and flowing to the westward, and, for a short distance, parallel to the Waiau (the waters of both of which are even colder
than those of the latter), contain an abundance of Eels of excellent quality. Nor is there any difference whatsoever in the character of the rocks over which these several rivers flow; the mountains are generally composed of crystalline sandstones, the main rivers running with their strike, whilst the tributaries usually cut through them nearly at right angles. Nor can the absence of these fish be accounted for by want of appropriate food, for Lake Guyon and all the smaller and less rapid streams abound in various species of Galaxias, and in other forms of animal life.
We are, therefore, driven to conclude, either that migration to the sea is essential to the Eel of this country, and that some physical obstacle exists which prevents its return to the head waters of the river in question; or that it has been introduced into the river below the rapids (where it is abundant) since the formation of some physical obstacle to its further ascent.
If the absence of the fish in the upper parts of the river is to be attributed to the existence of a physical obstacle to its ascent, then the line of rapids to which I have referred as occurring some thirty miles below its source must be that obstacle. At this point the valley is very narrow, and the river which there contains a great body of water, has cut a channel nearly forty feet deep and about half a mile in length, through solid rock, along which it flows with great force. Judging, too, from the presence of numerous twirls and whirlpools, the bottom of these rapids appears to be rocky and uneven, whilst the rock on the sides, and, doubtless on the bottom also, has been highly polished by the attrition of the silt brought down during floods.
But it may be urged that Eels are well known to breed freely in Europe in fresh water habitats, without attempting to seek the sea, and that during the winter season they manage there to protect themselves from the increased rigour of the temperature by burying themselves in mud, or by hiding in holes in the banks of the rivers and ponds. Mr. Yarrell, indeed, expressly cites the Mole, the Wey, and the Longford rivers, and various ponds, as localities in which the Eel is found to breed freely, but from which it does not attempt to reach the sea; and we may be asked why should not the Eels of this country follow the same habit in the Upper Waiau, assuming that the rapids referred to prevent their ascent of the river? The coldness of the water during the winter season would not be sufficient to account for their absence, for Mr. Yarrell has shown that they are able to endure, without injury, a very rigorous temperature, and certainly the winter season of the district in question is not so inclement as that of many parts of England.
We are, therefore, driven back upon the two alternatives mentioned in the earlier part of these observations, and of these two I am disposed to rely upon the first, namely, that while migration to the sea is essential to the Eels of this country, a time arrived at which, although descent was practicable,
they could no longer overcome the physical obstacle to their ascent of the river, presented by the line of rapids referred to. I am the more inclined to adopt this opinion, because there is no obstacle to the passage of Eels from the Clarence or the Maruia into the upper waters of the Waiau. Maling's Pass is a low bog-saddle between the Clarence and the Waiau, from which water flows to each of these rivers. The Maruia, in like manner, is separated from the Ada (a large tributary of the Upper Waiau) by a similar bog-saddle, on which there are numerous ponds in direct communication with the waters of the two rivers; but, no doubt, any Eels which may find their way across these saddles into the Upper Waiau would run down the river at the spawning season.
It is interesting to observe that the valleys of the Waiau and Ada were on the direct line of route of the East Coast natives during their excursions to the West Coast in search of greenstone, or for man-hunting, and the Gorge of the Maruia, through which they passed before striking the head waters of the Grey, is known to this day by the name of the Kopi o kai tangata, or Cannibals' Gorge. During these excursions the natives evidently camped near Lake Guyon, for I have there obtained stone implements, fragments of the shell of the mutton fish, and other articles, and in a cave not far from the lake, the skeleton of a man, some fragments of matting, and a portion of an eel-basket, were found.
I do not conclude from the latter circumstance that Eels were to be found in the lake, or in the upper parts of the Waiau or its tributaries, at the time when the excursions referred to took place, but rather that it was intended for use either in the lakes on the western side of the Spencer Range, or in those at Tarndale on the route to the Kaikoura, which have long been celebrated amongst the natives of the latter place for the abundance and quality of their Eels.
On the whole I am disposed to attribute the absence of these fish from the district in question to the necessity for migration to the sea or to warmer parts of the river during the spawning season, and the inability of the fry, or even of the adult fish, to re-ascend the river beyond the line of rapids before referred to.