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The Fresh-Water Eels of New Zealand.
[Received by Editor through Mr. A. E. Hefford, Chief Inspector of Fisheries, Marine Department, 8th November, 1927; issued separately, 14th February, 1928.]
1. Introduction.
After having concluded my investigations into the classification and migrations of the Atlantic species of eel, researches which have occupied many years,1 I have turned my attention to the eels of the Indo-Pacific region.2
The first essential here was to reduce the classification to order; for how could one hope to explain the distribution and life-history of the different species without knowledge of the characters by which the species in question could be distinguished one from another?
I had obtained excellent results in the classification of the European, American, and Japanese eels by the use of numerical characters, such as number of vertebrae, of fin rays, etc., and I therefore introduced this method in my studies of the Indo-Pacific species.
The first part of my researches here consisted in studying the material of Indo-Pacific eels to be found in most of the important museums of the world, and very liberally placed at the disposal of the Carlsberg Laboratory.
Very important results were arrived at from this preliminary work alone, not least through our being able to apply the abovementioned method to nearly all the existing type-specimens and other specimens noted in the literature, most of which were inadequately characterized in the descriptions given. We have now X-ray photos of most of these eels from museums in different parts of the world, and have thus been enabled to determine, for instance, the number of vertebrae in every single specimen. It was, of course, out of the question to skeletonize the types, and the process of X-ray photography here represents a great advance in these researches, as the number of vertebrae is a character which cannot be dispensed with.
The comparatively few specimens from the museums, however, were not sufficient for a complete description, and I had therefore to procure a more extensive supply of material by other means.
With this end in view, I set out, in 1926, on a voyage to the Southern Pacific, visiting Australia, New Zealand, and Tahiti, and obtaining on the way great quantities of eels, sufficient for a statis-
[Footnote] 1 Johs Schmidt: The breeding Places of the Eel (Smithsonian Report for 1924, Washington, 1925).
[Footnote] 2 Jobs Schmidt: On the distribution of the Fresh-water Eels (Anguilla) throughout the World.—2. Indo-Pacific Region (Mem. Acad. Royale Sciences et Lettres de Danemark, 8 Ser. t. 10, No. 4, Copenhagen, 1925).
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tical investigation on the lines I had previously adopted in the case of eels of Europe and America (and Japan).1
As regards the eels of Tahiti, I have published the results of my researches in the French Journal La Nature, No. 2765, 1927, in an article entitled “Les Anguilles de Tahiti.” In this, a description is given of the three Anguilla species characteristic of the tropical portion of the South Pacific, viz., the two long-finned and spotted species Anguilla mauritiana Bennett and Anguilla megastoma Kaup, together with the short-finned, uniformly-coloured Anguilla obscura Gthr., which I was able to show was a distinct species, not identical with the Anguilla australis Rich. An account of the four species of cels which I have ascertained exist on the continent of Australia will, it is hoped, shortly be published elsewhere. I shall in the following pages confine myself to the eels of New Zealand. It is with great pleasure that I here acknowledge the interest with which my investigations have been regarded in New Zealand, not only in public institutions, as specially the Marine Department, with Mr. A. E. Hefford as Chief Inspector of Fisheries, but also among a number of scientists and others. I wish to acknowledge the assistance of Mr. H. G. Maurice, Secretary of the English Department of Fisheries and President of the International Council, for having introduced me to the New Zealand authorities. My thanks are also due to the following gentlemen, all of whom have helped in the work by contributing material: Mr. Gilbert Archey, Auckland; Professor W. B. Benham, F.R.S., Dunedin; Mr. T. W. Downes, Wanganui; Mr. H. Jensen, Thames; Mr. W. J. Phillips, Wellington, and Professor R. Speight, Christchurch. During my stay in New Zealand, I received much assistance from the Danish Consul at Wellington, Mr. S. A. Longuet, and in the course of my researches at Pipiriki, on the Wanganui River, I was effectively supported by Mr. Page, Pipiriki House, and the Rev. Henry Keremereta.
To all these gentlemen I beg to offer my best thanks. I have also to thank Mr. H. Luebbert, Director of Fisheries, Hamburg, for a sample of New Zealand eels kindly sent me in 1912 from a consignment received in Hamburg.
Last, but not least, I thank Mr. Vilh. Ege, M.Sc., and Miss E. Hansen, who, with me, have examined the New Zealand material at the Carlsberg Laboratory in Copenhagen.
2. Classification.
The fresh-water eels are probably more abundant in New Zealand than anywhere else in the southern hemisphere. For the Maori, they were of the utmost economical importance, as is evident, for instance, from the highly developed technique in methods and implements for the capture of these fish, possessed by the natives prior to the arrival of Europeans. Thanks to the numerous interesting
[Footnote] 1 Johs. Schmidt: First and Second Report on Eel Investigations (vols. 18 and 23 des Rapports et Procès-Verbaux du Conseil International pour l'Exploration de la Mer, Copenhagen 1913 and 1915).
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Fig. 1.—Anguilla aucklandi Rich., the long-finned eel. Semi-schematic drawing from a specimen 49 cm. in length, by Mr. Vilh. Ege, M.Sc.
Fig. 2.—Anguilla australis Rich., the short-finned eel. Semi-schematic drawing from a specimen 54 cm. in length, by Mr. Vilh. Ege, M.Sc.
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descriptions given by New Zealand investigators, especially T. T. Downes, Best and Hamilton, I have been able, in my work “On the Distribution of the Fresh-water Eels throughout the World (l.c. p. 347–353), to give a brief survey of the New Zealand eels, with special reference to the Maoris and their relations with these fish.
As regards the scientific investigation of the New Zealand eels, their classification and distribution, for instance, it was plain that much was still to be desired; as matters stood, it might seem doubtful how many of the different “species” of eel recorded from New Zealand could be maintained as such in the light of modern requirements as to distinction of species.
By means of statistical and other investigation of nearly 1,500 eels from New Zealand, I have now definitely ascertained that there are two valid species of the genus Anguilla, both highly variable, though hardly more so than the European eel. They should rightly be called Anguilla australis Rich. and Anguilla aucklandi Rich. Taking the most conspicuous point of difference between them, viz., the length of the dorsal fin, I suggest that they should be called in English the short-finned eel (A. australis) and the long-finned eel (A. aucklandi). As regards coloration, both species are uniformly coloured (as with the European and the American species); neither has the spotted or marbled coloration which distinguishes other South-Pacific species such as, for instance, Anguilla reinhardti.
The difference between the two New Zealand species is noticeable when we compare Fig. 1 (A. aucklandi) and Fig. 2 (A. australis). In the former the dorsal fin extends a considerable distance in front of the vent, whereas in A. australis, the corresponding distance is only short.
Fig. 3.—a—–-d/t × 100 in 168 specimens of the long-finned eel (Anguilla aucklandi Rich.) from Pipiriki, Wanganui River (A) and 93 specimens of the short-finned eel (Anguilla australis Rich.) from Pipiriki (44), Thames (24), and Christchurch (B); averages: 11.05 per cent. (A. aucklandi), and 2.41 per cent. (A. australis).—Each dot denotes a specimen.
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This character: the distance between front of the dorsal fin and the vent (a—d) is of great value in the classification of the Anguilla species. In our investigations, therefore, we determine a—d in each specimen, and express it as a percentage of the total length (a—d/t × 100).
Fig. 3 shows graphically a—d/t × 100 in two samples of A. aucklandi and A. australis respectively. Each dot denotes one eel. It will be noticed that in the 168 specimens of Anguilla aucklandi, the value varied between 8–9% and 13–14%, whereas in the sample of the shortfinned Anguilla australis, the value did not exceed 4–5%. The average values were: for A. aucklandi 11.05% and for A. australis 2.41%.
Fig. 3 thus shows that a—d/t × 100 is a “good” character, inasmuch as there was no overlapping in these fairly large samples
Fig. 4.—a—d/t × 100: Schematic representation of the variation of this value in the two samples represented graphically in fig. 3. A and B= average values; a1 and b1=highest, a2 and b2 lowest values in longfinned eel (Anguilla aucklandi) and short-finned eel (Anguilla australis) respectively.
of the two species. The same is apparent from the schematic Fig. 4 where the variation of a—d/t × 100 in the two species is shown in the same figure.1
Taking a—d in the New Zealand eels, there will be very few specimens which cannot be referred with certainty either to the long-finned A. aucklandi or to the short-finned A. australis. There are, however, a series of other characters which can be employed. Among these should be noted first of all the dentition, or form of the teeth-bands. Fig. 5 shows the teeth-bands of the upper jaw in 6 eels, 3 of either species.
[Footnote] 1 When investigating very large samples, the range of variation will of course be somewhat increased. Up till now, we have found the extreme limits of A. australis to be + 5.7% and — 1.4%. (The value is 0 when the dorsal begins immediately above the vent, and negative when the point of commencement lies behind the vent).
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These figures, for which I have taken type specimens where possible, illustrate fairly well some of the commonest variations of the dentition in the two New Zealand species. The teeth-bands can, however, be considerably broader, especially in older specimens.
The difference between the two species lies more particularly in the vomerine band, which is longer and narrower in A. aucklandi than in A. australis. In the latter, the vomerine band is short in proportion to the maxillary bands, and its greatest breadth lies
Fig. 5.—Teeth-bands of the upper jaw in 6 eels, 3 of Anguilla aucklandi, the long-finned eel (a, b, c,) and 3 of Anguilla australis, the short-finned eel (d, e, f).
a: Anguilla aucklandi Rich., Auckland Island, from type in the British Museum.
b: Anguilla Dieffenbachii Gray, New Zealand, from type in the British Museum.
c: Anguilla waitei Phillips (N.Z. Journal of Science and Technology, 8, No. 1, 1925) Wellington, from type in the Dominion Museum, Wellington.
d: Anguilla australis Rich., Tasmania, from type in the British Museum.
e: Anguilla schmidtii Phillips (N.Z. Journal of Science and Technology, 8, No. 1, 1925) Foxton, from type in the Dominion Museum, Wellington.
f: Anguilla australis Rich., Pipiriki, from specimen collected by the author. Drawings by Mr. Vilh. Ege, M.Sc.
behind the middle,2 whereas the greatest breadth in A. aucklandi lies farther forward. The vomerine band of A. australis is therefore not infrequently shaped like the tongue or clapper of a bell (see figures 5 d, e, f). In A. aucklandi, the shape of the teeth bands is extremely variable; the maximal breadth of the vomerine band, however, is hardly ever found to lie behind the middle, as in A. australis. The maxillary bands are often much narrower than in A. australis.
[Footnote] 2 Anguilla australis is distinguished from the other short-finned species of Anguilla by its vomerine band, which is generally short and clapper-shaped (see for instance the figure of A. obscura Gthr. in my previously quoted work on the Eels of Tahiti).
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The number of vertebrae is not a good distinctive character in the case of the two New Zealand species, as it is in so many other
Fig. 6.—Total number of vertebrae in 163 specimens of the long-finned eel (Anguilla aucklandi) from Pipiriki, Wanganui River (A) and in 165 specimens of the short-finned eel (Anguilla australis) from Poroporo Stream, Waiapu, East Cape (B); averages: 112.66 (A. aucklandi) and 111.64 (A. australis). — Each dot denotes a specimen.
cases.1 The total number of vertebrae is shown in the graph Fig. 6. From this it will be seen that the average number is about 1 higher in A. aucklandi than in A. australis (112.66 as against 111.64).
A rather better character than the total number is the number of praehaemal vertebrae; these are shown graphically in Fig. 7, from which it will be seen that the average is higher in A. australis (45.67 as against 44.25).
Fig. 7.—Praehaemal number of vertebrae in 99 specimens of the short-finned eel (Anguilla australis) from Kaipara Harbour and Thames (A) and in 163 specimens of the long-finned eel (Anguilla aucklandi) from Pipiriki (B); averages: 45.67 (A. australis) and 44.25 (A. aucklandi).—Each dot denotes a specimen.
[Footnote] 1 The slight difference in number of vertebrae is a point which will render it difficult to distinguish between the larvae of the two New Zealand species of Eel, and is thus an obstacle to the study of their life history. It will be impossible, for instance, to distinguish between the larvae by number of myomeres alone, as I was able to do in the Atlantic with the larvae of the European and of the American eel, found in the same places.
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Other numerical characters investigated, such as the number of branchiostegal rays and number of pectoral rays, showed slight average differences between the two species.
As will be seen from Figs. 1 and 2, the mouth in A. aucklandi is larger than in A. australis; the same applies to length of head (distance from gill aperture to point of lower jaw). Furthermore, it will be noticed that the angle of the mouth in A. aucklandi extends back a considerable distance beyond the eye, whereas in A. australis, this angle lies approximately below the hind margin of the eye. This character is easily discernible in specimens of any reasonable size; it is advisable, by the way, to avoid as far as possible characters which, like the size of the eye and the pectorals, shape of head, etc., depend largely on the age and degree of development of the individual.
It may further be notod that the body in A. australis is rather more cylindrical in shape than that of A. aucklandi, which is higher, or more laterally compressed.
We have now considered various characters which render it, on the whole, a matter of no great difficulty to distinguish between the two New Zealand species of fresh-water eel. If it is desired to identify one or more specimens, the following should be investigated:
| 1. |
a—d/t × 100, or the distance between front of dorsal fin and vent expressed in percentage of total length (see Figs. 1.2, 3.4). |
| 2. |
Shape of the teeth-bands (see Fig. 5). By means of these two characters, it should be possible in practically every case to determine whether a given specimen belongs to Anguilla australis or Anguilla aucklandi; finally, one can also take: |
| 3. |
The position of the eye in relation to the angle of the mouth (see Figs. 1–2). |
The eels of New Zealand differ in many ways from those of Europe; notably, however, in attaining a far greater size. The European eel rarely attains a length of 4 feet and a weight of 10–12 lbs. T. W. Downes records New Zealand specimens weighing 38, 46 and 32 lbs., and mentions that on the 2nd May, 1917, fourteen eels were taken in the Moumahaki River, the smallest of which weighed 12 lbs. (Trans. N.Z. Inst., vol. 50, 1918, pp. 300–302.) It is not known whether it is the long-finned or the short-finned species, or both, which attain such enormous weight.1 In future observations of gigantic eels it would therefore be very desirable to ascertain, in addition to length and weight, the species to which they belong. It will be seen from the foregoing that this can be determined by measuring a—d and total length; for an expert, examination of the head alone will suffice to show whether it is that of A. aucklandi or A. australis.
[Footnote] 1 I should here mention that Mr. T. W. Downes, of Wanganui, in a letter dated 2nd April, 1926, sent me a sketch of the dentition of an eel, weighing 23 lds., which he had caught. It appears from the sketch that the specimen belonged to Anguilla aucklandi, the long-finned eel. The maxillary bands were extremely broad, and the vomerine band of peculiar shape, something like that shown in Fig. 5 c, but still more pronounced.
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Distribution.
Having had at my disposal some twenty-odd samples, comprising nearly 1,500 fresh-water eels, collected from the most widely different localities in New Zealand, I have endeavoured to ascertain from this material whether A. aucklandi and A. australis are equally distributed throughout the country, or whether any peculiarities are discernible in the distribution.
Fig. 8.—Distribution of the New Zealand eels according to the examination of a number of samples consisting of about 1,500 specimens.
The result of the investigations in this connection will be seen from the chart, Fig. 8. Fully blacked circles denote that 100% of the sample consisted of A. australis, blank circles that 100% were A. aucklandi. Half black, half white denotes that there were 50% of each, and so on.1
The chart shows that the distribution of the two species is not uniform. There can be no doubt, for instance, but that Anguilla aucklandi belongs mainly to the south and west, Anguilla australis chiefly to the north and east.
Further observations are certainly needed, and such will, it is to be hoped, shortly be available; we can already, however, discern a
[Footnote] 1 Only in the case of fairly large samples have the percentages been thus noted; in samples consisting of relatively few specimens, the number belonging to each species is noted. 1 + 4, for instance, indicates that the sample contained in 1 specimen of A. aucklandi and 4 of A. australis.
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characteristic distribution of the two species, which is probably of fundamental importance in biological respects. I will not, however, go further into this question here.
In conclusion, I would merely note the possibility that other species than the two common ones: A. aucklandi and A. australis may be discovered in New Zealand. It is hardly probable, but should such be found they will most likely be stray specimens of tropical species which have found their way to the northern parts of the North Island. The most likely species is probably Anguilla reinhardti, which I found to be common in Lord Howe Island (off New South Wales). It is easily distinguished from the two uniformly coloured New Zealand species however, by its spotted colouring, as well as by many other characters.1
Finally, I venture to hope that this brief article may help to arouse further interest in the fresh-water eels of New Zealand. Once the two species are generally recognized as distinct the way will be open for more profitable study of their distribution and life-history.
Carlsberg Laboratory, July 18, 1927.
Postscript.
On page 366 of my paper on the distribution of the Fresh-water Eels (Anguilla) throughout the World, Copenhagen, 1925, (see footnote 2 at the beginning of the present paper) I said about Anguilla australis.
“Anguilla australis Rich. nec. Boulenger, nec. Weber and Beaufort (New Zealand, Australia and Tasmania). The latter species (i.e., Anguilla australis) must probably be subdivided.”
After having examined a large number of samples of Anguilla australis covering the whole of its area I am now able to say definitely that the species must be subdivided into two forms differing by slight but constant average differences in the number of vertebrae, a—d, etc. I expect to deal with this in a more detailed manner in a paper on the Fresh-water Eels of Australia now under preparation. I may, however, already state here that I propose to divide the species into two forms: Anguilla australis Rich. f. occidentalis n.f. inhabiting Australia (N.S. Wales and Victoria), Tasmania and Lord Howe Island and Anguilla australis Rich. f. orientalis n.f. inhabiting New Zealand, Chatham Island, New Caledonia and Fiji, probably also Norfolk Island.
The two species of Fresh-water Eels of New Zealand should thus rightly be called Anguilla aucklandi Rich. (long-finned eel) and Anguilla australis Rich. forma orientalis Johs Schmidt (short-finned eel).
Carlsberg Laboratory, October 22, 1927.
[Footnote] 1 In New Caledonia (about 800 miles from New Zealand) there are, besides A. reinhardti, two other spotted species, Anguilla mauritiana Bennett and Anguilla megastoma Kaup, as well as the short-finned Anguilla obscura Gthr. In regard to these, I would refer to my article l.c. on The Fresh-water Eels of Tahiti, from which it will be seen that Anguilla obscura Gthr. differs greatly from A. australis both in the dentition and in the far smaller number of vertebrae (from 101 to 107, average 103.88).