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Volume 81, 1953
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Dasyatis thetidis Waite, a Second Species of Giant Stingray in New Zealand Waters.

[Read before a meeting of the Wellington Branch, August 28, 1952. Received by the Editor, September 1, 1952.]

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In 1951, trawling off Cape Campbell, the “Maimai” took a specimen of a giant stingray which was too large to retain; but before discarding it, the tail was cut off 1 1/2 feet from the disc, and this came into our hands through Mr. T. Caithness. This portion of the tail is 5 1/4 feet long, so that the whole tail approximated to 6 3/4 feet in length. It was obviously not a tail from Dasyatis brevicaudatus (Hutton, 1875), our common stingray known of large size, but clearly from a member of the F. Dasyatidae and of the g. Dasyatis. We have surveyed this genus, and find that the tail is from a specimen of D. thetidis Waite 1899, a species known from New South Wales and Tasmania, where it has been recorded up to a length of 11 feet. Since in D. thetidis the tail is 1 1/2 times the length of the disc, the “Maimai” giant stingray must have been close in size to the Australian record fish.

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It is remarkable that a second species of giant stingray has existed unrecognised in our waters, but large specimens are rare, and even McCulloch (1921) admits difficulty in distinguishing between the somewhat similar D. brevicaudatus and D. thetidis. D. brevicaudatus has a disc entirely free from large tubercles excepting one or two in the mid-dorsal line close to the base of the tail; the tail always short, its length equal to or less than the length of the disc, so that the well-developed serrated spine extends over part of the posterior half of the tail; the ventral fold on the tail is deep. In D. thetidis there are several rows of large tubercles on the mid-dorsal aspect of the disc; the tail, longer, 1 1/2 times the lenght of the disc; the serrated spine, anterior, its tip falling far short of the mid-length of the tail; the ventral fold, low. From these characters it is clear that the large stingray caught by Mr. Seymoui George (1881) off Kawau in 1880, which was 10 feet in length, with a tail 6 feet long, and a long and two shorter rows of “spines” on the back of the disc, was actually a specimen of D. thetidis. His brief account seems to give us all we know of a complete specimen from our waters. Otherwise this giant stingray is known here only from fragments.

We have examined the collection of stingray tails in the Dominion Museum, which still includes a tail recognisable as that described by Hutton (1872), and three others from D. brevicaudatus, one of which has five spines. These agree with the brief data given by McCulloch (1921). The tail is relatively short. The serrated spine is attached less than twice the length of the spine from the tip of the tail, which is depressed anteriorly but compressed posteriorly and nowhere cylindrical. The tail is armoured with tubercles, each a basal plate carrying a more or less erect spine. These tubercles are everywhere spaced out so that rarely are two in contact, and excepting distally the interspace is seldom less and generally more than the diameter of the basal plate. Anterior to the serrated spine there is a mid-dorsal row of one or more (up to 7, the most anterior on the disc) ovoidal to circular finely striated basal plates each bearing a much compressed strong long-based spine, the tip sited over the posterior third of the basal plate. These are nearly all spaced more than the length of the basal plate from each other. The lateral aspect anterior to the serrated spine has widely spaced, essentially non-linear small circular tubercles with a coarsely ridged basal plate and an erect sharp conical centrally-placed spine. The number diminishes anteriorly so that the first half of the region is naked laterally and ventrally. Posterior to the origin of the serrated spine, there is a naked groove beneath the spine and mid-dorsal tubercles are present only close to the tip as a row not one half the length of the serrated spine. The sides are uniformly armed with small tubercles, few of which have the basal plate in contact and the rest are spaced out. These have a circular base and conical spine, diminish in size posteriorly, but increase in frequency. The ventral fold commences beneath the origin of the serrated spine and continues almost to the tip of the tail as a deep fold

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throughout most of its length equal to the depth of the tail at the same level. It is chiefly naked, armed only with a few widely-spaced minute tubercles along the edge of the posterior portion of the fold. The diameter of the basal plates of lateral tubercles is never half the depth of the ventral fold and generally one-third or less of the basal plates of the anterior mid-dorsal tubercles.

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The “Maimai” specimen corresponds to three dried tails in the Dominion Museum, one of which, collected by Buller, is only the distal portion, but from a fish probably as large as that taken by the “Maimai”. One is a fragment, but the third is complete, 3 1/2 feet in length and from a smaller fish. In the “Maimai” and the third specimens, the tail is long. The serrated spine extends over a naked area longer than the spine and possibly indicating the maximum length of the serrated spine. Using this as the maximum length, the origin of the serrated spine is anterior on the tail, not less than five times this length from the distal end, which is cylindrical for about the length of the naked strip from the tip, subcylindrical anteriorly to the vicinity of the spine, and increasingly depressed anterior to this. The tubercles are somewhat linear, large, crowded, most rarely isolated or more than the diameter of the basal plate from each other. Anterior to the serrated spine there is a mid-dorsal row of large crowded tubercles with subcircular to obtusely elliptical coarsely ridged basal plates mostly with a conical erect central spine, but a few anterior, with the spine posteriorly over the plate. On the sides the tubercles are smaller but numerous, appear as two rows with others scattered between, the basal plates circular and coarsely ridged, the spines, conical, central and erect. In this anterior region, the diameter of the basal plates is but rarely less than half the length of the basal plates of the mid-dorsal tubercles and generally more than half the depth of the ventral fold. Posterior to the origin of the serrated spine, the tubercles are numerous, everywhere crowded, increase in frequency but diminish in size distally so that the terminal cylindrical portion is minutely but richly spiny. The ventral fold commences beneath the origin of the serrated spine and extends nearly to the tip of the tail, but is low, nowhere more than one-third the depth of the tail at the same level and minutely but richly spiny from the tip of the serrated spine to the termination of the fold.

From the above, it is possible to distinguish the two species in our waters, and we hope that a careful account of D. thetidis will be prepared from New Zealand material. In examining small specimens it should be kept in mind that these have fewer tubercles than do the larger. Fowler (1941) regards the species as a synonym of D. latus, but it lacks the dorsal keel of that species. It is difficult to follow Whitley's (1933) diagnosis of Bathytoshia, but we find no reason to remove thetidis from Dasyatis as generally recognised.

References

Fowler, H. W., 1941. US. Nat. Mus. Bull. 100, vol. 13, p. 413.

George, S., 1881. T.N.Z.I., vol. 13, p. 426.

Hutton, F. W., 1872. Cat. Fishes N.Z., p. 85.

Hutton, F. W., 1875. Ann. Mag. Nat. Hist., ser 4, vol. 16, p. 317.

Mc Culloch, A. R., 1921. Proc. Linn. Soc. N.S.W., vol. 46. p. 462.

Waite, E. R., 1899. Mem. Austr. Mus., no. 4, p. 46.

Whitley, G. P., 1933. Rec. Austr. Mus., vol. 19, p. 61.