WAYS OF THE WILD.

Auckland Star, Volume LXI, Issue 15, 18 January 1930, Page 1 (Supplement)

WAYS OF THE WILD.

A NATURALIST'S NOTEBOOK. NEW ZEALAND SHARKS. * (By A. T. PYCROFT.) j Mr. Eric'T. Marshall, of 27, KennetS 'Avenue, Moi" nin 8 Bide >"writes that wMI» fishing Off Island Bay,* on the Upp* Waitemata, on Christmas Day, he caugl# a shark 6ft Bin in length. Mr. Marshall states it had no large dorsal fin but only a small one near the tail, its grey back was marked by a few dark .splotches, the head was blunt and the eyes small. The mouth was very large, its lower teeth being arranged in over- V lapping saw-edge plates. Jits tail was long and thin. Mr.Marshallßtate3.it was very different from a shark 4ft 9in in length which he caught at the same place on the previous Saturday. This smaller shark had a large dorsal fin., I am asked if I can identify _ the chark and supply some information about New Zealand's sharks, and if: apy of them are dangerous to bathers. Fropi Mr. Marshall's description I believeitfte shark :is • the' seven-gilled lieptranchiasindieus. Sharks can be identified if an outline of \tho body. i» supplied showing the exact pos won ol all'the fins, the number of gill slits and their position, the shape and position of the teeth—some are functional teetfc, upright and triangular with serrated » edges, others are pavement like, in oblique rows and others, like the mako«, are long and flexuous. It should alsq. be noted'if the nictitating membrane is present or not. This is a thin, membrane found; in' many animals .at the inner angle or beneath the lower lid of the eye, and capable of being drawn across the eye ball. • It is sometimes called the. third.eyelid., . . - Cartilaginous Fishes. Sharks, rays, which includes t4r-;v stingarees, skates, and several othfer species are known as elasmobranch fishes. 'They belong to a sub-class dietinguished.by their cartilaginous skeletons. Mr. W. J. Phillips* of , Dominion Museum staff, has classified certain, families of' sharks which are presented in New Zealand waters. Ekr ' cept in isolated instances, a fish may be defined as an aquatic vertibrate, whi«h use® gills to assimilate oxygen dissolved in the water; In general there are two main classes;of the group fishes, thq elasmobranchii and the teleostei, true ot. bony fishes. . The order selachii, fronji the; Greek, a fish having cartilages id-: / stead of bones, includes that portion of the. class elasmobranchii, commonly known; 1 to us as sharks. »t. ' . In appearance and structure a typical . shark presents numerous features by which it may be immediately The body ,is cylindrical, and torpedo I shaped, with a distinct snout /beyond the mouth. The skin is rough. The vertebral .column .extends'to the- tail, ; whereas in the true fishes it does not do so. On each side immediately behind i. the head are a number of more or less i vertical- gill-clefts, i .In ;all other fishes the gills are protected by a shield, one., end being free, giving a common open--1 ing to-the, exterior. As a- rule • most} I •; parts of the skeleton consist of cartilage, : though ascertain .-amount of calcification, ii : evident, due to the deposition "of calckreous salts. The, Seyea-Gilled Shark. - Th'e seven-gilledshark, to - which species I,believe the one caught.by Mi*. Marshall,belongs, is a viviparous species, that is, its young are produced in a liv-ing-state similar to the young of mammals, whereas some other species; ate oviparous, that is, the young are produced from eggs, which are generally separated from the-; animal. ; Phillipps - states that the seven-gilled. shark frequents the. open ocean and is taken. I am of the opinion,; however, that it is not uncommon in our; harbours. A specimen; 7ft'Bin in length, caught off Hokianga in 1877, is described as follows: The iris of the"eye.is light brown, the back fins and sides are dark purple, and the lower surface white'. Except on the vertical 1 surface the whole of the body ;and the fins are spotted with' numerous dark irregular spots. Interspersed among these .spots are ia number 1 of large white and almost irre- y,; gular spots. - ■ ■ y The School Shark and Others. ' This shark is one of the small, socalled dogfish, commonly taken h by trawlers around New Zealand. The aver-age-length of this shark ,is 4Jft. Its colour varies from slaty purple or bluish grey to brown, being lighter underneath. Sometimes the..ventral surface is almost white. The fins are, dark. There are two dorsal fins. The nictitating membrane in this shark is a transversely moving eyelid rising from the inner corner over about two-thirds of the eyeball. The species in common with all of this family is viviparous and as many as 34 young have been taken from".a single female, it is harmless to man. , The round-finned, whaler ,is a shark | which grows to a length of ten feet, frequents harbours and is a greedy scavenger. It is a notorious man-eating shark in tropical, seas. Fortunately it is not common around New Zealand. 1 The sharp-finned whaler is, however, > common around the North Island; two large specimens are in the Auckland , Museum. lam unaware of any record ' of its having attacked man. The trueblue shark of the Atlantic has 'been qc- !. casionally caught," Its body is slender and, snout long and its_ long scytheshape . pectoral fin distinguishes- tins 1 species as quite distinct. This '■ is widely' distributed; and, may attain, a ; length of 22ft, and is dangerous to man. ; The bammer-headed .shark is d,s^"" cruished by the eyes, .being situated late..- : ally near the anterior corner of each wing of the head,- the shape seen from above. has given rise to this shark s . popular name..' It is regarded as very dangerous to man and has been known to attain a length of 15ft. The dog- tg fish, -cwhich has pavement-like teeth, -is 'f . common around our coasts and was a common food of the coastal Maoris!; -In .$ recent years it has been sold in our fish shops under another name. It il harmless. The carpet shark is so called on account of its black transverse oblong blotches, which tend to arrange »ftef the manner of the black squares on a draught board. It is a small shark, measuring several feet in length and is. believed to be .harmless. ;. Another harmless shark is the thresher. Its long tail is used to splash the; surface water and frighten-together the small surface •fishes; on -which it feeds. A fine specimen isto be seen in the Auckland Museum. Other species of sharks frequenting New Zealand waters will be described later.