Introduction

Maritime ‘waifs and strays’ of the animal world not infrequently strand on New Zealand's shores; among them we find four species of marine turtles and two sea snakes. Whether these animals should be regarded as accidental visitors, i.e. fallouts from shoals bypassing New Zealand, or part of the maritime fauna of the country is a moot point. I favour the latter proposition, for if we accept the former then some of the pinnipeds and cetaceans would have to be excluded from the New Zealand fauna! Our records of marine turtles and snakes are based mainly on the dead and dying which strand on our shores and come to the notice of some interested person, and not on the possible, regular off shore visitations of the animals.

As both marine turtles and snakes are normally inhabitants of the warmer tropical and subtropical waters of the globe, it is natural that their visits to New Zealand should vary annually in response to the flow of the currents, and possibly also to the movement of their food supply. Their strandings may be due to sudden changes of temperature which can spell disaster to most repitilian life. Strandings are commonest on the northern shores of New Zealand, but there are also some on the southern shores; the latter animals may have reached there by way of the East Australian Current.

Testudines: Turtles, Tortoises and Terrapins

The order Testudines is divided into two main suborders, Athecae comprising a single family, genus and species, the Luth, Leathery Turtle or Leatherback; and the Thecophora embracing all other living species. In addition to the Luth, only the members of the family Cheloniidae, the marine turtles, concern us.

Four species of marine turtles have been recorded from New Zealand: Dermochelys coriacea (Linn.), the Luth; Chelonia mydas (Linn.), the Green Turtle; Eretmochelys imbricata (Linn.), the Hawksbill Turtle; and Caretta caretta (Linn.), the Loggerhead Turtle.

Key to the Genera of Turtles Occurring in New Zealand

Dermochelys coriacea (Linn.)
The Luth, Leathery Turtle or Leatherback. Fig. 1.

The carapace of the Luth is composed of hundreds of polygonal, irregular bony plates, the largest forming seven regular longitudinal keels along the dorsal surface; these keels converge posteriorly into the free projection of the carapace. The plastron is devoid of dermal bones except along five longitudinal ridges in which the bony series is incomplete. These ventral ridges are not always present in the adults.

Colour: The adult is dark-brown or bluish-black above, spotted or blotched with pale yellowish or pale bluish-white about the throat, flippers and on part of the carapace.

Size: The Luth is the largest of the living chelonians attaining a length of over two metres and an estimated weight of 1800 Ibs.

Distribution: The Luth is an inhabitant of tropical waters throughout the world. In New Zealand it appears as an occasional straggler, most frequently seen in northern waters, but also recorded as far south as Otago and Foveaux Strait.

Chelonia mydas (Linn.)
The Green Turtle Fig. 2, A-B

Carapace with four pairs of costal shields, an intergular shield and a series of inframarginal plastral shields. Head covered with symmetrical shields; one pair of prefrontals. Dorsal shields juxtaposed. Jaws not hooked. Tail short.

Colour: Adult olive or brown, the shields with more or less distinct brown rays; yellow beneath.

Size: The carapace attains a length of 1,100 mm.

Distribution: The Green Turtle is worldwide in tropical and subtropical seas, and is an occasional visitor to New Zealand.

Note: The Green Turtle derives its name from the colour of its fat. It is the animal which provides the famous Turtle Soup of gourmets — the fat imparts its green colouring to the soup.

Eretmochelys imbricata (Linn.)
The Hawksbill Turtle Fig. 2, C-D

In the young the carapace is three-ridged and the dorsal shields are strongly imbricate; in the adult the ridges disappear and the scutes or shields may remain imbricate or become juxtaposed. There are twenty-five marginals, including the nuchal, strongly serrated posteriorly. Snout compressed in adults, jaws hooked (hence the popular name!. edges not or but feebly denticulated. Head with two pairs of prefrontal shields.

Colour: Young brown above, blackish below. Carapace of adult marbled yellowish and brown, plastron yellow; shields or scales of the head and limbs dark brown, margined with yellow.

Size: An adult carapace may attain a length of 900mm.

Distribution: Widely distributed in tropical and sub-tropical seas. In New Zealand the species is almost restricted to the north. Young occasionally strand along Ninety-Mile-Beach.

The Luth, Dermochelys coriacea (Linn.). New Plymouth, February 1895. Photo, W. Gordon. (By courtesy of the Dominion Museum).

Fig. 2. Head shields of Cheloniidae; A-B Chelonia mydas (Linn.); C-D Eretmochelys imbricata (Linn.); E-F Caretta caretta (Linn.). F= frontal; FP=frontoparietal; P=parietal; PF=prefrontal; SO=supraocular; T=temporal. (del. McCann).

Note: The Hawksbill Turtle is the species that provides the ‘Tortoise shell’ of commerce — ‘Turtle shell’ of commerce is derived from the other species. In the past this species was decimated for the sake of its shell, but in modern times synthetic materials have given it a respite. The beautiful translucent shields are used for ornamental purposes and for the manufacture of jewellery. The flesh is not palatable.

Caretta caretta (Linn.)
The Loggerhead Turtle Fig. 2, E-F; Fig. 3.

Carapace of young three-keeled, the keels disappearing with age or only the median one surviving as an elevated ridge on the first two anterior neurals; nuchal hexagonal; costals five or more pairs, symetrically or asymmetrically arranged. Marginals 26, occasionally asymmetrically arranged, 25 or 27. Inframarginals four, occasionally three or five, the fifth partly covering the bony structure beneath. Head large with strongly hooked jaws, symphysis of lower jaw very long; two pairs of prefrentals, occasionally subdivided. Tail short, not exceeding the carapace in females, extending beyond in males.

Colour: In the adult the carapace is a drab olive or olive grey or reddish brown; the under surface is yellowish or buff suffused in places with pink; beak yellowish horn.

Size: The carapace of the adult attains a length of 1,050 mm.

Distribution: The tropical waters of the Atlantic, Pacific and Indian oceans, and the Mediterranean Sea. It occurs along the Australian and Tasmanian coasts and is an occasional visitor to the New Zealand area.

Serpentes — Snakes

Only two species of marine snakes have been recorded from New Zealand waters: The Black-banded Sea Snake, Laticauda colubrina (Schneider) and the Yellow-bellied Sea Snake, Pelamis platurus (Linn.) Very occasionally a terrestrial snake may appear in cargoes of timber, fruit and other goods.

All sea snakes are poisonous and some of them are particularly deadly. However, the venom of Laticauda does not appear to be strongly toxic to human life. Sea snakes generally require a considerable amount of provocation before they can be induced to bite.

Key to the Marine Snakes Occurring in New Zealand

Fig. 3. Carapace and plastron of Caretta caretta: A=abdominal; AN=anal; C=costal, F=femoral; G=gular; H=humeral; IG=intergular; IM=inframarginal; M=marginal; N=nuchal; SC=supracaudal (included in marginals); V=vertebral or neu a., (del. McCann).

Laticauda colubrina (Schneider)
Black-Banded Sea Snake Fig. 4.

Description: Body subcylindrical. only slightly compressed, rostral scale higher than broad; an azygous scale separating the prefontals, sometimes absent. Labials 7 or 8, third (sometimes third and fourth) below the eye. 21-23 (rarely 25) rows of imbricate scales around body. Caudal scales along tail, 37 to 47 in males, 22 to 35 in females; anal scale divided.

Colour: Light or dark bluish grey above, yellowish below, with black bands of more or less uniform width throughout, or narrowing across the belly.

Size: Males smaller than females, 875mm long, tail 130mm; females 1.420 mm, tail 145 mm.

Distribution: Ranges from the Bay of Bengal to the seas of southern Japan, the coasts of Australia and islands of Oceania. An occasional visitor to New Zealand.

Fig. 4. Laticauda colubrina (Schneider). (del. McCann, partly after Smith).

Pelamis platurus (Linn.)
Yellow-bellied Sea Snake Fig. 5.

Head narrow, snout elongate; body much compressed, the greatest height posteriorly being more than twice that of the neck. Supralabial scales 7 to 8, fourth and fifth below the eye, usually separated from it by subocular scales. 49 to 67 scales around the thickest part of the body. Scales more or less hexagonal or quadrangular, the lowermost each with two or three small tubercles, strongest in adult males.

Colour: there are numerous colour varieties of this species and all possible intergrading takes place. The colour form occurring in the New Zealand area is described as ‘black above, yellowish or brown yellow below, with a lateral series of black spots which may be confluent into stripes, head black above, upper lip usually yellow.”

Fig. 5.Pelamis platurus (Linn.). (del. McCann).

I have seen specimens from our area which were truly bicoloured, blackish above and yellow beneath, the two colours well demarcated.

Size: Total length of male 720 mm, tail 80 mm; female 880 mm, tail 90 mm.

Distribution: Pelamis is the most widely distributed of all the sea snakes. It is truly pelagic and has been found hundreds of miles out at sea. It is confined to salt water and does not frequent the mouths of rivers.

Note: (A more comprehensive paper on the Marine Turtles and Snakes of New Zealand is awaiting publication.)