T A N E 26,1980

R E P T I L E S O F T H E N O R T H E R N M O K O H I N A U G R O U P

by J . M c C a l l u m Department of Geology, University of Auckland, Private Bag, Auckland

S U M M A R Y

A total of seven islands and stacks were visited in the Mokohinau Group, from which five l izard species were recorded. These were the gecko Hoplodactylus pacificus and the skinks Cyclodina aenea, C. oliveri, Leiolopsima smithi and L. suteri.

The effect of reptile numbers and diversity before and after invasion of islands by rodents is discussed.

I N T R O D U C T I O N

D u r i n g the A u c k l a n d Univers i ty F ie ld Club scientific tr ip to the Mokohinau Group from M a y 21 to M a y 27,1979, the reptil ian fauna of the following islands was studied : Burgess, L i zard , M a o r i B a y , Motupapa, T r i g , "S tack D " and "Stack H " (see fig. 1., Wr ight 1980). Due to adverse weather conditions, distance from the base camp and difficulty i n landing, twelve smaller islands and stacks were not visited.

The northern camp was based on Burgess Island, where most of the observations were made, including two night searches. Single half-day trips were made to the other islands listed, while two visits were made to M a o r i B a y Island.

M o s t of the islands examined have been modified considerably by man; they have been burnt by muttonbirders and fishermen, browsed by goats and more recently by the lighthousekeeper's livestock.

Kiore (Rattus exulans) were evident on a l l islands visited except "Stack H " . Previous workers have discussed predation by this rat on reptile populations (Bettesworth 1972; Crook 1973; Hi tchmough 1977; Towns 1972; Whitaker 1973, 1978) and their findings are relevant to this study. Previous Herpetological Research In 1890, Sandager, the assistant lighthouse keeper on Burgess Island in the 1880's observed: "The tuatara l izard is found in abundance on two of the islands, and I have noted the occurrence of six other species, but in no case more than two kinds on any one i s land . "

H u t t o n and Drummond (1904) recorded a western Pacific gecko (Gehyra oceanica), as occurring on the Mokohinaus and a specimen from there was reputedly deposited i n the B r i t i s h M u s e u m (McCann

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1955). M c C a n n (1955) named another exotic gecko, Lepidodactylus lugubris, as being present in this group. The specimen to which he referred was placed in the Wanganui Publ ic Museum. It was wrongly identified as G. oceanica previous to this work. M c C a n n also l isted museum material of Leiolopisma suteri, L.s. smithi, L. moco and L . homalonotum from the Mokohinau Group.

Sharell (1966) recorded Hoplodactylus pacificus from the Mokohinau Islands and H a r d y (1977) examined specimens of L. moco, L. smithi, L. suteri, Cyclodina aenea and C. oliveri from the group.

The Wildl i fe Service of the Department of Internal Af fa irs have recently surveyed the islands' fauna and comprehensive data have been compiled. (Veitch 1973, Whitaker 1978).

A N N O T A T E D S P E C I E S L I S T

The distributions and relative abundance of l izard species (and kiore) observed during the present survey or reported by H a r d y (1977) or by Whitaker (1978) are shown in Table 1. Nomenclature for geckos follows M c C a n n (1955) and Robb and Rowlands (1977) and for skinks follows H a r d y (1977).

Sphenodon punctatus B o t h this survey and that of Whitaker (1978) failed to locate any

tuataras and it is l ikely that it has become locally extinct. The last sightings were in 1922 on Fana l Island (Crook 1970) and in the Kn ights Group in the 1930s (R. Walters pers.comm.). Sandager's (1890) statement of the tuatara occurring in abundance on two islands, probably M a o r i B a y and either Fanal or Tr ig , is therefore significant.

A n n u a l burning by muttonbirders and the 1932 fires on M a o r i B a y Island and T r i g Island (Gil lham 1960) have modified the vegetation. This together wi th collecting and the introduction of kiore (Crook 1975) probably had a deleterious influence on exist ing tuatara populations.

Gehyra oceanica Recorded by H u t t o n (1904), which constituted the first record for

New Zealand, but has not been seen on subsequent visits . This species may have reached the Mokohinaus and other island groups off the Northland coast after surv iv ing amongst cargo dunnage discharged from ships p ly ing the South-west Pacific (J. Robb pers. comm).

Lepidodactylus lugubris A single specimen in the Wanganui Publ ic Museum, believed to be

from the Mokohinaus, may have been collected by D r H . Suter at the

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turn of the century (McCann 1955). Its locality is stated as " F l a t I s land" , a name which is no longer in use; i t may be L i z a r d Island. However, there is a F l a t Island situated off Great Barrier , some 24km south-east of the Mokohinau Group. This gecko may have arrived in a similar manner to Gehyra oceanica and although conditions are probably favourable for its survival , i t has not been reported recently.

Hoplodactylus duvauceli Although this l izard was reported as common on M a o r i B a y Island

and rare on T r i g Island during a Wildl i fe Service expedition (Whitaker 1978) none were seen during the visit . Populations may be relocated by more intensive searching, especially at night when this gecko is most active.

H. pacificus This gecko was found on only one islet during the survey. This is

probably due to the presence of kiore (see below) which appear to regulate reptil ian population densities on otherwise unmodified offshore islands.

O n "Stack H " large numbers of this gecko were found in numerous small groups situated in cracks i n the surface rock or under loose cover. The groups consisted of one to ten individuals, of various sizes and both sexes. Whitaker (1978) states that H. pacificus was rare on M a o r i B a y Island and T r i g Island, common on the steep cliffs of Burgess Island and abundant on L i z a r d Island.

Leiolopisma moco N o specimens of this s k i n k were seen on any of the islands visited,

although Whitaker (1978) confirmed their presence on a l l the islands inspected except Motupapa Island. They were reported to be especially common on Burgess Island, i n spite of the abundance of kiore. This could have resulted from the thick grass sward on the farm pastures which have been fenced to allow bush regeneration (Whitaker 1974).

The lack of sightings of L. moco during this study may have been due to low l izard act iv i ty because of colder temperatures.

L. smithi This skink was common on a l l boulder beaches examined on M a o r i

B a y Island and Burgess Island. O n Burgess Island, considerable numbers emerged from the boulder bank on sunny afternoons, to forage among the tidewrack and possibly to feed on the numerous kelp flies (Coelopa sp.). Ve i t ch (1973) recorded these skinks in flax on T r i g Island. It was noted as rare as "Stack H " and "Stack D " .

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L. suteri Only one indiv idual of this species was located and was at the

L a n d i n g B a y on Burgess Island. This species has also been recorded from L i z a r d Island (Whitaker 1978). M c C a n n (1955) mentions that the type specimen for this skink was probably collected from Great Barrier and its label was inadvertantly interchanged wi th the L. homalonotum type specimen from " F l a t I s land" , Mokohinau at a later date while in the Wanganui Publ ic Museum. H a r d y (1977) disagrees, as he considers the labelling correct and thinks that Boulenger confused the type localities for the two species when he described them in 1906. It is therefore possible the L. suteri holotype was collected in the Mokohinau Group.

Cyclodina aenea This species was fairly numerous on Burgess Island, where i t was

collected under loose rocks, sheets of t in and fallen wood. The Wildl i fe Service located seven individuals on this island and a few on L i z a r d Island (Veitch 1973).

C. oliveri Several individuals were found on "Stack H " under low vegetation

and beneath rocks and logs, often i n association wi th H. pacificus. I t is a species which has only been recorded from isolated islands between the Poor Knights Islands and the Aldermen Group (Towns and H a y w a r d 1973, H a r d y 1977).

Table 1. The distribution and relative abundance of lizard species and Rattus exulans on the Mokohinau Islands. X = recorded by Whitaker (1978) or by Hardy (1977) but not seen on this visit; A = abundant; C = common; R = rare; * = gained access to this island in 1978.

Mokohinau Islands Burgess Trig Maori Bay Motupapa Stack H Stack D Lizard Island Island Island Island Island

area (ha) 52 16 10 1.5 1.2 1.0 0.8

Gekkonidae Hoplodactylus duvauceli X(R) X(C)

H. pacificus X(C) X(R) X(R) A X(A)

Scincidae Cyclodina aenea C X(C) C. oliveri C Leiolopisma moco X(C) X(R) X(C) X(R) X(R) X(C) L. smithi C X(C) C X(R) X(R) X(C) L. suteri C

Rattus exulans

X(C)

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R O D E N T P R E D A T I O N

Various authors (Hitchmough 1977, Towns 1972 and Whitaker 1973, 1978) have suggested that the impoverished l izard fauna found on islands inhabited by kiore are the result of predation, competition for food sources, or both.

L i z a r d Island, although only 40 m from Burgess Island, had remained virtual ly unmodified by man for the greater part of its history. Several small species of seabird, which are normally sensitive to rat predation, have bred there and five species of l izard have been recorded.

D u r i n g early 1977, kiore reached this island, probably by swimming from Burgess Island via as intermediate stack (C.R. Ve i t ch pers. comm.). Poison was laid later that year and little sign of kiore was noted on L i z a r d Island during the 1979 visit .

Reptile abundance before 1977. D u r i n g November/December 1973, A . H . Whitaker conducted

three searches, including one at night, to L i z a r d Island; the results of which are summarised in Table 2. In 1973, L i z a r d Island had the second richest reptile fauna in the Mokohinau Group (Table 3).

Table 2. Reptile abundance on Lizard Island in 1973.

Method Time Species seen

H. ppacificus gecko C. aenea L. moco L. suteri (unidentified)

Search Pitfall trap

101 min 66 trap days

55 19 1 1 10 5 - - 9 1

Table 3. Reptile density in the Mokohinau Group, 1973. Data after Whitaker (unpubl.).

Island Lizards found per hour

Fanal Flax Burgess

Trig Maori Bay

0 (search time of 85 mins) 0 (search time of 45 mins) 6.0 ) 11.0 ) Various parts of the island 16.2 ) 6.7

15 2 ) ^g'g j Various parts of the island

Lizard "Stack H "

56.4 121.9

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Reptile abundance after 1977 D u r i n g this expedition, a 90 minute vis i t was made to L i z a r d

Island on 21.5.79. Despite careful searches in l ikely areas, no sign of any l izard species was found.

A s stated, L i z a r d Island, w i th an area of 0.8 hectares, had five species prior to 1977. Since the introduction of kiore, l izard density and diversity has decreased to the point where any species s t i l l surv iv ing must be rare. O n small islands wi th few habitats, such as this island, extinction of some or a l l of the species may have resulted.

D I S C U S S I O N

The presence of kiore on the majority of islands examined may have been the cause of low reptile densities. A o r a n g i Island, i n the Poor Kn ights Group, has been found to have gecko and skink densities of more than 2,500 individuals per hectare in suitable places (Whitaker 1968), in contrast w i t h the majority of islands i n the Mokohinau Group, where numbers would be significantly lower. The tuatara is now extinct i n the Mokohinaus, as collecting and repeated burning of its habitat probably compounded the effects of rat predation and hastened its decline.

M a n y of these skinks, especially of the genus Cyclodina, may be allopatric and are restricted to offshore islands. Hi t chmough (1977) has suggested that they may occupy equivalent ecological niches and interspecific competition on predator-free islands could allow only one of these species to thrive. This is exemplified by C. oliveri on "Stack H " . However, some islands hold exception to this trend, which may be the result of their larger size leading to increased habitat diversity.

Another indigenous gecko which could possibly occur at the Mokohinau Group, although not reported, is H. maculatus. Robb and Rowlands (1977) also noted that H. pacificus specimens from the Mokohinaus and the Three K i n g s Island "are particularly robust in a l l dimensions". This feature was readily observable on individuals examined on "Stack H " and is characteristic of offshore island specimens when compared to their mainland counterparts (J. Robb pers. comm.).

A C K N O W L E D G E M E N T S

The author wishes to thank the following: Associate Professor J . Robb and A . H . Whitaker for critically reading the manuscript; T . G . Lovegrove for assistance in its preparation; C.R. Veitch and R. Walters for information and references; and Jill Southee for typing. I am especially indebted to A . H . Whitaker who unstintingly shared data from his private notes concerning Mokohinau lizards.

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R E F E R E N C E S

Bettesworth, D .J . 1972: Rattus exulans on Red Mercury Island. Tane 18:117-118. Crook, I.G. 1970: Tuatara. Wildlife — a review 1970:16-19. Crook, I.G. 1973: The tuatara, Sphenodon punctatus Gray, on islands with and without

populations of the Polynesian rat, Rattus exulans (Peale). Proceedings of the New Zealand Ecological Society 20:115-120.

Crook, I.G. 1975: The tuatara. In Kuschel, G. (Ed.) "Biogeography and ecology in New Zealand". Junk, The Hague: 331-352.

Gillham, M . E . 1960: Plant communities of the Mokohinau Islands, northern New Zealand. Transactions of the Royal Society of New Zealand 8: 79-98.

Hardy, G.S. 1977: The New Zealand Scincidae (Reptilia Lacertilia); a taxonomic and zoogeographic study. New Zealand Journal of Zoology 4: 221-325.

Hitchmough, R.A. 1977: The lizards of the Moturoa Island Group. Tane 23:37-46. Hutton, F.W. and Drummond, J . 1904: "The animals of New Zealand - an account of the

Colony's air breathing vertebrates." Whitcombe and Tombs, Christchurch. 381p. McCann, C M . 1955: The lizards of New Zealand. Dominion Museum Bulletin 17. 127p. Robb, J . and Rowlands, R.P.V. 1977: Reinstatement of Hoplodactylus maculatus

(Boulenger) with redescription of H. pacificus (Gray). (Reptilia: Squamata: Gekkonidae). Records of the Auckland Institute and Museum 14:133-142.

Sandager, F. 1890: Observations on the Mokohinou Islands and the birds which visit them. Transactions of the New Zealand Institute 22: 286-294.

Sharell, R. 1966: "The tuatara, lizards and frogs of New Zealand". Collins, London. 94p. Towns, D.R. 1972: The reptiles of Red Mercury Island. Tane 18:95-105. Towns, D.R. and Hayward, B.W. 1973: Reptiles of the Aldermen Islands. Tane 19: 93-

100. Veitch, C.R. (Compiler) 1973: Unpublished Wildlife Service island survey of the

Mokohinau Group. Department of Internal Affairs, Wellington. 69p. Whitaker, A . H . 1968: Lizards of the Poor Knight Islands, New Zealand. New Zealand

Journal of Science 11:623-651. Whitaker, A . H . 1973: Lizard populations on islands with and without Polynesian rats,

Rattus exulans (Peale). Proceedings of the New Zealand Ecological Society 20:121-130.

Whitaker, A . H . 1974: Report on a visit to Mokohinau Islands, Hauraki Gulf, November 20 to December 4, 1973. Unpublished Report to the Commissioner of Crown Lands, Auckland. 4p.

Whitaker, A . H . 1978: The effects of rodents on reptiles and amphibians. In Dingwall, P.R., Atkinson, I .A.E. and Hay, C. (Eds) "The ecology and control of rodents in New Zealand nature reserves." Department of Lands and Survey Information Series No. 4:75-88.

Wright, A . E . 1980: Auckland University Field Club scientific trip to the Mokohinau Islands, May 1979. Introduction and Acknowledgements. Tane 26: 1-6.

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