Reptiles of Satawan Atoll and the Mortlock Islands, Chuuk ...

415

Reptiles of Satawan Atoll and the Mortlock Islands, Chuuk State,Federated States of Micronesia1

Donald W. Buden2

Abstract: Twenty species of reptiles are recorded from the Mortlock Islands,Chuuk, Federated States of Micronesia. The eight geckos and eight skinks to-gether comprise 80% of the herpetofauna; amphibians are absent. Most of thespecies are widespread in the west-central Pacific, but the recently describedgecko Lepidodactylus oligoporus is known only from the type locality on NamolukAtoll. Hemidactylus frenatus appears to be displacing Gehyra mutilata, which iscommon only on Namoluk Atoll, where H. frenatus is unrecorded. Five speciesof skinks of the genus Emoia are sympatric on Satawan Atoll. Partial habitat seg-regation was observed in three morphologically very similar species of Emoia,with E. cyanura being more frequently encountered in beach strand and otheropen, sun-exposed areas; E. caeruleocauda in shady forest; and E. impar in sun-dappled forest patches.

The Mortlock Islands of Chuuk (for-merly Truk), Federated States of Micronesia,are among the many small islands of thewestern Pacific that are poorly known biolog-ically. The reptiles of the Mortlocks havenever been surveyed systematically, and her-petological records are scanty. Schmeltz andKrause (1881) recorded Lamprolepis smarag-dina (as Lygosoma smaragdina) and Eumeces ru-fescens (¼ Eugongylus albofasciolatus?) from thesouthern Mortlocks (probably Satawan Atoll)and remarked on two species of sea turtles(almost certainly Chelonia mydas and Eret-mochelys imbricata) that nested on Uojta(¼ Weito) Island, Satawan Atoll. Their re-port is based on notes provided by JohannKubary, a naturalist and ethnographer em-ployed by the Godeffroy Museum in Ham-burg, Germany, who resided in the southernMortlocks (probably mainly on Ta Island, Sa-tawan Atoll) from March to the end of May1877. The use of sea turtles as food by the

Mortlockese was mentioned briefly in severalanthropological studies from the mid- to late1900s (Tolerton and Rauch 1949?, Nason1970, Marshall 1972, Borthwick 1977). In ad-dition, Marshall (1975) recorded four speciesof geckos (and one unidentified as to species)and five skinks from Namoluk Atoll based oncollections he made during June and July1971. There were no other herpetological re-ports on the Mortlock Islands until the studyreported here, which began as part of a bio-logical survey of terrestrial vertebrates andselected insect groups by me on SatawanAtoll in the southern Mortlocks, initially inDecember 2002 and with follow-up visits insummer 2003 and spring and summer 2004.All six major island groups composing theMortlocks were visited during summer 2004,chiefly to expand the survey of reptiles and toassess status of fruit bat populations.

Study Area

The Mortlock Islands of this study are a partof Chuuk, one of the four states (along withYap, Pohnpei, and Kosrae) composing theFederated States of Micronesia (FSM). Thename Mortlock Islands applies also, andsomewhat confusingly, to a small group of is-lands northeast of Bougainville in Papua NewGuinea. The FSM, along with the Republicof Belau (¼ Palau) to the west, make up the

Pacific Science (2007), vol. 61, no. 3:415–428: 2007 by University of Hawai‘i PressAll rights reserved

1 Manuscript accepted 14 August 2006.2 Division of Natural Sciences and Mathematics, Col-

lege of Micronesia-FSM, P.O. Box 159, Kolonia, Pohn-pei, Federated States of Micronesia 96941 (e-mail:[email protected]).

Caroline Islands, which span approximately3,200 km of the west-central Pacific Ocean(Figure 1). The Mortlocks are a chain of fiveatolls and one low coral island that stretchesapproximately 220 km southeastward fromNama Island, just south of Chuuk Lagoon,to Satawan Atoll (Figure 2).

The total land area of the Mortlocks is ap-proximately 12 km2 distributed among morethan 100 islands (Table 1). The maximum el-evations are only 3–5 m above sea level (asl).The Mortlocks fall within the equatorial rainbelt and are wet enough to support a meso-phytic vegetation (Mueller-Dombois and

Figure 1. Location map for Chuuk Lagoon and the Mortlock Islands, Federated States of Micronesia, and surround-ing Pacific islands (inset): G, Guam; K, Kosrae; NG, New Guinea; Pa, Palau; Po, Pohnpei; Y, Yap.

416 PACIFIC SCIENCE . July 2007

Figure 2. Location map for 33 islands of Satawan Atoll included in diurnal surveys of lizards during this study; namesof islands are in Table 4.

TABLE 1

Statistical Data for Mortlock Islands, Chuuk, Federated States of Micronesia

Island Group Land Area (km2)a No. of Islands Largest Island (km2)a Inhabited Islands No. of Residentsb

Nama Island 0.748 1 0.748 Nama 1 995Losap Atoll 1.025 10 0.562 Lewel 2 875Namoluk Atoll 0.834 5 0.310 Namoluk 1 407Ettal Atoll 1.893 20c 0.971 Ettal 1 267Lukunor Atoll 2.822 18 1.284 Likiniochd 2 1,432Satawan Atoll 4.589 65e 1.553 Ta 4 2,935

a Bryan (1971).b Based on the 2000 national census (Division of Statistics 2002).c Based on my count while walking along the outer edge of the reef flat, but Bryan (1971) recorded 18.d Formerly Lukunor Island.e Based on information given to me by Satawan Atoll residents, but the exact number is uncertain. Bryan (1971, unpaged) referred

to ‘‘approximately’’ 49 islands in the summary section for ‘‘Truk District,’’ but he included at least 80 named and unnamed islands inhis Satawan Atoll list of islands and mentioned one area in the northeast section as having ‘‘numerous small cays on edge of reef,’’without naming or numbering them.

Fosberg 1998), though many of the smallerislets lack a freshwater lens and are morexeric. Coconut (Cocos nucifera) forest is thepredominant vegetation type, and breadfruit(Artocarpus spp.) is a codominant tree in theinterior of the larger islands. Other large,common forest trees include Barringtonia asi-atica, Ficus spp., Guettarda speciosa, Hernandiasonora, Neisosperma oppositifolia, Pandanus spp.,and Terminalia samoensis. The forest abutsthe beach or merges abruptly with a narrowzone of coastal scrub or thicket dominatedby Tournefortia argentea and Scaevola taccada.Mangroves are scarce throughout. Some nat-ural depressions and pits excavated for tarocultivation hold water semipermanently, butthere is no permanent, standing freshwater.All six major island groups composing theMortlocks are inhabited, but only one tofour islands in each group have permanentsettlements. The other (uninhabited) islandsare visited with various degrees of frequencyto cultivate taro or to harvest natural islandcommodities such as coconuts, coconut andpandanus leaves, crabs, and firewood.

materials and methods

Fieldwork was conducted on Satawan Atollduring 17–26 December 2002, 7 July–1 Au-gust 2003, 30 March–9 April 2004, 22 June–6 July 2004, and 1–5 August 2004. The fiveother groups of islands were visited duringsummer 2004: Nama Island, 2–14 July; LosapAtoll, 10 July; Namoluk Atoll, 19–29 July;Ettal Atoll, 30 July–1 August; and LukunorAtoll (Likinioch Island only), 2 and 3 August.Transportation to the Mortlocks was by smallplane from Pohnpei and Chuuk to Ta Island,Satawan Atoll, which is the location of theonly airstrip in the islands. The other majorisland groups were reached by small boatswith outboard motors or by one of the sev-eral larger trading boats that service the is-lands irregularly from Weno (¼ Moen) inChuuk Lagoon. Within a single atoll, islandswere visited by small boat or, more fre-quently, by wading across the reef flats atlow tide and establishing campsites at themore distant locations. Place names are thoseused by local residents and closely follow

Bryan (1971); alternative names and varia-tions in spelling abound in the literature.

Of the 656 lizards collected, 648 werefixed in 10% formalin and transferred to35% isopropanol; one Lepidodactylus sp. (andtissue samples from seven others) was pre-served in ethanol. Specimens currently are inthe College of Micronesia collections. Cara-pace length of turtles was measured as thestraight-line distance from the midpoint ofthe nuchal notch to the posteriormost edgeof the shell, and carapace width as thestraight-line distance across the widest partof the shell. A Spearman rank order correla-tion coefficient for comparing island sizeagainst number of species was calculatedusing VassarStats: Web site for StatisticalComputation.

results

Turtles

Chelonia mydas (Linnaeus) and Eretmochelysimbricata (Linnaeus). The green turtle (Chelo-nia mydas) and the hawksbill turtle (Eret-mochelys imbricata) are the only turtlesrecorded in the Mortlock Islands. Marshall(1975:7) stated that on Namoluk Atoll bothspecies ‘‘frequent the lagoon and surroundingwaters, with the green turtle being far morecommon . . . [and] now and again they comeashore to lay their eggs on the seaward sideof Amwes [¼ Amas] Islet.’’ He (Marshall1975:7) went on to say that ‘‘turtles of anysize are killed whenever possible for theirhighly prized meat and for their shells whichare a valuable item of trade.’’ Marion Henry(in Pritchard 1977:51) reported ‘‘casualhawksbill nesting’’ in the three southernmostatolls (Ettal, Lukunor, and Satawan), ‘‘but notcommonly on the inhabited islands.’’ Toler-ton and Rauch (1949?) remarked briefly onthe spearing of ‘‘turtles’’ on Lukunor Atoll,and Borthwick (1977:26) reported that boththe green and the hawksbill turtle are foundin and around the Lukunor lagoon ‘‘but theyare not a frequent source of food.’’ Nason(1975:144), reporting on fish and shellfish inthe diet of Ettal Atoll residents, stated that‘‘green sea turtles, the only other marine re-


source utilized, are captured in the lagoon oron one of the islet lagoon beaches three orfour times a year.’’

I saw no hawksbills in the Mortlocks, andthe few green turtles I saw were captive ordead. On Satawan Island, Satawan Atoll, Isaw one female (carapace length 44.5 cm,width 36 cm) in an advanced state of decom-position on the beach on 20 December 2002(cause of death undetermined) and two othersthat were freshly killed and being preparedfor cooking on 23 July 2003, one measuring45.5 by 39.0 cm and the other 51.0 by 45.5cm. I saw two young (estimated carapacelength 15.0 cm) in captivity on Moch Island,Satawan Atoll, during mid-July 2003 and wastold that members of a resident family of is-landers frequently raise young turtles, eventu-ally releasing them into the lagoon. On NamaIsland, in July 2004, I was shown an excavatednest of a green turtle from which the eggshad been harvested during the first week ofJune, and I was informed by local residentsthat both green and hawksbills are occasion-ally seen on Nama and at nearby Losap Atoll.

Lizards

Geckos:Gehyra mutilata (Wiegman). The stump-

toed or mutilating gecko is common on Na-moluk Atoll, scarce to uncommon on Satawanand Kuttu Islands (Satawan Atoll), and un-recorded elsewhere in the Mortlocks; the 11specimens were collected on the walls ofbuildings at night.

Gehyra oceanica (Lesson). The oceanicgecko is widespread and common throughoutthe Mortlocks. It occurs in edificarian habi-tats commensal with humans as well as in for-ests and coastal thickets in the more remoteand uninhabited areas. It was most frequentlyencountered on the trunks of coconut trees atnight. Marshall (1975:6) did not record G.oceanica on Namoluk Atoll, but his mentionof a large gecko that ‘‘lives in the crown ofcoconut palms and has been observed eatingsmaller geckos’’ may pertain to this species.However, his estimate of body size (‘‘approx-imately 300 millimeters’’ [Marshall 1975:6]) ismuch larger than this species attains.

Hemidactylus frenatus Dumeril & Bibron.The house gecko is a relatively recent (post–World War II) introduction to many Pacificislands (Hunsaker 1966, Case et al. 1994), in-cluding the eastern Carolines (Buden 2000).It is locally common in the Mortlock Islandsand recorded here for the first time on fiveof the six main island groups. Its absencefrom only Namoluk Atoll may be real becauseit was not recorded by Marshall (1975), whoresided on Namoluk for 15 months during1968–1971, nor by me during 19–27 July2004. I recorded H. frenatus elsewhere in theMortlocks only in the settlements and only inedificarian habitats, where it was often themost abundant gecko. Five or six would oftenbe within a 1-m radius of an incandescentlamp, feeding on insects drawn to the light.The maximum encounter rate was 27 in 15min (108/hr) at Ta Island elementary school,24 December 2002.

Lepidodactylus oligoporus Buden. This newlydescribed species is known only from theholotype and four paratypes, all collected inScaevola shrubs on Toimon Island, NamolukAtoll, Mortlock Islands, at night on 20 July2004 (Buden 2007). I suggest the commonname Mortlock Islands scaly-toed gecko forthis species.

Lepidodactylus lugubris complex. The 75 ex-amples of geckos in the L. lugubris complexcollected from throughout the Mortlock Is-lands during this study include 18 males( based on external morphology and/oreverted hemipenes) and 57 females. Theyexhibit a bewildering array of variation in col-oration and pattern and appear to include ex-amples of L. moestus (Peters), different clonesof the unisexual species L. lugubris (Dumeril& Bibron), and hybrids. An assessment oftheir distribution and habitat preferences inthe Mortlocks requires further study.

Nactus pelagicus (Girard). The slender-toedor rock gecko is uncommon to locally com-mon throughout the Mortlocks. It is usuallyseen at night, perched low on tree trunks inrocky areas or foraging in coral rubble in theupper beach zone. Unlike the other geckospecies in Micronesia, which attempt to es-cape capture by ascending the trunk, N. pela-gicus usually evades pursuit by descending and

Reptiles of the Mortlock Islands . Buden 419

taking shelter in the interstices of the sur-rounding rocks or in the holes and crevicesat the base of the trunk. It is occasionally en-countered on cement and stone walls andlinings of wells and cisterns. The maximumencounter rates were 8 in 50 min (10/hr) ontree trunks and 5 in 50 min (6/hr) in coralrubble on Kuttu Island, Satawan Atoll, on 6April and 30 March 2004, respectively.

Perochirus ateles (Dumeril). The Microne-sian gecko is one of the most widespread andfrequently encountered geckos in the Mort-locks. It was recorded on all the island groupsand on 29 of the 35 islands surveyed on Sata-wan Atoll. The six islands where P. ateles wasnot encountered represent a diversity of hab-itats wherein it has been recorded elsewhereon the atoll. The lack of records in thesecases may be a result of incomplete sampling.Two of the islands (Moch and Kuttu) are rel-atively large and densely populated, one (Ma-sawech) is one of the smallest islets and isuninhabited and covered with xerophyticbeach scrub, and the three others (Lemasul,Lelang, and Foui) are small to moderatelysized, uninhabited, and forested. Perochirusateles occurs in edificarian and ruderal habi-tats as well as in the less-disturbed forest areasin the more remote and uninhabited islands,often syntopically with the similarly sized Ge-hyra oceanica, although, of the two species, P.ateles is more likely to be found in exclusivecolonies. The maximum encounter rate was45 in 15 min (180/hr) in palm leaf axils (witha maximum of eight in one palm) on EnekapIsland, Satawan Atoll, on 28 June 2004. Manyindividuals collected in the Mortlocks had atleast one or two small (1–2 mm in diameter)orange spots at various locations on the dor-sum, a feature not noted in specimens col-lected from Pohnpei State islands (pers. obs.).

Skinks:Emoia boettgeri (Sternfeld). The Boettger’s

skink is uncommon to common throughoutthe Mortlocks but inexplicably absent orscarce from some of the islands with seem-ingly suitable habitat. This species is most nu-merous in shady forest habitats with sparseground cover, including sites where pigs havebeen rooting, and it is usually seen on theground or low on tree trunks. It is also com-

mon along forest edges adjacent to rockybeaches. It was the only species of Emoiafound on tiny (0.17 ha) Aliare Island (SatawanAtoll), which was the only island in the Mort-locks where it was the sole member of the ge-nus. The maximum recorded encounter ratewas 10 in 13 min (46/hr) on Mariong Island,Satawan Atoll, on 11 July 2003.

Emoia caeruleocauda (De Vis). The Pacificblue-tailed skink is common throughout theMortlocks and was recorded on 17 of the 35islands surveyed on Satawan Atoll. This spe-cies occurs syntopically with E. impar but ismore often found in shaded forest than inopen sun-exposed areas, where the latter ismore abundant. The maximum encounterrate was 49 in 10 min (294/hr) on Foui Island,Satawan Atoll, on 20 July 2003, where theonly other Emoia species recorded was a sin-gle E. cyanura.

Emoia cyanura (Lesson). The brown-tailedcopper-striped skink is recorded in the Mort-lock Islands only on Satawan Atoll and onlyon 9 of the 35 islands surveyed, all in thenorthern part of the atoll—eight of the is-lands are in the Moch District, betweenMoch and Faupuker, and the other (Pien) ismore to the northwest, in Kuttu District.This species is usually seen in grassy, weedy,sand strand or in broad, open areas in forest.The record from Foui is based on a singlespecimen that was collected among numerousE. caeruleocauda; no others were seen. On theother hand, E. cyanura was unusually abun-dant on Fauchan Lengileng Island on 22 July2003, at which time much of the under-growth had been cleared; the encounter ratewas 52 in 5 min (624/hr).

Emoia impar (Werner). The blue-tailedcopper-striped skink is one of the most com-mon lizards in the Mortlocks. Its absencefrom Lukunor Atoll is probably an artifact ofsampling. It was recorded on 20 of the 35 is-lands sampled on Satawan Atoll and morefrequently in open, sun-exposed areas than incompletely shaded forest. The maximum re-corded encounter rate was 55 in 30 min(110/hr) on Onupuku Island, Satawan Atoll,on 9 July 2003.

Emoia jakati (Kopstein). The Jakati skink islocally common in open, sparsely vegetated


areas, especially in the vicinity of human hab-itation and in short grasses, weeds, and vinesin coastal strand. It is recorded throughoutthe Mortlocks though absent from many ofthe more remote and uninhabited islands.The maximum encounter rate was 26 in 30min (52/hr) on Moch Island, Satawan Atoll,on 17 July 2003. This species was unrecordedon Namoluk by Marshall (1975), who spentat least 15 months in residence during 1969–1971, and thus suggests the possibility of amore recent introduction there.

Eugongylus albofasciolatus (Gunther). Thewhite-striped cape skink (¼ reclusive litterskink) is fairly common throughout theMortlocks. The absence of records from Lu-kunor Atoll is almost certainly an artifact ofsampling. It was most frequently encounteredin or very near piles of trash or accumulatedplant debris, at the edges of grassy weedyareas, and among the exposed roots of trees.The animals often afforded only brief glimp-ses before retreating to shelter in under-ground holes or slithering beneath rocks andlogs. Several were observed feeding on coco-nuts that had been split open and left behindby islanders, probably as bait for coconutcrabs (Birgus latro).

Lamprolepis smaragdina (Lesson). The em-erald skink is common throughout the Mort-locks (maximum encounter rate 109/hr—seeNama Island notes later in this paragraph)and usually observed on tree trunks, less fre-quently on vines and on the ground. Amongthe 104 on Satawan Atoll for which dorsalcoloration was recorded, 97 (93%) werebrown, two were greenish brown, four were‘‘mustard’’ or yellowish brown, and two weregreen. Brown individuals predominated inother areas of the Mortlocks as well, includ-ing 61 (95%) of 64 recorded during a 35-min survey (109/hr) on Nama Island on 29July 2004, the 18 observed during a 20-minsurvey on Namoluk Island, Namoluk Atoll,on 29 July 2004, three of the four collectedon Losap Atoll, and the one each from Ettaland Lukunor Atolls during July and August2004.

Lipinia noctua (Lesson). The moth skinkis known in the Mortlocks from Namoluk,Ettal, and Satawan Atolls. It is probably more

widespread and more numerous than recordsindicate; its cryptic habits make assessmentdifficult. It was most frequently encounteredin palm leaf axils, in the fibrous matter at thepetiole bases of coconut palms, and beneaththe flaking bark of dead trees.

Monitor Lizards

Varanus indicus (Daudin). The water monitoris uncommon to common on at least one toseveral islands on each of the three southern-most atolls (Ettal, Lukunor, Satawan), but itis unexpectedly absent from immediately ad-jacent and seemingly very similar islands onthese atolls and it is unrecorded in the morenorthern Mortlocks. Monitors were observedon open sandy beaches, on the forest floor, ontree trunks in coconut forest, and resting atthe water’s edge in taro pits. Others wereheard scrambling through the undergrowthin dense coastal scrub and thickets or runningthrough the water in taro pits. Resident is-landers told me that monitors were intro-duced during the Japanese administration.On Satawan Atoll, I saw monitors frequentlyon Satawan Island and during brief visits toLemasul and Alengarik Islands. One residentof Ta told me of seeing monitors there occa-sionally during the 1970s and 1980s but nonerecently. Nason (1970:35) reported that ‘‘thegiant monitor was introduced [to Ettal Atoll]by the Japanese for rat control on Parang [Is-land],’’ and that it was still restricted to thatisland, at least through the 1960s. I saw threeV. indicus on Parang and one on adjacentAlenganmales Island on 31 July 2004. I sawno V. indicus on Likinioch Island, LukunorAtoll, during my brief visit but was told bylocal residents that they occur there and onseveral other islands on the atoll. Borthwick(1977) reported that monitor lizards were in-troduced to Likinioch by the Japanese.

Snakes

Pelamis platurus (Linnaeus). The yellow-bellied sea snake has been recorded occasion-ally in the waters of the Caroline Islands(Crombie and Pregill 1999, Buden 2000).


One ‘‘found in a drift log someone haddragged to the interior of [Pis-Losap Island,Losap Atoll] . . . March 1972’’ is the first rec-ord for the Mortlock Islands (Craig Sever-ance, e-mail with photo attached, October2005).

discussion

The herpetofauna of the Mortlock Islandsconsists of at least 20 species of reptiles, in-cluding eight geckos, eight skinks, two seaturtles, one monitor lizard, and one sea snake;amphibians are lacking. The marine toad, Bufomarinus, is introduced and widespread onnearby Chuuk and the other high islands ofthe FSM, including Yap, Pohnpei, and Kos-rae (Eldredge 2000, Lever 2001), but thereare no confirmed records for the Mortlock Is-lands. The report of B. marinus as being ‘‘es-tablished and expanding’’ in the MortlockIslands, Micronesia (ISSG Global InvasiveSpecies Database, 2006), with Lever (2001)given as a source, is almost certainly an errorin confusing the Mortlock Islands of Micro-nesia with the Mortlock Islands of PapuaNew Guinea. The Lever (2001) account hasno mention of B. marinus in the Mortlock Is-lands in the FSM section but does so forMortlock Islands in Bougainville, a part ofPapua New Guinea.

With few exceptions, the reptile speciesrecorded in the Mortlocks are widespreadthroughout the Carolines and often well be-yond. The recently described Lepidodactylusoligoporus, however, is known only from thetype locality on Namoluk Atoll and possiblyis endemic to the Mortlocks; other species ofLepidodactylus in the Group II complex (sensuBrown and Parker 1977) also are known onlyfrom very limited geographic areas (Buden2007). The monitor lizard Varanus indicus,which has a spotty distribution in Micronesia,is introduced and apparently confined in theMortlocks to a few islands in the three south-ernmost atolls, and the sea snake Pelamis pla-turus is known in the Mortlocks only from asingle record from Losap Atoll, but it is a pe-lagic species widespread throughout the trop-ical Pacific.

Habitat Preference

Among Mortlock Islands geckos, both Gehyramutilata and Hemidactylus frenatus are adventi-tious species recorded only in edificarianhabitats; G. mutilata is largely uncommon,whereas H. frenatus is the most abundant spe-cies in areas of human habitation, at least onSatawan Atoll (Tables 2 and 3). It is interest-ing that G. mutilata was most numerous onNamoluk Atoll, the only island group in theMortlocks where H. frenatus is unrecorded.Hemidactylus frenatus may be displacing G.mutilata in the Mortlocks as it has displacedseveral species in competitive situations else-where in the Pacific (Petren et al. 1993, Caseet al. 1994, McCoid 1996, Crombie and Pre-gill 1999). The other gecko species are morewidely distributed in several different habi-tats, including coconut forest, the predomi-nant vegetation type. Gehyra oceanica wasfrequently encountered on tree trunks andusually higher than 1 m above the ground,whereas Nactus pelagicus was encounterednearer the base of the trunk, usually within 1m of the ground. Members of the Lepidodac-tylus lugubris complex were most frequentlyencountered at night in Scaevola shrubs alongthe beach and on the walls of buildings. Butdetails of their distribution in the Mortlocksremain unclear because sight records couldnot confidently be assigned to species, andmuch of the collected material is as yet un-identified.

Of the eight species of skinks recorded inthe Mortlocks, Lipinia noctua was encoun-tered only in cryptic habitats, including palmleaf axils, the accumulated fibrous debris atthe base of coconut palm crowns, and underthe loose bark on both standing and fallentree trunks. Eugongylus albofasciolatus wassomewhat less secretive but usually affordedonly brief glimpses before disappearing fromview. It was most frequently encountered onthe ground and mainly during late afternoonand early evening. Of the six diurnally activeskinks, Lamprolepis smaragdina was the mostarboreal, although it was also often seen onthe ground. Conversely, Emoia boettgeri, E.caeruleocauda, and E. impar were usually seenon the ground and on low herbaceous ground


TABLE 2

Distribution of Reptiles in the Mortlock Islands, with Number of Specimens Collected during 2002–2004 Surveys

Atollsa

Species Nama I. Los Nam Ett Luk Sat

TurtlesChelonia mydas þb þb þc þd þe þd,f

Eretmochelys imbricata þb þb þc þg þe,g þg

GeckosGehyra mutilata 8 3G. oceanica 1 2 1 1 20Hemidactylus frenatus 3 1 3 2 14Lepidodactylus oligoporus 5L. lugubris complexh 10 1 14 4 3 43Nactus pelagicus 2 9 3 1 23Perochirus ateles 5 2 1 1 2 71

SkinksEmoia boettgeri 4 3 2 1 1 27E. caeruleocauda 8 8 5 2 3 105E. cyanura 45E. impar 3 3 2 1 101E. jakati 2 1 1 1 1 18Eugongylus albofasciolatus 2 1 3 1 6Lamprolepis smaragdina 4 4 1 1 1 18Lipinia noctua 1 1 6

Monitor lizardsVaranus indicus þ f þb þ f

SnakesPelamis platurus þi

a Los, Losap; Nam, Namoluk; Ett, Ettal; Luk, Lukunor; Sat, Satawan.b Based on information provided to me by local residents.c Marshall (1975).d Nason (1975).e Borthwick (1977).f Pers. obs.g Pritchard (1977).h Includes L. lugubris, L. moestus, and hybrids.i Based on a photograph by C. Severance—see species account.

TABLE 3

Observation Rate (Animals per Hour) and Percentage Frequency of Encounters of Geckos in Five Habitats onSatawan Atoll

Day Night

SpeciesPalm Leaf Axils13.1/38% [23]a

Tree Trunks8.3/24% [12]

Scaevola Shrubs5.5/16% [13]

Coral Rubble3.1/9% [6]

Edificarian4.5/13% [4]

Gehyra mutilata 1.1 (100%)Gehyra oceanica 2.7 (40.2%) 4.9 (47.1%) 0.2 (1.2%) 2.2 (11.5%)Hemidactylus frenatus 45.3 (100%)Lepidodactylus lugubris complex 1.5 (12.0%) 0.4 (1.8%) 15.1 (50.0%) 2.6 (4.8%) 11.6 (31.3%)Nactus pelagicus 2.8 (67.6%) 2.9 (26.5%) 0.4 (5.9%)Perochirus ateles 13.8 (66.2%) 1.8 (5.4%) 13.6 (27.3%) 0.7 (1.1%)

a Search effort indicated as number of observation hours/percentage of total observation time (34.4 hr), with total number of is-lands surveyed in brackets.

cover and less frequently on tree trunks, andE. cyanura was almost entirely terrestrial.

Distribution of Skinks on Satawan Atoll

Distribution patterns of lizards within theatolls are difficult to assess because of incom-plete surveys. However, the 314 specimens ofsix diurnal species of skinks from among 30islands of Satawan Atoll allow for at least apreliminary assessment. Five additional is-lands were surveyed, but no skinks wererecorded on them; two (Pielisiop and Tewa-nikich) were visited briefly and only at nightand are excluded from further comparisons,and the three others (Chacha, Masawech,and Letau) are among the smallest of the is-lands, each less than 0.4 ha (Table 4).

Eugongylus albofasciolatus and Lipinia noctuaare cryptic species that probably are morecommon and widespread than the relativelyfew records indicate; they are excluded fromfurther comparisons for lack of sufficientdata. Five of the other six species belong tothe genus Emoia. Four of them are small andoverlap broadly in snout-vent length (E. ja-kati 37–53 mm, E. impar 40–47 mm, E. caeru-leocauda 40–65 mm, E. cyanura 40–55 mm);one is medium-sized (E. boettgeri 60–77 mm);the other species, Lamprolepis smaragdina, ismuch larger (>100 mm); measurements arefrom Kiester (1983), Brown (1991), and Zug(1991).

The larger among the 33 islands surveyedtend to support a larger number of these sixspecies. The Spearman rank order correlationcoefficient for island area against the numberof species is 0.9268 (n ¼ 33, t ¼ 13:74,df ¼ 31, P < :000001). With the exceptionof Pike (5.18 ha), the 14 islands with onlyone or two species are less than 2.0 ha (Table4). However, Lamprolepis smaragdina possiblywas overlooked on Pike because it is presenton all the other islands surveyed in that partof the atoll, as well as on some much smallerislands elsewhere. The eight islands with threeto four species range in size from approxi-mately 2 to slightly more than 6 ha, and theseven islands with five species (lacking onlyE. cyanura) are all greater than 7.0 ha; Moch

(32.58 ha), the fourth largest island, is theonly one where all six were recorded.

Where only one of the six species occurson an island, it is invariably one of the smallspecies—E. impar in four cases, E. cyanura inthree, and E. caeruleocauda in one. An array ofdifferent combinations of species was foundamong islands with two to four species. Noconsistent pattern was evident in these in-stances although Lamprolepis smaragdina, thelargest species, and the most arboreal, waspresent on all islands with three or moreskink species (Table 5).

Three species of Emoia that are very sim-ilar in coloration and pattern as well as bodysize are sympatric (and to various degreessyntopic) in different combinations on Sata-wan Atoll. Emoia cyanura is the least common,being recorded on only nine of the 33 islandssurveyed. It occurred with both E. caeruleo-cauda and E. impar only on Moch, with justE. caeruleocauda on two other islands, withjust E. impar on two others, and without ei-ther of the two on four islands (Table 5). Itwas the only skink on three (33%) of thenine islands where it was recorded. Emoiacaeruleocauda and E. impar were recorded on17 and 20 islands, respectively, sympatricallyon 12. Resource utilization among these spe-cies was not investigated quantitatively, butspecimen records together with incidentalobservations indicate that E. cyanura is morecommon in beach strand and in broad, sun-exposed clearings and disturbed areas, where-as E. caeruleocauda and E. impar are morecommon in shady forest, with E. impar show-ing a greater predilection for patches of sun-light. All three were found in forest edgesalong the beach. Similar separation or partialseparation in habitat between E. cyanura andE. impar was recorded in Fiji (Zug 1991), theCook Islands (Bruna et al. 1996a), and Amer-ican Samoa (Schwaner and Ineich 1998).

Geographic patterns of distribution ofskinks on Satawan Atoll probably are due inlarge part to a concentration of smaller is-lands along the northeastern and eastern sidesof the atoll, where all but one of the 14 is-lands surveyed between Pis (Moch District)and Letau (Satawan District) are less than


1.0 ha in area. Emoia boettgeri and E. jakati arecompletely absent from these islands, andLamprolepis smaragdina was recorded only onManimwek. On the other hand, E. cyanurawas encountered more frequently on thesenorthern and northeastern islands, whereas

E. caeruleocauda and E. impar were more spot-tily distributed. Conversely, with the excep-tion of Pien Island in the northwest, E.cyanura was unrecorded elsewhere on theatoll, where E. boettgeri, E. caeruleocauda, andE. impar were more numerous.

TABLE 4

Distribution of Six Species of Skinks on 33 Islands of Satawan Atoll Based on Sight Records (SR) and 430 SpecimensCollected during 2001–2004

Emoiab

Island Area (ha) Timea No. of Species bt ca cy im ja Lsc

1 Moch 32.58d 3 d 6 SR 12 3 1 1 SR2 Oninuk 6.22e 1.5 hr 3 1 5 13 Lelang 6.73e 1 hr 4 1 5 5 SR4 Fecha 1.81e 1 hr 1 85 Wonalang 3.14 f 3 hr (2) 3 4 3 SR6 Pis 0.05 f 1 hr (2) 1 27 Manimwek 0.98 f 3 d 2 7 SR8 Foui 1.80 f 1 hr 2 8 19 Pokonopo 0.16 f 1 hr 1 210 Chacha 0.15 f 1.5 hr (2) 011 Fauchan 0.63 f 2 hr (2) 1 812 Faupuker 0.38 f 2 d 1 513 Pononkis 0.87g 2 hr 1 514 Pononlap 1.55g 1 d 2 5 415 Masawech 0.32g 1 hr (2) 016 Simelap 0.65g 2 hr (2) 1 517 Enekap 0.59g 3 hr 1 718 Ewal 0.89g 2 hr 2 4 319 Letau 0.11g 3 hr (2) 020 Fatikat 1.64 g 3 d 3 5 2 SR21 Satawan 112.15e 7 d 5 4 12 2 8 322 Ta 155.40e 19 d 5 2 13 9 3 623 Weito 7.77e 3 d 5 2 7 9 1 224 Aliare 0.17g 6 hr (2) 2 3 325 Onupuku 4.66e 10 hr (2) 3 1 3 SR26 Kuttu 35.27d 5 d 5 SR 6 11 1 227 Orin 11.40e 6 hr (2) 5 2 2 1 2 128 Pien 3.89e 4 hr (2) 3 7 12 SR29 Pike 5.18e 2 hr (2) 2 5 930 Mariong 5.96e 4 hr (2) 4 2 7 2 SR31 Apisson 6.45d 1.5 hr (2) 4 SR 3 SR SR32 Lemasul 7.37d 3 d 5 2 1 5 1 SR33 Alengarik 17.56d 6 hr (2) 5 2 4 7 1 SR

a Approximate number of days (d) or hours (hr) on each island, with number of visits (in parentheses) for islands visited for lessthan a day but on more than one day.

b bt, E. boettgeri; ca, E. caeruleocauda; cy, E. cyanura; im, E. impar; ja, E. jakati.c Lamprolepis smaragdina.d Calculated for me by D. Tabarosi based on a digitized U.S. Army Corps of Engineers topographic map, overlain with recent

satellite imagery to confirm accuracy.e From Bryan (1971).f Roughly estimated from hip chain measurements of island length and width made by me during this study.g Calculated with a Garmin Global Positioning System unit after walking the circumference of the island during this study.


Kiester (1983) discussed the zoogeographyof a similar ( but not identical) assemblage ofskinks on Arno Atoll in the Marshall Islands.He reported that the smallest islands had thefewest species and that single-species islandswere occupied by the smallest species, a pat-tern observed also on Satawan Atoll in thestudy reported here. However, the ‘‘single’’small species on Arno that Kiester (1983)identified as E. cyanura may have includedE. caeruleocauda and E. impar. Subsequent toKiester’s (1983) study, Ineich (1987) and In-eich and Zug (1991) presented morphologicalevidence for distinguishing between E. cya-nura and E. impar, which was later supported

biochemically (Guillaume and Boissinot 1994,Bruna et al. 1995). Bruna et al. (1996b) re-corded E. impar from Arno Atoll, and Brown(1991) recorded E. caeruleocauda there.

Different combinations of Emoia specieson Satawan Atoll are most in evidence onthe smaller islands. These populations areparticularly vulnerable to environmentalchanges such as those wrought by periodictropical storms and typhoons. Strong windsand high seas (tidal surges) may result insome islands being completely awash andnearly completely denuded of vegetation,depleting or locally extirpating animal popu-lations. Recolonization or the arrival of addi-

TABLE 5

Distribution of Different Combinations among Six Species of Skinks on Satawan Atoll

Species Island

No. of Species on Island Namea Size Classb Name Area (ha)

1 ca S Enekap 0.591 cy S Fauchan Lengeleng 0.631 cy S Faupuker 0.381 cy S Pokonopo 0.161 im S Fecha 1.811 im S Pis 0.051 im S Pononkis 0.871 im S Simelap 0.652 ca/im S/S Pike 5.182 ca/im S/S Ewal 0.892 ca/im S/S Pononlap 1.552 ca/cy S/S Foui 1.802 im/Ls S/L Manimwek 0.982 bt/Ls M/L Aliare 0.173 ca/cy/Ls S/S/L Pien 3.893 cy/im/Ls S/S/L Wonalang 3.143 im/bt/Ls S/M/L Onupuku 4.663 ca/bt/Ls S/M/L Fatikat 1.643 cy/bt/LS S/M/L Oninuk 6.224 cy/im/bt/Ls S/S/M/L Lelang 6.734 ca/im/bt/LS S/S/M/L Mariong 5.964 ca/ja/bt/LS S/S/M/L Apisson 6.455 ca/im/ja/bt/Ls S/S/S/M/L Satawan 112.155 ca/im/ja/bt/Ls S/S/S/M/L Ta 155.405 ca/im/ja/bt/Ls S/S/S/M/L Weito 7.775 ca/im/ja/bt/Ls S/S/S/M/L Kuttu 35.275 ca/im/ja/bt/Ls S/S/S/M/L Orin 11.405 ca/im/ja/bt/Ls S/S/S/M/L Lemasul 7.375 ca/im/ja/bt/Ls S/S/S/M/L Alengarik 17.566 ca/cy/im/ja/bt/Ls S/S/S/S/M/L Moch 32.58

a bt, Emoia boettgeri; ca, E. caeruleocauda; cy, E. cyanura; im, E. impar; ja, E. jakati; Ls, Lamprolepis smaragdina.b S, small; M, medium; L, large.


tional colonists can occur by independent dis-persal or assisted by human transport. Trad-ing boats and government supply shipsfrequently transport cargo from Chuuk mainislands to settlements throughout the Mort-locks, and the outer, uninhabited islands arefrequently visited by residents of the settle-ments, thus providing opportunities for theinadvertent translocation of lizards aboardcanoes and boats within and among suppliesbeing brought to the islands, and local com-modities (palm fronds, pandanus leaves, fire-wood, coconuts, taro) being brought back tothe settlements.

To what extent the different combinationsof species recorded among the islands of Sa-tawan Atoll may be distorted by sampling biasis uncertain. The species being surveyed areactive and conspicuous during the day, andtheir presence can usually be detected in ashort time. However, the lack of any sight-ings of Lamprolepis smaragdina during the first2 days on Manimwek Island, the addition ofE. cyanura to the Foui list based on only a sin-gle specimen that might easily have beenoverlooked, and the very likely possibility thatL. smaragdina was overlooked on Pike Islandgiven its presence on all nearby islands indi-cate a need for more extensive surveys to fur-ther assess patterns of distribution.

acknowledgments

I thank Aaron Bauer and Hidetoshi Ota fortheir assistance in identifying images of se-lected specimens in the Lepidodactylus lugubriscomplex; Kun Floyd and Joe Saimon for pre-paring digital images of the study area maps;and Gordon Rodda and George Zug for re-viewing the manuscript. I am especially grate-ful for the assistance and courtesies extendedto me by the people of the Mortlock Islandsduring my visits.

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