SHALLOW WATER LAGOON AND REEF FISHES OBSERVED AT NUKUNONU ATOLL

Tokelau comprises three small atolls in the central Pacific Ocean and is rarely visited by biologists due to its difficult access. Despite occasional visits by fisheries officers and some scientific collections made in the 1960s, very little has been recorded of the diversity of the fish fauna, and no checklist of the fishes of Tokelau has ever been published. In 2012 seven sites around Nukunonu atoll were snorkelled and the fish species recorded. A total of 143 species in 37 families were identified and the majority photographed, including four species with unusual or rare color forms and one hybrid. The species recorded indicate a diverse fish fauna comparable to those of Tokelau’s neighbors. Using the results of this study, the specimens held in the scientific collections, and species mentioned in the literature, a provisional checklist of the fishes of Tokelau has been developed.

Each of Tokelau's three atolls consists of a ring-shaped coral reef surrounding a central lagoon (Yaldwyn and Wodzicki, 1979;Ono and Addison, 2009).Scattered along the reef top are many small islets (motu), some with vegetation and others bare.The population of each atoll inhabits only one or two of these islets.The total land area of Tokelau is very small-only 12 km 2 -with most islets less than 200 meters wide and often not very much longer (although some are a few kilometers in length).
Nukunonu, the largest of the three atolls with a land area of around 4.5 km 2 and a 109 km 2 lagoon (Huntsman and Hooper, 1996), is 16 km across at its greatest width (McQuarrie, 2007).It has more than 30 small islets, the largest of which is only 1.5 km 2 (Yaldwyn and Wodzicki, 1979).The population of around 300 are confined to Nukunonu Village on the islets of Vao and Motuhaga in the southwest of the atoll (Figures 2 and 3).
Because of the small size of the islets, none of the atolls in Tokelau have ever had an airstrip (McQuarrie, 2007;Pasilio et al., 2013).Furthermore, none of the three atolls have a deepwater passage Fakaofo is 500 kilometers north of Samoa.The ocean around and between the atolls is 4,000 meters deep (Robertson and Kibblewhite, 1966).Image from Google Earth.Data from SIO, NOAA, U.S. Navy, NGA, GEBCO, LDEO-Columbia, NSF.  for ships to pass through the reef and into the lagoon (van Pel, 1958;Huntsman and Hooper, 1996;Passfield, 1998;Pasilio et al., 2013) and there is no safe anchorage for ships outside the narrow reef as it drops sharply into the ocean depths (McQuarrie, 2007).This lack of accessibility has resulted in Tokelau remaining largely isolated from the rest of the world: a small, twice-monthly cargo ship from Apia, Samoa, is its only contact.Even this cargo ship is unable to dock or moor to a buoy; a barge (a large, flatbottomed aluminium boat with outboard motors) from the island pulls alongside the larger ship to allow passengers and goods to be transferred between the two vessels.The barge then returns to the atoll through a shallow channel dynamited in the reef flat for this purpose (McQuarrie, 2007).Presumably as a consequence of this difficult access, very few zoological studies have been conducted in Tokelau.
During the 1960s, scientific collections of fishes were made on all three atolls.The Smithsonian's National Museum of Natural History lists 239 lots (representing 1,657 specimens) in their collection, with all but eight collected in 1965 (NMNH, 2015).Likewise, the Academy of Natural Sciences in Philadelphia has 76 lots collected between 1960and 1965(ANS, 2015) ) and the California Academy of Sciences has two lots (D.Catania, personal communication).The Natural History Museum in England has nine specimens that were registered into the collection in 1930 (J.Maclaine, pers. comm.).No publications or reports have been made about any of these collections.
The few publications of the marine fauna of Tokelau tend to be concerned with fisheries in general (van Pel, 1958;Hinds, 1971;Gillett, 1990;Chapman et al., 2005;Pasilio et al., 2013) and commercially valuable fish species in particular (Tuna Programme, 1983;Gillett, 1985;Passfield, 1998;Zylich et al., 2011).No comprehensive checklist appears to exist, although Passfield (1998) compiled a list of Tokelauan fish names derived from multiple sources (including the Tokelau Dictionary [Simona, 1986] and his own questionnaires).He also conducted surveys of Fakaofo's lagoon and reef; however, it is unclear from the list which species he actually sighted, and many of the fish are not identified to species level.Similarly, Ono and Addison (2009) compiled a list of fish names from the Tokelau Dictionary (Simona, 1986) and other sources and by showing Atafu fisherman illustrations of fish in books.However, the two books used were guides to fishes of Southeast Asia and Japan; consequently their list includes at least 30 species of fish not found in this part of the Pacific Ocean.
The goal of this fish survey is therefore to provide a comprehensive inventory of reef fishes inhabiting Nukunonu Atoll.

MATERIALS AND METHODS
This author visited Nukunonu Atoll from 22 August 2012 to 7 September 2012 and took the opportunity to photograph and observe the lagoon and reef fishes in order to produce a record of the species found on this atoll.Accommodation was provided on Motuhaga (Figure 2) and four of the sites were adjacent to this islet.On this islet and the neighboring Vao, the reef has three zones on the ocean side.The first is a conglomerate platform, the remains of the reef that were exposed several thousand years ago when the sea levels in the Pacific dropped (Woodroffe and Biribo, 2011).Projecting out from under the islet like a ledge, it is usually just above the high tide level, but during spring tides the water may break over the edge, and during storm surges the platform may be completely submerged.Seaward of the platform is a reef flat that is shallowly submerged at low tide with some rocks and corals exposed.The seaward edge beyond the low algal crest is characterized by spurs and grooves, and below this is a narrow fore-reef with extensive hard coral cover.The outer edge of the fore-reef is a vertical drop-off.On the lagoon side of the islet the conglomerate platform is covered by a narrow beach composed of coral rubble and sand; beneath the waterline is a sandy substrate that angles sharply into the lagoon.Patch reefs and pinnacles, none of which were seen to break the water's surface, occur within the lagoon.
There are no dive facilities or scuba equipment in Tokelau so most observations in this study were made by snorkelling from the surface down to about six or seven meters.Other observations were made by walking the reef flats or alongside the channels or by observing fish that had been caught by the locals.Snorkelling was conducted for a total of more than 20 hours at seven sites, including three sites in the lagoon, a shallow channel between the lagoon and the reef flat, the reef flat, a manmade channel in the reef flat, and a single site on the outer reef (Table 1; Figures 4 and 5).Further observations of the individual sites are in Appendix A.
No fish were collected but most species were photographed.While the majority could be identified visually, these identifications are provisional; sampling and analysis of morphometrics, meristics, and DNA are required to confirm identifications.Fish references used for identifications include Allen et al. (2003) and Randall (2005).
Photography was taken with either a Canon D20 compact underwater camera or a Canon 550D camera and a Canon 100mm macro lens in a Nauticam waterproof housing with an Inon Z240 strobe.A GoPro Hero2 on a chest harness recorded movie images of most snorkelling sessions and on a few occasions was removed from the harness, attached to a weight, positioned in front of some coral, and left recording for a short period.These recordings were later used to confirm identifications of species that were not photographed and, in one case, a cryptic species that the author did not see.The Coral Fish Diversity Index (CFDI) is a method for predicting the approximate total number of fish species in an area by counting the number of species in six key families of conspicuous fish (Chaetodontids, Pomacanthids, Pomacentrids, Scarids, Labrids, and Acanthurids).The total for these families was counted for Nukunonu Atoll, and the total number of species expected (TSE) was calculated using Allen and Werner's (2002) formula for small reefs: TSE = 3.39(CFDI) -20.595.

RESULTS
A total of 143 species were identified, albeit some tentatively, and an additional 11 that could not be positively identified to species level were also sighted (Table 2).One species-Neocirrhites armatuswas not actually seen by the author but was recorded when the GoPro camera was left on the reef for a short period.Two positive identifications were made from juveniles only (Scarus altipinnis and S. frenatus); no adults of these species were seen/identified by the author.Another species-Chaetodon ephippium-was not sighted alive by the author, but a dead specimen collected by a fisherman for food was seen.
Table 2. Fish species seen at different sites.The classification of families follows Nelson (2006).Not all unidentified species have been listed; those that might be an already recorded species have not been listed (e.g., scarids, holocentrids) to avoid inflating total numbers.A checkmark () indicates the species was observed at the site.An asterisk (*) indicates tentative identification.

DISCUSSION
A total of 143 species and one hybrid were identified, six of them tentatively.Two epinephalids-Epinephalus fuscoguttatus and E. polyphekadion-are similar and may be misidentified (Randall and Ben-Tuvia, 1983;Randall and Heemstra, 1991;Randall, 2005;Craig et al., 2011).Furthermore, the most common serranid sighted-E.merra-appeared to have a variable pattern, and some individuals identified as E. merra may prove to be another species.A brief glimpse of what was thought to be Aprion virescens may have been a misidentification, and the Kyphosus vaigensis may have actually been the similar K. biggibus or K. pacificus.The single Balistoides viridescens briefly seen at Site 4 was not viewed clearly due to the amount of sediment in the water but was identified tentatively by the obvious pale area on the body anterior to the caudal peduncle.
A further 11 could not be confidently identified to species.The belonid is most likely Platybelone argalus, but neither photographs nor observations could confirm this.Myripristine holocentrids were seen at several sites and may represent more than one species, possibly Myripristis berndti or M. kuntee or both.One of the Chrysiptera species may be Chrysiptera brownriggi or C. unimaculata, and the Chromis is probably Chromis virescens.At most of the sites, one or more scarids defied identification, having variable color patterns that made positive identification difficult.One individual scarid, seen at Site 1, may have been Chlorurus bleekeri, although it lacked the distinctive green cheek markings.The acanthurid seen in reasonable numbers (20+) at Site 4 was not seen clearly due to the sediment in the water but appeared to be black (or very dark) with a white ring around the base of the caudal fin.The species may have been Acanthurus nigricauda, although the A. nigricauda seen at Site 3 had a completely white tail and a more streamlined body shape; alternatively, it may have been A. blochi.
The hybrid Acanthurus achilles X nigricans (Plates 1 and 2) was sighted at three different locations-Site 3 and Site 7, which are contiguous, and Site 5, which is approximately eight kilometers from the other sites-suggesting this may be a rare but not unusual occurrence.Randall (1960;2001:15) reports this hybrid from the Phoenix Islands, the island of Hawaii, Caroline Atoll, and the Tuamotu Archipelago.Some unusual coloration was observed in four species of fish.A lone Aphareus furca was sighted on the reef at Site 7 on two consecutive days.This species is normally a silvery color, but this individual was dusky with a reddish tinge and a bright yellow irregular splotch on the head just anterior to the first dorsal fin (Plates 3 and 4); this has been described as a rare color form (Randall, 2005:242).Examples of the red version of Chlorurus microrhinos were also sighted on the reef at Site 7.This morph is reported as an "occasional color morph" by Randall (2005:450) and as "generally rare" by Allen et al. (2003:177).The specimens of Abudefduf septemfasciatus that were seen all had irregular black markings on the posterior edges of the second dorsal, anal, and caudal fins, giving the fins a ragged appearance, as if they had been chewed (Plates 5 and 6).These markings do not appear to have been previously recorded, and both Allen and Randall have not seen it before (G.Allen, West Australian Museum, pers.comm.;J. E. Randall, Bishop Museum, pers. comm.).However, this author has seen this pattern in A. septemfasciatus in Niue, about 1,000 kilometers to the south.The tail of Acanthurus nigricauda usually is dark with a white ring at the base, but as mentioned above, those seen in Nukunonu have a completely white tail (Plates 7 and 8).
Visual assessments are an easy and effective way to rapidly assess and record common fish species, but pelagic and deepwater species are rarely sighted and small cryptic species are often overlooked (McDermond and Wass, 1986;Williams et al., 2006).However, Allen and Werner (2002) showed that the approximate total number of fish species in an area can be predicted by counting the number of species in six key families.Of the 154 species sighted, a total of 80 species were found in the six key families, and thus, using the formula for small reefs, the predicted total number of species expected for Nukunonu Atoll is 251 species, suggesting another 97 species are still to be recorded.This predicted total of 251 species is low compared to Tokelau's nearest neighbors: Samoa has 991, Wallis Island has 648, Tuvalu has 607, and the Phoenix Islands have 516 (Wass, 1984;Williams et al., 2006;Job and Ceccarelli, 2012;Allen and Bailey, 2011).
There are two reasons why this predicted total is less than half the known numbers of Tokelau's neighbors.As mentioned previously, deepwater and pelagic species as well as cryptic species are not recorded during shallow water visual surveys.Second, a limited number of sites were surveyed, and the windward reef was not visited at all.The coral composition on this exposed reef would be different from the single reef site visited in this survey, resulting in a differing assemblage of fish fauna.In contrast, Tokelau's neighbors have been surveyed more extensively (Schultz, 1943;Wass, 1984;Wantiez and Chauvet, 2003;Williams et al., 2006;Job and Ceccarelli, 2012;Allen and Bailey, 2011).
Despite the relatively low number of species recorded for Nukunonu, the assemblage is similar to those of Tokelau's nearest neighbors.Comparing the species listed in Table 2 to published checklists for the fishes of Samoa (Wass, 1984), Wallis Island (Williams et al., 2006), Tuvalu (Job and Ceccarelli, 2012), and the Phoenix Islands (Allen and Bailey, 2011), reveals that 96% of the species seen in this study in Nukunonu are recorded in Samoa, 90% in the waters around Wallis Island, 92% in Tuvalu, and 95% in the Phoenix Islands.The species seen in Nukunonu but not recorded for Samoa were Epinephalus polyphekadion, Letherinus  As would be expected on a small remote island, fishing is an important part of everyday life for the population (Huntsman and Hooper, 1996;Chapman et al., 2005;Elders, 2012), and fish make up a significant part of their diet (Passfield, 1998;Zylich et al., 2011).It was noted by Yaldwyn and Wodzicki (1979:9) that "there is a rich and varied lagoon and offshore fauna of marine fishes still undocumented," yet since that time there does not appear to have been an attempt to accurately document the species native to these atolls.Furthermore, in the Tokelau National Strategic Plan: 1 July 2010-30 June 2015 it is noted that coral bleaching is now an annual event and has led to "degradation of coral reefs both inside and outside the lagoon.... This has greatly affected the quantity and quality of food supply from the inshore fish population.The life cycle of in-shore fish is also affected by the extreme weather conditions which has seen the decrease in the number and gradual disappearance of some species of fish from the lagoons" (OCOG, 2010:10).
Clearly, further research is needed, especially sampling specimens for collections to confirm identification.Documenting the fish fauna found deeper than 10 meters, surveying more sites, especially on the eastern reefs, and utilizing ichthyocides to sample small and cryptic fishes will give a better indication of the true number of species present in the waters of Nukunonu Atoll.
Plates 1 and 2. Hybrid surgeonfish, Acanthurus achilles X nigricans.Photos copyright of the author.This channel, approximately 300 meters long, separates Vao and Motuhaga islets and is spanned by a concrete bridge.Maximum depth is one meter in a pool at the reef flat end, less than one meter elsewhere.During spring tides and storm surges the channel swells with water from the lagoon and covers a larger area before draining onto the reef flat.This site was frequently visited on foot due to its proximity to the author's accommodation but was rarely snorkelled because of its shallow depth.Site 3: Reef flat (Figures A3 and A4) The reef flat on Motuhaga is around 500 meters in length and about 150 meters wide (to the edge of the reef).The reef was walked, and several pools on the reef flat were visited at both high and low tide.At low tide most of the flat is still under water, varying in depth from a few centimeters to 0.75 meters in the pools.A sandy substrate and lots of corals.Visibility up to seven meters.Visited 23 August 2012, 24 August 2012, 30 August 2012, 4 September 2012, and twice on 5 September 2012 for a total of 531 minutes.

Site 4: Wharf and channel (Figure A5)
A manmade channel in the reef flat for the barge to ferry passengers and cargo from the wharf to the cargo ship.GPS coordinates are taken from the wharf.Snorkelled the channel itself and the reef flat either side.The channel acts as a drainage for the reef flat, and water breaking onto the flats runs into the channel and then out to the ocean.As a result, there are very strong outward currents toward the mouth of the channel, particularly within the channel itself.Consequently, that end of the channel was not snorkelled.Substrate was mainly rock with some sand, and corals on the reef flat.Visibility up to seven meters, but variable due to the amount of sand and sediment that is washed into the channel.Probably as a result of all this sediment, this site had the highest density of fishes with large numbers of fistularids, scarids, and acanthurids seen.Maximum depth up to four meters.Visited 23 August 2012 and 27 August 2012 for a total of 101 minutes.Entered the water from a boat launching site on the southeast side of the government building and swam along the reef 50-75 meters into the lagoon, and southeast along the shore for 20 meters.The lagoon bed was sandy, rock around the seawall and shoreline.A reef extends from the shore straight out into the lagoon for several hundred meters.Maximum depth around 5-6 meters in the area surveyed; very few corals on reef.Visited 28 August 2012 for a total of 90 minutes; session finished early after a facial encounter with a stinging jellyfish.From there I swam over the reef approximately 50 meters in each direction.The edge of the reef flat drops around 4.5 meters to the fore-reef, which then slopes down for 50 meters to a depth of about eight meters before ending in a vertical drop-off.The reef crest where the waves break is mostly bare rock with spurs and grooves, but the fore-reef has extensive coral cover, mostly hard corals.Visibility 30+ meters.Visited on 2 September 2012, 3 September 2012, and 6 September 2012, for a total of 143 minutes.

Figure 1 .
Figure 1.Tokelau in relation to Samoa.Fakaofo is 500 kilometers north of Samoa.The ocean around and between the atolls is 4,000 meters deep(Robertson and Kibblewhite, 1966).Image from Google Earth.Data from SIO, NOAA, U.S. Navy, NGA, GEBCO, LDEO-Columbia, NSF.

Figure 2 .
Figure 2. Nukunonu Atoll is the largest of the atolls with an area of 109 km 2 .The village is on the southwest islets.Although the population live on only two neighboring islets, they regularly visit the other islets to fish or collect coconuts.Image from Google Earth.Image © 2014 TerraMetrics.Image © 2014 DigitalGlobe.Data from SIO, NOAA, U.S. Navy, NGA, GEBCO, LDEO-Columbia, NSF.

Figure 5 .
Figure 5. Survey site adjacent to Te Fakanava motu, five kilometers from the village.Pinnacles were common at this site and most fish species were sheltering in or around the pinnacles.Several species (including Gymnothorax javanicus, Kuhlia mugil, Dascyllus aruanus, Scarus schlegeli, S. frenatus, Valenciennea sexguttata, Ptereleotris evides, and Arothron meleagris) were seen at this site only.Image from Google Earth.Image © 2014 DigitalGlobe.

Figure 4 .
Figure 4. Survey sites around Nukunonu Village.Despite their proximity to each other, the sites varied in substrate, depth, water clarity, water movements, coral cover, shelter, and fish assemblages.See Table 1 and Appendix A for details of the individual sites.Image from Google Earth.Image © 2014 DigitalGlobe.
4. A rare color morph of Aphareus furca.Photos copyright of the author.
6. Abudefduf septemfasciatus with unusual black edging to second dorsal and caudal fins.Photos copyright of the author.
8. Unusual tail coloration in Acanthurus nigricauda.Photos copyright of the author.
After entering the water the author swam southeast 150-200 meters following the beach and reef.Maximum depth here was about five meters.The beach and shoreline were composed of broken coral rubble, but the lagoon bed was sandy away from shore.Some human rubbish (mainly plastic, wood, and metal) in the shallows close to shore.Visibility up to eight meters.Almost no corals seen.Visited twice, on 23 August 2012 and 24 August 2012 for a total of 174 minutes.

Figure A1 .
Figure A1.Site 1: Lagoon shore of Motuhaga looking southeast.The entry point for the surveys is in the foreground.Common families at this location were Holocentrids, Mullids, Labrids and Acanthurids.Photo copyright of the author.

Figure A2 .
Figure A2.Site 2: Channel between Motuhaga (left) and Vao (right), looking towards the ocean.Only seven species were sighted here: Gymnothorax pictus; juvenile Abudefduf septemfasciatus and A. sordidus; Chrysiptera glauca; Halichoeres trimaculatus; Acanthurus triostegus; and a juvenile Arothron nigropunctatus.Most of these were seen around the spring tide when the channel and neighboring pools were full.Photo copyright of the author.

Figure A3 .
Figure A3.Site 3: Reef flat by Motuhaga at high tide.The Conglomerate Platform is in the immediate foreground.The platform appeared popular with Gymnothorax pictus, and in a short walk one afternoon seven were seen, including two juveniles and an adult half out of the water chasing a crab.Photo copyright of the author.

Figure A4 .
Figure A4.Site 3: Reef flat on Motuhaga at low tide, looking northwards.The island on the right is Vao.Sixty-six species were seen here, plus the hybrid acanthurid.Chaetodontids, Labrids and Acanthurids were the most speciose families.Photo copyright of the author.

Figure A5 .
Figure A5.Site 4: The channel in front of the wharf (foreground) at high tide.Photo copyright of the author.

Figure A6 .
Figure A6.Site 5: Lagoon at Te Fakanava Motu, looking south toward Nukunonu Village (center frame) approximately eight kilometers away.Several large pinnacles occur as close as 30 meters from shore, and are the focal points for most of the 71 species recorded here.The hybrid acanthurid was also seen here.Photo copyright of the author.

Figure A7 .
Figure A7.Site 6: Lagoon next to Vao motu, looking north.The structure on the left is a seawall next to the government building, built on a reef that extends out into the lagoon.Forty species were sighted here.Photo copyright of the author.

Figure A8 .
Figure A8.Site 7: The fore-reef next to Motuhaga.A total of 85 species were recorded, including the hybrid acanthurid, and several families were represented at this site only: Aulostomidae, Echeneidae, Kyphosidae, Cirrhitidae, and Sphyraenidae.Photo copyright of the author.

Table 1 . Site coordinates, depth, visitation details. Depths
are estimates and are provided for illustrative purposes only.