Southern Cook Islands Research Articles

Stability in the South Pacific surface marine 14C reservoir over the last 750 years. Evidence from American Samoa, the southern Cook Islands and the Marquesas

Although minor climatic and sea-level changes have been documented for the South Pacific during the late Holocene, our understanding of the consequent impact of these changes on the marine 14C reservoir, and therefore the 14C content of shellfish, is limited. Ultimately, this has implications for documenting the chronology of human movement and adaptation in this region. In this paper we compare marine reservoir (Δ R) data obtained from tightly controlled archaeological proveniences with known-age, pre-AD 1950 shells from the southern Cook Islands, American Samoa, and Marquesas Islands. Results indicate that there has been no significant change in the near-shore marine reservoir in these three locations over the last ca. 750 years. Furthermore, known-age, pre-AD 1950 shell samples provide more precise Δ R values for use in sample calibration than archaeological paired shell/charcoal samples. This is attributed in part to the limitations of assigning provenance and age to material from archaeological sites. On the basis of these results we conclude that the known-age, pre-AD 1950 shell derived Δ R values can be used to calibrate shell 14C results from deposits of late Holocene age.

Subtropical sea-level history from coral microatolls in the Southern Cook Islands, since 300 AD

Relative sea-level (RSL) history is reconstructed for the Southern Cook Islands since 300 AD using Porites sp. coral microatolls. The upper surface or height of living coral of the modern microatolls on Rarotonga was rigorously determined by 400 laser survey measurements to be constrained by the sea-level − 0.36 m (below Mean Sea Level) with a standard deviation of ± 0.008 m, that is equivalent to midway between Mean Low Water Neaps and Mean Low Water Springs tidal datums. Fossil microatoll history on the fringing reefs is fragmentary due to multi-decadal to centennial windows of microatoll growth, cyclone destruction, and preservation through coastal progradation. The mid-late Holocene highstand ceased prior to 500 BC and RSL fell from + 1.3 ± 0.1 m to 0.45 ± 0.15 m by 1000 AD at a rate of − 0.5 mm/yr. The RSL minimum occurred during the late 1700s to 1800s AD at − 0.2 m below present, before rising during the 1900s. During the past 500 yr RSL fluctuated, including an abrupt fall at ~ 1750 AD following a sustained multi-decadal high anomaly. Similarly, low RSL anomalies and slow coral growth rates during the 950 to 1000 AD period are indicative of Pacific Basin-wide climate variability and are consistent with extreme La Niña-like climate anomalies previously reported around the Pacific basin. The fall in RSL during the first millennium AD crossed-over tidal thresholds for rapid coastal progradation, when ambient Mean High Water Neaps and Mean High Water Springs fell below the low tide level of the mid-late Holocene high stand. This coastal response is inversely analogous to the projected response to sea-level rise during the latter part of the modern century.

REVIEWS

Book reviewed in this article:Cargo, Cult and Culture Critique. Edited by Holger JebensReturn to Culture: Oral Tradition and Society in the Southern Cook Islands. By Anna‐Leena Siikala and Jukka SiikalaConscripts of Modernity: The Tragedy of Colonial Enlightenment. By David ScottMana Tuturu: Mäori treasures and intellectual property rights. By Barry BarclayCreative Spirits. Bark Painting in the Washkuk Hills of North New Guinea. By Ross BowdenAnimals the ancestors hunted: an account of the wild mammals of the Kalam area Papua New Guinea. By Ian Saem Majnep and Ralph Bulmer (Edited by Robin Hide and Andrew Pawley).Other Malays: Nationalism and Cosmopolitanism in the Modern Malay World. By Joel S. Khan

Prehistoric inter-archipelago trading of Polynesian tree snails leaves a conservation legacy

Inter-archipelago exchange networks were an important aspect of prehistoric Polynesian societies. We report here a novel genetic characterization of a prehistoric exchange network involving an endemic Pacific island tree snail, Partula hyalina. It occurs in the Society (Tahiti only), Austral and Southern Cook Islands. Our genetic data, based on museum, captive and wild-caught samples, establish Tahiti as the source island. The source lineage is polymorphic in shell coloration and contains a second nominal species, the dark-shelled Partula clara, in addition to the white-shelled P. hyalina. Prehistoric inter-island introductions were non-random: they involved white-shelled snails only and were exclusively inter-archipelago in scope. Partulid shells were commonly used in regional Polynesian jewellery, and we propose that the white-shelled P. hyalina, originally restricted to Tahiti, had aesthetic value throughout these archipelagoes. Demand within the Society Islands could be best met by trading dead shells, but a low rate of inter-archipelago exchange may have prompted the establishment of multiple founder populations in the Australs and Southern Cooks. The alien carnivorous land snail Euglandina rosea has recently devastated populations of all 61 endemic species of Society Island partulid snails. Southern Cooks and Australs P. hyalina now represent the only unscathed wild populations remaining of this once spectacular land snail radiation.

New Evidence from the East Polynesian Gateway: Substantive and Methodological Results from Aitutaki, Southern Cook Islands

East Polynesia was the geographic terminus of prehistoric human expansion across the globe and the southern Cook Islands, the first archipelago west of Samoa, a gateway to this region. Fourteen new radiocarbon dates from one of the oldest human settlements in this archipelago, the Ureia site (AIT-10) on Aitutaki Island, now indicate occupation from cal AD 1225–1430 (1σ), nearly 300 yr later than previously suggested. Although now among the most securely dated central East Polynesian sites, the new age estimate for Ureia places it outside the settlement period of either the long or short chronology models. The new dates have, however, led to a comfortable fit with the Ureia biological evidence, which suggests not a virgin landscape, but a highly a modified fauna and flora. The results also provide the first systematic demonstration of inbuilt age in tropical Pacific trees, a finding that may explain widely divergent 14C results from several early East Polynesian sites and has implications for the dating of both island colonization and subsequent intra-island dispersals.

Translocation of Rarotonga Monarchs Pomarea dimidiata within the southern Cook Islands

The translocation of species to a new site plays an important role in the conservation of many threatened birds; however, the problems and processes involved in planning and implementing such translocations are rarely reported. In order to establish a second secure ‘insurance’ population of the endangered Rarotonga Monarch Pomarea dimidiata, or Kakerori, 30 young birds were moved from the Takitumu Conservation Area on Rarotonga to the 2,700 ha island of Atiu between 2001 and 2003. The translocation of this single-island endemic was to a site outside the historical range of the species, because the small, but rapidly growing, population on Rarotonga was considered to be highly vulnerable to a catastrophe, such as a cyclone, or the arrival of a new bird disease or predator. The translocation followed consultation with local communities, an assessment of the suitability of islands in the southern Cook Islands, and an assessment of the disease risk posed by the translocation. The translocation appears to have been successful because Rarotonga Monarchs have bred well in a variety of forest habitats on Atiu.

Fished Up or Thrown Down: The Geography of Pacific Island Origin Myths

Myths recalling how islands were “fished up” or “thrown down” by (demi)gods are widespread in the Pacific Islands. Fishing-up myths are more numerous and are concentrated in a heartland comprising parts of Samoa, Tonga, the southern Cook Islands, and the Society Islands of French Polynesia. Geological details in many fishing-up myths suggest these recall the activities of shallow submarine (jack-in-the-box) volcanoes, notably in Tonga, and that these myths diffused to places where such volcanoes do not exist. Other fishing-up myths—particularly those recalling rapid emergence and/or successive uplift events and tectonic instability during the process of fishing-up—are suggested as recalling coseismic-uplift events (uplift coincident with large earthquakes), which are comparatively common in islands along the convergent plate boundaries of the southwest Pacific (including parts of Tonga and New Zealand). Throwing-down myths are less common in the Pacific, being effectively confined to places (near) where volcanoes erupted within the period of human occupation. Throwing-down myths are interpreted as recalling volcanic eruptions.

A Novel Application of Molecular Techniques to Pacific Archaeofish Remains*

Until recently, the identification of fish bone from Pacific archaeological sites generally relied upon morphological analysis of a relatively restricted number of skeletal elements. Limited morphological variation within fish families, amongst other things, has often restricted Pacific archaeofish determinations to the level of family or, in some cases, genus. We suggest that these relatively imprecise determinations may mask important aspects of prehistoric human fishing practices and subsistence patterns. This paper describes a molecular technique that allows for more precise taxonomic determinations, initially applied to the large and diverse family of Serranidae. The technique involves extraction, amplification, sequencing and analysis of mitochondrial DNA variation in the 16s ribosomal RNA gene. Following development of protocols and primers for modern reference materials, the technique was applied to an archaeological faunal assemblage from Aitutaki, southern Cook Islands.

Resolving Long-Term Change in Polynesian Marine Fisheries

There is growing evidence that patterns of marine fisheries on some Pacific islands underwent significant changes over the period of human occupation. One such island is Aitutaki in the Southern Cook Islands. Over the millennia of human occupation, there were shifts in habitat use, changes in targeted prey, and the abandonment of some fishing technologies. However, the most striking trend was an apparent decline in fishing altogether. This paper brings together several lines of evidence in an effort to understand why fishing became less important on this small Polynesian "almost-atoll." The possibility of over-harvesting or resource depression is considered. Resource depression could have been a factor at one mainland locality, where occupations were at least semipermanent, but was apparently not involved in declines at an offshore islet site where occupations were short term but intensive. However, fishing on the offshore islet, and deeper water fishing in general, may have been adversely affected by the loss of a key raw material traditionally used for fishhooks, namely pearlshell (Pinctada margaritifera). Further consideration of the offshore islet assemblages is assisted by mtDNA analyses, which have allowed for species level determinations within a key family, the Serranidae. Considering the suite of changes as a whole, the costs of fishing apparently increased significantly over the 1000-year period of occupation. What is less certain is the potential role that terrestrial components (i.e., agriculture and animal husbandry) of subsistence played in fishing declines. Stable isotope studies, now underway, may further elucidate the relationships between marine and terrestrial components of subsistence.

Genetic algorithms for geophysical parameter inversion from altimeter data

SummaryA new approach for inverting several geophysical parameters at the same time from altimeter and marine data by implementing genetic algorithms (GAs) is presented. These original techniques of optimization based on non-deterministic rules simulate the evolution of a population of candidate solutions for a given objective function to minimize. They offer a robust and efficient alternative to gradient techniques for non-linear parameter inversion. Here genetic algorithms are used for solving a discrete gravity problem of data associated with an undersea relief, to retrieve seven parameters at the same time: the elastic thickness, the mean ocean depth, the seamount location (longitude/latitude), its amplitude, radius and density from its observed gravity/geoid signature. This approach was also successfully used to adjust lithosphere parameters in the real case of the Rarotonga seamount [21.2°S; 159.8°W] in the Southern Cook Islands region, where GA simulations provided robust estimates of these seven parameters. The GA found very realistic values for the mean ocean depth and the seamount amplitude and the precise geographical location of Rarotonga Island. Moreover, the values of elastic thickness (∼14–15km) and seamount density (∼2850–2870kgm−3) estimated by the GA are consistent with the ones proposed in earlier studies.

Changing fish use on Mangaia, southern Cook Islands: resource depression and the prey choice model

AbstractThis study applies the prey choice model from foraging theory to explain changing human use of fish during the 700‐year occupation of Tangatatau Rockshelter, Mangaia, southern Cook Islands. The prey choice model suggests that predators will focus initially on high ranked prey, turning to lower ranked prey if abundance of higher ranked prey declines. It is suggested that increasing human population size would have resulted in increases in harvesting pressure and ultimately prey resource depression. To apply the prey choice model to archaeological faunal records and based on previous research, prey ranks are estimated using overall attributes of taxon body size; the larger the taxon, the higher the rank. Two indices, the Marine and Freshwater Fish Index, are developed to estimate the ratio of high to low ranked prey and are calculated for each zone of the rockshelter. Over time, the indices show a decreasing abundance of high ranked prey and increasing abundance of low ranked prey, which supports the view of resource depression. Skeletal elements from two of the high ranked prey, Serranidae and Anguilla sp., are measured to examine taxon‐specific changes in fish body size/age that would indicate direct human exploitation pressure. Evidence for a decline in Serranidae body size over time suggests that some of the decline in prey abundance and encounter rates results from direct harvesting pressure along with behavioural adjustments in the prey. Sample sizes for Anguilla were insufficient for statistical treatment. Environmental and technological factors that might also affect prey abundance and taxonomic representation do not satisfactorily account for the patterns. Overall, the increasing use of lower ranked prey suggests a decline in foraging efficiency, given higher energetic costs associated with their use. The study adds to a growing body of evidence that Polynesians profoundly affected the indigenous biota on islands they colonized. Copyright © 2001 John Wiley & Sons, Ltd.

Humpback whales in the Southern Cook Islands, South Pacific

The presence of humpback whales in the Southern Cook Islands (South Pacific) was investigated during a three-week exploratory survey conducted at Palmerston Atoll in September and October of 1998 and during a three-month survey conducted at Rarotonga, Aitutaki and Palmerston Atoll from July to October in 1999. During a total of 48 survey days in both years and all areas, 50 sightings of 83 humpback whales were made. All classes except mother/calf/escort trios were observed, including singers, mothers and calves, and one competitive group. To date, 31 humpbacks have been individually identified from natural markings, 29 sloughed skin samples were collected for genetic analysis and 15.6 hours of song recordings were made. Reports of whales in other areas of the Cook Islands were also noted, and included records of mother/calf pairs. The Cook Islands region appears to represent a breeding ground for humpback whales, presumably from the little-studied Area VI population. The relationship of humpbacks in this region to those in adjacent tropical areas remains largely unknown, although recent matches between the Cook Islands and both Tonga and French Polynesia indicate some movement through Oceania.

Household Units in the Analysis of Prehistoric Social Complexity, Cook Islands

Polynesian and other Oceanic societies have often informed research into social complexity. McGuire (1983) has proposed a means of measuring complexity that does not assume any particular organizational form. The examination of prehistoric household remains allows archaeologists to compare common units of social organization across societies for more meaningful comparisons of past social organization. This paper discusses house remains excavated on three islands in the Southern Cook Islands of central Polynesia for the information they provide about past social organization on the islands and provides comparison between three closely related island societies.

The Pacific Banyan in the Cook Islands: have its pollination and seed dispersal mutualisms been disrupted, and does it matter?

Fig trees (Ficus spp., Moraceae) are pollinated by species-specific fig wasps and have seeds that are mainly dispersed by fruit bats and birds. Consequently, they should be strongly dependent on mutualisms with animals for their reproductive success. As elsewhere in the Pacific, extinctions of potential seed dispersers have occurred on the islands in the southern Cook Islands archipelago. The abundance of the Pacific Banyan, Ficus prolixa, was found to be unrelated to the extent of potential seed disperser extinctions on different islands. There was no evidence of recruitment on Rarotonga, which has the most diverse bird and bat assemblage, and healthy populations on Mangaia, where all the native avian frugivores are extinct. Despite its very small population sizes on some of the islands, the trees pollinators are still present, showing that this mutualism has not yet been disrupted. Habitat loss, rather than a loss of mutualists, appears to be the main problem facing this species.

The 'Ura or Rimatara Lorikeet Vini kuhlii: its former range, present status, and conservation priorities.

SummaryFossils and other evidence from the Southern Cook Islands show that the Rimatara Lorikeet Vini kuhlii, known as the Kura, was widespread in the group during prehistoric times and, it was probably extirpated due to exploitation for its red feathers. Today, it survives only on Rimatara in the Austral Islands, where it is known as the ‘Ura. On Rimatara during 5-11 August 1992 we saw/heard 263 ‘Ura, and estimated the total population at 900 birds. The mixed horticultural belt, about 32% of the island, was the most favoured habitat at 2.2 birds ha1 and it supported about 61% of the total population. The species was uncommon in the coastal coconut plantations and central hills, and rare in the makatea/feo. Rats, especially Rattus rattus, have often been associated with the loss of forest birds on oceanic islands and R. rattus is thought to be responsible for the decline in other lorikeets of French Polynesia. A preliminary trapping study located R. norvegicus and R. exulans, but not R. rattus. The highest conservation priority should be given to confirming the absence of R. rattus on Rimatara and the implementation of a major quarantine programme to ensure that it is not accidentally introduced. We recommend reintroducing the lorikeet to islands within its former natural range.

Viscosity structure of the oceanic lithosphere inferred from the differential late Quaternary sea-level variations for the southern Cook Islands

SUMMARY Late Quaternary sea-level variations for the southern Cook Islands such as Rarotonga and Mangaia provide information on the time-dependent crustal movement due to viscoelastic arching in response to loading by the Pleistocene volcanic island of Rarotonga. The lithospheric responses to both external and internal loads have been investigated to estimate the viscosity of the lower part of the lithosphere and to examine the initial stage of swell formation. Detailed observations of sea-level variations for the past 125 kyr indicate that the crustal uplift for Mangaia is greater than 10 m, while Rarotonga was apparently stable for this period. The following geophysical implications for the lithospheric rheology and loading model are derived from these observations. The observed differential crustal movement implies that the viscous relaxation associated with this volcanic loading is still proceeding in the lithosphere. The layer supporting stresses has therefore been migrating with time from weaker lower zones into the stronger upper zones for a lithosphere with a depth-dependent viscosity structure. This fact provides an important constraint on the viscosity of the lower part of lithosphere. The observation that Rarotonga has been apparently stable for this period is indicative of a local buoyant internal load in the upper mantle. This load may be related to small-scale and secondary convection in the asthenosphere. Surface uplift due to an internal load is therefore required to cancel the subsidence by volcanic loading. This problem has been examined for two simplified background density models. One is a model in which the density of the lithosphere is equal to that of the asthenosphere. For this model, very large mass anomalies which are 10 times larger than the external load are required beneath the lithosphere in order to explain the observed differential crustal movement of the islands. For an earth model for which the density of the lithosphere is greater than that of the asthenosphere, which is possible for mature oceanic lithosphere, the observed differential crustal movement is explained for an internal-load model with density anomalies of less than 20 kg m-j. The volume of the internal load is at most twice the volume of the external load. A high-viscosity layer with an effective viscosity of Pa s and with a thickness of greater than 60 km is required beneath the top elastic layer with a thickness of 10-15 km. The thickness of thermal lithosphere estimated by the plate age of this region is approximately 80-90 km, regardless of the age-thickness relationship adopted. It is therefore suggested that the major part of the thermal lithosphere is composed of a viscoelastic layer with an effective viscosity of

Extreme HIMU in an oceanic setting: the geochemistry of Mangaia Island (Polynesia), and temporal evolution of the Cook—Austral hotspot

New isotope and trace-element data are presented for volcanic rocks from the island of Mangaia in Polynesia, which forms the most extreme example of the HIMU mantle endmember known at the present time.Observations from these data, coupled with published results, provide strong support for an origin of the HIMU signature related to recycling of oceanic crust. Evidence exists for carbonate metasomatism within the mantle beneath Polynesia; however, it is likely that this is also related to the recycling process, rather than being responsible itself for generating HIMU. The elevated U/Pb ratios observed in the HIMU source appear to be largely a result of Pb loss rather than U uptake. The apparent rarity of “pure” HIMU and its relation to other OIB types is presented within a simple recycling framework; to a first approximation, the spectrum of OIB compositions between HIMU and EM may reflect simple mixing between subducted oceanic crust and sediment sources.Temporal/genetic relationships with the other islands in the Cook-Austral archipelago are investigated. Within the Macdonald-Mangaia segment relatively well-defined age progressions require a common heat source. In contrast, isotopic compositions do not follow a simple trend—there is a decrease of the HIMU influence with time, but it is not clear whether this change was abrupt or gradual. The southern Cook islands appear to be largely unrelated to volcanism within the Macdonald-Mangaia segment.

The Ngati Tiare Adze Cache: further evidence of prehistoric contact between West Polynesia and the Southern Cook Islands

AbstractBoth morphology and ethnohistory suggest that the adzes in the Ngati Tiare cache (Rarotonga, Southern Cook Islands) are derived from Samoa. If true, this is further documentation of post‐colonisation contact between West and East Polynesia, regions which were generally throught to have remined isolated from one another following human settlement. The results of geochemical analysis and thin section petrography indicate a very high probability that the adzes are Samoan with a close match to the islands of Manu'a. This provides a close correspondence with Rarotongan oral tradition. These sourcing results are discussed along with those available for adzes from other sites in the Southern Cooks. This evidence demonstrates significant interaction with West Polynesia during the early phase of Southern Cooks prehistory.

Notes on the status of Kuhl's LorikeetVini kuhliiin the Northern Line Islands, Kiribati

SummaryKuhl's LorikeetVini kuhliihas a precarious status reflected by its disjunct distribution in the Pacific, with surviving populations in the Northern Line (Kiribati) and Austral Islands (French Polynesia) some 3,000 km apart, possibly as a result of Polynesian trade in red feathers. The species is extinct in the southern Cook Islands. On Rimatara (Austral Islands), where it is believed indigenous, it is still common but the recent introduction of theRattus norvegicusis of concern. In the Northern Line Islands,R. rattusappears to have all but extirpated the lorikeet on Tabuaeran (Fanning Island), but one small population has apparently survived for over 70 years, an explanation for which may guidein situconservation ofVinilorikeets on ship-rat-infested islands elsewhere. The arid and unpredictable climate of Kiritimati (Christmas Island) may preclude the establishment of lorikeets. Only on Teraina (Washington Island), where over 1,000V. kuhliisurvive, are there no confirmed threats and goodin situconservation potential.

Late Quaternary history of Henderson Island, Pitcairn Group

Henderson Island is an emergent limestone island. It rises to 33.5 m above modern sea-level (MSL) from a sea-floor depth of about 3500 m and conforms to the pattern of an elevated atoll, although no field evidence was found pertaining to the pre-atoll volcanic history of the island. The emergence of this coral atoll can be explained by lithospheric flexure processes subsequent to the emplacement of the Pitcairn Island volcano, built by two phases of volcanism (estimated at 855 and 540 kyr by K-Ar dating). U-Th dates obtained from Henderson Island indicate that the majority of the presently visible fossil corals have an age between 404-225 kyr. Henderson Island first became emergent above MSL when sea level dropped subsequent to 380 kyr, as the period 440-380 is thought to have been characterized by sea level at least several metres above MSL in the Central Pacific. As a result Henderson Island would have become subaerially exposed from 380 kyr onwards. The uplift rate of Henderson Island is approximately 0.093-0.10 mm/yr indicating that flexure-induced uplift component above MSL commenced between 360-335 kyr, 500 kyr after the initial, and 190 kyr after the last phase of construction of the Pitcairn volcano. The time-lag following the loading of the Pitcairn volcano and the present continuation of uplift on Henderson support the theory that the lithosphere behaves in a visco-elastic manner. Field relations and U-Th dates indicate three main periods of reef development: (1) A prolific reef-building period (440-380 kyr [Unit 1] and 330-300 kyr [Units 2 & 3]) dominated by large, stout branching coral colonies; (2) A shorter period of reef growth (285-275 kyr [Unit 4]) dominated by well-formed large in situ coral colonies and Tridacna maxima; (3) A less prolific period of reef growth (230-215 kyr [Unit 5]) dominated by platy corals enveloping the previous lithologies below 19.6 m. The absence of dateable material from the last interglacial, oxygen isotope substage 5.5 (= 5e) at Henderson Island is in marked contrast to the Late Pleistocene reefs in the southern Cook Islands where reefs of substage 5.5 age skirt older carbonate complexes.