Rakaia River Research Articles

Redistribution of fine gold from hydrothermal sources to sedimentary sinks, Rakaia River, Canterbury, New Zealand

ABSTRACT The Rakaia River in the South Island of New Zealand is a unique catchment in which to trace active detrital gold transport, deformation and concentration from near-coeval orogenic sources. The catchment hosts widespread small late Cenozoic hydrothermal alteration zones, some of which are gold-bearing, in actively rising and eroding mountain headwaters. Detrital gold liberated from the sources is distinctively porous with abundant micron-scale silicate inclusions, especially albite. Fine gold (∼200–100 µm) has been transported >100 km downstream, but coarse gold remains highly diluted in proximal fluvial sediments. Fine gold is also diluted by coarse fluvial sediments that form the upper kilometre of the Canterbury sedimentary basin southeast of the mountain front. Minor re-concentration of fine gold occurs in a bedrock gorge at the mountain front, and on steep ocean beaches beyond the river mouth. Despite the long-distance transport, the fine gold particles have been only superficially modified by surface smearing and minor flattening. The gold may have travelled in suspension in the river, buoyed by electrostatically adhering fine micas, in contrast to detrital garnets that were rounded in bed-load. In contrast, detrital gold on the western side of the mountains has been flattened to thin flakes during bed-load transport.

Cosmogenic 10Be constraints on deglacial snowline rise in the Southern Alps, New Zealand

Geochronological dating of glacial landforms, such as terminal and lateral moraines, is useful for determining the extent and timing of past glaciation and for reconstructing the magnitude and rate of past climate changes. In the Southern Alps of New Zealand, well-dated glacial geomorphological records constrain the last glacial cycle across much of the Waitaki River basin (e.g. Ōhau, Pukaki, Tekapo) but its southern sector such as the Ahuriri River valley remains comparatively unconstrained. Recently, there has been debate on the scale and rapidity of mountain glacier retreat during the last glacial termination, particularly the 20–17 ka period in New Zealand. Missing from this debate is well-constrained equilibrium-line altitude (ELA) and associated temperature reconstructions, particularly over the period around 17 ka, which can help us to develop a more complete picture of how past temperature changes drove glacier retreat. Here we report the first glacial chronology dataset from the Last Glacial Maximum (LGM) and subsequent deglaciation from the Ahuriri River valley, Southern Alps, New Zealand (44°23′54″S, 169°39′48″E) based on 38 beryllium-10 (10Be) surface-exposure ages from terminal moraine systems and glaciated bedrock situated at the lower and middle sections of the valley. Our results show that the former Ahuriri Glacier reached its maximum extent at 19.8 ± 0.3 ka, which coincides with the global Last Glacial Maximum. By 16.7 ± 0.3 ka, the glacier had retreat ∼18 km up-valley suggesting at least ∼43% glacier-length loss relative to its full LGM extent. This deglaciation was accompanied by the formation of a shallow proglacial lake. Using the accumulation area ratio (AAR) method, we estimate that the ELA was lower than present by ∼880 m (∼1120 m a.s.l.) at 19.8 ± 0.3 ka, and ∼770 m lower (∼1230 m a.s.l.) at 16.7 ± 0.3 ka. Applying an estimate for temperature lapse rate, this ELA anomaly implies that local air temperature was 5 ± 1 °C colder than present (1981–2010) at 19.8 ± 0.3 ka, while it was 4.4 ± 0.9 °C colder at 16.7 ± 0.3 ka, assuming no change in precipitation. The substantial glacier retreat in response to a relatively small accompanying increases in ELA (110 m) and temperature (0.6 °C) may have been a result of the high glacier-length sensitivity of this glacier system due to its low gradient of former ice surface. Our low warming estimate differs markedly from other deglaciation studies, specifically from Rakaia River valley, which reports a much larger temperature increase at the onset of the last deglaciation. This precisely-dated moraine record along with reconstructed ELA as proxies for atmospheric conditions, provides new insight into post LGM glacier behaviour and climate conditions in New Zealand.

Planform change of the Río Chubut (~42°S, ~70°W, Argentina) in response to climate drivers in the southern Andes

The Río Chubut (southern Argentina) displays complex geomorphological and sedimentological responses to long-term variations in hydrology and sediment supply. A 75 km study reach located 65 km downstream of the former ice margin and proglacial lake (Lago Epuyen) at the foothills of the Andes shows that the river has previously undergone large-scale planform changes from a braided to a meandering regime. The new luminescence chronology presented here constrains the timing of changes in fluvial characteristics in the Chubut valley, including the waning and abandonment of a braid plain dated at four locations, the minimum age for the shift to the modern meandering regime, and the timespan of activity for an alluvial fan. Sedimentology, geomorphology and geochronology findings show that the Río Chubut maintained a braided planform during the last deglaciation until the water supply to the headwaters in the Andes decreased because the mid-latitude storm tracks and westerlies in the Southern Hemisphere weakened and shifted southwards causing drier conditions across Patagonia. This encouraged a time-transgressive shift in the Río Chubut between 12.3 ± 1.0 ka and 9.4 ± 0.8 ka from a braided planform to the meandering system active today. These findings highlight that modern braided rivers (e.g., the Rakaia River, New Zealand) that are experiencing a reduction in discharge could be vulnerable to similar large-scale planform changes with the potential to impact upon unique habitats and ecosystems.

Who, Where, What, Wren? Using Ancient DNA to Examine the Veracity of Museum Specimen Data: A Case Study of the New Zealand Rock Wren (Xenicus gilviventris)

Museum specimens provide a record of past species distribution and are an increasingly important resource for conservation genetic research. The scientific value of these specimens depends upon the veracity of their associated data and can be compromised by inaccurate details; including taxonomic identity, collection locality, and collector. New Zealand contains many endemic species that have been driven to extinction or reduced to relict distributions following the arrival of humans and mammalian predators, including the Acanthisittid wrens (of which only two of the eight species presently persist). One of these is the New Zealand rock wren (Xenicus gilviventris), currently classified as an endangered species and experiencing ongoing population declines. Here we analyse ancient DNA retrieved from New Zealand rock wren museum skins to establish the veracity of their recorded collection localities – New Zealand rock wrens exhibit strong north-south genetic structuring along the Southern Alps of New Zealand’s South Island. We include the only specimen reportedly collected from New Zealand’s North Island, outside the known range of New Zealand rock wrens, specimens collected by Henry Hamersley Travers, a collector known for poor record keeping and potentially fraudulent specimen data, and type specimens of proposed Xenicus taxa. Multiple instances of inaccurate collection locality were detected, including that of the New Zealand rock wren reportedly collected from the North Island, which matches individuals from the southern South Island. Syntypes of X. haasti, and a syntype of X. gilviventris clustered with individuals belonging to the northern New Zealand rock wren lineage. Our results suggest that New Zealand rock wrens have not been historically extirpated from New Zealand’s North Island, and that caution must be taken when utilising museum specimens to inform conservation management decisions. Additionally, we describe the type locality of both X. gilviventris and X. haasti, with genetic and historical evidence suggesting that the specimens used to describe these taxa were collected from the headwaters of the Rakaia River. This study demonstrates that ancient DNA analysis can add value to museum specimens by revealing incorrect specimen data and inform the conservation management and taxonomy of endangered species.

A laboratory experiment on the behaviour of soil-derived core and intact polar GDGTs in aquatic environments

Abstract. We have performed incubation experiments in order to examine the behaviour of soil-derived branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids upon entering an aquatic environment and to evaluate the processes that potentially take place during their fluvial transport from land to sea. We incubated a soil from the Rakaia River catchment on the South Island of New Zealand using Rakaia River water and ocean water collected near the river mouth as inocula for a period of up to 152 days. The concentrations, as well as the relative distribution of brGDGTs derived from intact polar ("living"; IPL) lipids and core ("fossil"; CL) lipids remained unaltered over the course of the experiment. Although the stability of the brGDGTs may be a consequence of the higher than natural soil : water ratio used in the laboratory experiment, the substantial increase (27–72%) in the total pool of isoprenoid GDGTs (isoGDGTs) in all incubation setups, including the control using distilled water, indicates that entering an aquatic environment does influence the behaviour of soil-derived GDGTs. However, the availability of water appears to be more important than its properties. As a consequence of increasing isoGDGT concentrations, a decrease in Branched and Isoprenoid Tetraether (BIT) index values – a proxy for the relative input of fluvially discharged soil material into a marine system – became evident after an incubation period of 30 days, with a maximum final decrease of 0.88 to 0.74 in the experiment with river water. The relative distribution within the isoGDGT pool shows changes with time, suggesting that isoGDGT producers may either have different rates of membrane adaptation or production/degradation, or that preferential release from the soil matrix or a shift in source organism(s) may take place. While the apparent stability of soil brGDGTs during this incubation experiment reinforces their potential as tracers for land–sea transport of soil organic carbon and their use in paleoclimate reconstructions, the distributional differences between GDGTs in river water and nearby soil, as well as in river and ocean water, indicate that further research is needed to pinpoint the sources of GDGTs that are ultimately discharged to the oceans and are subsequently archived in continental margin sediments.

Faulting and folding beneath the Canterbury Plains identified prior to the 2010 emergence of the Greendale Fault

Prior to the 2010–2011 earthquake sequence, several fault and fold structures were mapped beneath the Canterbury Plains using seismic reflection surveys and surface observations and depicted on the Christchurch and Aoraki 1:250,000 scale geological maps. Localised grabens associated with east-southeast-striking normal faults formed largely during the Late Cretaceous. South of Rakaia River, some graben-bounding faults show minor normal offset extending into the late Cenozoic. Near Ashley River, proximity to a Late Cretaceous–Paleogene graben suggests that the active, predominantly contractional, east-striking Ashley Fault is at least in part a rejuvenated pre-existing normal fault. The easterly strike of the previously unknown Greendale Fault implies that it too may be a reactivated Late Cretaceous fault. Northeast-striking, southeast-facing reverse faults and fault-propagation folds beneath the western and northern parts of the plains are primarily late Cenozoic features. Variation in the distributions of Miocene sedimentary strata strongly suggests that contractional faulting was initiated as early as the Miocene. The overall late Cenozoic tectonic pattern is extension beneath the southern Canterbury Plains and contraction farther north.

Semiautomated Analysis of Data from an Imaging Sonar for Fish Counting, Sizing, and Tracking in a Post-Processing Application

Dual frequency identification sonar (DIDSON) is an imaging sonar that has been used for numerous fisheries investigations in a diverse range of freshwater and marine environments. The main purpose of DIDSON is fish counting, fish sizing, and fish behav ioral studies. DIDSON records video-quality data, so processing power for handling the vast amount of data with high speed is a priority. Therefore, a semiautomated analysis of DIDSON data for fish counting, sizing, and fish behavior in Echoview (fisheries acoustic data analysis software) was accomplished using testing data collected on the Rakaia River, New Zealand. Using this data, the methods and algorithms for background noise subtraction, image smoothing, target (fish) detection, and conversion to single targets were precisely illustrated. Verification by visualization identified the resulting targets. As a result, not only fish counts but also fish sizing information such as length, thickness, perimeter, compactness, and orientation were obtained. The alpha-beta fish tracking algorithm was employed to extract the speed, change in depth, and the distributed depth relating to fish behavior. Tail-beat pattern was depicted using the maximum intensity of all beams. This methodology can be used as a template and applied to data from BlueView two-dimensional imaging sonar.

Longitudinal size distributions of bluegill bullies (Gobiomorphus hubbsi) and torrentfish (Cheimarrichthys fosteri) in two large New Zealand rivers

This study compared the longitudinal size distribution of bluegill bullies (Gobiomorphus hubbsi) from Hutt River with existing data on the size distributions of bluegill bullies and torrentfish (Cheimarrichthys fosteri) from Rakaia River, New Zealand. All populations had longitudinal trajectories that showed some increase in size with distance upstream. This increase in size appeared to primarily reflect the influence of amphidromous life styles, where juveniles diffuse upstream from the sea. However, a quantile regression analysis revealed differences in growth and migration rate between the two bluegill bully populations; bluegill bullies from Rakaia River grew at a slower rate and showed variation in migration rate within their population that was not evident in the Hutt River population. Null models were also generated for each population to test for the presence of all size classes of fish in the lower reaches of each river. Both bluegill bully populations showed a significant absence of the largest size classes in the lower reaches and the size trajectories differed significantly from the null models. This difference suggests that all individual bluegill bullies continuously move upstream throughout their lives. In comparison, the size distribution of torrentfish closely resembled the null model, indicating that some individuals did not migrate upstream to the same extent as others.

Alternative interpretations of structural evidence at Rakaia River Mouth, New Zealand

AbstractPostholes and other features at Rakaia River Mouth, New Zealand, are interpreted by Jacomb (2005) as remains of a large house and associated structures. This is plausible, but on the same evidence storage structures can be inferred. Alternative interpretations emphasize problems in defining Archaic houses. My interpretation of the Rakaia River Mouth evidence suggests, however, a full Archaic domestic unit might be exposed by extending excavations to the west.

Transport and concentration of detrital gold in foreland basins

Economic concentrations of detrital gold are rare in young foreland basins due to paucity of significant gold sources, and a paucity of sediment recycling processes during filling of the foreland basin. Gold shed into the foreland basins is typically widely dispersed in an overwhelming volume of immature basin-fill detritus of no economic significance. In the actively forming Canterbury Basin of New Zealand, minor gold concentration occurs at the mountain front in the bed of the Rakaia River, and 60 km downstream on beaches and the crest of foredunes at the river mouth. The Cretaceous–Tertiary Denver and Western Canada Basins in North America also have minor gold concentrations at the mountain front, and minor gold dispersal into the basin. Tectonic quiescence in the middle Tertiary in the Denver Basin kept gold within 20 km of the mountain front, where renewed uplift in late Tertiary caused minor economic concentrations to form in modern streams. Gold has been transported ca. 200 km across the Western Canada basin by progressive recycling of gravel during slow (ca. 10 to 50 m/Ma) middle Tertiary–Recent regional uplift and tilting, but little concentration has occurred. Development of significant placers in a foreland basin, the generally accepted setting for the Witwatersrand Au-U palaeoplacers, appears to require specific tectonic conditions during and/or after basin evolution to drive the sedimentary recycling necessary for significant placer development. Such tectonic conditions have not occurred in an any of the three young foreland basins examined in this study.

A fourteenth-century house from the Rakaia River Mouth, Canterbury, New Zealand

Abstract Large-scale areal excavations at the Rakaia River Mouth moa-hunting site exposed an array of post holes indicative of a substantial building. Also found were the remains of a possible cooking shelter and oven, several fire scoops, and early type artefacts, all contained within a fenced enclosure. Radiocarbon dates provide a fourteenth-century age estimate. The structural features provide important new insights into the nature of intra-site spatial patterning and of house society both in early New Zealand and a wider Pacific context. Keywords: Radiocarbon dates, house, Maori, moa hunting, Archaic, artefacts, post holes. Introduction Archaeological information about buildings and their relationships to other features is important, not just for what it can tell us about the architecture of the time and a community's use of space, but for what it can tell us about such things as social organisation and ideology. Gaining access to the relevant information, however, requires extensive areal excavations that are costly and rarely carried out in New Zealand. Those few relatively large-scale areal excavations that have been undertaken at Archaic sites, such as Shag River Mouth, Heaphy River Mouth and Houhora, have not yielded much useful information about structures. The currently available data are therefore insufficient to provide detailed information on intra-site spatial patterning in the early settlement phase of prehistoric New Zealand except at a very general level. All of these sites had post holes, and evidence of activity areas where such things as cooking or tool manufacture were undertaken. However, the areas excavated did not provide the opportunity to examine the layout or construction of particular buildings, especially houses, or the spatial relationships between structures, activity areas and open spaces. The basic residential unit of any community is the household cluster (Flannery 1976) of which the dominant component is the residential structure or house. In Polynesian society the house is more than simply a residence, however. It is integral to the relationships of individuals to their kin, their ancestors and their deities. This is especially so in the case of the important (e.g. chiefs') houses, which are focal points for each settlement or village. Recent studies have shown striking commonality of theme, structure and use of space throughout the Austronesian-speaking world (e.g. Fox 1993a, Kirch and Green 2001). Houses are given special significance in Austronesian societies, where they provide a physical link with the past and are often the focus of ritual and performance. The aspects of houses that are shared across these societies suggest a considerable time-depth to this house culture. While some progress has been made on houses and intrasite settlement pattern in East Polynesia (e.g. Walter 1993, 1998), archaeological evidence of the houses and other buildings of the early, Archaic, phase of settlement in New Zealand has so far proved elusive. It is limited to inferred evidence for simple, round huts at several sites (Allingham n.d., Anderson 1986), a square structure from the early fourteenth century AD Wairau Bar site (Anderson 1989) and a rectangular dwelling house from the Moikau Valley in Palliser Bay currently dated to the twelfth century AD, but see discussion below (Prickett 1979). Excavations over 300 [m.sup.2] at the Rakaia River Mouth site (L37/4) in the South Island of New Zealand revealed evidence for a unique set of features including a large, rectangular structure with its posts set deep into the ground. Radiocarbon dates, material culture and faunal remains all indicate an occupation near the beginning of Polynesian settlement in New Zealand. The results of the excavations contribute to a wider understanding of Archaic settlement and life in a new land, and enable comparisons both regionally and chronologically in a Polynesian context. …

Holocene paleoearthquakes on the strike‐slip Porters Pass Fault, Canterbury, New Zealand

The Porters Pass Fault comprises a series of discontinuous Holocene active traces which extend for c. 40 km between the Rakaia and Waimakariri Rivers in the foothills of the Southern Alps. There have been no historical earthquakes on the Porters Pass Fault (i.e., within the last 150 yr), and the purpose of this paper is to establish the timing and magnitudes of displacements on the fault at the ground surface during Holocene paleoearthquakes. Displaced geomorphic features (e.g., relict streams, stream channels, and ridge crests), measured using either tape measure (n = 20) or surveying equipment (n = 5), range from 5.5 to 33 m right lateral strike slip and are consistent with six earthquakes characterised by slip per event of c. 5–7 m. The timing of these earthquakes is constrained by radiocarbon dates from four trenches excavated across the fault and two auger sites from within swamps produced by ponding of drainage along the fault scarp. These data indicate markedly different Holocene earthquake histories along the fault length separated by a behavioural segment boundary near Lake Coleridge. On the eastern segment at least six Holocene earthquakes were identified at 8400–9000, 5700–6700, 4500–6000, 2300–2500, 800–1100, and 500–600 yr BP, producing an average recurrence interval of c. 1500 yr. On the western segment of the fault in the Rakaia River valley, a single surface‐rupturing earthquake displaced Acheron Advance glacial deposits (c. 10 000–14 000 yr in age) and may represent the southward continuation of the 2300–2500 yr event identified on the eastern segment. These data suggest Holocene slip rates of 3.2–4.1 mm/yr and 0.3–0.9 mm/yr on the eastern and western sections of the fault, respectively. Displacement and timing data suggest that earthquakes ruptured the western segment of the fault in no more than one‐sixth of cases and that for a sample period of 10 000 yr the recurrence intervals were not characteristic.

Introduction to farming in the Central Canterbury area

On the east side of the Southern Alps of the South Island lies the province of Canterbury. Within this province there are five district regions, North, Central, Mid, and South Canterbury (all running from the mountains to the sea and separated by major rivers), and Banks Peninsula. Central and Mid Canterbury are home to the Selwyn and Ashburton District Councils (respectively) and sit side by side in the centre of Canterbury. Selwyn District has a northern boundary with the Waimakariri River, Christchurch City, and Banks Peninsula. Ashburton District has a southern boundary with the Rangitata River. The mighty braided Rakaia River is the dividing boundary between the two districts. Canterbury Regional Council (ECAN), based in Christchurch, has control over environmental issues in the area.

Sodium deficiency in Canterbury and Central Otago sheep pastures

Sheep diets are likely to be deficient in sodium (Na) if pasture contains less than 0.04% Na (lambs and maintenance) or 0.05% Na for ewe flushing and lactation. Herbage from four species was sampled in autumn 2002 from 12 sites on a transect south of the Rakaia River from the coast to 110 km inland. All species had >0.10 % Na near the coast but browntop and cocksfoot declined to < 0.10% Na at 10 km and 20 km inland respectively. White clover and ryegrass declined to about 0.10% Na at 40 km and 80 km respectively. In autumn 2003, soil and herbage samples were collected from 8 farms over a range of distances from the coast. Soil quick test (QT) Na from the 8 farms had a strong negative correlation with distance from the sea. Soil QT Na was

Modern environments of the Canterbury Plains and adjacent offshore areas, New Zealand -- an analog for ancient conglomeratic depositional systems in nonmarine and coastal zone settings

ABSTRACT Modern depositional environments of the Canterbury Plains provide an analog for ancient conglomeratic depositional systems in nonmarine and coastal zone settings. The Canterbury Plains are up to 70 km wide and 185 km long, covering approximately 8000 km2. The Plains are dominated by extreme geological and geomorphological processes -- primarily climate, tectonics, and wave climate. The Canterbury gravels are primarily the deposits resulting from the coalescence of broad fluvial megafans that flowed into a high-energy coastal environment. Most fluvial channels in the basin are gravelly braided rivers. During the present sea-level highstand, a large portion of the plains can be considered as being situated in a low accommodation setting. Most sediment progradation and aggradation occurred and took place near the end of multiple glacial maxima and their associated sea level lowstands. As such, the fluvial megafans are nonmarine lowstand to early transgressive deposits. Valley entrenchment subsequently took place on the seaward side of the plains during the ensuing sea level rise and highstand. On the inner plains, tectonic uplift of the Southern Alps caused fluvial incision during highstand with coastal retreat concomitant with valley incision. The modern coastline is highly variable, being, at different places, progradational, retrogradational, and stable. The southern coast is dominated by powerful southerly swell conditions, which are highly erosive, and set up high rates of net northwards longshore drift. Consequently, the southern coast, south of Rakaia River, is transgressive, retreating at about 1 m/yr. All southern rivers are incising into the floodplain. In contrast, the northern coastline is situated in the wave shadow of a large, natural groyne formed by volcanic rocks of Banks Peninsula, resulting in lower wave conditions affecting that coast. The Pegasus Bay coastline progrades as a highstand wave-dominated delta. Since the last deglaciation, sea level has risen until a relatively stable period was reached about 6500 years ago. During this period of sea-level rise and subsequent highstand, the Waimakariri, Ashburton, Rangitata, Raikaia, and Hinds rivers became entrenched, forming sets of relatively steep terraces in proximal areas, which decrease in relief downstream from the mountains until a zone of no or minimal erosion is reached 8 to 15 km inland of the coast. Other environments of the Canterbury Plains include estuaries, the large brackish and shallow Lake Ellesmere into which a birds foot delta is prograding, a progradational strandplain, and localized occurrences of aeolian sediments on the progradational coast and on the plains. Steep gradients of rivers that are incised into the coastline prevent extensive estuarine conditions from developing on the transgressive coastline. One of the dominant controls on sedimentation is climate, mainly extreme amounts of precipitation. Large rivers commonly flood as a result of extreme precipitation derived from advecting moist, subtropical air from the west, rising over the Southern Alps, combined with spring and summer snow melt. In contrast, smaller rivers flood during winter months as a result of stationary easterly frontal systems. Maximum coastal erosion and littoral sediment transport occurs from large oceanic storms originating from the south and southeast. End_Page 389------------------------

Dust accumulation in the New Zealand region since the last glacial maximum

Loess is widespread in New Zealand; deposits >1 m thick cover 10% of the land area. It has mainly been derived from dust deflated from river floodplains during the last glacial maximum (LGM). Dust accumulation continues today downwind of major river floodplains. Most loess is quartzofeldspathic, having its origins in Mesozoic and Neogene rocks of the axial ranges and hill country. In the central North Island there are deposits of volcanic loess derived from aeolian reworking of tephras. Loess morphology and properties vary greatly due to diverse parent materials, post-depositional climates and drainage conditions. The widespread 26,170 cal. yr Kawakawa Tephra provides a datum for calculating mass accumulation rates (MARs). Rates are mostly within the range 70–150 g m −2 yr −1, but enhanced deposition at one site gave a rate of 360 g m −2 yr −1. Contemporary MARs of 40–100 g m −2 yr −1 were determined for distances of 1.75–0.4 km downwind of the Rakaia River. LGM MARs of quartz for two marine cores (P69 & Q858) drilled 100–300 km east of New Zealand are 40–70 g m −2 yr −1. The MAR of the aeolian component of P69 is estimated to be ca 15 g m −2 yr −1.

A new longjaw galaxias species (Teleostei: Galaxiidae) from the Kauru River, North Otago, New Zealand

A population of “longjaw galaxias”, long known to be present in the Kauru River, a small tributary of the Kakanui River in North Otago, is shown to be a distinct species using both morphological and molecular characters. It is described here as Galaxias cobitinis n. sp., which has: origin of anal fin anterior to that of dorsal fin, only 15 principal caudal fin rays, only 5 pelvic fin rays, and only 51–53 vertebrae. In these and other morphological characters it differs from G. prognathus Stokell. One specimen from the Hakataramea River, lower Waitaki River system appears to also be G. cobitinis. Molecular evidence suggests long isolation from the Kauru River of “true” longjaw galaxias G. prognathus and from rivers draining the high Southern Alps (type locality: Wilberforce River, tributary of the Rakaia River), perhaps dating back as long as 11–4 million years ago (late Miocene‐early Pliocene). This prolonged isolation contrasts with hypothesised more recent isolation of populations of the Galaxias vulgaris species group in the Kakanui River from other populations of that species group. Thus, sympatric species of Galaxias have contrasting biogeographic histories in the Kakanui River.

Synthesis of extreme wave climate for the Canterbury Bight, New Zealand

Numerical models of the marine wind field and wave generation offer a technique for estimating the severity of extreme wave events. Measured and modelled waves in the Canterbury Bight, New Zealand, were used to examine the hypothesis that extreme conditions can be more confidently estimated by modelling the wave climate over a decade than by analysing shorter measured records. The meteorological conditions causing high waves in the Canterbury Bight were examined by inspecting wind measurements at Christchurch Airport and wave buoy measurements made in 1983–85 near the Rakaia River mouth. Although the arrival of high waves was sometimes associated with wind changes at the airport, peak wave heights generally occurred at least several hours after such wind changes and were associated with south‐westerly or southerly winds in the Bight and a depression south‐east of the South Island. Wave conditions at the buoy site for 1980–89 were modelled using marine winds obtained from a global circulation model, running a wave generation model for the seas around New Zealand, and then applying a refraction model. The decade modelled included two El Niño events and one La Niña event, and the ocean wind climate should therefore have been reasonably representative of the long‐term range of conditions. The model results were verified against the buoy measurements. Estimates of extreme wave heights were then made from 10 years of modelled record and also the measured buoy record. Application of the Gumbel distribution to the monthly maxima gave a significant wave height of 9.5 m for the wave event with an annual exceedance probability of 1 in 50. Model predictions indicate that the most severe waves arrive in the Bight from due south. Estimates of extremes from the measurements and model hindcast were close, indicating that the hindcast represents a population of events similar to those measured.

Fry-to-adult survival of natural and hatchery-produced chinook salmon (Oncorhynchus tshawytscha) from a common origin

Fry-to-adult survival rates for chinook salmon (Oncorhynchus tshawytscha) from Glenariffe Stream, a tributary of the Rakaia River, New Zealand, were estimated for fish of both natural and hatchery origin. Survival of naturally produced fry, most of which leave Glenariffe Stream within 24 h of emergence, averaged 0.079% (range 0.013-1.17%). For hatchery fish released at 8-12 months, standardised to a mean weight of 38 g, survival covaried with weight at release consistently across all brood years and averaged 0.34% (range 0.008-3.28%). Survival rates for hatchery fish were four times higher than for naturally produced fry, but were extremely poor relative to their size at release. Survival rates for fish of natural and hatchery origin were positively correlated, suggesting that recruitment of both stocks is primarily controlled by common influences within the marine environment, probably during the first winter at sea. Stock-recruitment analysis for the natural population showed little tendency for recruitment to increase with stock size, suggesting that marine survival rates may be density dependent. Although the reasons for the relatively poor survival of hatchery fish are unclear, the results provide a case study in which hatchery fish appear to have a poorer ``fitness to survive'' than their natural counterparts.

The Holocene evolution of a well nourished gravelly barrier and lagoon complex, Kaitorete “Spit”, Canterbury, New Zealand

Morphological, stratigraphical, micropaleontological and radiocarbon dating investigations of the gravelly Kaitorete “Spit” system, Canterbury, New Zealand show that a barrier/spit system has existed at this site for the last 8000 yr. Kaitorete “Spit” developed as a true spit extending north from near the Rakaia river mouth, during sea level rise in the Late Pleistocene and Early Holocene. This produced an estuarine coastline along the southwestern flank of Banks Peninsula. The spit extended to Banks Peninsula sometime in the early mid-Holocene creating a barrier lake complex behind the spit. Since the mid-Holocene, there have been at least three fluctuations between lacustrine and estuarine/lagoonal conditions in the barrier blocked system. The most recent fluctuation, which resulted in the present barrier lake complex, occurred within the last 200–500 yr.These fluctuations are associated with the avulsion of a large braided river, the Waimakariri, to and from the Lake Ellesmere basin. When the river flows through the basin, a permanent channel is maintained to the ocean with estuarine conditions present. When the river flows elsewhere, the barrier closes and a freshwater lake system forms behind it. This study emphasises the importance of fluvial control on the evolution of gravelly coastlines where sediment supply is not the limiting factor. Both the sediments and the water in the back barrier area are predominantly derived from the terrestrial catchment. We highlight the absence of true marine influence in the back barrier area, except in the vicinity of the tidal channel, even when such a channel is present. Marine processes have been limited to the gradual re-orientation of the barrier system from drift to swash alignment.