Population viability analysis of New Zealand sea lions, Auckland Islands, New Zealand’s sub-Antarctics: assessing relative impacts and uncertainty

A common issue faced in wildlife management is how to assess the uncertainty of potential impacts on the viability of a species or population. The pup production of New Zealand (NZ) sea lions (Phocarctos hookeri) has declined 50% in the last 12?years at their main breeding area, the Auckland Islands. The two major known atypical impacts on NZ sea lions are as follows: (1) the direct mortality as bycatch of trawling and (2) bacterial epizootics, which can affect reproduction and mortality. Both of these impacts include high levels of uncertainty, with fisheries data being variable due to percentage observer coverage and the effect of sea lion exclusion devises, while the timing and severity of bacterial epizootics are not predictable. In this paper, an age-structured model of the NZ sea lion population at the Auckland Islands was built to examine the predicted effects of fisheries mortality and catastrophes (bacterial epizootics), both separately and then combined, on population viability over a 100-year period using the VORTEX population viability analysis programme. These models are then compared against 15?years of empirical field data to determine the actual level of impacts being observed. Model results indicate that although naturally occurring epizootics reduce the growth rate of the population, it does not cause a decline in the Auckland Island population. However, sustained fisheries bycatch at current estimated levels, particularly considering its potential impact on adult female survival, could result in a population decline and possible functional extinction over the modelled time period.     

Dynamics of an endangered New?Zealand skink: accounting for incomplete detectability in estimating patch occupancy

The endangered grand skink (Oligosoma grande) is a New?Zealand endemic lizard that persists as metapopulations occupying rock patches within matrices of mixed native vegetation and modified agricultural pasture. Parameterisation of metapopulation models applied in conservation biology assumes complete detectability of target species. Incomplete detectability may result in underestimates of occupancy and biased estimates of extinction and colonisation rates. Recent techniques use multiple surveys of sampling sites to model detectability and derive robust estimates of occupancy, and extinction and colonisation rates. Five years (1998?2002) of presence/absence survey data were analysed to determine grand skink site occupancy and estimate colonisation and extinction rates. Mean site occupancy was 0.38 (SE 0.07), compared with a na?ve estimate of 0.29. Occupancy, extinction and colonisation probabilities were habitat specific, varying according to tussock or a modified pasture matrix. Colonisation probability was higher in tussock than in pasture, whereas extinction probability was higher in pasture. Derived model-averaged estimates showed that occupancy was higher in tussock (range 0.515(0.02) ? 0.532 (0.02)) than in pasture (range 0.226 (0.03) ? 0.234 (0.01)), with a slight trend of decline in pasture areas and increase in tussock areas over time, with the result that overall occupancy has been reasonably static over the 5 years. Detectability varied interannually, ranging from 0.63 to 0.83. The difference between the na?ve occupancy estimate and the model-averaged estimate highlights the importance of deriving robust estimates of metapopulation parameters that take incomplete detectability into account. Unbiased estimates allow managers to predict and track responses to management interventions.     

Single large or several small? Population fragmentation in the captive management of endangered species

Captive populations of endangered species are typically maintained effectively as single random-mating populations by translocating individuals between institutions. Genetic, disease, and cost considerations, however, suggest that this may not be the optimal management strategy. Genetic theory predicts that a pooled population derived from several small isolated populations will have greater genetic diversity, less inbreeding, and less genetic adaptation to captivity than a single large population of equivalent total size, provided there are no population extinctions. These predictions were tested using populations of Drosophila with effective size comparisons of 50 vs. 2 × 25; 100 vs. 2 × 50 vs. 4 × 25, and 500 vs. 2 × 250 vs. 4 × 100 + 2 × 50 vs. 8 × 25 + 6 × 50. Populations were maintained at the indicated sizes as separate pedigreed populations for 50 generations. The several small treatments were subsequently pooled and maintained for eight to 10 generations prior to determination of fitness and evolutionary potential. Several small populations (pooled), when compared to single large populations of equivalent total size, were found to have lower average inbreeding coefficients, significantly higher reproductive fitness under competitive conditions, similar fitness under benign captive conditions, higher genetic diversity, and equivalent evolutionary potential. Trends favored the several small (pooled) populations in all comparisons at population sizes of 50 and 100. We recommend that endangered species in captivity be maintained as several small populations, with occasional exchange of genetic material. This has genetic benefits over current management both in captivity and especially for reintroductions, as well as reducing translocation costs and risks of disease transfer. Zoo Biol 17:467–480, 1998. © 1998 Wiley-Liss, Inc.     

Population dynamics and resource use of red deer after release from harvesting in New?Zealand

Despite periods of extensive government-funded control, fluctuating commercial exploitation and ongoing recreational hunting, little is known about how red deer (Cervus elaphus scoticus L?nnberg) in New?Zealand respond to the cessation of harvesting in terms of population growth rate and resource use. We describe the population dynamics and resource use of red deer in a montane catchment over 5?years (1962?67) following cessation of intensive government-funded control in 1961. Locations and sex?age classes of deer were observed monthly along a fixed route in the Harper-Avoca catchment, inland Canterbury. A total of 2036 red deer groups were observed. The number of groups observed annually increased during the study but no trends in median (2 or 3) or modal (1 or 2) group sizes were found. Population growth rates (r) of deer were extraordinarily high in the first two years (e.g. 2.33 ? 0.22 for adult females and 1.61 ? 0.23 for adult males), but decreased in subsequent years and were not biologically possible without substantial immigration and/or changes in detectability of deer. Sexual segregation and selection of vegetation types (alpine grassland, montane grassland, and forest) and 10 topographic landforms showed stronger intra-annual than inter-annual patterns. Segregation was greatest in spring and summer, least in the rut, and variable in winter. In all seasons, sexual segregation was greatest at 25- and 50-ha scales, moderate at 100-ha, and absent at the 500- and 1000-ha scales. Selection of vegetation types also varied seasonally, with deer of both sexes preferring montane grasslands in spring and summer and alpine grasslands in the rut. Backslopes were preferred landforms in spring and summer, spurs during spring and the rut, and hollows during the rut. Our results highlight the need to consider spatial scale, immigration, and detectability in the design of red deer culling and harvesting programmes. Studies of home-range size and use, migration patterns, dispersal rates and distances are required to better understand the impacts of red deer on New?Zealand ecosystems and the effects of management on red deer populations.     

Immature stages of Curculionoidea — the weevils of The Snares islands,New Zealand

Abstract

The following weevil species are known from The Snares islands: Anthribidae — Cacephatus aucklandicus, Lichenobius littoralis; Curculionidae — Exeiratus laqueorum, Pentarthrum spadiceum, Notacalles planidorsis, Lyperobius sp., Hadramphus stilbocarpae, Phrynixus laqueorum, Gromilus laqueorum, Nestrius laqueorum, Catoptes brevicornis australis, Oclandius vestitus. The larvae and pupae are described and figured, and keys for their separation are given.     

Acaricidal resistance and genetic affinities of some two‐spotted spider mite populations in New Zealand

Toxicological tests on the present status of resistance to acaricides in six strains of the two‐spotted spider mite (Tetranychus urticae Koch) in New Zealand are reported. Resistance to parathion appears widespread; cross‐resistance to formetanate is developed. Resistance to Plictran has not developed, and there is no indication of high levels of Kelthane resistance. The levels of genetic incompatibility operating between the strains are also investigated. The causes of such incompatibilities and their possible exploitation in integrated control programmes are discussed.     

The nature of natural: defining natural character for the New?Zealand context

New?Zealand has a long-standing statutory policy goal to preserve the natural character of the coastal environment and various freshwater environments and their margins. In the absence of an authoritative definition, it has not been possible to develop a method to measure natural character and its change, nor the outcomes of the long-standing national policy goal. Here we develop a definition of natural character that is relevant and useful in the New?Zealand environmental, cultural and legal/policy context. Literature-derived interpretations of natural character and equivalent concepts are evaluated as to their potential suitability for developing a biophysical definition of natural character. Using a set of carefully designed criteria a subset of interpretations are condensed into a definition of natural character. The application of this definition is qualified following consideration of the literature addressing human perception and experiences of natural character. Appropriate reference conditions and baselines for evaluating natural character in different contexts are discussed.     

Do New Zealand invertebrates reflect the dominance of birds in their evolutionary history?

Pre-human New Zealand had some unusual feeding guilds of birds (e.g. the herbivorous moa fauna), thought to have developed as a result of the absence of a ?normal? mammal fauna. Insectivorous birds, on the other hand, are an integral part of all the world?s ecosystems, regardless of the presence or absence of mammals. While it is acknowledged the overall predation impact from birds in New Zealand is unlikely to have differed greatly from elsewhere, the low impact of mammalian insectivores (apart from microbats), coupled with the presence of a specialised avian feeding guild that concentrated on ground-active prey, might have exerted certain unique selection pressures. Do New Zealand invertebrates reflect this? It would be necessary to compare the New Zealand invertebrate fauna with that of mammal-dominated lands in greater detail than is available today before we could assert whether any unique anti-predator characteristics have evolved. Knowledge of the insects that succumbed to extinction when mammals invaded New Zealand should provide clues to avian-adapted features that might have rendered them particularly vulnerable to introduced rodents. Predation by kiwi (Apteryx spp.), an extraordinarily mammal-like nocturnal bird, may to some extent have prepared the invertebrate fauna for the arrival of small mammals.     

New Population and Life Expectancy Estimates for the Indigenous Population of Australia's Northern Territory, 1966–2011

Background

The Indigenous population of Australia suffers considerable disadvantage across a wide range of socio-economic indicators, and is therefore the focus of many policy initiatives attempting to ‘close the gap’ between Indigenous and non-Indigenous Australians. Unfortunately, past population estimates have proved unreliable as denominators for these indicators. The aim of the paper is to contribute more robust estimates for the Northern Territory Indigenous population for the period 1966–2011, and hence estimate one of the most important of socio-economic indicators, life expectancy at birth.

Method

A consistent time series of population estimates from 1966 to 2011, based off the more reliable 2011 official population estimates, was created by a mix of reverse and forward cohort survival. Adjustments were made to ensure sensible sex ratios and consistency with recent birth registrations. Standard life table methods were employed to estimate life expectancy. Drawing on an approach from probabilistic forecasting, confidence intervals surrounding population numbers and life expectancies were estimated.

Results

The Northern Territory Indigenous population in 1966 numbered between 23,800 and 26,100, compared to between 66,100 and 73,200 in 2011. In 1966–71 Indigenous life expectancy at birth lay between 49.1 and 56.9 years for males and between 49.7 and 57.9 years for females, whilst by 2006–11 it had increased to between 60.5 and 66.2 years for males and between 65.4 and 70.8 for females. Over the last 40 years the gap with all-Australian life expectancy has not narrowed, fluctuating at about 17 years for both males and females. Whilst considerable progress has been made in closing the gap in under-five mortality, at most other ages the mortality rate differential has increased.

Conclusions

A huge public health challenge remains. Efforts need to be redoubled to reduce the large gap in life expectancy between Indigenous and non-Indigenous Australians.     

Legacy of avian-dominated plant?herbivore systems in New Zealand

Avian herbivores dominated New Zealand?s pre-settlement terrestrial ecosystems to an unparalleled extent, in the absence of a terrestrial mammal fauna. Approximately 50% (88 taxa) of terrestrial bird species consumed plant foliage, shoots, buds and flowers to some degree, but fewer than half these species were major herbivores. Moa (Dinornithiformes) represent the greatest autochthonous radiation of avian herbivores in New Zealand. They were the largest browsers and grazers within both forest and scrubland ecosystems. Diverse waterfowl (Anatidae) and rail (Rallidae) faunas occupied forests, wetlands and grasslands. Parrots (Psittacidae) and wattlebirds (Callaeidae) occupied a range of woody vegetation types, feeding on fruits/seeds and foliage/ fruits/nectar, respectively. Other important herbivores were the kereru (Columbidae), stitchbird (Notiomystidae) and two honeyeaters (Meliphagidae). Cryptic colouration, nocturnal foraging and fossil evidence suggest that avian populations were strongly constrained by predation. With the absence of migratory avian herbivores, plant structural, constitutive defences prevailed, with the unusual ?wire syndrome? representing an adaptation to limit plant offtake by major terrestrial avian browsers. Inducible plant defences are rare, perhaps reflecting longstanding nutrient-limitations in New Zealand ecosystems. Evidence from coprolites suggests moa were important dispersers of now rare, annual, disturbance-tolerant herb species, and their grazing may have maintained diverse prostrate herbs in different vegetation types. The impact of moa on forest structure and composition remains speculative, but many broadleaved woody species would likely have experienced markedly reduced niches in pre-settlement time. Several distinctive avian-mediated vegetation types are proposed: dryland woodlands, diverse turf swards, coastal herb-rich low-forest-scrubland, and conifer-rich forests. Since human settlement (c. 750 yrs ago), c. 50% of endemic avian herbivore species or c. 40% overall have become extinct, including all moa, 60% of waterfowl and 33% of rail species. Numerically, avian herbivore introductions (c. 24 taxa) since European settlement have compensated for extinctions (c. 27 taxa), but the naturalised birds are mostly small, seed-eating species restricted to human-modified landscapes. Several naturalised species (e.g. Canada goose, Branta canadensis; brown quail, Coturnix ypsilophorus) may provide modes and levels of herbivory comparable with extinct species. The original avian and current introduced mammal herbivore regimes were separated by several centuries when New Zealand lacked megaherbivores. This ?herbivory hiatus? complicates comparisons between pre-settlement and current herbivore systems in New Zealand. However, predation, animal mobility, feeding mode, nutrient transfer patterns and soil impacts were different under an avian regime compared with current mammalian herbivore systems. Levels of ecological surrogacy between avifauna and introduced mammals are less evident. Ungulates generally appear to have impacts qualitatively different from those of the extinct moa. Because of New Zealand?s peculiar evolutionary history, avian herbivores will generally favour the persistence of indigenous vegetation, while mammalian herbivores continue to induce population declines of select plant species, change vegetation regeneration patterns, and generally favour the spread and consolidation of introduced plant species with which they share an evolutionary history.     

Ground Beetles (Coleoptera, Carabidae) in Forest Fragments of the Manawatu, New Zealand: Collapsed Assemblages?

Botanically diverse and well-maintained, protected forest fragments in the Manawatu area of the North Island of New Zealand contained very species-poor carabid assemblages. In a nearby large forest tract, the potential source area, nine species were caught in pitfall traps, while the largest forest remnant had two species, and a well-managed suburban forest patch had three species but only one with a potentially reproducing population. Lack of grazing and high botanical diversity was insufficient to maintain the potential carabid assemblage in these fragments. Predation risk and a low dispersal power in endemic New Zealand ground beetles, combined with fragment size and degree of isolation could contribute to this collapse. Active management of ground-active invertebrate species seems necessary to protect them in isolated forest fragments in New Zealand.     

Recruitment of Anguilla spp. glass eels in the Waikato River,New Zealand. Evidence of declining migrations?

The timing of Anguilla spp. glass eel recruitment into the Waikato River, North Island, New Zealand, was studied over a 2 year period (2004–2005). While glass eels of both the shortfin eel Anguilla australis and the endemic longfin eel Anguilla dieffenbachii were caught, the former comprised >97% of the species composition. There was a positive correlation of glass eel migrations with spring tides, with peak migration periods typically occurring within a few hours of the peak of high tide, and between 2 and 4 days after the day of spring tide. Both water temperature and discharge had significant inverse relationships with glass eel catches, with temperature explaining >30% of the variance in catch periodicity. Comparison of catch data 30 years apart showed that main migration periods appear to occur several weeks earlier today than previously. Reduced catch per unit effort and duration of runs from recent years' sampling (compared with the 1970s) indicate that a reduction in recruitment may also have occurred during this period, something recorded in other temperate species of Anguilla .     

Historical and ecological context, pattern and process, in the derivation of New Zealand?s freshwater fish fauna

This paper explores distribution patterns exhibited by New Zealand?s freshwater fish fauna, both fossil and extant, and seeks to clarify processes that have generated these patterns. Knowledge of a Miocene New Zealand terrestrial/freshwater fossil fauna is based substantially on lacustrine deposits in Central Otago. It reflects an ecologically very different fauna from that known today. Nothing is known of the Miocene fluvial fauna. Present-day patterns of distribution and diversity reflect a deep ecological dichotomy. About half the fauna is diadromous, and the habit of these species, of moving to and from the sea, provides them with great resilience in the face of major known landscape perturbations resulting from orogeny and land submergence, glaciation and volcanism. The diadromous species tend to be widespread throughout New Zealand. In contrast, non-diadromous species are more strictly confined to freshwater habitats, and a major means of spread relates to changes in directions and connections of stream flows. As a result, species are much less resilient, they exhibit complex patterns of sympatry, and their ranges are much more localised. Despite all elements in the fauna living across the same landscape in space and time, distribution patterns of the varying species groups display great differences in pattern.     

Abstracts of papers presented at the 12th Biennial Conference of the Society for Research on Amphibians and Reptiles in New Zealand,University of Otago,Dunedin, New Zealand, 9–11 February 2007

Abstract

This study of customary harvests of sooty shearwater Puffinus griseus chicks by Rakiura Maori compares the utility of Traditional Ecological Knowledge (TEK) and ecological science for understanding patterns in prey availability. We recorded TEK of 28 muttonbirders about emergence patterns and variation in chick size at different aspects of 14 breeding islands and in their coastal fringe compared to inland areas. Spatial and temporal variation of chick availability were measured using the methods of ecological science in the 2001 harvest season across Putauhinu Island, south west of Rakiura, New Zealand. As predicted by TEK, titi emerged earlier from west than east coast locations on Putauhinu. Scientific measures were also consistent with an earlier emergence in coastal compared to inland areas as asserted by TEK, but conclusive inference is potentially confounded by movement of chicks between burrows just before fledging. A TEK construct predicting heavier chicks on the west coast was not supported by scientific measurements. We also measured the characteristics of areas preferred for harvesting so that we could gauge representativeness of the areas “sampled” by the muttonbirders to accumulate their TEK. Within forested habitat, areas harvested by muttonbirders had 62–65% higher chick density than unharvested areas. The muttonbirders concentrated harvesting where there was less ground cover and taller canopy cover and only hunted on nights and times of the season when harvesting was most profitable. Therefore, TEK may be less able to detect wider‐scale variation and harvest impacts on prey in particular. Short runs of scientific information from spatially and temporally stratified sampling will complement and assist inference from longer term TEK. As shown in this case study, TEK and science often agree on pattern, but are likely to disagree on why a pattern exists.     

Three new species of the genus Philopteroides Mey, 2004 (Phthiraptera,Ischnocera, Philopteridae) from?New?Zealand

We describe and illustrate three new species of chewing lice in the genus Philopteroides parasitic on passerines (Order Passeriformes, families Acanthizidae, Rhipiduridae and Petroicidae) from New Zealand. They are: Philopteroides pilgrimisp. n. from Gerygone igata igata; Philopteroides fuliginosussp. n. from Rhipidura fuliginosa placabilis and Rhipidura fuliginosa fuliginosa; and Philopteroides macrocephalussp. n. from Petroica macrocephala macrocephala and Petroica macrocephala dannefaerdi. The identity of Docophorus lineatus Giebel, 1874 is discussed based on its morphology and host association. We also transfer Tyranniphilopterus beckeri to the genus Philopteroides, and provide a key to identify adults of 12 of the 13 species now included in Philopteroides.     

Travelling seeds? Examples from New Zealand

New Zealand is an archipelago isolated in time and space. Flowering plants have evolved in the almost-complete absence of terrestrial mammals, some of the most prolific seed-dispersers from the rest of the world, and fascinating mechanisms for spreading seeds have developed.