Dispersal of breeding, adult male Phocarctos hookeri: Implications for disease transmission, population management and species recovery

Dispersal impacts on a range of population parameters making it a key piece of information in species conservation. Despite its importance, dispersal is poorly characterized for many species: pinnipeds are no exception. Understanding dispersal patterns of the New Zealand sea lion Phocarctos hookeri is crucial in the conservation management of the species as its recovery to a non-threatened status hinges on range recolonisation. In this study, we examined the movements of breeding adult male New Zealand sea lions within and following the breeding season of the 2002/03 austral summer using a novel multi colony approach. Based on resightings of 202 individually identifiable adult males, we found (1) a previously unappreciated, high level of dispersal by adult territorial males between breeding colonies during the pupping period and (2) that breeding males disperse to the extremes of the species’ range at the end of female oestrous. Our findings are contrary to the current paradigm of otariid breeding behaviour, which is believed to consist of prolonged, uninterrupted male territoriality based on intense male-male competition and sustained fasting. Adult male dispersal between colonies and across the species range has important implications for adult males as vectors of disease in three recent epizootics, species management and species recovery via recolonisation as males are apparently remaining part of a localized, vulnerable breeding population.     

Predation by New Zealand sea lions (Phocarctos hookeri) as a threat to the viability of yellow-eyed penguins (Megadyptes antipodes) at Otago Peninsula, New Zealand

This study presented evidence that creates a quandary for conservation management: predation by one threatened species, New Zealand sea lion (Phocarctos hookeri), threatens the viability of another threatened species, yellow-eyed penguin (Megadyptes antipodes), at Otago Peninsula, South Island, New Zealand. Otago Peninsula holds the largest population of yellow-eyed penguins on South Island and the only breeding population of New Zealand sea lions on the New Zealand mainland. New Zealand sea lions here represent the vanguard of re-colonisation within their prehistoric range, with nine females and 50-70 males resident in 2005. The initial indication of a potential problem was an attack on a yellow-eyed penguin by a New Zealand sea lion witnessed in 1996. The majority of 20 records for attacks were at two neighbouring sites, where they coincided with decreases in penguin nest numbers and adult annual survival. In contrast, penguin nest numbers increased at a third site, the main base for male sea lions at Otago Peninsula. Evidence from prey remains indicated that male sea lions did not eat yellow-eyed penguins but that females ate 20-30 annually, with one individual possibly responsible for most kills. Modelling indicated that the penguin population at any one site could not remain viable if it was the sole source of penguins killed. The dilemma is either to do nothing, and risk collapse of the Otago Peninsula population of yellow-eyed penguins, or to take action against known culprits, and risk failure in re-colonisation of the New Zealand mainland by New Zealand sea lions.     

Predictive modelling and ground validation of the spatial distribution of the New Zealand long-tailed bat (Chalinolobus tuberculatus)

The use of predictive models is continually increasing, but few models are subsequently field-checked and evaluated. This study evaluates the statistical strength and usefulness for conservation purposes of a predictive habitat use model developed for Chalinolobus tuberculatus, a threatened microchiropteran bat species found in the temperate rainforests of New Zealand. The relationship between various environmental variables and the presence/absence of the species was investigated using generalised linear modelling. The model developed was coupled with GIS data to develop maps of predicted occurrence within the West Coast region of New Zealand’s South Island. It was found that distance to forest boundary, slope, presence of Nothofagus, general land cover, variability in mean annual solar radiation, and mean ambient winter minimum temperature were significantly associated with the occurrence of the species. Evaluation of the statistical strength of the distribution model with independent data of species’ occurrence collected at 152 sites found that the C. tuberculatus model showed a moderate ability to predict both species presence and absence (τ(b) coefficient = 0.37). The field detection rate (0.45) using this model was significantly higher than that of historical surveys (0.12). The value of the species habitat model and the need to evaluate its utility in the development of conservation strategies is discussed.     

Estimating the rate of quasi-extinction of the Australian grey nurse shark (Carcharias taurus) population using deterministic age- and stage-classified models

Grey nurse sharks off the east coast of Australia are listed nationally as “critically endangered” under Schedule 1 of the Environmental Protection and Biodiversity Conservation Act (1999) and may number no more than 300 in New South Wales and southern Queensland waters. They are an inshore, coastal dwelling species and were severely depleted by spearfishing in the 1960s. The population has continued to decline despite protection since 1984. Their life history (long-lived to 25+ years), late maturation (6-8 years), low fecundity (maximum 2 live young biennially), specific habitat requirements, limited inshore distribution, and small population size render them particularly vulnerable to extinction. We estimated the time to quasi-extinction (years elapsed for the population to consist of ?50 females) for the grey nurse shark population off the east coast of Australia based on current estimates of abundance and known anthropogenic rates of mortality. Estimated minimum population size was 300 as of 2002, and minimum anthropogenic mortality assessed from recovered carcasses was 12/year of which 75% were females. We modelled time to quasi-extinction using deterministic age- and stage-classified models for worst-, likely and best-case scenarios. Population size was estimated at 300 (worst), 1000 (likely) and 3000 (best). Anthropogenic mortality was added to the model assuming either all carcasses are being recovered (best), or conservatively, that only 50% are reported (realistic). Depending on model structure, if all carcasses are being reported, quasi-extinction times for worst-, likely and best-case scenarios range from 13 to 16 years, 84-98 years and 289-324 years, respectively. If under-reporting is occurring, time to quasi-extinction ranges from 6 to 8 years, 45-53 years and 173-200 years, respectively. In all scenarios modelled the grey nurse shark population will decline if no further steps are taken to remove anthropogenic sources of mortality. Because estimates of quasi-extinction rate depend on initial population size, and sensitivity analysis revealed that population rate of change was most sensitive to changes in the survival probability of the smallest length classes, obtaining precise estimates of abundance and annual survival of young females is critical.     

Comparing population growth rates using weighted bootstrapping: Guiding the conservation management of Petrogale xanthopus xanthopus (yellow-footed rock-wallaby)

In this study we compare estimates of the long-term mean stochastic population growth rates, E[r] for Petrogale xanthopus xanthopus (yellow-footed rock-wallaby), a threatened Australian species. In fluctuating environments such as semi-arid areas, herbivore populations respond directly to changes in the biomass of food resources. Biomass is generally correlated with rainfall, so it is often useful to model annual population growth rates of herbivores directly with rainfall. Models of this nature are referred to as numerical response models. The factors that are thought to threaten this species include competition from introduced herbivores and predation from foxes. Annual aerial survey data collected from 1997 to 2004 over approximately 600 km of transect line were analyzed in seven zones within South Australia. Using the Ivlev numerical response model, the annual population growth rates were found to correlate best with the rain that fell in the seven-month period immediately prior to the surveys. Not surprisingly, positive growth rates were found to be associated with higher rainfalls in this period, while negative growth rates were associated with lower rainfalls. We also used weighted bootstrapping to calculate confidence intervals around our estimates of long-term mean stochastic population growth rates, E[r]. The findings suggest that the estimates of E[r] are positive in areas where there is fox and herbivore management. However, we found no evidence that this species will decline in the absence of these treatments.     

Factors influencing survival and long-term population viability of New Zealand long-tailed bats (Chalinolobus tuberculatus): Implications for conservation

A population viability analysis is important for the management of endangered populations and requires the estimation of survival parameters. The long-tailed bat (Chalinolobus tuberculatus) is one of only two native terrestrial mammals currently found in New Zealand and is classed as vulnerable. Its viability in temperate beech (Nothofagus) forest, Eglinton Valley, Fiordland, New Zealand was estimated using mark-recapture data collected between 1993 and 2003 using the Program MARK. Survival was estimated based on a total of 5286 captures representing 1026 individuals. Overall annual survival varied between 0.34 and 0.83 but varied significantly among three sub-populations and with sex and age. Females generally had a higher survival rate compared to males; and adults had higher survival relative to juveniles. Survival of all bats was lower in years when the number of introduced mammalian predators was high and when the winter temperature was warmer than average. High numbers of introduced predators occurred during three of the 10 years in the study. Climate change may mean that the conditions that promote high predator numbers may occur more frequently. A preliminary population viability analysis using a projection matrix on the overall adult female population showed an average 5% decline per year (λ = 0.95). Increased predator control targeting a range of predators is required in years when their numbers are high in order to halt the decline of this population of long-tailed bats. Population estimates using minimum number alive estimates supported the population estimates derived from Program MARK and a population viability analysis using matrices.     

Relationship between population size and genetic diversity in endangered populations of the European bullhead (Cottus gobio): implications for conservation

This study investigated the relationship between the current size of endangered bullhead (Cottus gobio) populations and microsatellite genetic variability. Additionally, the microsatellite data were used to evaluate whether a genetic test for population bottlenecks was able to provide evidence of recent severe population declines. Finally, our results were used to develop conservation priorities and measures. Population size appears to be a crucial parameter in determining the amount of genetic diversity that can be preserved in bullheads, since a significant positive correlation was observed between both variables. Furthermore, in some populations we were able to detect genetic signatures of the documented decline in population size. We suggest that the most immediate goal for bullhead conservation should be to increase the size and the range of the populations, and in doing so minimise or even reverse further genetic erosion. Potential management actions like habitat quality improvement, reduction of river fragmentation and supplementation programmes (translocation, supportive breeding) are discussed.     

HeathMod: a model of the impact of seasonal grazing by sheep on upland heaths dominated by Calluna vulgaris (heather)

The dwarf shrub heather Calluna vulgaris is an important component of the UK landscape, with value for amenity, nature conservation and animal production. A model, called “HeathMod”, is described, which investigates the impact of grazing on upland heather. It combines an empirical model of production with a simple process-based model of grazing impacts. Validation from short-term studies in the literature indicated that the model predicts grazing impacts well, although more studies of grazing impacts are required to confirm the model’s accuracy. Analysis of the model allowed derivation of a simple general formula for predicting sustainable levels of grazing, given knowledge of local site productivity. Predicted levels of sustainable grazing were lower than previous estimates, mainly because the model predicts the long-term impacts of sustained grazing. Application of the model is most appropriate in areas where heather is in mixed-age stands, because there is inadequate information available to model interactions between grazing and degeneration in even-aged stands of heather.     

Partitioning of molecular variation at local spatial scales in the vulnerable neotropical freshwater turtle, Hydromedusa maximiliani (Testudines, Chelidae): implications for the conservation of aquatic organisms in natural hierarchical systems

Hydromedusa maximiliani is a vulnerable freshwater turtle endemic to mountainous regions of the Atlantic rainforest in southeastern Brazil. Random amplified polymorphic DNA (RAPD) were surveyed with the purpose of assessing the genetic structure and determining the partitioning of molecular variation in H. maximiliani across the natural spatial hierarchical scale of its habitat. The goal of the study was to integrate ecological data with estimates of molecular genetics diversity to develop strategies for the conservation of this freshwater turtle. Specimens were sampled from rivers and streams across three drainages. Nine of the 80 primers used generated 27 scoreable bands of which 10 (37%) were polymorphic and produced 16 RAPD phenotypes. Significant heterogeneity was found in the distribution of RAPD molecular phenotypes across the three drainages. Analysis of molecular variance for molecular phenotypes showed that the heterogeneity had a spatial structure since a significant amount (22%) of the total variance was attributable to variation among rivers and streams. Since the genetic variation of this turtle seems to be structured according to the natural hierarchical system of rivers and streams within drainages, it is suggested that local populations should be considered as separate management units.