Trudi Webster - Academia.edu (original) (raw)

Papers by Trudi Webster

Yellow-eyed penguins (Megadyptes antipodes), or hoiho in te reo Māori, are predicted to become ex... more Yellow-eyed penguins (Megadyptes antipodes), or hoiho in te reo Māori, are predicted to become extinct on mainland Aotearoa New Zealand in the next few decades, with infectious disease a significant contributor to their decline. A recent disease phenomenon termed respiratory distress syndrome (RDS) causing lung pathology has been identified in very young chicks. To date, no causative pathogens for RDS have been identified. In 2020 and 2021, the number of chick deaths from suspected RDS increased four- and five-fold, respectively, with a mortality rate of >90%. Here, we aimed to identify possible pathogens responsible for RDS disease impacting yellow-eyed penguins. Total RNA was extracted from tissue samples collected during post-mortem of 43 chicks and subject to metatranscriptomic sequencing. From these data we identified a novel and highly abundant gyrovirus in 80% of tissue samples. This virus exhibited only 41% amino acid identity within VP1 to its closest relative, Gyrovirus...

Aquatic Conservation: Marine and Freshwater Ecosystems

The number of automatically detected upcalls per recording vs the number of upcalls detected by t... more The number of automatically detected upcalls per recording vs the number of upcalls detected by the analyst has been displayed in a figure. Points required jittering by 0.6 to offset and reveal overlapping points

A Zero Inflated Model with a negative binomial distribution was used to evaluate whether particul... more A Zero Inflated Model with a negative binomial distribution was used to evaluate whether particular seasons and/or diel periods were important for explaining differences in right whale call presence and call rate. This script runs the ZIM and conducts a log-likelihood ratio test to determine whether a poisson or negative binomial distribution best fitted the count data

This spreadsheet contains data on the performance of the automated detector (the eXtensible BioAc... more This spreadsheet contains data on the performance of the automated detector (the eXtensible BioAcoustic Tool (XBAT) written in MATLAB) which was developed for upcall vocalisations produced by North Atlantic right whales. Manual and automated detections were compared to test the effectiveness and sensitivity of the algorithm for detecting SRW upcalls. We randomly selected 10% of the total number of recordings for verification analysis and annotated the detection events as either true or false based on the manual classification. Two measures of detector performance were applied: Positive Predictive Value (PPV) which represents the percentage of the upcalls logged by the detector that were judged by the human analyst to have been correctly assigned, and True Positive Rate (TPR) which represents the percentage of upcalls detected by the analyst also logged by the detector

This spreadsheet contains data on the presence of right whale vocalisations for all of the record... more This spreadsheet contains data on the presence of right whale vocalisations for all of the recordings from the DSG recorder. Subsequent tabs in the spreadsheet contain the analysis of calls by season, month, per day, diel period and hour and call typ

Autonomous recorders are frequently utilised for examining vocal behaviour of animals, and are pa... more Autonomous recorders are frequently utilised for examining vocal behaviour of animals, and are particularly effective in remote habitats. Southern right whales are known to have an extensive acoustic repertoire. A recorder was moored at the isolated sub-Antarctic Auckland Islands for a year to examine whether the acoustic behaviour of southern right whales differed seasonally and throughout the day at their main calving ground in New Zealand. Recordings were made in each month except June, and vocalisations were audible in all months with recordings except January. A total of 35,487 calls were detected, of which upcalls were the most common (11,623). Call rate peaked in August (288±5.9 [SE] calls/hour) and July (194±8.3). Vocal behaviour varied diurnally with highest call rates detected at dusk and night, consistent with the concept that upcalls function primarily as contact calls. Zero-inflated model results confirmed that seasonal variation was the most important factor for explaining differences in vocal behaviour. An automated detector designed to expedite the analysis process for North Atlantic right whales correctly identified 80% of upcalls, although false detections were frequent, particularly when call rates were low. This study is the first to attempt year-round monitoring of southern right whale presence in New Zealand

Autonomous recorders are frequently used for examining vocal behaviour of animals, and are partic... more Autonomous recorders are frequently used for examining vocal behaviour of animals, and are particularly effective in remote habitats. Southern right whales are known to have an extensive acoustic repertoire. A recorder was moored at the isolated sub-Antarctic Auckland Islands for a year to examine whether the acoustic behaviour of southern right whales differed seasonally and throughout the day at their main calving ground in New Zealand. Recordings were made in each month except June, and vocalizations were audible in all months with recordings except January. A total of 35 487 calls were detected, of which upcalls were the most common (11 623). Call rate peaked in August (288 ± 5.9 [s.e.] calls/hour) and July (194 ± 8.3). Vocal behaviour varied diurnally with highest call rates detected at dusk and night, consistent with the concept that upcalls function primarily as contact calls. Zero-inflated model results confirmed that seasonal variation was the most important factor for explaining differences in vocal behaviour. An automated detector designed to expedite the analysis process for North Atlantic right whales correctly identified 80% of upcalls, although false detections were frequent, particularly when call rates were low. This study is the first to attempt year-round monitoring of southern right whale presence in New Zealand.

iii Acknowledgements v Table of contents viii List of tables x List of figures xi List of abbrevi... more iii Acknowledgements v Table of contents viii List of tables x List of figures xi List of abbreviations xiv CHAPTER 1 GENERAL INTRODUCTION 16 1.1 Vocal communication 16 1.2 Sound in the marine environment 17 1.3 The impact of sound 18 1.4 Right whales 19 1.5 Southern right whales in New Zealand 21 1.6 Sounds made by right whales 25 1.7 Thesis overview 26 CHAPTER 2 QUANTITATIVE ANALYSIS OF THE ACOUSTIC REPERTOIRE OF SOUTHERN RIGHT WHALES 29 2.

Royal Society Open Science, 2019

Autonomous recorders are frequently used for examining vocal behaviour of animals, and are partic... more Autonomous recorders are frequently used for examining vocal behaviour of animals, and are particularly effective in remote habitats. Southern right whales are known to have an extensive acoustic repertoire. A recorder was moored at the isolated sub-Antarctic Auckland Islands for a year to examine whether the acoustic behaviour of southern right whales differed seasonally and throughout the day at their main calving ground in New Zealand. Recordings were made in each month except June, and vocalizations were audible in all months with recordings except January. A total of 35 487 calls were detected, of which upcalls were the most common (11 623). Call rate peaked in August (288 ± 5.9 [s.e.] calls/hour) and July (194 ± 8.3). Vocal behaviour varied diurnally with highest call rates detected at dusk and night, consistent with the concept that upcalls function primarily as contact calls. Zero-inflated model results confirmed that seasonal variation was the most important factor for expl...

Marine Biology, 2017

Passive acoustic detectors are widely used for monitoring distribution of cetaceans. Autonomous v... more Passive acoustic detectors are widely used for monitoring distribution of cetaceans. Autonomous visual methods are less frequently employed; they are limited to detections during daylight and good weather, but offer potential advantages due to certainty of species' identification and longevity of deployment. To compare performance of acoustic and visual methods, temporal changes in distribution of southern right whales, Eubalaena australis, were monitored in the remote sub-Antarctic Auckland Islands (50°31′S, 166°16′E). A time-lapse camera was deployed for 2 years from August 2010, taking an image every 70 min. The presence of whales was scored for each image taken during daylight (n = 8295). A passive acoustic recorder was deployed in August 2011, recording for 3.75 min every hour until battery life expired after 10 months. Each recording (n = 6978) was aurally reviewed. Both methods revealed a similar seasonal distribution; maximum detection rates were in the austral winter and no whales were detected in January or February. However, at the peak of right whale occurrence, the proportion of samples with whales detected was much higher for the acoustic recorder (93.9% in August) than the time-lapse camera (14.8%). A generalised additive model fitted to the visual data revealed significant effects of sea state and visibility. Acoustic detection rates were higher, probably because detection range is greater, and less affected by weather. The solar-powered time-lapse camera system, however, functioned effectively for much longer. We discuss the relative merits of visual and acoustic detectors and attempt to draw conclusions about their efficacy for different focal species and monitoring locations.

The Journal of the Acoustical Society of America, 2018

Marine Mammal Science, 2018

New Zealand Journal of Marine and Freshwater Research, 2017

ABSTRACT Southern right whales (Eubalaena australis) were widespread in New Zealand waters before... more ABSTRACT Southern right whales (Eubalaena australis) were widespread in New Zealand waters before commercial whaling in the nineteenth century caused drastic declines in their abundance and distribution. Following the cessation of whaling, the population has been recovering and is now slowly recolonising its former range. Estimates of population demographics, including reproductive output, are essential for predicting the trajectory of this population. We gathered photo-identification data on female southern right whales during annual field trips to the Auckland Islands, the principal calving area in New Zealand waters. Forty-five calving intervals were observed between 2006 and 2013 (mean interval = 3.31 years, 95% CI = 3.06–3.57). Incorporating the effects of possible missed calving events produced a plausible range of mean calving intervals from 3.17 to 3.31 years. Our results suggest that the calving interval of New Zealand southern right whales is similar to that found in populations elsewhere.

New Zealand Journal of Marine and Freshwater Research, 2016

A central question to any understanding of ecology is how animals use their habitat, and how habi... more A central question to any understanding of ecology is how animals use their habitat, and how habitat use is influenced by temporally changing features of the environment. Previous research on Hector's dolphins at Akaroa Harbour, New Zealand suggested that dolphins leave inshore, harbour environments during or after rough weather. To test this hypothesis, visual sightings (2000-2012) and acoustic detections (2007-2008) of Hector's dolphins in Akaroa Harbour were modelled to test for a relationship with swell height and swell direction. Sighting rates and acoustic detection rates in Akaroa Harbour were significantly lower on days after big swell events and in some linear models after swell events from the south. These results indicate that swell events influence Hector's dolphin movements in and around Akaroa Harbour. Possible reasons for this behaviour are diverse and need further investigation. However, this information can be used both to predict daily dolphin movement for conservation and research purposes, and to suggest how dolphins may react in future if extreme weather events are becoming frequent.

The Journal of the Acoustical Society of America, 2016

Quantitatively describing the acoustic repertoire of a species is important for establishing effe... more Quantitatively describing the acoustic repertoire of a species is important for establishing effective passive acoustic monitoring programs and developing automated call detectors. This process is particularly important when the study site is remote and visual surveys are not cost effective. Little is known about the vocal behavior of southern right whales (Eubalaena australis) in New Zealand. The aim of this study was to describe and quantify their entire vocal repertoire on calving grounds in the sub-Antarctic Auckland Islands. Over three austral winters (2010-2012), 4349 calls were recorded, measured, and classified into 10 call types. The most frequently observed types were pulsive, upcall, and tonal low vocalizations. A long tonal low call (15.5 s duration) and a very high call (peak frequency $750 Hz) were described for the first time. Random Forest multivariate analysis of 28 measured variables was used to classify calls with a high degree of accuracy (82%). The most important variables for classification were maximum ceiling frequency, number of inflection points, duration, and the difference between the start and end frequency. This classification system proved to be a repeatable, fast, and objective method for categorising right whale calls and shows promise for other vocal taxa. V

The Southern right whale (SRW) was hunted to near extinction and is endangered. The Auckland Isla... more The Southern right whale (SRW) was hunted to near extinction and is endangered. The Auckland Islands (AI) are the stronghold for SRWs in New Zealand waters, and are likely their primary calving/breeding grounds. Although well studied in some right whale populations, acoustic behaviour of SRWs has received little attention in Australasia. This research aims to provide a quantitative analysis of vocal repertoire, quantify associations between vocalisations and behaviour, analyse temporal variation in calls and measure background noise. A successful pilot study was conducted as part of a winter 2010 AI expedition. Acoustic recordings were made on a custom-built hydrophone array to localise sounds and a calibrated Sonatech hydrophone to allow precise measurement of sound levels. A pinger deployed during recordings provided a reference sound source. In total, 24 recordings were made comprising 20+ hours of SRW vocalisation and environmental noise data. Initial analysis showed that SRWs a...

Quantifying age structure of a population is important for modelling its growth and understanding... more Quantifying age structure of a population is important for modelling its growth and understanding its biology. While estimating age is possible from dead dolphins, it is difficult from live ones without resorting to tooth extraction procedures. This research investigates the viability of a new, non-invasive method for measuring Hector’s dolphins at sea. The system comprises a digital camera with two parallel laser pointers mounted 10cm apart, and secured to the tripod mount. An identification photograph of a dolphin’s dorsal fin is taken with the laser dots projected onto it. Graphics software is then used to calibrate the image using the known distance between the dots. Fin dimensions can then be obtained from the digital image. Collated autopsy data (n=194) of measured and aged dolphins are used to plot growth curves and then estimate total length and age from the dorsal fin photographs. There are several photogrammetric errors; horizontal axis error (subject not perpendicular to ...

Aquatic Conservation: Marine and Freshwater Ecosystems

Royal Society Open Science, 2019

Autonomous recorders are frequently used for examining vocal behaviour of animals, and are partic... more Autonomous recorders are frequently used for examining vocal behaviour of animals, and are particularly effective in remote habitats. Southern right whales are known to have an extensive acoustic repertoire. A recorder was moored at the isolated sub-Antarctic Auckland Islands for a year to examine whether the acoustic behaviour of southern right whales differed seasonally and throughout the day at their main calving ground in New Zealand. Recordings were made in each month except June, and vocalizations were audible in all months with recordings except January. A total of 35 487 calls were detected, of which upcalls were the most common (11 623). Call rate peaked in August (288 ± 5.9 [s.e.] calls/hour) and July (194 ± 8.3). Vocal behaviour varied diurnally with highest call rates detected at dusk and night, consistent with the concept that upcalls function primarily as contact calls. Zero-inflated model results confirmed that seasonal variation was the most important factor for expl...

Marine Biology, 2017

The Journal of the Acoustical Society of America, 2018

Marine Mammal Science, 2018

New Zealand Journal of Marine and Freshwater Research, 2017

New Zealand Journal of Marine and Freshwater Research, 2016

The Journal of the Acoustical Society of America, 2016