William Rayment

Offshore distribution of Hector's dolphins at Banks Peninsula, New Zealand: Is the Banks Peninsula Marine Mammal sanctuary large enough?

Abstract Aerial surveys of Hectors dolphins were carried out to evaluate the effectiveness of the Banks Peninsula Marine Mammal Sanctuary. In summer, the proportion of sightings inside the 4 nautical mile offshore boundary of the sanctuary was 79%. This dropped to just over 35% in winter. These estimates were used in a population viability analysis to determine whether the sanctuary needs to be extended to reduce dolphin bycatch to sustainable levels. We followed the standard procedure for setting limits on marine mammal bycatch in the United States to calculate a bycatch limit of 1.6 or 2.8 dolphins per year (depending on whether the sanctuary population is included). If the offshore boundary was extended to 15 nautical miles, the sanctuary would need to be extended alongshore north and south by more than 30 nautical miles to reduce bycatch to 2.8, or north and south by 60 nautical miles to reduce bycatch to 1.6 dolphins per year.

Distribution of southern right whales on the Auckland Islands calving grounds

Abstract Southern right whales (Eubalaena australis) were virtually extirpated from New Zealand by commercial whaling, but are now recovering. Previous research at the Auckland Islands has suggested that Port Ross, a sheltered embayment at the northern end of the islands, is the primary calving ground for right whales in New Zealand. However, an abundance of potentially suitable calving areas exist outside Port Ross, raising the question of whether the growing population might be expanding its distribution to occupy new or former habitats. To address this we conducted the first systematic line-transect survey of potential right whale calving habitat at the Auckland Islands in winter 2011. High densities of southern right whales were sighted inside Port Ross, including all but one of the 21 mother-calf pairs recorded. The survey confirmed that Port Ross is the principal calving area for southern right whales in the Auckland Islands. This conclusion has implications for the estimation of demographic parameters of right whales in New Zealand, which have thus far relied on data gathered largely in Port Ross, and highlights the importance of protecting this habitat.

Observations of Hector's dolphins (Cephalorhynchus hectori) associating with inshore fishing trawlers at Banks Peninsula, New Zealand

Abstract Fishing activities have the potential to alter the behaviour of cetaceans and pose a threat through bycatch. We present observations concerning the influence of inshore trawling on group size and behaviour of Hectors dolphins (Cephalorhynchus hectori) at Banks Peninsula, New Zealand, made during photo‐ID surveys from 2003 to 2007. Aggregations of dolphins, typically involved in what we assumed to be foraging behaviour, were observed following small inshore trawlers year‐round. Group size was larger for aggregations of dolphins following trawlers (mean ± SE = 22.9 ± 1.3, n = 83) than for non‐trawler groups (3.7 ± 0.2, n = 439), and dolphins were typically in a more “excited” state, frequently exhibiting aerial and sexual behaviours. We suggest that trawlers increase the availability of prey for Hectors dolphins and hence foraging behind trawlers is an energetically favourable activity. However, following trawlers probably also increases the risk of being caught in trawl nets, compounding the threats faced by this endangered species.

Listening to Echolocation Clicks with PODs

Monitoring echolocation using SAMs—static acoustic monitors—such as T-PODs or, more recently, C-PODs—has provided a wealth of information on the fine-scale distribution and activity of dolphins, porpoises and other toothed whales. Effects of marine construction noise on these animals have been identified at much longer ranges than expected. Strong diel, tidal and seasonal patterning of the animals’ habitat use has been found including coastal sites that are regularly used only at night. Arrays of SAMs are now being used for longer term monitoring to assess smaller population trends of lower density populations than could previously be assessed within the limits of economic feasibility. PODs have given insights into the significance of seabed ultrasonic noise from sediment in suspension and diel patterns of activity of benthic organisms, and have also revealed unknown sources of very fast trains of tonal clicks.

Quantitative analysis of the acoustic repertoire of southern right whales in New Zealand

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.

Distribution and abundance of Hector's dolphins off Otago, New Zealand

Abstract Data on the distribution and abundance of Hectors dolphins (Cephalorhynchus hectori) along the Otago coastline, between Taieri Mouth and Ōamaru (approximately 130 km alongshore), were collected in 2010–2011. Alongshore surveys were conducted in small boats, travelling approximately 400 m from shore, at speeds of 10 to 15 knots. Photographic identification was used to establish sighting histories of identifiable individuals, and mark rate (36%, CV=12%, CI=28–45). Hectors dolphins were found in two areas: between Taiaroa Head and Cornish Head; and in the vicinity of Moeraki. Encounter records suggest there is little exchange between these zones. The Huggins closed capture method was used to estimate the number of marked individuals between Taiaroa Head and Cornish Head (approximately 22 km alongshore), and this value was scaled by mark rate to estimate a total population size of 42 individuals (CV=41%, CI=19–92). A closed population Bayesian analysis yielded a similar estimate of 37 individuals (CV=42%, CI=25–75).

Seasonal variation in occurrence of the sevengill shark, Notorynchus cepedianus, in two inshore habitats of southern New Zealand

ABSTRACT Despite being a large, relatively abundant predator, the distribution and seasonal occurrence of the broadnose sevengill shark, Notorynchus cepedianus, in New Zealand is poorly understood. During 71 sampling trips conducted from July 2013 to May 2015, sharks were attracted to coastal sampling sites in southern New Zealand at Ōtākou/Otago Harbour and Te Whaka ā Te Wera/Paterson Inlet, Stewart Island, using chum. Using a logistic regression model, water temperature was identified as a key predictor of encountering sevengill sharks. In addition, location, cloud cover and sea state were also identified as influential predictors. At Ōtākou, a clear seasonal pattern of sevengill shark sightings emerged. Sharks were detected on 86% of survey trips in summer, whilst no sharks were detected in winter or spring. At Te Whaka ā Te Wera, sharks were sighted throughout all seasons, but a decline in shark encounters occurred during winter. This study represents the first systematic data on seasonal habitat use by sevengill sharks in New Zealand.

Estimated calving interval for the New Zealand southern right whale (Eubalaena australis)

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.

A time-based method for defining associations using photo-identification

Photo-identification is an invaluable method for documenting associations. Based on the assumption that individuals photographed close together in time are physically close in space, the metadata associated with digital photography offers an opportunity to base association analyses on time between images. This was tested via analysis of associations within a population of bottlenose dolphins ( Tursiops truncatus ) in Doubtful Sound, New Zealand. We compared the widely used group-membership method and an alternative time-based method. Overall social structures between methods were similar; high degrees of association among all individuals and little support for sub-groups. Results also indicated an increase in the precision of pairwise indices for the time-based method. This study validated the approach of using time as a basis for analyses of associations. Importantly, this method can be retrospectively applied to any photo-ID data set in which images of uniquely identifiable individuals are time-stamped by the camera.

Hector's dolphin movement patterns in response to height and direction of ocean swell

ABSTRACT 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 Hectors 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 Hectors 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 Hectors 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.