Chandra P. Salgado Kent

Topographic determinants of mobile vertebrate predator hotspots: current knowledge and future directions

Despite being identified as a driver of mobile predator aggregations (hotspots) in both marine and terrestrial environments, topographic complexity has long remained a challenging concept for scientists to visualise and a difficult parameter to estimate. It is only with the advent of high‐speed computers and the recent popularisation of geographical information systems (GIS) that terrain attributes have begun to be quantitatively measured in three‐dimensional space and related to wildlife dynamics, making the well‐established field of geomorphometry (or ‘digital terrain modelling’) a discipline of growing appeal to biologists. Although a diverse array of numerical metrics is now available to describe the shape, geometry and physical properties of natural habitats, few of these are known to, or adequately used by, ecologists. In this review, we examine the nature and usage of 56 geomorphometrics extracted from the ecological modelling literature over a period of 32 years (1979–2011). We show that, in studies of mobile predators, numerous topographic variables have largely been overlooked in favour of single basic metrics that do not, on their own, fully capture the complexity of continuous landscapes. Based on a simulation approach, we assess the redundancy and correlation structure of these metrics and demonstrate that a majority are highly collinear. We highlight a suite of 7–8 complementary metrics which best explain topographic patterns across a bathymetric grid of the west Australian seafloor, and contend that field and analytical protocols should prioritise variables of these types, particularly when the responses of predator populations to physical habitat features are of interest. We suggest that prominent structures such as canyons, seamounts or mountain chains can serve as useful proxies for predator hotspots, especially in remote locations where access to high‐resolution biological data is often limited.

Fish choruses off Port Hedland, Western Australia

Abstract Australian waters are home to a number of vocal species of fish. Cataloguing the acoustic characteristics and temporal patterns of choruses and their locations can provide significant information for long-term monitoring of vocal fishes and their ecosystems. In coastal waters off Port Hedland, Western Australia, two seafloor positioned sea-noise loggers, located 21.5 km apart in 8 and 18 m of water, recorded for an 18-month period. Numerous sound sources were detected, including mooring and vessel noise, humpback whale song and a large variety of fish signal types. Seven fish choruses were identified, occurring predominantly between late spring and early autumn (wet season) and displaying energy from 50 Hz to >4 kHz. Many of these choruses exhibited acoustic characteristics similar to choruses previously reported elsewhere, for some of which the source species or families have been identified. Distinct diurnal patterns in the choruses were observed, associated with sunrise or sunset and in some cases, both. While choruses were predominantly recorded on different days, there were at total of 80 days when more than one chorus was present at the same site. Some pairs of choruses present on the same day exhibited various combinations of temporal and frequency partitioning, while others displayed predominant overlap in both spaces.

Reduced Detection of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) in an Inner Harbour Channel During Pile Driving Activities

There is limited information on the impacts of anthropogenic noise on dolphin behaviour, making assessment and mitigation of impacts from anthropogenic noises difficult. As the use of echolocation and other vocalizations are of vital importance for cetaceans, it is important to better understand the potential impact of anthropogenic acoustic disturbance. The small Indo-Pacific bottlenose dolphin (Tursiops aduncus) community that inhabits the Fremantle Inner Harbour regularly travels through an area where impact and vibratory pile driving occurred during wharf upgrading. The overall aim of this study was to measure the noise energy created by pile driving associated with wharf construction activities in the Fremantle Inner Harbour and to determine whether the reduced detection of dolphins within the vicinity of the wharf was associated with pile driving activities. Measuring noise was accomplished with noise loggers and a hand-held digital acoustic recorder, under water, allowing identification of signals produced by impact and vibratory pile drivers and calculating the energy of recorded noise. Dolphin detections in the Inner Harbour were conducted by examination of high-definition video recordings. The association of pile driving and dolphin detections was assessed using Generalized Estimating Equations (GEEs), using observations before and during pile driving. The final model indicated that there was a difference in detections between the two treatments, with more dolphin detections observed when there was no pile driving activity taking place (mean = 0.26 +/- 0.03 SE) than during pile driving (mean = 0.18 +/- 0.04 SE). Knowledge generated by this study on the impact of noise on bottlenose dolphins improves the scientific basis for managing

Behavioral response of Australian humpback whales to seismic surveys.

The first of four major experiments in project behavioural response of australian humpback whales to seismic surveys (BRAHSS) was conducted on the east coast of Australia in September and October 2010. The project aims to understand how humpback whales respond to seismic surveys and to provide the information that will allow these surveys to be conducted efficiently with minimal impact on whales. It also aims to determine how the whales react to ramp up or soft start, and to assess how effective this is in mitigation. The 2010 experiment used a single air gun. Four air guns will be used in the next two experiments and a full seismic array in the final experiment in 2013. During the 2010 experiment, behavior and tracks of whales were recroded by four theodolite stations on elevated coastal positions and DTAGs used on some whales. Vocalizing whales were tracked with a wide base line hydrophone array. A further four acoustic recorders were used to measure propagation loss and to characterize the sound field throughout the area. A wide range of variables likely to affect whale response was measured. [Work sponsored by the JIP E&P Sound & Marine Life and Bureau of Ocean Energy Management, Regulation and Enforcement.]

Whisker spot patterns: a noninvasive method of individual identification of Australian sea lions (Neophoca cinerea)

Reliable methods for identification of individual animals are advantageous for ecological studies of population demographics and movement patterns. Photographic identification, based on distinguishable patterns, unique shapes, or scars, is an effective technique already used for many species. We tested whether photographs of whisker spot patterns could be used to discriminate among individual Australian sea lion (Neophoca cinerea). Based on images of 53 sea lions, we simulated 5,000 patterns before calculating the probability of duplication in a study population. A total of 99% (± 1.5 SD) of patterns were considered reliable for a population of 50, 98% (± 1.7 SD) for 100, 92% (± 4.7 SD) for 500, and 88% (± 5.7 SD) for 1,000. We tested a semiautomatic approach by matching 16 known individuals at 3 different angles (70°, 90°, and 110°), 2 distances (1 and 2 m), and 6 separate times over a 1-year period. A point-pattern matching algorithm for pairwise comparisons produced 90% correct matches of photographs taken on the same day at 90°. Images of individuals at 1 and 2 m resulted in 89% correct matches, those photographed at different angles and different times (at 90°) resulted in 48% and 73% correct matches, respectively. Our results show that the Chamfer distance transform can effectively be used for individual identification, but only if there is very little variation in photograph angle. This point-pattern recognition application may also work for other otariid species.

A lack of correlation between air gun signal pressure waveforms and fish hearing damage

Offshore marine petroleum seismic surveys involve the repetitive use of intense, short bursts of low-frequency noise, the reflections of which are used to image subsea geology. The seismic signal is produced by a spatial array of sources, usually air guns that violently release high-pressure compressed air into the water column. Although the signal produced by a single air gun is largely omnidirectional at low frequencies (typically, most energy over 10–150 Hz), the signal received by a spatial array of individual air guns is highly directional and dependent on the array configuration and receiver orientation.

Underwater recordings of the whistles of bottlenose dolphins in Fremantle Inner Harbour, Western Australia

Dolphins use frequency-modulated whistles for a variety of social functions. Whistles vary in their characteristics according to context, such as activity state, group size, group composition, geographic location, and ambient noise levels. Therefore, comparison of whistle characteristics can be used to address numerous research questions regarding dolphin populations and behaviour. However, logistical and economic constraints on dolphin research have resulted in data collection biases, inconsistent analytical approaches, and knowledge gaps. This Data Descriptor presents an acoustic dataset of bottlenose dolphin (Tursiops aduncus) whistles recorded in the Fremantle Inner Harbour, Western Australia. Data were collected using an autonomous recorder and analysed using a range of acoustic measurements. Acoustic data review identified 336 whistles, which were subsequently measured for six key characteristics using Raven Pro software. Of these, 164 ‘high-quality’ whistles were manually measured to provide an additional five acoustic characteristics. Digital files of individual whistles and corresponding measurements make this dataset available to researchers to address future questions regarding variations within and between dolphin communities.

Spatial and Temporal Variation in the Acoustic Habitat of Bottlenose Dolphins (Tursiops aduncus) within a Highly Urbanized Estuary

There is growing awareness of underwater noise in a variety of marine habitats, and how such noise may adversely affect marine species. This is of particular concern for acoustically-specialised species, such as dolphins. In order to ascertain the potential impacts of anthropogenic noise on these animals, baseline information is required for defining the soundscape of dolphin habitats. The Swan-Canning River system in Western Australia flows through the city of Perth, and experiences numerous anthropogenic activities. Despite this, the river system is home to a community of Indo-Pacific bottlenose dolphins (Tursiops aduncus). To provide a baseline soundscape description of dolphin habitat, over 11,600 h of acoustic data were analysed from five sites within the Swan River (from Fremantle Inner Harbour to 20 km upstream) across an eight-year period. Multiple sound sources were recorded at these sites, including: snapping shrimp; fishes; dolphins; pile-driving; bridge and road traffic; and vessel traffic. The two most prevalent sound sources, vessel traffic and snapping shrimp, likely have very different effects on dolphin communication with the former expected to be more disruptive. Sites were characteristic in their prominent sound sources, showing clear among-site variations, with some sites being ‘noisier’ than others based on broadband noise levels, octave-band noise levels, and power spectrum density percentiles. Perth Waters had the highest broadband noise (10 Hz – 11 kHz; mean 113 dB re 1 µPa rms), whilst Heirisson Island was quietest (mean 105 dB re 1 µPa rms). Generalised estimating equations identified variation in broadband noise levels within sites at a fine temporal scale, although sites differed in the significance of temporal variables. At Mosman Bay, a long-term dataset spanning eight years highlighted inter-annual variation in broadband noise levels, but no overall upwards or downwards trend over time. Acoustic habitats of the Swan River displayed significant variations at a variety of temporal and spatial scales, throughout areas frequented by the local dolphin community. Such variations should be quantified when assessing dolphin acoustic habitat as they may provide significant clues to dolphin behaviour.

Blue whale calling in Australian waters

Calling from the Antarctic true blue whale (Balaenoptera musculus intermedia) and the tropical subspecies (brevicauda, or pygmy blue) have been recorded across southern Australia with the pygmy blue calls also recorded along the Western Australian (WA) coast. The subspecies have a believed common downsweep and markedly different longer, tonal calls. The frequency of most energy in the tonal calls is offset between the subspecies suggesting sound‐space partitioning. The pygmy blue three‐part tonal call is typically 120 s long repeated every 200 s, has several variants, and includes a complex two‐source component. The nature of the pygmy blue call allows counts of instantaneous calling individuals, giving relative abundance. These estimates in the Perth Canyon, a localized seasonal feeding area, show patterns in usage of space and through time within and between seasons, such as the sudden departure of animals at a season end, which varies by approximately 2 weeks between years. Sea noise records along the ...

Effects of vessel traffic and underwater noise on the movement, behaviour and vocalisations of bottlenose dolphins in an urbanised estuary

AbstarctThe potential disturbance of dolphins from tourism boats has been widely discussed in the literature, in terms of both physical vessel presence and associated underwater noise. However, less attention has been paid to the potential impact of non-tourism vessels, despite these being much more widespread and occurring in greater numbers throughout coastal dolphin habitats. The Indo-Pacific bottlenose dolphin (T. aduncus) community using the Fremantle Inner Harbour, Western Australia, is exposed to high levels of vessel traffic. To investigate whether behavioural responses could be occurring, a non-invasive combination of visual and acoustic monitoring was conducted using a theodolite and an autonomous acoustic logger. Dolphins significantly increased their average movement speeds in high vessel densities, but only for some activity states. Behavioural budgets also changed in the presence of vessels, with animals spending greater time travelling and less time resting or socialising. Finally, multiple whistle characteristics varied with rising levels of broadband noise, and other contextual variables. Despite being acoustically specialised for higher frequencies, dolphins had the strongest acoustic variation during low-frequency noise. This study highlights the complexity of disturbance responses in this species, confirming the need for consideration of both surface and acoustic behaviour alongside appropriate contextual data.