Echolocation click parameters and biosonar behaviour of the dwarf sperm whale (Kogia sima)

PhD and fieldwork funding were provided by the Danmarks Grundforskningsfond (27125 to P.T.M.), the Oticon Fonden (18-0340 to C.E.M.) the Dansk Akustisk Selskab (to C.E.M.), the South Africa National Research Foundation (research career advancement fellowship to S.E.) and the Claude Leon Foundation (postdoctoral fellowship to T.G.).Dwarf sperm whales (Kogia sima) are small toothed whales that produce narrow-band high-frequency (NBHF) echolocation clicks. Such NBHF clicks, subject to high levels of acoustic absorption, are usually produced by small, shallow-diving odontocetes, such as porpoises, in keeping with their short-range echolocation and fast click rates. Here, we sought to address the problem of how the little-studied and deep-diving Kogia can hunt with NBHF clicks in the deep sea. Specifically, we tested the hypotheses that Kogia produce NBHF clicks with longer inter-click intervals (ICIs), higher directionality and higher source levels (SLs) compared with other NBHF species. We did this by deploying an autonomous deep-water vertical hydrophone array in the Bahamas, where no other NBHF species are present, and by taking opportunistic recordings of a close-range Kogia sima in a South African harbour. Parameters from on-axis clicks (n=46) in the deep revealed very narrow-band clicks (root mean squared bandwidth, BWRMS, of 3±1 kHz), with SLs of up to 197 dB re. 1 µPa peak-to-peak (μPapp) at 1 m, and a half-power beamwidth of 8.8 deg. Their ICIs (mode of 245 ms) were much longer than those of porpoises (<100 ms), suggesting an inspection range that is longer than detection ranges of single prey, perhaps to facilitate auditory streaming of a complex echo scene. On-axis clicks in the shallow harbour (n=870) had ICIs and SLs in keeping with source parameters of other NBHF cetaceans. Thus, in the deep, dwarf sperm whales use a directional, but short-range echolocation system with moderate SLs, suggesting a reliable mesopelagic prey habitat.Publisher PDFPeer reviewe

First<i> in situ</i> passive acoustic monitoring for marine mammals during operation of a tidal turbine in Ramsey Sound, Wales

The development of marine renewables has raised concerns regarding impacts on wildlife, and environmental monitoring is often required. We examined 3 mo of continuous passive acoustic monitoring (PAM) data collected at the Tidal Energy Ltd. DeltaStream turbine deployment in Ramsey Sound, UK. We aimed to assess the performance of the PAM system at an operational turbine, describe the 3D movements and behaviours of small cetaceans in the vicinity of the turbine, and model changes in detection rates against temporal and environmental variables. The PAM system was designed to acoustically detect, classify and track porpoises and dolphins via their vocalisations within a ∼100 m radius of the turbine. In total, 247 small cetacean encounters were identified from click detections, which were also used to reconstruct the spatial movements of porpoises and dolphins, including close approaches to the turbine. Not all hydro - phones were functional, which limited the ability to localise porpoise clicks; the probability of detecting and localising a click decreased by 50% at a range of ∼20 m. Mechanical sounds on the turbine may have alerted cetaceans of its presence. In models examining acoustic detection patterns, the tidal state, time of day, low low-frequency noise levels and moon phase best explained the acoustic presence of porpoises. The limited duration of turbine operation yielded insufficient data to understand the effect of turbine rotation on animal presence and movement near the turbine. This is the first description of how small cetaceans behave and move around a tidal turbine, and we present recommendations regarding how PAM can be used to improve environmental monitoring at future tidal energy sites.</p

Echolocation click parameters and biosonar behaviour of the dwarf sperm whale (<i>Kogia sima</i>)

Dwarf sperm whales (Kogia sima) are small toothed whales that produce narrow-band high-frequency (NBHF) echolocation clicks. Such NBHF clicks, subject to high levels of acoustic absorption, are usually produced by small, shallow-diving odontocetes, such as porpoises, in keeping with their short-range echolocation and fast click rates. Here, we sought to address the problem of how the little-studied and deep-diving Kogia can hunt with NBHF clicks in the deep sea. Specifically, we tested the hypotheses that Kogia produce NBHF clicks with longer inter-click intervals (ICIs), higher directionality and higher source levels (SLs) compared with other NBHF species. We did this by deploying an autonomous deep-water vertical hydrophone array in the Bahamas, where no other NBHF species are present, and by taking opportunistic recordings of a close-range Kogia sima in a South African harbour. Parameters from on-axis clicks (n=46) in the deep revealed very narrow-band clicks (root mean squared bandwidth, BWRMS, of 3±1 kHz), with SLs of up to 197 dB re. 1 µPa peak-to-peak (μPapp) at 1 m, and a half-power beamwidth of 8.8 deg. Their ICIs (mode of 245 ms) were much longer than those of porpoises (&lt;100 ms), suggesting an inspection range that is longer than detection ranges of single prey, perhaps to facilitate auditory streaming of a complex echo scene. On-axis clicks in the shallow harbour (n=870) had ICIs and SLs in keeping with source parameters of other NBHF cetaceans. Thus, in the deep, dwarf sperm whales use a directional, but short-range echolocation system with moderate SLs, suggesting a reliable mesopelagic prey habitat.</p

Narwhal (<i>Monodon monoceros</i>) echolocation click rates to support cue counting passive acoustic density estimation

Estimating animal abundance is fundamental for effective management and conservation. It is increasingly done by combining passive acoustics with knowledge about rates at which animals produce cues (cue rates). Narwhals (Monodon monoceros) are elusive marine mammals for which passive acoustic density estimation might be plausible, but for which cue rates are lacking. Clicking rates in narwhals were investigated using a dataset from sound and movement tag records collected in August 2013-2016 and 2019 in East Greenland. Clicking rates were quantified for ∼1200 one-second-long systematic random samples from 8 different whales. Generalized additive models were used to model (1) the probability of being in a clicking state versus depth and (2) the clicking rate while in a clicking state, versus time and depth. The probability of being in a clicking state increased with depth, reaching ∼1.0 at ∼500 m, while the number of clicks per second (while in a clicking state) increased with depth. The mean cue production rate, weighted by tag duration, was 1.28 clicks per second (se = 0.13, CV = 0.10). This first cue rate for narwhals may be used for cue counting density estimation, but care should be taken if applying it to other geographical areas or seasons, given sample size, geographical, and temporal limitations.</p

Narwhal (Monodon monoceros) echolocation click rates to support cue counting passive acoustic density estimation

Estimating animal abundance is fundamental for effective management and conservation. It is increasingly done by combining passive acoustics with knowledge about rates at which animals produce cues (cue rates). Narwhals (Monodon monoceros) are elusive marine mammals for which passive acoustic density estimation might be plausible, but for which cue rates are lacking. Clicking rates in narwhals were investigated using a dataset from sound and movement tag records collected in August 2013-2016 and 2019 in East Greenland. Clicking rates were quantified for ∼1200 one-second-long systematic random samples from 8 different whales. Generalized additive models were used to model (1) the probability of being in a clicking state versus depth and (2) the clicking rate while in a clicking state, versus time and depth. The probability of being in a clicking state increased with depth, reaching ∼1.0 at ∼500 m, while the number of clicks per second (while in a clicking state) increased with depth. The mean cue production rate, weighted by tag duration, was 1.28 clicks per second (se = 0.13, CV = 0.10). This first cue rate for narwhals may be used for cue counting density estimation, but care should be taken if applying it to other geographical areas or seasons, given sample size, geographical, and temporal limitations.</p

An autonomous hydrophone array to study the acoustic ecology of deep-water toothed whales

For vocal animals with distinctive calls, passive acoustic monitoring can be used to infer presence, distribution, and abundance provided that the calls and calling behaviour are known. Key to enabling quantitative acoustic surveys are calibrated recordings of identified species from which the source parameters of the sounds can be estimated. Obtaining such information from free-ranging aquatic animals such as toothed whales requires multi-element hydrophone arrays, the use of which is often constrained by cost, the logistical challenge of long cables, and the necessity for attachment to a boat or mooring in order to digitise and store multiple channels of high-sample rate audio data. Such challenges are compounded when collecting recordings or tracking the diving behaviour of deep-diving animals for which the array must be deployed at depth. Here we report the development of an autonomous drifting deep-water vertical passive acoustic array that uses readily available off-the-shelf components. This lightweight portable array can be deployed quickly and repeatedly to depths of up to 1000 m from a small boat. The array comprises seven ST-300 HF SoundTrap autonomous recorders equally spaced on an 84 m electrical-mechanical cable. The single-channel digital sound recordings were configured to allow for synchronisation in post-processing using an RS-485 timing signal logged by all channels every second. We outline how to assemble the array, and provide software for time-synchronising the acoustic recorders. To demonstrate the utility of the array, we present an example of short-finned pilot whale clicks localised on the deep-water (700 m) array configuration. This array method has broad applicability for the cost-effective study of source parameters, acoustic ecology, and diving behaviour of deep diving toothed whales, which are valuable not only to understand the sensory ecology of deep-diving cetaceans, but also to improve passive acoustic monitoring for conservation and management

Data from: Narwhal (Monodon monoceros) echolocation click rates to support cue counting passive acoustic density estimation

The datasets correspond to the data used to obtain the results shown in the manuscript "Narwhal (Monodon monoceros) echolocation click rates to support cue counting passive acoustic density estimation". When the manuscript is accepted we will also edit and add here the full reference including the DOI of the publication