Detections of Whale Vocalizations by Simultaneously Deployed Bottom-Moored and Deep-Water Mobile Autonomous Hydrophones

Abstract

Advances in mobile autonomous platforms for oceanographic sensing, including gliders and deep-water profiling floats, have provided new opportunities for passive acoustic monitoring (PAM) of cetaceans. However, there are few direct comparisons of these mobile autonomous systems to more traditional methods, such as stationary bottommoored recorders. Cross-platform comparisons are necessary to enable interpretation of results across historical and contemporary surveys that use different recorder types, and to identify potential biases introduced by the platform. Understanding tradeoffs across recording platforms informs best practices for future cetacean monitoring efforts. This study directly compares the PAM capabilities of a glider (Seaglider) and a deep-water profiling float (QUEphone) to a stationary seafloor system (High-frequency Acoustic Recording Package, or HARP) deployed simultaneously over a 2 week period in the Catalina Basin, California, United States. Two HARPs were deployed 4 km apart while a glider and deep-water float surveyed within 20 km of the HARPs. Acoustic recordings were analyzed for the presence of multiple cetacean species, including beaked whales, delphinids, and minke whales. Variation in acoustic occurrence at 1min (beaked whales only), hourly, and daily scales were examined. The number of minutes, hours, and days with beaked whale echolocation clicks were variable across recorders, likely due to differences in the noise floor of each recording system, the spatial distribution of the recorders, and the short detection radius of such a highfrequency, directional signal type. Delphinid whistles and clicks were prevalent across all recorders, and at levels that may have masked beaked whale vocalizations. The number and timing of hours and days with minke whale boing sounds were nearly identical across recorder types, as was expected given the relatively long propagation distance of boings. This comparison provides evidence that gliders and deep-water floats record cetaceans at similar detection rates to traditional stationary recorders at a single point.

Autonomous Surface and Underwater Vehicles as Effective Ecosystem Monitoring and Research Platforms in the Arctic—The Glider Project

“…The results presented here corroborate the effectiveness of gliders equipped with passive acoustic monitoring devices in collecting long-term marine mammal data and anthropogenic noise across a wide geographical area, with minimal disturbance to animals [11,37]. The novel Seaglider ® -integrated hydrophone used in this study was able to record cetacean vocalizations.…”

“…A well-known challenge with autonomous acoustic surveys is the identification of the acoustic targets based only their acoustic signal. To identify targets, additional sampling might be performed by trawl, net, or occasionally optical sampling [15,37,38]. Zooplankton composition, abundance, and vertical distribution in an area overlapping with the track of the Sailbuoy in June 2018 (6 stations west of Vesterålen, 10 stations north on Tromsøflaket) was assessed during an independent research cruise aboard RV Helmer Hanssen (see https://lofoten-research.no/ accessed on 7 October 2021) using a Hydrobios Multinet (mesh size 180 µm, opening area 0.25 m 2 ), a Tucker Trawl (1500 µm, 1 m 2 ), a Video Plankton Recorder (Seascan Inc.), and a Laser Optical Plankton Counter (ODIM-Brooke Ocean Rolls Royce Canada Ltd.) following the methods described in [39].…”

Three types of pulsed signal trains emitted by Indo-Pacific humpback dolphins (Sousa chinensis) in Beibu Gulf, South China Sea

“…The differences in the frequency and energy are most significant for high-frequency signals (Martin et al, 2018), but the difference is very small in D and almost none in IPIs. It is feasible to classify the train types according to the parameters of the received signals (Martin et al, 2018;Yang et al, 2021;Arranz, 2016;Martin et al, 2018;Fregosi et al, 2020). In the present study, IPIs_m and D were identified as very important for classification according to PC1 (Table 2).…”

Detection probability and density estimation of fin whales by a Seaglider

“…The primary advantage of gliders is increased spatial coverage compared to a stationary sensor and increased temporal coverage compared to a vessel-based survey. Gliders have been used to acoustically detect and survey for a variety of cetacean species (e.g., Baumgartner et al, 2013;Cauchy et al, 2020;Fregosi et al, 2020a;Klinck et al, 2016;Kowarski et al, 2020;Silva et al, 2019), and there is an interest in using these systems to estimate cetacean population densities (Gkikopoulou, 2018;Harris et al, 2017;K€ usel et al, 2017;Marques et al, 2013). However, applying passive acoustic density estimation methods to glider data is not straightforward because of the glider's slow movement, the combination of horizontal and vertical glider movement, low-frequency flow noise generated through glider movement, and the glider's relatively small size, which limits the available aperture for multiple acoustic sensors.…”