Comparison of fin whale 20 Hz call detections by deep-water mobile autonomous and stationary recorders

Abstract

Acoustically equipped deep-water mobile autonomous platforms can be used to survey for marine mammals over intermediate spatiotemporal scales. Direct comparisons to fixed recorders are necessary to evaluate these tools as passive acoustic monitoring platforms. One glider and two drifting deep-water floats were simultaneously deployed within a deep-water cabled hydrophone array to quantitatively assess their survey capabilities. The glider was able to follow a pre-defined track while float movement was somewhat unpredictable. Fin whale (Balaenoptera physalus) 20 Hz pulses were recorded by all hydrophones throughout the two-week deployment. Calls were identified using a template detector, which performed similarly across recorder types. The glider data contained up to 78% fewer detections per hour due to increased low-frequency flow noise present during glider descents. The glider performed comparably to the floats and fixed recorders at coarser temporal scales; hourly and daily presence of detections did not vary by recorder type. Flow noise was related to glider speed through water and dive state. Glider speeds through water of 25 cm/s or less are suggested to minimize flow noise and the importance of glider ballasting, detector characterization, and normalization by effort when interpreting glider-collected data and applying it to marine mammal density estimation are discussed.

Evaluating the Efficacy of Acoustic Metrics for Understanding Baleen Whale Presence in the Western North Atlantic Ocean

“…The models performed the best for fin whales, predicting their presence with an 88% precision at both sites. This is similar performance to that reported for fin whale detectors in other studies (e.g., Buchan et al, 2019;Fregosi et al, 2020). The model also performed well for NARW at the slope site (15% false discovery rate) and humpback whales at the shelf site (21% false discovery rate).…”

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

“…Underwater gliders are similar to deep-water profiling floats in their operation and communication, but have the added advantage of being able to traverse currents (Rudnick et al, 2004). However, this horizontal movement comes at the cost of increased lowfrequency (<100 Hz) noise from water flow and noise from platform operation which could mask cetacean sounds of interest (Fregosi et al, 2020). Further, the continual movement (both horizontally and vertically) means that local sound propagation conditions and therefore the detection radius around a mobile platform may be continually changing (Helble et al, 2013;Gkikopoulou, 2018).…”

“…Acoustically equipped mobile autonomous platforms, such as underwater gliders and profiling floats, can effectively record a variety of marine mammal species (Baumgartner et al, 2013;Matsumoto et al, 2013;Nieukirk et al, 2016;Küsel et al, 2017) including beaked whales (Klinck et al, 2012), delphinids (Silva et al, 2019), and minke whales (Klinck et al, 2015). Detection rates of the low-frequency fin whale (Balaenoptera physalus) 20-Hz pulse have been quantitatively compared to a cabled bottom-mounted hydrophone array (Fregosi et al, 2020). However, no quantitative comparison has been made of detection capabilities for these platforms relative to other well-characterized bottom-moored systems, such as the Highfrequency Acoustic Recording Package (HARP; Wiggins and Hildebrand, 2007).…”

Deep Ocean Passive Acoustic Technologies for Exploration of Ocean and Surface Sea Worlds in the Outer Solar System

“…A better option would be to position the hydrophone on a tether, or possibly use a winch system to deploy an array of hydrophones some distance from the vehicle's hull, while the electronics would remain inside and thermally controlled. A recent study of flow noise on ocean gliders demonstrated that lower vehicle speeds (<25 cm s -1 ) result in lower ambient noise levels in the 50-200 Hz band, to the point where ambient noise levels were comparable to fixed acoustic recorders (Fregosi et al, 2020). In contrast, increased vehicle speeds will increase flow noise energy.…”