Real-time Passive Acoustic Monitoring Research Articles

SEADETECT: developing an automated detection system to reduce whale-vessel collision risk

With the continuous intensification of marine traffic worldwide, whale-vessel collisions at sea (or “ship strikes”) have become one of the primary causes of mortality for cetaceans and a widely recognised cause of concern for human safety and economic losses. The Mediterranean Sea is a global hotspot for whale-vessel collisions, with one of the highest rates involving large cetaceans, especially the endangered fin whales (Balaenoptera physalus) and sperm whales (Physeter macrocephalus). Evidence indicates that both species are experiencing higher chances of a fatal collision than what predictions have estimated so far, with ship strikes being the main human-induced threat in the area. Regional and international organisations have stressed the need to address the issue by investigating the projected impacts of ship strikes on whale populations and by identifying possible mitigation measures to reduce chances of collision. Amongst the most popular and feasible options, there is the improvement of animal detection during navigation. Here, we present SEADETECT, a LIFE project that aims at developing an automated detection system to reduce vessel collision risk with marine mammals and unidentified floating objects (UFOs), combining state-of-the-art and novel technologies with existing approaches in the study of large whale ecology. This detection system consists of three elements; an automated onboard detection system composed of several sensors, a real-time passive acoustic monitoring (PAM) network at sea and a real-time detection-sharing and alert system (REPCET®). In this paper, we propose the development of a mitigation measure framework tailored for the issue of collision with fin and sperm whales in the north-western Mediterranean Sea, but that has the transferability features necessary for its application in other high-risk areas for ship strikes worldwide.

A real-time passive acoustic monitoring system to detect Yangtze finless porpoise clicks in Ganjiang River, China

Phocoenidae live in fresh, coastal waters where they often share a significant portion of their habitat with humans. As a result, local activities (e.g., coastal fisheries and shipments) cause underwater noise pollution and threaten their ecosystem. To better conserve the habitat of porpoises, we aimed to study their activities in these waters by recording their echolocation clicks using a passive acoustic monitoring (PAM) system. However, because the off-line PAM instruments were often used in the past that need to be periodically deployed and recovered, data acquisition is typically obtained and analyzed in batches, rather than in real-time. A real-time PAM detection system would help minimize the impact of underwater noise on approaching porpoises. Furthermore, issues of bad quality data–with gaps due to loss or damage of the off-line PAM instruments–could be avoided with a real-time detection system. Therefore, in this study, we developed the Real-time Porpoise Click Detector-II (RPCD-II), equipped with a digital hydrophone, main memory (2 TB storage), a central processing unit, and a wireless transmission module. We deployed the RPCD-II under a docked fishing vessel at the Ganjiang River in Yangzi Zhou Town Fisheries Village, Nanchang City (8–9 December 2021), where it recorded signals of Yangtze finless porpoise and produced a real-time report. To validate the results of RPCD-II, another underwater sound recorder, the SoundTrap 300HF (ST), was also set up (as a control device) under the docked fishing vessel. Both devices recorded consistent results of 9330 clicks, further demonstrating RPCD-II’s ability for the real-time detection of Yangtze finless porpoise in the field.

Recent developments, observations and lessons learned in the use of real-time passive acoustic monitoring from ocean gliders in order to mitigate harm to North Atlantic Right Whales and Southern Resident Killer Whales

JASCO’s novel passive acoustic monitoring (PAM) system, OceanObserver was deployed in Canada’s Gulf of Saint Lawrence (GoSL) in autumn 2018 aboard a Slocum G3 glider. The purpose of this mission was to assist in the search for endangered North Atlantic Right Whales and other threatened cetaceans, and to report detections in near-real-time so that appropriate mitigation actions could be taken. This proposed presentation will provide results and lessons learned based upon the rigorous analysis and comparison of the real-time, in situ detections with the automated and manual detections derived from post-trial analysis of the recorded raw acoustic data. This post analysis has permitted an assessment of the performance of the automated detectors deployed at sea and the effectiveness of the real-time communication management software in getting marine mammal detections to shore-based stakeholders in a timely manner. It also has permitted the evaluation of the effectiveness of shore-based acoustic analysts tasked with the validation of the automated detections sent to shore.Whether the mission objective of “no false positives” in order to ensure the correctness of mitigation decisions will be discussed. The method of assessing performance will be described and empirical results presented. The application of this technology to SRKW conservation will be discussed.

Near real time passive acoustic monitoring in the Santa Barbara Channel

The coastal waters off Southern California are feeding grounds for a variety of baleen whale species including blue whales, fin whales, and humpback whales. The feeding grounds overlap with highly used shipping lanes in the Santa Barbara Channel (SBC), increasing the risk of ship-whale interactions. In November 2019, a buoy equipped with a digital acoustic monitoring (DMON) instrument was deployed in the SBC and has been actively recording sounds and transmitting detection information in near real time since then. Data are transmitted in fifteen-minute summary periods of detected pitch tracks, which are reviewed by an analyst onshore for blue, fin, and humpback whale calls. Humpback whales were the most prolific callers, with detection rates reaching 80% of daily summary periods, whereas fin and blue whales rarely exceeded 20%. Baleen whale detections were low in late fall, with humpback whale detections increasing throughout winter and in spring and blue whale detections peaking during the summer. As part of the Benioff Ocean Initiative project to reduce whale strikes, these data are combined with visual surveys in the SBC and habitat models to produce a whale presence metric. This metric can be used by regional stakeholders to guide policy decisions and enhance conservation efforts.

Eavesdropping on dolphins: Investigating the habits of bottlenose dolphins (Tursiops truncatus) through fixed acoustic stations.

This study investigates the bottlenose dolphin (Tursiops truncatus, Montagu 1821) habitat use in the Portofino marine protected area (NW Italy) and adjacent waters, a core area for the dolphins and a highly touristic area in the Mediterranean Sea. A permanent automated real-time passive acoustic monitoring system, able to detect and track dolphins continuously, was tested in the area within the activities of the Life+ Nature project ARION. The habits of bottlenose dolphins was investigated considering the resident rate inside the area, which quantifies the amount of time dolphins spent in these waters, by means of random forest regression. The dependency of dolphin resident rate was analyzed in relation to four explanatory variables: sea surface temperature, season, time of day, and proximity to the coast. Dolphins spent more time in the area during spring and when sea surface temperature ranged between 15–16°C. Summer resulted the season with lower dolphin residency with significant difference between working day and weekend, in the last the lowest residency was recorded. Main findings provide important information to properly manage the area in order to protect bottlenose dolphins.

Real-time passive acoustic monitoring results of the 2018 Pacific Region International Survey of Marine Megafauna off Western Canada

Real-time passive acoustic monitoring (PAM) was conducted as part of the first large-scale systematic survey of marine mammal distribution and abundance in territorial outer-coastal waters off western Canada. The survey was conducted for approximately five weeks, from early July to mid-August, 2018 using a 69-m Canadian Coast Guard and Fisheries Vessel. A four-element, towed hydrophone array and sonobuoys (type AN/SSQ-53F and AN/SSQ-53G) were deployed and monitored in real-time 24/7 by experienced bio-acousticians. The towed array was deployed for approximately 640 h (78% of the time underway). Approximately 145 independent detections of marine mammals were made. Sperm whales (n = 53) and porpoises (n= 49) represented just over two-thirds of all detections. Ten near real-time localizations of sperm whales and 31 localization of porpoises were made, representing just over 60% of all (n = 67) all high-quality localizations. Sonobuoy effort consisted of semi-systematic deployments day and night and when sightings of large baleen whales occurred. A total of 112 sonobuoys were deployed successfully and monitored in directional (DIFAR) mode. Marine mammal calls were recorded on 32% (36) of sonobuoys. Sonobuoy detections included killer whales calls and clicks, sperm whale clicks, dolphin clicks, fin whale calls, and blue whale calls (both B and D type calls).

A Permanent Automated Real-Time Passive Acoustic Monitoring System for Bottlenose Dolphin Conservation in the Mediterranean Sea.

Within the framework of the EU Life+ project named LIFE09 NAT/IT/000190 ARION, a permanent automated real-time passive acoustic monitoring system for the improvement of the conservation status of the transient and resident population of bottlenose dolphin (Tursiops truncatus) has been implemented and installed in the Portofino Marine Protected Area (MPA), Ligurian Sea. The system is able to detect the simultaneous presence of dolphins and boats in the area and to give their position in real time. This information is used to prevent collisions by diffusing warning messages to all the categories involved (tourists, professional fishermen and so on). The system consists of two gps-synchronized acoustic units, based on a particular type of marine buoy (elastic beacon), deployed about 1 km off the Portofino headland. Each one is equipped with a four-hydrophone array and an onboard acquisition system which can record the typical social communication whistles emitted by the dolphins and the sound emitted by boat engines. Signals are pre-filtered, digitized and then broadcast to the ground station via wi-fi. The raw data are elaborated to get the direction of the acoustic target to each unit, and hence the position of dolphins and boats in real time by triangulation.

Real-time passive acoustic monitoring of baleen whales from autonomous platforms

An automated low-frequency detection and classification system (LFDCS) was developed for use with the digital acoustic monitoring (DMON) instrument to detect, classify, and report in near real time the calls of several baleen whale species, including fin, humpback, sei, bowhead, and North Atlantic right whales. The DMON/LFDCS has been integrated into the Slocum glider and APEX profiling float, and integration projects are currently underway for the Liquid Robotics wave glider and a moored buoy. In a recent evaluation study, two gliders reported over 25,000 acoustic detections attributed to fin, humpback, sei, and North Atlantic right whales over a 3-week period during late fall in the Gulf of Maine. The overall false detection rate for individual calls was 14%, and for right, humpback, and fin whales, false predictions of occurrence during 15-minute reporting periods were 5% or less. Agreement between acoustic detections and visual sightings from concurrent aerial and shipboard surveys was excellent (9 of 10 visual detections were accompanied by real-time acoustic detections of the same species by a nearby glider). We envision that this autonomous acoustic monitoring system will be a useful tool for both marine mammal research and mitigation applications.

Real-time reporting of baleen whale passive acoustic detections from ocean gliders

In the past decade, much progress has been made in real-time passive acoustic monitoring of marine mammal occurrence and distribution from autonomous platforms (e.g., gliders, floats, buoys), but current systems focus primarily on a single call type produced by a single species, often from a single location. A hardware and software system was developed to detect, classify, and report 14 call types produced by 4 species of baleen whales in real time from ocean gliders. During a 3-week deployment in the central Gulf of Maine in late November and early December 2012, two gliders reported over 25,000 acoustic detections attributed to fin, humpback, sei, and right whales. The overall false detection rate for individual calls was 14%, and for right, humpback, and fin whales, false predictions of occurrence during 15-min reporting periods were 5% or less. Transmitted pitch tracks--compact representations of sounds--allowed unambiguous identification of both humpback and fin whale song. Of the ten cases when whales were sighted during aerial or shipboard surveys and a glider was within 20 km of the sighting location, nine were accompanied by real-time acoustic detections of the same species by the glider within ±12 h of the sighting time.

Real-Time Passive Acoustic Monitoring of HIFU-Induced Tissue Damage

Thermal ablation by high-intensity focused ultrasound (HIFU) shows great promise as a noninvasive cancer therapy. This work proposes a novel method of real-time HIFU treatment monitoring that uses the passively monitored acoustic signal emanating from the focus during HIFU exposure. We performed 212 exposures in seven freshly excised ox livers using 1.067-MHz HIFU at a 95% duty cycle for a range of insonation durations and acoustic intensities. Acoustic emissions were recorded using a 15-MHz passive detector aligned confocally and coaxially with the HIFU transducer. Lesion presence and size were ascertained by slicing the tissue in the transverse and axial focal planes post exposure. Our results demonstrate that successful formation of HIFU lesions in ex vivo ox liver is highly correlated with the presence of pronounced dips in the magnitude of the received signal at integer harmonics of the insonation frequency. A detector based on this observation predicted lesioning with >80% accuracy in regimes that were very likely to create lesions (≥60 J of energy) and had an error rate of <6% for exposures that were too short to cause lesioning (≤1 s long). The overall sensitivity and specificity of the detector were 75.6% and 74.2%, respectively. The proposed detector could therefore provide a low-cost means of effectively monitoring clinical HIFU treatments passively and in real time.

Space–time and hybrid algorithms for the passive acoustic localisation of sperm whales and vessels

In the frame of the European Sea-floor Observatory Network (ESONET) and in preparation of the Demonstration Mission Listening to the Deep-Ocean Environment (LIDO) algorithms for the automated real-time detection, classification and localisation of cetaceans have been developed. Such Passive Acoustic Monitoring techniques have the potential to play a key role in cetaceans’ conservation for they allow a non-invasive study of their behaviour, a better knowledge of their population dynamics, and a better understanding of their dynamic relationship with their environment. This paper investigates the development of efficient and accurate techniques to be used as the basis of a localisation module for an automated real-time Passive Acoustic Monitoring system. An opportunity to assess the capabilities of the developed localisation modules was given by recordings collected with a bottom-mounted (around 2080 m depth) tetrahedral compact hydrophone array located offshore the port of Catania (Sicily) during the NEMO-ONDE campaign in the years 2005–2006 by INFN and CIBRA [2]. A well-known class of methods for acoustic source localisation is based on time differences of arrival (TDOA). Its capabilities have shown to be useful even in adverse situations (i.e., few sensors, high noise levels and/or poor calibration). A second class of methods, the space–time methods, originated in underwater applications such as sonar but reached its most significant achievements over the last 20 years in digital communications with recent progress in the treatment of broadband signals. These developments are here revisited under the scope of the localisation and tracking of cetacean vocalisations. Various broadband space–time methods were implemented and allowed to map the sound radiated during the detected clicks and to consequently localise both sperm whales and vessels. Hybrid methods were also developed which improved the robustness of space–time methods to noise and reverberation and reduced processing time. In most cases, the small variance obtained for these estimates lessened the necessity of additional statistical clustering. Even though not independently confirmed by sightings, the tracks derived in the proposed frame can be considered to be consistent with the known movements of sperm whales and vessels.