Detection Of Cetaceans Research Articles

Odontocete detections are linked to oceanographic conditions in the Hawaiian Archipelago

Understanding environmental drivers of species’ behavior is key for successful conservation. Within cetacean research, studies focused on understanding such drivers often consider local conditions (e.g., sea surface temperature), but rarely include large-scale, long-term parameters such as climate indices. Here we make use of long-term passive acoustic monitoring data to examine relationships between eight classes of toothed whales and climate indices, specifically El Niño Southern Oscillation, Pacific Decadal Oscillation, and North Pacific Gyre Oscillation, as well as local surface conditions (temperature, salinity, sea surface height) at two sites in the Hawaiian Archipelago. We find that El Niño Southern Oscillation most influenced cetacean detections at monitored sites. In many cases, detection patterns matched well with combinations of one or more climate indices and surface conditions. Our results highlight the importance of considering climate indices in efforts to understand relationships between marine top predators and environmental conditions.

Seas the DNA? Limited detection of cetaceans by low‐volume environmental DNA transect surveys

AbstractEnvironmental DNA (eDNA) has begun to show promise as a robust and reproducible tool for monitoring cetaceans in coastal and offshore waters. Some limiting factors preventing the wider application of eDNA for cetacean monitoring includes lack of species‐specific qPCR assays and limited in situ validation. In this study, we determined 15 monitoring stations within cetacean hotspots in Chatham Sound (British Columbia, Canada), from which we collected a combination of visual and acoustic data, and low‐volume eDNA samples (equivalent to ~250 mL seawater). We designed novel eDNA assays for gray whale and Dall's porpoise and validated existing assays for harbor porpoise, killer whale, and humpback whale. Overall, we collected a total of 120 paired eDNA samples across four sampling intervals, 60 preserved with absolute ethanol and 60 preserved with propylene glycol antifreeze. Positive rates for visual (18%) and acoustic (4%) detections were higher than the eDNA detection rate (<3%), with only one sample (antifreeze‐preserved) producing a positive detection for humpback whales at one of the stations. We discuss factors which could have influenced the lack of detections and highlight the need for higher sample volumes and species‐specific sample approaches to improve detection success and confidence in eDNA applicability for cetacean monitoring.

Evaluation of a coastal acoustic buoy for cetacean detections, bearing accuracy and exclusion zone monitoring

Abstract There is strong socio‐political support for offshore wind development in US territorial waters and construction is planned off several east coast states. Some of the planned development sites coincide with important habitat for critically endangered North Atlantic right whales. Both exclusion zones and passive acoustic monitoring are important tools for managing interactions between marine mammals and human activities. Understanding where animals are with respect to exclusion zones is important to avoid costly construction delays while minimizing the potential for negative impacts. Impact piling from construction of hundreds of offshore wind turbines likely require exclusion zones as large as 10 km. We have developed a three‐hydrophone passive acoustic monitoring system that provides bearing information along with marine mammal detections to allow for informed management decisions in real‐time. Multiple units form a monitoring system designed to determine whether marine mammal calls originate from inside or outside of an exclusion zone. In October 2021, we undertook a full system validation, with a focus on evaluating the detection range and bearing accuracy of the system with respect to right whale upcalls. Five units were deployed in Mid‐Atlantic waters and we played more than 3500 simulated right whale upcalls at known locations to characterize the detection function and bearing accuracy of each unit. The modelled results of the detection function error were then used to compare the effectiveness of a bearing‐based system to a single sensor that can only detect a signal but not ascertain directivity. Field trials indicated maximum detection ranges from 4–7.3 km depending on source and ambient noise levels. Simulations showed that incorporating bearing detections provide a substantial improvement in false alarm rates (6 to 12 times depending on number of units, placement and signal to noise conditions) for a small increase in the risk of missed detections inside of an exclusion zone (1%–3%). We show that the system can be used for monitoring exclusion zones and clearly highlight the value of including bearing estimation into exclusion zone monitoring plans while noting that placement and configuration of units should reflect anticipated ambient noise conditions.

Arctic Marine Data Collection Using Oceanic Gliders: Providing Ecological Context to Cetacean Vocalizations

To achieve effective management and understanding of risks associated with increasing anthropogenic pressures in the ocean, it is essential to successfully and efficiently collect data with high spatio–temporal resolution and coverage. Autonomous Underwater Vehicles (AUVs) are an example of technological advances with potential to provide improved information on ocean processes. We demonstrate the capabilities of a low-power AUV buoyancy glider for performing long endurance biological and environmental data acquisition in Northern Norway. We deployed a passive acoustic sensor system onboard a SeagliderTM to investigate presence and distribution of cetaceans while concurrently using additional onboard sensors for recording environmental features (temperature, salinity, pressure, dissolved oxygen, and chlorophyll). The hydrophone recorded over 108.6 hours of acoustic data during the spring months of March and April across the continental shelf break and detected both baleen and odontocete species. We observed a change in cetacean detections throughout the survey period, with humpback whale calls dominating the soundscape in the first weeks of deployment, coinciding with the migration towards their breeding grounds. From mid-April, sperm whales and delphinids were the predominant species, which coincided with increasing chlorophyll fluorescence values associated with the spring phytoplankton blooms. Finally, we report daily variations in background noise associated with fishing activities and traffic in the nearby East Atlantic shipping route. Our results show that gliders provide excellent platforms for collecting information about ecosystems with minimal disturbance to animals, allowing systematic observations of our ocean biodiversity and ecosystem dynamics in response to natural variations and industrial activities.

X-Band Radar for Cetacean Detection (Focus on Tursiops truncatus) and Preliminary Analysis of Their Behavior

Cetaceans are protected species all over the world, most of them are vulnerable, endangered, or data deficient (according to International Union for Conservation of Nature - IUCN red list). X-band radars detect the echo of the electromagnetic signal reflected by an obstacle or a ship (target). The application of X-band radar to the detection of cetaceans is a new and innovative field of research that could improve the automation of marine mammal data collection, and this is the first time in the Mediterranean Sea. The aim of this work was to test the capability of X-band radar installed along the coast (ground-based) to detect and track cetaceans in a range of approximately 2.5 nautical miles from the radar antenna. Data collection included a part of field work, implemented through the acquisition of photographic images and target’s radar detection (by the panoramic terrace Santa Maria in Corniglia), and a part, performed in the laboratory, of data analysis. The work was undertaken between May and November 2018. During this period, 30 days of monitoring were carried out (about 300 h) and about 10,000 radar images were recorded. The first results showed that we were able to recognize the target “cetacean” from the other common targets (boats, buoys, etc.) detected by the radar. In particular 70 dolphins were sighted by visual census; 12 of them were recognized on radar images. Radar images allowed extraction of dolphin dive time (between 2 and 15 s). The next step will be to allow the radar to identify the presence of marine mammals itself since it also works at night and with low visibility. This technique could complement the protection measures of cetaceans, highlighting their presence at sea even if it is impossible with waves higher than 0.8 m and over distances greater than 2.5 km.

Review of Automatic Detection and Classification Techniques for Cetacean Vocalization

Cetaceans have elicited the attention of researchers in recent decades due to their importance to the ecosystem and their economic values. They use sound for communication, echolocation and other social activities. Their sounds are highly non-stationary, transitory and range from short to long sounds. Passive acoustic monitoring (PAM) is a popular method used for monitoring cetaceans in their ecosystems. The volumes of data accumulated using PAM are usually big, so they are difficult to analyze using manual inspection. Therefore different techniques with mixed outcomes have been developed for the automatic detection and classification of signals of different cetacean species. So far, no single technique developed is perfect to detect and classify the vocalizations of over 82 known species due to variability in time-frequency, difference in the amplitude among species and within species' vocal repertoire, physical environment, among others. The accuracy of any detector or classifier depends on the technique adopted as well as the nature of the signal to be analyzed. In this article, we review the existing techniques for the automatic detection and classification of cetacean vocalizations. We categorize the surveyed techniques, while emphasizing the advantages and disadvantages of these techniques. The article suggests possible research directions that can improve existing detection and classification techniques. In addition, the article recommends other suitable techniques that can be used to analyze non-linear and non-stationary signals such as the cetaceans' signals. Several research have been dedicated to this topic, however, there is no review of these past results that gives a quick overview in the area of cetacean detection and classification. This review will help researchers and practitioners in the field to make insightful decisions based on their requirements.

Who’s better at spotting? A comparison between aerial photography and observer-based methods to monitor floating marine litter and marine mega-fauna

Pollution by marine litter is raising major concerns due to its potential impact on marine biodiversity and, above all, on endangered mega-fauna species, such as cetaceans and sea turtles. The density and distribution of marine litter and mega-fauna have been traditionally monitored through observer-based methods, yet the advent of new technologies has introduced aerial photography as an alternative monitoring method. However, to integrate results produced by different monitoring techniques and consider the photographic method a viable alternative, this ‘new’ methodology must be validated. This study aims to compare observations obtained from the concurrent application of observer-based and photographic methods during aerial surveys. To do so, a Partenavia P-68 aircraft equipped with an RGB sensor was used to monitor the waters off the Spanish Mediterranean coast along 12 transects (941 km). Over 10000 images were collected and checked manually by a photo-interpreter to detect potential targets, which were classified as floating marine macro-litter, mega-fauna and seabirds. The two methods allowed the detection of items from the three categories and proved equally effective for the detection of cetaceans, sea turtles and large fish on the sea surface. However, the photographic method was more effective for floating litter detection and the observer-based method was more effective for seabird detection. These results provide the first validation of the use of aerial photography to monitor floating litter and mega-fauna over the marine surface.

The effect of a multi-target protocol on cetacean detection and abundance estimation in aerial surveys.

A double-platform protocol was implemented in the Bay of Biscay and English Channel during the SCANS-III survey (2016). Two observation platforms using different protocols were operating on board a single aircraft: the reference platform (Scans), targeting cetaceans, and the ‘Megafauna’ platform, recording all the marine fauna visible at the sea surface (jellyfish to seabirds). We tested for a potential bias in small cetacean detection and density estimation when recording all marine fauna. At a small temporal scale (30 s, roughly 1.5 km), our results provided overall similar perception probabilities for both platforms. Small cetacean perception was higher following the detection of another cetacean within the previous 30 s in both platforms. The only prior target that decreased small cetacean perception during the subsequent 30 s was seabirds, in the Megafauna platform. However, at a larger scale (study area), this small-scale perception bias had no effect on the density estimates, which were similar for the two protocols. As a result, there was no evidence of lower performance regarding small cetacean population monitoring for the multi-target protocol in our study area. Because our study area was characterized by moderate cetacean densities and small spatial overlap of cetaceans and seabirds, any extrapolation to other areas or time requires caution. Nonetheless, by permitting the collection of cost-effective quantitative data for marine fauna, anthropogenic activities and marine litter at the sea surface, the multi-target protocol is valuable for optimizing logistical and financial resources to efficiently monitor biodiversity and study community ecology.

Mapping underwater noise, detection of ships and cetaceans using a SeaExplorer glider at a basin level: Feedback from the first 1000 km-long acoustic exploration of the Western French Mediterranean Sea

In response to concerns about the impact of man-made noise on marine ecosystems, researchers and environmental managers are currently collecting in situ measurements of oceanic noise levels. The objectives of in situ measurements are to provide the acoustic signatures of individual ships, with the use of AIS databases, to feed the models; to calibrate the model for mapping of shipping noise, and to assess marine biodiversity through the sounds emitted by marine animals (invertebrates, fishes, and cetaceans). The usefulness of the data collected depends on the duration of acquisition and the diversity of the measurements (e.g., shipping density and water depth). Gliders are ideal vehicles to collect noise level data across oceanic basins and over long time periods. Here, we show results from a SeaExplorer glider equipped with a high quality acoustic payload travelling for 30 days (09/15/2017-10/15/2017) along a 1000 km-long transect of the Western French Mediterranean Sea. The trajectory of the glider was chosen to sample the highest and lowest shipping densities. We here report on the statistical distribution of oceanic noise levels in the bandwidths assessed by the European Marine Framework Strategy Directive as well as on the detection of cetacean and ship sounds along the transect.

Thermal Imaging and Biometrical Thermography of Humpback Whales

Determining species distributions through time and space remains a primary challenge in cetacean science and conservation. For example, many whales migrate thousands of kilometers every year between remote seasonal habitats along migratory corridors that cross major shipping lanes and intensively harvested fisheries creating a dynamic spatial and temporal context that conservation decisions must take into account. Technological advances enabling automated whale detection have the potential to dramatically improve our knowledge of when and where whales are located, presenting opportunities to help minimize adverse human-whale interactions. Using thermographic data we show that near-horizontal (i.e. high zenith angle) infrared images of humpback whale (Megaptera novaeangliae) blows, dorsal fins, flukes and rostrums record similar magnitude brightness temperature anomalies relative to the adjacent ocean surface. Our results demonstrate that these anomalies are similar in both low latitude and high latitude environments despite a ~16°C difference in ocean surface temperature between study areas. We show that these similarities occur in both environments due to emissivity effects associated with oblique target imaging, rather than differences in cetacean thermoregulation. The consistent and reproducible brightness temperature anomalies we report provide important quantitative constraints that will help facilitate the development of transient temperature anomaly detection algorithms in diverse marine environments. Thermographic videography coupled with laser range finding further enables calculation of whale blow velocity, demonstrating that biometrical measurements are possible for near-horizontal datasets that otherwise suffer from emissivity effects. The thermographic research we present creates a platform for the delivery of 3 important contributions to cetacean conservation: 1) non-invasive species-level identifications based on whale blow shapes and velocities recorded by infrared videography; 2) reduced ship-strike rates through automated thermographic cetacean detection systems deployed in high traffic areas; 3) monitoring the spatial and temporal distributions of endangered animals in remote habitats.

Cetacean sightings and acoustic detections during a seismic survey off Nicaragua and Costa Rica, November-December 2004

Although the wider Eastern Tropical Pacific has been systematically surveyed during summer/fall, relatively little effort has focused on shelf and slope waters of Nicaragua and Costa Rica. Such data are useful for establishing baseline information and assessing potential changes in cetacean occurrence and distribution relative to natural (e.g., El Niño-Southern Oscillation, climate change) and anthropogenic factors. A visual-acoustic survey for cetaceans occurred as part of a monitoring and mitigation program during an academic geophysical seismic study off Nicaragua and Costa Rica, during November-December 2004. Approximately 2 067 cetaceans representing at least seven species were seen in 75 groups during 373 h (3 416 km) of daytime observations from the seismic research vessel (R/V) Maurice Ewing. The humpback whale (Megaptera novaeangliae) and the pantropical spotted dolphin (Stenella attenuata) were the most frequently sighted species (30 % of all groups sighted); both were seen in shelf waters < 100 m deep and in slope waters. The bottlenose dolphin (Tursiops truncatus; 10 % of sightings) was the third most frequently sighted species and was only seen in water > 100 m deep. In addition, sightings were made of spinner dolphins (S. longirostris), short-beaked common dolphins (Delphinus delphis), Risso’s dolphins (Grampus griseus), short-finned pilot whales (Globicephala macrorhynchus), and unidentified dolphins and whales. Unconfirmed sightings of a minke whale (Balaenoptera acutorostrata) and a pod of false killer whales (Pseudorca crassidens) were also recorded. An additional six groups of dolphins (50 % confirmed to species, all pantropical spotted dolphins) were made during 187 h (1 549 km) of observation effort during darkness, two of which were detected within 30 m of the vessel bow using a night vision device. A total of 217 cetacean detections occurred during 633 h of passive acoustic monitoring. A small concentration of 12 humpback whales was seen in eight groups, and two humpbacks were recorded singing in the Gulf of Fonseca on 9 December 2004. To our knowledge, such concentrations of humpback whales, particularly singing humpbacks, have not been previously reported in this specific area. In addition, a humpback mother-calf pair, likely from the Northern Hemisphere population, was seen off Northern Costa Rica on 25 November 2004. Although cetacean sighting rates were significantly different during seismic and non-seismic periods even when corrected for differential detection probability related to sea conditions, our survey results do provide information to address previous data gaps on cetacean occurrence in shelf and slope waters off the Pacific coast of Central America during late fall.

Improved passive acoustic band-limited energy detection for cetaceans

Acoustic detection of cetaceans is challenged by the variability of calls and the presence of variable background noise. One detection method is to start with frequency band-limited signal and noise estimates, and apply a likelihood ratio test (LRT). These detectors suffer from false alarms when broadband signals overlap the band of interest, triggering detection. Some detectors only consider previous samples, causing further false alarms. The authors propose a method of reducing false alarms by defining a guard band that is not expected to contain energy from the species of interest. A second LRT is performed by testing the ratio of the signal estimate in the signal band with the signal estimate of the guard band. This method is shown to reduce false alarms with a small reduction in detection performance. A detection method is also presented that can be optimized for high processing efficiency, while improving false-alarm rejection from signals that are longer in duration than the signal of interest. Performance is demonstrated on real cetacean recordings and ocean noise. The detection algorithm is implemented in PAMGUARD, an open source Java application designed for passive acoustic monitoring (PAM) of cetaceans.

Patterns of Occurrence and Marine Mammal Acoustic Behavior in Relation to Navy Sonar Activity Off Jacksonville, Florida.

Passive acoustic data collected from marine autonomous recording units deployed off Jacksonville, FL (from 13 September to 8 October 2009 and 3 December 2009 to 8 January 2010), were analyzed for detection of cetaceans and Navy sonar. Cetaceans detected included Balaenoptera acutorostrata, Eubalaena glacialis, B. borealis, Physeter macrocephalus, blackfish, and delphinids. E. glacialis were detected at shallow and, somewhat unexpectedly, deep sites. P. macrocephalus were characterized by a strong diel pattern. B. acutorostrata showed the strongest relationship between sonar activity and vocal behavior. These results provide a preliminary assessment of cetacean occurrence off Jacksonville and new insights on vocal responses to sonar.

An Italian proposal on the monitoring of underwater noise: Relationship between the EU Marine Strategy Framework Directive (MSFD) and marine spatial planning directive (MSP)

In recent years, many studies have evaluated the effects of anthropogenic acoustic disturbance on marine organisms. Sounds associated with shipping, seismic surveys, sonar, and many other such sources induce several types of effect on fish and marine mammals. In this regard, the European Marine Strategy Framework Directive 2008/56/EC has not only defined underwater acoustic noise as “the intentional or accidental introduction of acoustic energy in the water column from impulsive and diffuse sources”, but has also expressly identified it as a form of pollution.In 2014, the first Italian proposal has been defined with the aim of developing a widespread monitoring plan for sub-regions in European Union waters with respect to two different sub-programs concerning impulsive (Descriptor 11.1) and continuous low frequency (Descriptor 11.2) sounds. The objective of Marine Strategy Framework Directive is the implementation of a recording system for temporal-spatial data regarding impulsive sound sources arising from anthropogenic activities. The pressure, for Descriptor 11.1, is measured by evaluating the source level, or a suitable proxy for anthropogenic sound sources, measured over the frequency band 10 Hz–10 kHz (and up to 40 kHz for cetacean detection), that could have an impact on marine organisms.The Descriptor 11.2 would monitor trends in the ambient noise level within the 1/3 octave bands 63 and 125 Hz (centre frequency) (re 1 μΡa RMS; average noise level in these octave bands over a year) via observation stations. This monitoring plan aims to obtain noise maps of sea regions for the frequency band 10 Hz–10 kHz (and up to 40 kHz for cetacean detection) by improving existing geophysical/acoustic observation stations, e.g. those of the National Institute of Geophysics and Volcanology (INGV) and the National Institute of Nuclear Physics (INFN), as well as other medium- and long-term monitoring stations. The program also wants to define the level of damage caused by underwater noise, using underwater noise as an example to evaluate the impact of this type of noise on different marine organisms.Maritime spatial planning (MSP) and integrated coastal management (ICZM) have to employ an ecosystem-based approach that ensures the protection of the natural resources and provides the basis for carrying out the various monitoring activities. The Italian monitoring proposal on Descriptor 11 of Marine Strategy Framework Directive (MSFD) was used in order to analyze the strategic vision of the integrated maritime policy (IMP) between MSFD and MSP programs in terms of achieving Good Environmental Status (GES).

Cetacean encounters around the island of Montserrat (Caribbean Sea) during 2007 and 2010, including new species state records

A total of 168.4 hours of visual cetacean survey work was carried out in association with two geophysical surveys in Montserrat waters (eastern Caribbean) during December 2007 and May 2010, using a seismic vessel as a platform of opportunity. Nine cetacean sightings were recorded: pantropical spotted dolphin Stenella attenuata ( N = 2), Fraser's dolphin Lagenodelphis hosei ( N = 1), sperm whale Physeter macrocephalus ( N = 1), humpback whale Megaptera novaeangliae ( N = 1), and sightings of unidentified dolphins ( N = 1) and large whales ( N = 3). A total of 73.3 hours of acoustic monitoring effort was carried out during December 2007, resulting in 19 cetacean detections. Sperm whale ( N = 10) and unidentified dolphin ( N = 7) detections predominated. Two acoustic detections were of pantropical spotted dolphins, corresponding with visual sightings. An opportunistic sighting of 14 pygmy killer whales Feresa attenuata during October 2008 was reported. Although the humpback whale was known previously for Montserrat waters, the sightings of other species represent the first verified records for the state.

Automated real-time detection of cetaceans at the Station ALOHA Cabled Observatory

Hawaiian waters support a wide variety of cetacean species, however, little is known about their occurrence in offshore waters. A cabled ocean bottom observatory located at Station ALOHA (Station ALOHA Cabled Observatory - ACO) provides a unique opportunity to study the occurrence of cetaceans in real-time and over long time scales at a deep ocean research site located 100 km north of Oahu. A retired electro-optical telecommunications cable provides power and broadband Ethernet communications capability to the ACO, allowing real-time continuous acoustic monitoring. The ACO has been operational since February 2007 and includes a hydrophone with a bandwidth of 0.01Hz to 40kHz. Automated methods for detection and identification of cetacean calls have been developed and data are processed in nearly real-time. Several cetacean species have been detected, including: dolphins and humpback, minke, fin, and sperm whales. The relationship between the occurrence of different species and changes in the environment has been explored using near-monthly shipboard oceanographic observations collected at Station ALOHA. In addition, seasonal trends in the occurrence of minke whales, a species that has been especially difficult to study using visual methods due to their cryptic behavior, have been examined.

Using T-PODs to investigate the echolocation of coastal bottlenose dolphins

We investigated the feasibility of using a T-POD, a passive acoustic dolphin detector system, to monitor bottlenose dolphins in the Shannon Estuary, Ireland, from 27 June to 18 August 2005. A v.3 T-POD, logging alternate minutes, was moored in view of an observation site. Land-based theodolite tracking was used to record the position of the closest animal, school size and activity of the closest dolphin school to the T-POD. All cetacean detections on the T-POD synchronous with shore watches in sea states ≤2 were analysed. A total of 94 schools were observed at distances up to 8000 m from the observer. Acoustic detections corresponded well with visual detections, with 82% of the dolphin schools observed within 500 m of the T-POD detected acoustically. The furthest distance dolphins were observed from the T-POD during periods of acoustic detection was 1246 m. Twelve acoustic encounters were logged without corresponding visual detections, four of which may represent false positives. School size did not affect the acoustic detectability of the dolphins, as there was no difference in the size of schools observed with or without corresponding acoustic detections (Kruskal–Wallis, P=0.64). Similarly no relationship was found between acoustic detections and school sizes at different distances to the T-POD (linear regression P=0.5, r2=0.01). Acoustic encounters did not vary in relation to diel patterns (Mann–Whitney, P=0.13) but were related to tidal state (χ2=40.2, P=0.00, df=11) with more encounters logged in the 4 h after high water, probably reflecting prey-related changes in habitat use. T-POD detections correlated well with visual observations and although detection is likely to vary according to T-POD specification, sensitivity and the conditions at the deployment site, the T-POD is a useful tool that has been shown to offer the possibility of continuous monitoring, something that is difficult to achieve with visual methods alone.