Listen to the BLUE: Towards a pan-Antarctic monitoring system and blueprint of analysis methods to study fin and Antarctic blue whales in the Southern Ocean

The Southern Ocean Research Partnership (SORP) is an international collaborative initiative to develop novel research techniques and conduct non-lethal research on whales in the Southern Ocean. One of SORP’s original five research projects is the Blue and Fin Whale Acoustic Trends Project which aims to implement a long term acoustic research program examining trends in Southern Ocean blue and fin whale population growth, distribution, and seasonal presence using passive acoustic monitoring techniques. Passive acoustic monitoring is a robust means of monitoring whales in remote and difficult to study areas such as the Antarctic over long time periods. Analysis of a wide range of available passive acoustic data has demonstrated spatial and temporal patterns in the occurrence of blue and fin whales in the Southern Ocean. However, the lack of overlap in years and locations monitored, and differences among instrumentation and analysis methods used, underlines the need for coordinated effort. To best exploit passive acoustic methods for monitoring purposes in the future, the SORP Acoustic Trends steering group proposes the placement and maintenance of a pan-Antarctic monitoring system with consistent spatial and temporal coverage in each of the six IWC management areas. Further, blueprints for instrument choice, hardware configurations and analysis methods are being prepared to suggest how data might be best collected and analyzed in a uniform manner to best address the specific research questions for each study species. Through a consistent multi-disciplinary approach with international collaborators, the Blue and Fin Whale Acoustic Trends Project aims to use passive acoustic recordings to measure long term distribution, seasonal occurrence, and population growth trends of fin and Antarctic blue whales in the Southern Ocean

ANALYSE DES SIGNAUX ACOUSTIQUES D'ORIGINE BIOLOGIQUE ENREGISTRES DANS L'OCEAN INDIEN : IMPLICATIONS DANS LE RECENSEMENT ET LE SUIVI DES MOUVEMENTS SAISONNIERS DES CETACES

L'Océan Austral est formé par la réunion de trois océans : l'Océan Atlantique, l'Océan Pacifique et l'Océan Indien entourant le continent antarctique ainsi que de nombreuses îles ou archipels d'îles (Figure 1.1). Sa limite nord peut se définir par la confrontation des eaux froides antarctiques et des eaux plus chaudes subantarctiques. Cette limite, appelée convergence Antarctique ou zone frontale, est large (150 km) et située vers 45°S (Laws 1985). De par ses structures hydrologiques (zones frontales) et la dynamique de la banquise Antarctique, l'Océan Austral est un écosystème riche abritant, d'abondantes populations de prédateurs. L'abondance du phytoplancton dans l'Océan Austral suit un cycle saisonnier très fort, imposé par les grandes variations de lumière. A la fin de l'hiver, la fonte de la glace de mer libère des quantités importantes de nutriments qui deviennent alors disponibles pour le phytoplancton. On observe une forte augmentation de la biomasse phytoplanctonique à cette époque, caractérisée par une floraison (ou « bloom ») localisée en bordure de glace. La floraison phytoplanctonique est la base trophique du zooplancton, en particulier le krill Antarctique (Euphausia superba). Or, le krill Antarctique est une espèce clef dans l'écosystème de l'Océan Austral (Laws 1985) ; il représente la principale ressource alimentaire de nombreuses espèces de poissons, oiseaux et mammifères marins. Par conséquent, sa forte disponibilité à la fin de l'hiver et durant le printemps et l'été fait de l'Océan Austral une zone d'alimentation exceptionnelle. Dans l'Océan Austral, le krill est la principale ressource alimentaire des mysticètes encore appelés baleines à fanons (Nemoto 1970, Laws 1977, Kawamura 1980, 1994, Lockyer 1981). On y trouve par conséquent sept espèces ou sous-espèces de baleines à fanons dont 6 de la famille des balaenopteridae ou rorqual : la baleine bleue Antarctique (Balaenoptera musculus intermedia), la baleine bleue pygmée (B. m. brevicauda), le rorqual commun (B. physalus), le rorqual boréal (B. borealis), le petit rorqual (B. acutorostrata), la baleine à bosse (Megaptera novaeangliae) et une espèce de la famille des balaenae, la baleine franche australe (Eubalaena..

Analyse des signaux acoustiques d'origine biologique enregistrés dans l'océan Indien (implications dans le recensement et le suivi des mouvements saisonniers des cétacés)

L objectif de cette thèse est d apporter des éléments de réponses sur la présence et la répartition des grandes baleines dans le secteur Indien de l Océan Austral. En effet, ces espèces ont très fortement souffert de la chasse industrielle menée au cours du XXème siècle. Leur présence et leur répartition actuelle dans l Océan Austral restent largement méconnues ; les rares observations visuelles de grandes baleines apportent très peu d informations et soulignent les difficultés de cette approche classique pour l étude de ces animaux. Dans cette étude, une année d enregistrements acoustiques provenant d un observatoire d écoute localisé en zone subantarctique (Crozet) a été analysée afin de repérer les signaux acoustiques typiques émis par les grandes baleines et témoins de leur présence. Les résultats suggèrent que quatre espèces ou sous-espèces de grandes baleines sont présentes dans le secteur Indien de l Océan Austral (le rorqual commun, la baleine bleue Antarctique, la baleine bleue pygmée de Madagascar et d Australie) dans une zone d écoute estimée au maximum à 250km (d après le modèle de propagation du son utilisé). Les variations saisonnières dans le nombre et dans l intensité des cris mais aussi dans les estimations des distances de présence, indiquent une présence occasionnelle, saisonnière ou permanente de ces grandes baleines. Dans ce secteur, le rorqual commun est présent occasionnellement durant l hiver et l automne, alors que la baleine bleue Antarctique, est détectée toute l année. Une forte diminution du nombre de cris de cette espèce, l été, suggère qu une partie de la population quitte la zone durant la période estivale, certainement pour migrer vers les aires d alimentation des hautes latitudes. Cependant, des cris sont toujours détectés durant l été et au début de l automne, ce qui suggère qu une partie de la population n effectue pas de migration et reste en zone subantarctique. Or, exclusivement du milieu de l été à la fin de l automne, une autre sous-espèce de baleine bleue, la baleine bleue pygmée de type Madagascar est détectée. Cette période coïncide avec l activité d alimentation de l espèce. La présence de ces deux sous-espèces autour de Crozet durant l été et l automne suggère alors que cette zone subantarctique semble être une aire d alimentation privilégiée pour ces deux grandes baleines.The main goal of this PhD was to improve knowledge about the current occurrence and seasonal distribution pattern of baleen whales in the southwestern Indian Ocean. The intensive whaling during the 20th century reduced dramatically baleen whale population to near extinction. The lack of information about the current occurrence and distribution of baleen whale underscore the difficulty to study these species with traditional visual survey in the Southern Ocean. Here, one year of acoustic observations in sub Antarctic area (near Crozet archipelago) was examined to assess baleen whale presence by using species specific calls in a detection distance range of approximately 250km (estimate from parabolic equation propagation loss models). Fin whale calls, Antarctic blue whale calls and pygmy blue whale (Madagascar type and Australia type) calls were detected. The variation of call number over one year revealed different patterns of whale occurrence. Detection of fin whale calls were very scarce and occur only during winter and fall time. Antarctic blue whale calls were detected year round, but the decrease of calls number during summer time suggests, on the one hand, one part of Antarctic blue whale population leave the area during winter, probably to migrate and spend feeding period in higher latitude, and on the other hand another part of the population seems to stay in the sub Antarctic area. In the same time, and only during this specific feeding season, pygmy blue whale calls were detected in this area. Occurrence of these two blue whale sub-species during summer period suggests that this specific area could be a high biological productivity region which represents a baleen whale feeding ground.LA ROCHELLE-BU (173002101) / SudocSudocFranceF

Detection of Mysticete Calls: a Sparse Representation-Based Approach

This paper presents a methodology for automatically detecting mysticete calls. This methodology relies on sparse representations of these calls combined with a detection metric that explicitly takes into account the possible presence of interfering transient signals. Sparse representations can capture the possible variability observed for some vocalizations and can automatically be learned from the time series of the digitized acoustic signals, without requiring prior transforms such as spectrograms, wavelets or cepstrums. The proposed framework is general and applicable to any mysticete call lying in a linear subspace described by a dictionary-based representation. The potential of the detector is illustrated on North Pacific blue whale D calls extracted from the DCLDE 2015 low frequency database as well as on ``Madagascar'' pygmy blue whale calls extracted from the OHASISBIO 2015 database. Receiver operating characteristic curves (ROC) are calculated and performance is compared with three other methods used for automatic call detection: the XBAT bank of matched spectrograms, a bank of matched filters derived from a generalized likelihood ratio approach and a kernel-based spectrogram detector. On the test data, the ROC curves show that the proposed detector outperforms these three methods

Detection range modeling of blue whale calls in Southwestern Indian Ocean

International audienceIn the Southwestern Indian Ocean, one year of continuous acoustic data from calibrated hydrophones maintained by the International Monitoring System provided data on blue whale calls from two subspecies Antarctic and pygmy blue whales. Using an automatic detection method with a fixed threshold, both call types were detected and received levels were measured for each detected call. By using a parabolic equation loss model configured with the precise characteristics of the biological source, hydroacoustic station, and environment in the study area, distances at which calls could be detected were estimated. These methods were used to define the maximum detection range around each array of hydrophones and the influence of the seasonal variation of the ambient noise and sound velocity on the detection ranges. Results showed that detection ranges were critically dependent on the choice of the biological source's input parameters, including frequency bandwidth and source level. Over the course of the year, detection distances were different for both subspecies; the pygmy blue whale seemed to be consistently closer to the station than the Antarctic blue whale. The distribution of the estimated distances confirmed the presence of both subspecies of blue whales near the Crozet Islands showing the importance of this sub-Antarctic area for these endangered species, especially during the austral summer feeding season

Sounds from airguns and blue whales recorded from a long term hydrophone network in the Southern Indian Ocean

International audienc

Seasonal and geographical occurrence of blue whale stereotyped and non-stereotyped calls in the Southern Indian Ocean

International audienc

Long‐term acoustic monitoring of nonstereotyped blue whale calls in the southern Indian Ocean

International audienceMonitoring the presence of blue whale (Balaenoptera musculus ssp.) stereotyped calls has been a widely used method to assess the different populations' distribution worldwide. All blue whale populations also produce nonstereotyped vocalizations, or D-calls. Here, we monitored the presence of D-calls in long-term records from a large hydrophone array located in the open southern Indian Ocean, using an automated detection method and manual validation of the detections. D-calls were detected at all sites of the array, which extends from 24°S to 56°S, but the majority of them were detected at the two southernmost sites. We observed a latitudinal shift in their seasonal occurrence, with more D-calls in the north during austral autumn and winter and more in the south during austral spring. The geographical occurrence of D-calls compared to that of songs indicates that blue whale acoustic behavior switches from a song-intensive and sparse-D-call emission in the north to song-moderate and more intensive D-call emissions in the south. These findings support the hypothesis that both call types are used for different purposes, as D-calls are mainly detected around foraging grounds and songs in wintering grounds. Monitoring both call types might therefore be a relevant acoustic indicator of blue whale behavior

Detection strategy for long-term acoustic monitoring of blue whale stereotyped and non-stereotyped calls in the Southern Indian Ocean

International audienceThe most common approach to monitor mysticete acoustic presence is to detect and count their calls in audio records. To implement this method on large datasets, polyvalent and robust automated call detectors are required. Evaluating their performance is essential, to design a detection strategy adapted to study the available datasets. This assessment then enables accurate post-analyses and comparisons of multiple independent surveys. In this paper, we present the performance of a detector based on dictionaries and sparse representation of the signal to detect blue whale stereotyped and non-stereotyped vocalizations (D-calls) in a larg acoustic database with multiple sites and years of recordings in the southern Indian Ocean. Results show that recall increases with the SNR (Sound to Noise Ratio) and reaches 90% for positive SNR stereotyped calls and between 80% and 90% for high SNR D-calls. A detailed analysis of the influence of dictionary composition, SNR of the calls, manual ground truth as well as interference types and abundance, on the performance variability is presented. Eventually, a detection strategy for long term acoustic monitoring is defined