Unsupervised Individual Whales Identification: Spot the Difference in the Ocean

International audienceIdentifying organisms is a key step in accessing information related to the ecology of species. But unfortunately, this is difficult to achieve due to the level of expertise necessary to correctly identify and record living organisms. To try bridging this gap, enormous work has been done on the development of automated species identification tools such as image-based plant identification or audio recordings-based bird identification. Yet, for some groups, it is preferable to monitor the organisms at the individual level rather than at the species level. The automatizing of this problem has received much less attention than species identification. In this paper, we address the specific scenario of discovering humpack whales individuals in a large collections of pictures collected by nature observers. The process is initiated from scratch, without any knowledge on the number of individuals and without any training samples of these individuals. Thus, the problem is entirely unsupervised. To address it, we set up and experimented a scalable fine-grained matching system allowing to discover small rigid visual patterns in highly clutter background. The evaluation was conducted in blind in the context of the LifeCLEF evaluation campaign. Results show that the proposed system provides very promising results with regard to the difficulty of the task but that there is still room for improvements to reach higher recall and precision in the future

Etude des interactions mère/jeune chez la baleine à bosse

In humpback whales (Megaptera novaeangliae), maintaining social bonds between females and their newborns involves different sensory modalities such as hearing, touching and vision. While acoustic communication in male singers of this species has been extensively studied, social sounds, especially those produced by the females and their newborns have been poorly documented. This study describes the social sounds present in acoustic recordings focused on mother-calf groups and discusses the vocalizations used by females and calves in mother-offspring interactions. By considering the most frequent sounds from their vocal repertoire, an analysis focused on the determination of the source of the low-frequency sounds produced by the mother have been carried out and analyses were performed to investigate the individuality of some vocalizations belonging to the mothers and the calves. A description of the behavioural context of their vocal production was performed and the diving profiles of mother-calf pairs were described. Moreover, females with their calves spend a lot of time on the water surface. Mothers are often static at the surface while calves move around them. This study is also dedicated to the understanding of their surface behaviours, considering the behaviours initiated by calves. A series of analyses were carried out to determine whether calves exhibited lateralization behaviours in relation to their mothers. Finally, by using photogrammetry method, mother-calf lengths were measured, and calves spatial range around their mothers was investigated.Chez les baleines à bosse (Megaptera novaeangliae), le maintien des liens sociaux entre les femelles et leurs nouveau-nés implique différentes modalités sensorielles telles que l'ouïe, le toucher et la vision. Si la communication acoustique chez les mâles chanteurs de cette espèce a été largement étudiée, les sons sociaux, en particulier ceux produits par les femelles et leurs nouveau-nés, ont été peu reportés. Cette étude décrit les sons sociaux présents dans les enregistrements acoustiques axés sur les groupes mère-baleineau et discute des vocalisations produites par les femelles et les baleineaux dans les interactions mère-jeune. En considérant les sons les plus fréquents de ce répertoire vocal, une analyse centrée sur la détermination de la source des sons de bass fréquence produits par la mère a été effectuée et des analyses ont été réalisées pour mettre en évidence l'individualité de certaines vocalisations appartenant à la mère et à son petit. Une description du contexte comportemental de leur production vocale a été réalisée et parallèlement, les profils de plongée des mères et de leurs nouveau-nés ont été décrits. En outre, les femelles et leurs petits passent beaucoup de temps à la surface de l'eau. Les mères sont souvent statiques à la surface tandis que les baleineaux évoluent autour d'elles. Cette étude est également consacrée à la compréhension de leurs comportements de surface, en tenant compte des comportements initiés par les baleineaux. Des séries d’analyses ont été réalisées pour déterminer si les baleineaux présentaient des comportements de latéralisation par rapport à leur mère. Enfin, en utilisant la méthode de photogrammétrie, les tailles des femelles et des nouveau-nés ont été mesurées, ainsi que l'espace utilisée par les baleineaux autour de leur mère

First insights on spatial and temporal distribution patterns of humpback whales in the breeding ground at Sainte Marie Channel, Madagascar

The Sainte Marie Channel on the northeast coast of Madagascar is an important breeding ground for humpback whales; the first observation of birth was documented there, yet it has never been investigated for phenology and habitat use of humpback whales. The present study was aimed at examining temporal and spatial distribution patterns and the encounter rate of different social groups of humpback whales during the breeding season. We used a large set of opportunistic sightings data collected from whale-watching boats. A total of 3 247 sightings were collected during 897 whale-watching trips conducted between June and September from 2009 to 2013. Our study complements previous information on the seasonal presence of humpback whale social groups by demonstrating a persistent and well-structured temporal pattern in the succession of the different groups. Over the different years of the study period, groups without calves consistently dominated the first 30 days of the breeding season, followed by an increase in groups with calves. Interannual differences were observed in the encounter rates, with significantly higher global encounter rates in 2009, 2011 and 2013 (2.2, 2.3 and 2.3 sightings h–1, respectively), and likewise for the mean encounter rates for groups with calves. In contrast, the encounter rate of groups without calves was similar over the study period. Although our study area exhibits a narrow configuration and poorly contrasting physiographic features due to its restricted spatial extent, we report a spatially segregated pattern of humpback whale social groups in the Sainte Marie Channel. A general linear model showed that groups with calves were influenced by water depth and distance from shore, being observed mostly in shallow waters (to 20m depth) and close to the coastline (6 km). Our findings will be useful for the development of strategic sustained management plans by providing baseline information on humpback whale distribution at an important but poorly documented breeding site.Keywords: habitat use, Indian Ocean, Megaptera novaeangliae, phenology, seasonality pattern, social group

Do the new-born calves of humpback whales (Megaptera novaeangliae) have a preference to position themselves at the side of their mother?

Spatial proximity to mothers is a key factor in offspring survival in group-living mammals. In humpback whales (Megaptera novaeangliae), an extreme migrating species, new-born calves stay close to their mothers. This proximity can be modified by the presence of other congeners or other species. The spatial relationship between mother and calf can therefore vary with social contexts. The position of the calf relative to its mother was investigated in different social contexts: alone, with one or several escorts; and in the presence of free divers. The positions of the calves in the 3D space surrounding their mothers were recorded using video footage of mother-calf pairs in 3 breeding sites located in the Indian and Pacific oceans, with the space methodically divided into ten positions. Calves mainly preferred positions above their mother, either on the right or the left; a strategy allowing the calf to be in an optimal position to breathe and to benefit from the hydrodynamic aspiration flow of its mother. A position below the mother was significantly related to resting behaviour, involving physical contacts with the mother and thus reinforcing their social bond. Finally, calves in the presence of free divers neither approached nor moved away from them, suggesting limited direct impact on their behaviour.

Morphometric study of humpback whale mother-calf pairs in the Sainte Marie channel, Madagascar, using a simple drone-based photogrammetric method

Morphometric studies of humpback whales (Megaptera novaeangliae) occurring in the Indian Ocean area have been limited by the technology currently available. In the Sainte Marie channel, Madagascar, straightforward aerial single-camera photogrammetry was tested on mother-calf pairs that combines standard Unoccupied Aerial Vehicle (UAV) with free, easy-to-access, and user-friendly software. The goals of the study were to estimate mother and calf body measurements and to investigate the effect of maternal parity (primiparous versus multiparous, based on length) on calf size. A mean length of 12.4±1.2 m for mothers (N = 16) and 5±0.9 m for calves (N = 16) was estimated. The size of calves did not depend significantly on maternal parity. The photogrammetry method used was simple and cost-effective, yet produced convincing morphometric measurements with acceptable precision and accuracy. The coefficients of variation (CVs) of repeated estimates and the level of error were relatively low (CV = 2.31 % for a known-sized object and average CV = 2.52 % for individual whales; average error = 1.8 % for a known-sized object). These results will encourage more teams to study the morphometry of large marine mammals despite limitations in terms of resources