The expansion of the world's fisheries and the decline in fish stocks have increased conflicts between humans and marine megafauna. These conflicts result from negative interactions that are either direct (bycatch and/or depredation on catches) or indirect (competition for resources). They have socio-economic costs for the human communities dependent on the fishing activity and they impact the survival of the megafauna species and the ecosystems involved. However, long-lasting solutions for coexistence between fisheries and marine megafauna, which require inter- and trans-disciplinary research to be identified, remain limited. Therefore, the aim of my PhD is to produce integrated knowledge that can help in identifying the conditions required for megafauna species conservation, the sustainability of exploited resources and the socio-economic viability of the fishing activity. Specifically, under a co-supervision combining social sciences and marine ecology, I will use the principles of Sustainability Science and a multi-site approach (longline fisheries - marine megafauna conflicts in the French Southern lands and in New Caledonia) i) to understand both the anthropogenic and ecological drivers and consequences of these conflicts, and ii) to examine new management approaches that can ensure the sustainability of the whole socio-ecosystems involved.

Managing conflicts between humans and marine predators is hampered by limited knowledge on the ecological and behavioural mechanisms leading species to interact with humans. Among these mechanisms, the drivers of variation in the propensity of individuals to take risks by approaching humans, including the role of personality traits, remain poorly understood. The killer whale is among the species most frequently involved in conflicts with humans in the marine environment, mainly through depredation on fishery catches, a behaviour that has been acquired by many populations of the world. From the case conflict associated with killer whales feeding on fisheries catches around the Crozet islands, the main objective of my PhD project is to examine how inter-individual heterogeneity in behaviours are associated with variation in personality traits, and to investigate how these traits contribute, among other factors, to the response of individuals to a human activity involving risks and how they influence population dynamics.

Killer whales play a fundamental role in many marine ecosystems as apex predators affecting food web dynamics. However, within the Southern African Subregion (split between southern Africa and the Southwest Indian Ocean [SWIO]) many knowledge gaps and a lack of regional understanding regarding connectivity, predatory behaviour, demographics and ecosystem impacts persist. These data remain vital to understanding the species in general, its ecosystem use, impacts on other species within the ecosystem, and for conservation management. Additionally, depredation has and is affecting longline fisheries targeting tuna and Patagonian toothfish throughout the region, resulting in major economic losses, conservation concerns, and unquantified ecosystem effects, all of which are devoid of assessment for southern Africa specifically. My PhD project aims to establish a baseline of ecological understanding for the species both locally around southern Africa and regionally throughout the SWIO, incorporating depredation as a likely contributor to role alteration. To achieve this a multifaceted approach using (i) genetics, (ii) stable isotopes, (iii) photo-identification and (iv) ecosystem modelling will be used to: (i) provide an evolutionary template for connectivity, identify populations, and assess gene flow, effective population sizes, and diversity; (2) act as a proxy for predatory behaviour and trophic interactions (skin), provide a timeline of potential dietary shifts (teeth); (iii) assess population size, health, movements and association with depredation; and (iv) quantify and understand the ecological role and ecosystem effects of killer whales with and without competing fisheries.

The killer whale (Orcinus orca) is the undisputed marine apex predator. Consequently, understanding the factors influencing its distribution, habitat use, and foraging ecology is crucial for assessing the impact of environmental changes on its population trajectories, prey dynamics, and overall marine ecosystem health. Over recent decades, killer whales have increasingly been observed interacting with commercial fisheries worldwide, particularly by removing high-value fish from long-line hooks. This depredation behaviour poses significant challenges, including financial losses for fisheries, inaccurate fish stock assessments, and ecological consequences for marine ecosystems and killer whales alike. In south-eastern Australia, killer whales are known to frequently interact with and depredate blue-eye trevalla and tuna long-line fisheries, yet little is known about their distribution, movements, feeding ecology, and demographics. A similar depredation behaviour is exhibited by the population of killer whales around St. Paul and Amsterdam Islands in the southern Indian Ocean. My research focuses on developing habitat models to explore the environmental drivers of killer whale distribution and movement in these regions. This work provides essential insights into managing fisheries and conserving the marine ecosystems upon which killer whales depend by addressing critical gaps in our understanding of killer whale populations in the Southern Hemisphere and their adaptive feeding strategies.

Patagonian toothfish fisheries have become the primary economic activity in Subantarctic waters. However, these fisheries undergo a high level of depredation by two large toothed whale species; killer whale and sperm whale. Understanding whales foraging behavior is necessary to estimate socio-economic and ecological implications of depredation. Therefore, using satellite tracking data collected for killer whales in southern Indian and southern Atlantic, my research project addresses three key research questions: 1)  what are the areas used by killer whales as foraging grounds in absence of fishing vessels? 2) to what extent do these areas overlap with those used by fisheries? 3) At what distance and during which stages of fishing operations do killer whales detect fishing vessels?

Killer whales of the Crozet islands have undergone a sharp decline in the late 1990s / early 2000s. This additive mortality event was largely due to whales being exposed to lethal control practices when interacting with illegal fisheries and was shown to have deeply affected the social organisation of the population. However, to what extent kinship drives this social organization is still poorly known.

Therefore, using both photo-identification data and tissue samples, the aim of my study is to characterize the social organisation of the Crozet’s killer whales over the last two decades, their genetic diversity and the pedigree (kinship) among them.

As apex predators, killer whales have a significant influence on ecosystem dynamics, and understanding their diet is essential to define their ecological niche and assess their interactions with both prey and human activities such as fisheries. Around the Saint Paul and Amsterdam Islands in the southern Indian Ocean, killer whales  feed on fish caught on fishing lines of the local fishery targeting blue-eye trevalla (Hyperoglyphe antarctica), striped trumpeter (Latris lineata), and hapuku (Polyprion oxygeneios),  but the prey they naturally feed on, nor the contribution of blue-eye trevalla to their diet, are unknown.  

This study assessed the diet of killer whales around Saint Paul and Amsterdam through a stable isotope (δ¹³C and δ¹⁵N) analysis on skin samples collected between 2022 and 2025.  Specifically, the study aimed to i) investigate how killer whale skin conservation methods (ethanol vs. dry) could affect the isotopic signatures and lipid contents of the samples; ii) determine the trophic niche of individuals and to compare it with that of other killer whale populations, and iii) to estimate the relative importance of the fish species targetted by the fishery to the diet of individuals. 

Killer whales rely on a sophisticated communication system that includes clicks, buzzes, whistles, and stereotyped (or pulsed) calls. The latter are stable over time, and form dialects that may be unique to each population, or social group. While dialect differences have been demonstrated for Northern Hemisphere populations, acoustic studies on Southern Hemisphere killer whales remain limited, particularly in subantarctic regions. This applies especially for the Crozet killer whale population, which, despite long-term monitoring since the 1980s, are still poorly acoustically known.  This study presents the first catalogue of stereotyped calls from different social groups of Crozet killer whales population. Acoustic and visual data were collected during Patagonian toothfish longline fishing operations with which killer whales interacted at various sites across the archipelago in January 2024. From the 2,398 pulsed calls detected, only high-quality ones were retained, using an innovative method combining automatic SNR calculation and visual examination. Preliminary results reveal a structured acoustic repertoire characterized by recurring sound patterns potentially specific to certain social groups. Spectral and temporal comparisons with calls from other killer whale populations suggest distinctive acoustic signatures, potentially reflecting cultural or ecological specificity. This catalogue lays the groundwork for further studies on the acoustic diversity of this population and could contribute to future studies on dialect evolution. Moreover, this study paves the way for more effective PAM of this population, leading to better comprehension. 

The socio-economic and ecological implications of depredation are especially strong in the Patagonian toothfish longline fisheries and the sub-Antarctic ecosystems they operate in. These fisheries have become the primary economic activity of sub Antarctic waters and vessels experience high levels of depredation by two large toothed whale species; killer whales and sperm whales.  The amount of fish these species remove from the fishing gear pose a real challenge for the assessment of targeted stocks, and the behaviour is known to impact depredating killer and sperm whale populations, which are subject to high conservation concerns. Together with the socio-economic costs depredation incurs to fishers and fishing companies, these impacts make the development of mitigation solutions a priority.  However, these solutions are still hampered by a lack of understanding of the natural feeding ecology and distribution of the whales, and the factors determining their decisions to switch behaviour to depredation. Therefore, using satelite tracking data collected for 35 killer whales in the southern Indian and Altantic oceans, my research project addresses three key research questions: 1)  what areas killer whales use as foraging grounds in absence of fishing vessels? 2) to what extent do these areas overlap with those use by fisheries? 3) At what distance and during which stages of fishing operations do toothed whales detect fishing vessels? 

I have been working on conspecific aggression in killer whales as part of my MSc at the University of Montpellier. The project involves using conspecific scars visible in photo-identification images as a proxy for physical interactions and aims to determine whether prey preferences and social structure influence scarring rates by comparing three distinct populations: the "Bigg's" and "Northern resident" killer whales in British Columbia, and the killer whales of the Crozet archipelago. It also considers whether demographic factors such as age and sex may influence physical interactions as well as how conspecific scars heal over time. The work is a collaboration between the UMR MARBEC (France) and Bay Cetology (Canada).