Lola Gilbert, PhD candidate
Role of marine mammals in nutrient fluxes and carbon storage
The research carried out as part of my PhD aims to study the biofeedback mechanisms that marine mammals can have on the ecosystem, particularly through their role in providing the photic zone with nutrients and micronutrients via their faeces. The idea is to quantify the role of marine mammals no longer just as consumers of upper levels of trophic networks but also on the development of primary levels by stimulating the growth of phytoplankton, and thus indirectly the storage of carbon within trophic networks. Based on bioenergetic models linking the absorption of nutrients through the consumption of prey and the excretion of residues, the approach developed as part of my work will include different spatial and temporal scales, different ecosystems and different communities of marine mammals. The data mobilised will include population estimates from aerial census campaigns, telemetry data, analyses of prey and faeces nutrient content and stranding data. Thanks to models predicting the impacts of changes in the abundance of these predators on the dynamics of nutrients in surface waters at the different spatiotemporal scales studied, the aim of this work is to provide scientific arguments to guide public conservation policies.
Mathilde Chevallay, MSc
Fine scale adaptation of foraging behaviours in relation to prey capture success in fur seals
The main objective of this research is to investigate decision process of northern and Antarctic fur seals during foraging according to their foraging success. Optimal Foraging Theory predicts that predators which adopt hunting strategies that maximise their energy intake per unit of time would have more energy to allocate to reproduction and survival over a lifetime, and thus should show a greater overall fitness. Within this framework, predators must maximise acquisition and assimilation of prey and minimise the costs linked to the search, pursuit and capture of prey. As predators are foraging in a prey patch, prey abundance will decrease with the time spent in the patch, the optimal time when a predator should leave a patch to search for a more profitable one, is hypothesized to be when the local capture rate decreases below the average capture rate of the environment. As predators do not have a perfect knowledge of the spatial distribution and the quality of prey patches in their environment, they likely use their past prey capture experiences to estimate when it is optimal to leave a patch.Thanks to recent improvements in biologging, we can obtain information on both the fine-scale foraging behaviour of cryptic marine animals and indices of prey availability, and therefore provide new insights in the study of decision-making processes in cryptic marine animals that have been difficult to study up to now. Understanding decision-making processes in predators is essential to understand how they respond to prey availability and subsequently how they may respond to environmental changes.
Jade Chevassu, MSc
Relationships between oceanographic parameters, marine organism assemblage and foraging efficiency of Southern elephant seals through cutting-edge biologging data
Marine ecosystems are currently subject to drastic and rapid changes from the physico-chemical level to biological levels with consequences on trophic web structures and dynamics, on top predators foraging behaviours and success. However, consequences of environmental changes on ecosystem functioning often remain poorly assessed. It is therefore essential to better assess the horizontal and vertical distribution of marine organisms, including the zooplankton and fish populations, in relation to environmental parameters, as well as the impact these have on the distribution and foraging behaviours of top marine predators, such as southern elephant seals (Mirounga leonina). The objective of my study is to better understand how southern elephant seals successfully use their environment to forage during their months-long trips at sea by 1 - classifying density and size classes of organisms in 3D in the water column on the path of elephants – including temporal variations due to nyctemeral migrations – using functional data analyses (FDA) on active acoustic profiles, 2 - assessing the relationships between these density and size classes of organisms and the characteristics of water masses (temperature, salinity) and bioluminescence events on one hand, and with elephant seals prey capture attempts and changes in body conditions on the other hand. The results will provide a greater understanding on the relationship between physico-chemical properties of the elephant seal habitats, the plankton and nekton assemblage of the food web they feed into, and the foraging efficiency related to these different ecosystemic assemblage.
Swann Heliot, MSc
Impacts of oceanographic environment on Hooded seal movement and foraging performances
Arctic ecosystems face one of the fastest environmental change on Earth, but the ecological consequences of these changes remain poorly understood due to the difficulties to collect in situ oceanographic and ecological data. As top marine predators, hooded seals integrate the cascade of events occurring from the bottom to the top of the food chain and are considered early warning indicators of environmental changes. Their life cycle depends on pack ice for access to foraging ground, and for a haul-out substrate for breeding and moulting. They are also deep divers, range throughout the Atlantic side of the high Arctic, and feed on a wide range of prey from krill to fish and squids. As such, they are the perfect platform to widely sample fast changing northern and polar ecosystems. Consequently, the goal of this study is to understand how local variations in oceanographic conditions – especially sea ice coverage, temperature, salinity, light, currents, winds and/or primary productivity – as well as prey availability affect and drive the movement patterns, foraging success and body conditions of seals. This will help us assess the physical and biological environment of “sentinel” seals and evaluate ecological consequences to environmental changes in terms of foraging strategies, efficiency and distribution.
Maria Isabel Barros, MSc
Categorization of marine organisms detected by seal-borne micro-sonar tags using machine learning methods.
To understand the consequences of environmental changes on ecosystem functioning and particularly on intermediate trophic levels (i.e. nekton: zooplankton, gelatinous, fish and squid ...), a new, innovative, state-of-the-art biological recorder was developed that allows active echosounding of water masses, and therefore record the vertical distribution and density of zooplankton and mesopelagic fish in the water column. This new recorder (i.e. micro-sonar) was deployed on twelve southern elephant seals (Mirounga leonina) and recorded on average for 30 days and at a ping frequency of 25Hz. Consequently, the volume of high-resolution acoustic data recovered, as well as other types of data recorded (high-resolution acceleration, depth, salinity, temperature etc...) is large (250GB per deployment) and growing rapidly, which consequently prohibit prohibit manual analysis in their entirety. To get the full benefit of the information recorded by such tags, our objectives were to develop a micro-sonar image processing methodology based on machine learning to regularly extract relevant information from the obtained echograms. The goal was to i) determine the overall density, frequency and size of organisms in water bodies (whether or not they are targeted by predators), ii) isolate the portion of the dataset where relevant predator-targeted prey encounter signals are present in the echograms, and classify these extracted signals into isolated vs. schooling prey, active vs. passive prey, as well as acoustic signal size and intensity categories, and iii) identify vibrissae deployment events in the echograms.