Copyright : Laboratoire LEMAR- 2018
Maxence DUMORTIER
Gonçalo Marques et Marie Vagner
Région Bretagne /EDSML
Small pelagic fish communities that make up the so-called Eastern-boundary upwelling ecosystems, which are the most productive ecosystems in the world, are only rarely compared. However, if we look at the Humboldt (Peru), Baja California (Mexico) and Benguela (South Africa) ecosystems, the most abundant species are of the same genus: e.g. Sardinops spp, Engraulis spp, Etrumeus spp. etc. These species are all characterized in these systems by strong variations in abundance that are difficult to predict. Characterizing the similarities and differences between these populations in terms of life history traits, diet, and reproductive strategy is an approach that has never been done before at this scale and should reveal some of the factors controlling these variations. The thesis proposes here to characterize the ecological diversity of these species within the conceptual framework of DEB (Dynamic Energy Budget) theory and to compare ecological diversity and observed dynamics of these populations by means of DEB-IBM (Individual-Based Models) population models forced by simplified representations of the environment from existing physical-biogeochemical models of these systems. The hypothesis tested in this thesis work will be the importance of bottom-up control over these populations via a mechanistic individual and population modeling approach. This work will also provide a basis for the development of community scale models. The data used will be the growth, reproduction and energy content monitoring data from the fisheries institutes partners of the EUR ISblue funded OMEGA project on "Effects of declining trophic availability in OMEGA 3 on global small pelagic and human populations". The differences in Omega 3 content between populations that will be established during the project will also be taken into account in the DEB modelling approach. The experiment on the effects of omega 3 deficiency on sardine (Sardina pilchardus) conducted in the framework of this project will also provide calibration data for the DEB models. The objectives of the thesis will be: i) to characterize the ecological diversity of these species in terms of growth, development, energy content and reproductive strategy, ii) to develop a new method for multi-species estimation of the parameters of a DEB model applied to small pelagics, based on the phylogenetic distance between species and iii) to test the sensitivity of DEB-IBM population models to the different sets of estimated parameters. The responses obtained from the different population models will allow the formulation of hypotheses on the specific control factors of each small pelagic community. Keywords : Small pelagic fish, upwelling ecosystem, life cycle models, Dynamic Energy Budget theory, multi-species parameter estimation, population dynamics, bottom-up control
2025
Discovery
