Mémoire

Abstract

The spatio-temporal distribution of prey is one of the main drivers of marine megafauna dynamics but the lack of prey data is a common limitation in ecological studies. The objective of this study was to investigate the spatio-temporal distribution of the epipelagic low- and mid- trophic level biomass in the Azores, using outputs from the ecological model SEPODYM- LMTL. The spatial distribution and overall biological productivity of three model variables: net primary production (NPP), zooplankton and micronekton, were analyzed from 1998 to 2023. Based on these long-term biomass, three categories of productivity zones were defined (recurrent, occasional and unfavorable) in order to classify the abundance of the preys. Additionally, the productivity was assessed within the newly established Marine Protected Area (MPA) network to evaluate whether MPAs were located in areas of high productivity, which could represent attractive habitat for marine megafauna. The importance of these productivity zones for cetaceans was also evaluated using the long-term dataset (2001-2015) of sightings collected by the Azorean Fisheries Observer Program (POPA). Important inter-annual variabilities were observed for the three model variables, with no global trend in the biomass or phenology of NPP and zooplankton. The spatial distribution of resources exhibited a strong latitudinal gradient, with a productive area around the islands and north of 37°N, corresponding to the Azores Counter Current (AzCC). In the MPA network assessment, fully protected areas exhibited higher productivity from April to November for the three variables. In contrast, highly protected areas had similar or lower productivity than unprotected areas. Regarding cetacean distribution, for the three variables, baleen whales were observed in higher proportions in the occasional zones, especially in July, and no clear patterns were found for dolphins and deep divers’ groups. The spatial patterns obtained provided an essential baseline to evaluate the ecological importance of the new MPA network, as fully protected areas overlapped with more productive waters. The analysis of cetacean functional groups further illustrated the potential relevance of these productivity zones for higher trophic levels, although additional environmental predictors and long-term monitoring will be required to fully assess their ecological significance.