A standarized approach of data based indicators to monitor long-term evolutions and track biodiversity losses in West african marine ecosystems: Description of the approach and implementation in Guinea.

An integrated analytical approach is proposed for monitoring and assess the ecological status of the coastal marine ecosystems in West Africa subject to strong anthropogenic pressures. This approach is based on a certain number of conceptual foundations, i.e. guiding principles resulting from methodological constraints identified and discussed in a previous study (Jouffre et al. 2023 - WP4 PESCAO-DEMERSTEM project) and which will be recalled here. These foundations are dictated above all by a major operational objective : that of the routine production of quantitative results, easily interpretable, as robust as possible, and able to be used within the framework of scientific support for public policies related to environmental and fisheries sustainable management in west-african countries. Following from the previous considerations, the approach is mainly based on the estimation of simple ecosystem indicators adapted to the field data available in this region. Thus several of these indicators are directly derived from historical data series from national scientific trawling campaigns available in several countries of the region from the period of the 1980s to present (in Guinea, Senegal and Mauritania). They are calculable and their updating is possible routinely using R script. This is among others the case for indicators designed for the West African marine macrofauna biodiversity monitoring, a set of indicators on which we will focus in this presentation. Temporal (multi-decadal series) and/or spatial estimates of such indicators will be presented and discussed in order to concretely illustrate our approach and its implementation on concrete data. Based on this Guinean case study, our conclusion will address the question of the potential advances that a periodic and generalized monitoring of West African coastal ocean waters based on this indicator methodology could bring. We will try to highligth why it could achieve a very useful – even major – contribution in terms of scientific information on the health, dynamics and future trajectory of the ocean, and on its conservation and sustainable uses, in a region that remains largely under-documented with regards to these aspects.