Ecological Knowledge of Local Fishers, Economic Importance, Morphological and Genetic Variations of Parachanna Obscura (Gunther, 1861) Populations in the Context of Climate Change and Anthropogenic Pressures in West Africa.

Abstract

This thesis aimed to contribute to the development of appropriate strategies to ensure the conservation and sustainable management of fisheries resources, in general, and Parachanna obscura in particular, under changing climatic conditions and expanding human activities, for future use in aquaculture in West Africa. We specifically investigated (1) fishers’ perception of climate change, its drivers and other anthropogenic activities affecting freshwater fish biodiversity, as well as the species of fish locally threatened in the Ivorian freshwater ecosystems; (2) fishers’ knowledge of the goods and services provided by P. obscura, and on local threats to populations of the fish in Côte d’Ivoire freshwater ecosystems; (3) morphological variation among populations of P. obscura according to climate and habitat gradient; (4) genetic diversity and structure of P. obscura populations from the West Africa region. Face-to-face interviews and a structured questionnaire were used for data collection from 381 fishers in the first two objectives. The morphological variation was assessed based on geometric morphometric (GM) method. We developed a set of 21 highly polymorphic microsatellite markers for studying genetic diversity and population structure. The result indicated a high proportion of fishers’ awareness of climate change, and its drivers. The majority of fishers observed decreases in precipitation (87.9%) and increases in temperature (76.1%) over the past years. A significant decrease in fish abundance was also observed by fishers, with climate change and many anthropogenic activities pointed out as the main causes for this decline. Many fish species were listed as locally threatened within Ivorian freshwater ecosystems. Our results further showed that P. obscura is an economically important fish for local communities with consistent market price (the kg sold between 1.5 and 3 € on average). Fishers stated that the species is not yet produced in aquaculture, and expressed their willingness to support its introduction into aquaculture. A significant decrease in the abundance of this fish was observed, perceived mainly due to overfishing, lack of rainfall, and other anthropogenic activities. We found significant morphological variations among P. obscura populations, but only modest effects of climate and habitat variables on fish shape were obtained. Spatial distance and isolation among populations increased morphological distances, but this trend was likewise relatively weak. The results of genetic diversity showed a relatively low intra-genetic diversity in the fish populations, certainly attributable to the confinement of fish in segregated catchments, resulting in limited gene flow, and local adaptation processes. Additionally, a strong genetic differentiation (FST>0.5) was found between most putative populations, reflecting the allopatric evolution in watersheds without hydraulic connectivity. The information obtained from this study constitutes a prerequisite for developing and implementing studies or policies aimed at mitigating and combating the negative effect of climate change and anthropogenic activities on freshwater ecosystems. Our results are also relevant for the sustainable management and conservation of P. obscura fisheries resources, and for deciding to cultivate the species in order to support the regional demand for fisheries products.