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October 13, 2022

Anissa Volanandiana, PhD student, on her study of fish diversity in Ranobe Bay

The subject of my thesis is the logical continuation of my Masters. I am a beneficiary of the ARTS scholarship of the IRD (Institut de la Recherche pour le Développement) to work on the biodiversity of reef fishes in southwestern Madagascar, in collaboration with the ARMSRestore project.

Marine resources exploited by small-scale fisheries play an important role in the food security of Malagasy coastal inhabitants, particularly the coastal communities of southwestern Madagascar. However, population growth and an increase in fishing pressure is leading to a decrease in the size of the fish landed and the overall biomass of the catch. The assessment of the status of the reef fisheries in southwestern Madagascar remains difficult due not only to the lack of regular monitoring data on landings, but also to the challenges of accurate species identifications.

My study aims to improve the knowledge of the exploited fish diversity with respect to those that are caught and the perceptions held by the fishermen. The collection of data on the study of the ichthyological diversity caught by small-scale fishermen in 12 villages of Ranobe Bay is being carried out from October 2021 to December 2022 within the framework of the monitoring of fish landings. My work is based on the collection of images and fin tips of the fish caught by the six main gears used in this area: gillnets, handline, speargun, beach seine, bottom seine and mosquito net trawl.

For the overall diversity in the areas exploited by the fishermen of Ranobe Bay, I will use the fin tips and environmental DNA metabarcoding. Water samples will be collected from the sites where the six artificial reefs will be constructed and also from nearby natural coral reefs, considered as control sites. Environmental DNA sampling will be done prior to the installation of the artificial reefs scheduled for December 2022 and one year after the artificial reef installation.

The study of exploited fish diversity and overall diversity will be combined with a study of fish diversity as perceived by fishermen. It will be based on a survey of the fishermen of the area. 

The collection of images and fins of fish will be completed at the end this year. The next step in data collection will be the first environmental DNA sampling at the end of the year, to know the global ichthyological diversity before the installation of artificial reefs in Ranobe Bay.