A bi-frequency discrimination method of copepods in the Senegalese coast [résumé]
Résumé
The Canary Current Large Marine Ecosystem (CCLME) is one of the most productive marine ecosystem worldwide and is key for food security for numerous African countries. Nevertheless, its function remains poorly described and ecosystemic data collection are rare. Copepods are the key macrozooplankton group in the CCLME but their dynamic, their distribution and even their abundance remain poorly documented. Multinet net data allowed identifying large Copepod in CCLME. As small pelagic fish assessment acoustics survey were routinely done using 38 and 120 kHz frequencies, we used the same frequencies to propose a bi-frequencies inversion method to discriminate Copepod. We identified copepod backscatter using differences in volume backscat-tering strength (Sv). A close significant relationship were found between the size values of Cope-pod from multinet samples with those calculated by the acoustic highpass model. The correlation between copepod abundance and corresponding Sv were positive. This work showed that 38-120 kHz frequency can be used on Copepod and thus open the way to retrospective analysis in the CCLME. These results were important to better understand marine ecosystem, and constitute a first step for Copepod biomass estimation in the context of ecosystemic approach of small pelagic fish management and climate change.