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Preliminary data on Zooplankton community structure in Nosybe Madagascar – Whale shark (Rhincodon typus) feeding ecology project



It is known that juveniles whale sharks (Rhincodon typus) have tendency to gather, seasonally, in a few coastal areas around the world to feed on zooplankton; however little is known about their food preferences. The CSS (Centro Studi Squali) scientific coordinator of the project “Whale shark feeding ecology” (in partnership with University of Calabria, University of Siena, ISPRA, University of Naples Federico II, Stazione Zoologica Anton Dohrn), in 2016, started the study of these aggregations. During field observations we collected zooplankton samples and we observed feeding behaviour of sharks to understand the main characteristics of the zooplankton community that appears to cause said gatherings. So far two expeditions (2017 and 2018) have been carried out in the channel of Mozambique, in the coastal waters of the Nosy Be (MG). Here whale sharks are present in the last four months of the year: data were collected in the eastern part of the island in late November-early December which is the peak season for whale shark sightings in the area. Zooplankton samples were collected vertically from 10 m depth to surface, using a net with 200 µm mesh aperture. The samples were concentrated using a 50µm filter and fixed with alcohol (70%) and lugol (1%). At the same time, location, water temperature and transparency, shark presence/absence and feeding behaviour were recorded. Quantitative and qualitative analysis of zooplankton samples were performed at Stazione Zoologica Anton Dohrn and ISPRA laboratories. We calculated zooplankton biomass and abundance. We identified at species level the most important zooplanktonic taxa (copepods, chetognats etc) and moreover we calculated their size spectra.
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