“Whale Shark Expedition”: Observations on Rhincodon typus from Arta Bay, Gulf of Tadjoura, Djibouti Republic, Southern Red Sea

Rezzolla D., Storai T.

Date de parution: juin 2010
Volume: 34
Number: 2
Pagination: 195–206
Résumé

The present work is the report of two ecotouristic expeditions carried out in the Gulf of Tadjoura (Djibouti Republic, Southern Red Sea) and having as main objectives a contribution to the increasing of biological and ecological knowledge about whale shark Rhincodon typus (Smith, 1828) in these waters by means of observations and photo-identification tools. The survey was conducted for five days in January-February 2007 and for six days in January 2009, recording a total of 55 encounters (89% of which occurring in Arta Bay) with 32 juvenile whale sharks. Nineteen of them were males, five were females; it was not possible to determine the sex of eight of them. The estimate total length of these specimens ranged from 300 to 500 cm, averaging to 431 cm. Cooperating with Ecocean Whale Shark Photo ID Program, a 450 cm male, already photographed in 2005 and in 2006, was seen again also in 2007, contributing to hypothesize a philopatric instinct in whale sharks participating to the Djibouti seasonal feeding aggregations. Feeding strategies were observed, either in presence of abundant food source, or with depleting zooplankton bloom. Investigations about the trophic relations and observations about environmental influence on their abundance have been carried out. According with scientific literatures, a pattern of eight models of interaction with humans (CIH) have been used as a tool for a preliminary evaluation on shark tolerance towards the ecotourism impact in the area.

Mots-clés: Djibouti - Ecotouristic expeditions - Field observations - Photo-identification - Red Sea - Rhincodon typus - Rhincodontidae - Whale shark
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