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Survey on the bottlenose dolphin population in the Bay of Bizerte

Dolphin in Bizerte bay

The bay of Bizerte lies in the northeastern coast of Tunisia. The bay is known to be an important fishing ground for the local fishing community in Bizerte city and nearby urban areas. Walking around the city, one can see several indications that dolphins might bee an important part of the community culture (figure 1).

Based on several indications, the Regional Activity Centre for Special Protected Area (SPA/RAC) in association with the Tunisian Association for Taxonomy (ATUTAX) and the University Of Aberdeen (in the UK), has promoted a survey to investigate the status of the dolphin population and give basic assessment on the interaction local fisheries.

Both researchers Ibrahim BENAMER and Mehdi AISSI started the survey in June 2015, looking mainly into: How many dolphins are there in the bay? And why they are in the bay?




Figure (2)
Figure (1): different wall art and labels within Bizerte city depicting dolphins.




Both questions were answered based on a mark-recapture approach (a.k.a. photo-identification). The technique involves taking high-resolution images of the dorsal fin of every encountered dolphin in the survey. A large proportion of these dolphins usually have distinctive markings on their dorsal fins (notches, scratches, pigmentations) which gave each individual a distinctive "face" that can be recognized (figure 2). At the end of the survey, a catalogue of marked individuals is built and this catalogue is used to calculate the abundance of dolphins in the area.




Figure (2)
Figure (2): using a digital camera with a 300mm extension to take pictures of the dorsal fin for each dolphin. At top right, a dorsal fin with distinctive markings.




Results pointed out the presence of at least 84 dolphin individual in the bay of Bizerte. During the survey, most of the dolphins observed were interacted in either social or feeding behavior which promotes the bay to be an important area for the dolphins (e.g a Cetacean Critical Habitat – CCH). The dolphins were also sighted frequently feeding close to fishing gear operating in the bay (figure 3) and this rises the issue of bycatch and interaction. A separate survey should be designated to investigate this matter thoroughly and to promote action plans for conservation and mitigation.




Figure (3)
Figure (3): dolphins feeding close to fishing gear, (A) fixed net, (B) trawler




However short, this survey should be considered a pioneer stage to more continuous studies that should follow in the future to know more about this Vulnerable species in the Bay of Bizerte.