Auteurs : HARMELIN JG., BEN LAMINE E., GHANEM R., ZARROUK A., AGREBI S.

Année : 2010

Ile : La Galite

Pays : Tunisie

The first evaluation of fish populations around the Galite archipelago of Galite leaded in May 2008, aimed to assess the local eco-biological conditions and to test for the

first time a census method adapted to these conditions and monitoring objectives. On the other hand, the other objective of these submarine interventions was the settlement of a non-destructive fish monitoring in the Galite Bay, which could serve as a time reference and can be repeated by managers. Thus, the first census has been based on a visual count of selected target species, for which the number and size of individuals were quantified on transects 25 m long and 5 meters wide. In total, 23 transects were realized on the western and eastern coasts of the Galite Bay. Thus, the 2008 census resulted in a list of 16 target species, supplemented with 3 other species present on the sites (Serranus cabrilla, S. scriba et Coris julis), considered as good indicators of the impact of fishing line. The target species most regularly present was Labrus merula and secondarily Diplodus vulgaris (rock) and Diplodus annularis (seagrass). Other data were acquired like the degree of occurrence, average abundance, individual sizes, the average number of target species, etc …

However, the aim of the missions in June, August and September 2010 on the Galite archipelago was turned more towards the acquisition of accurate quantitative data, in order to define the status of fish populations around the archipelago, and to develop a zero state of these populations which could serve as reference for future monitoring. Meanwhile, a simplified monitoring protocol was tested and implemented with a training of local staff. This protocol is based on the identification method by snorkelling, which is easier and faster (based on the realization of swimming transects on shallow depths (<6-7 m) and the counting of fish encountered during these transects, considering the number and size of individuals). Besides, during the same mission, a marine census more developed has also been effectuated. Thus, the results revealed the presence of all species observed and identified during the previous mission, but with species more frequent than others like the Diplodus vulgaris and sargus, Labrus merula, Sciaena umbra, Mycteroperca rubra and Epinephelus marginatus. Thus, these six species reflected the most part of the fish composition of Galite waters. However, the investigations leaded on Galite archipelago in 2010 revealed a low abundance of fish species, especially for common species, including bream, whose frequency is surprisingly low. On the other hand, a deficit of small individuals for these species has been observed, which generate a question about the fish recruitment in the archipelago and its real potential to provide sustainable populations.