Spatial distribution of tuna larvae in the Gulf of Gabes (Eastern Mediterranean) in relation with environmental parameters

Abstract

Spatial distribution and ecology of the larvae of three tuna species (Thunnus thynnus, Auxis rochei and Euthynnus alletteratus) were studied during an ichthyoplankton survey carried out in the Gulf of Gabes (Tunisia) in June and July 2009. A total of 80 stations, distributed on a regular sampling grid, were sampled. The main objectives of this survey were to provide information on tuna larvae distribution in the Gulf of Gabes in relation to the environmental parameters. Regarding small tunas, larvae of A. rochei (bullet tuna) showed the more widespread distribution, being found at both inshore and offshore stations. E. alletteratus (Atlantic black skipjack) larvae were mainly found at the inshore stations covering the wide continental shelf of this region. On the other hand, larvae of the large migratory tuna T. Thynnus (Atlantic bluefin tuna), were mainly recorded at offshore stations, suggesting that spawning possibly takes place mainly near the shelf break. Regarding the biological and physical parameters examined, our results indicate that tuna larvae were mainly collected in oligotrophic and mixed waters resulting from the confluence of surface water of recent Atlantic origin and resident surface Mediterranean waters, as shown by their preference for lower chlorophyll a concentrations (from 1.4 to 2.5 mg m -3 ) and moderate salinity values (between 37.35 and 37.75). Significantly, tuna larvae seemed to avoid the more eutrophic and saltier waters of the gulf situated very close to the coast and around Kerkennah and Djerba islands.

Environmental conditions influencing the larval fish assemblage during summer in the Gulf of Gabes (Tunisia: South central Mediterranean)

“…On the other hand, the larvae of four tuna species (T. thynnus, A. rochei, E. alletteratus and T. alaunga) were found in our plankton samples, which confirmed that the Gulf of Gabes was a spawning area for these tuna species, as previously stated in Koched et al (2013).…”

“…The observed high variation of horizontal distribution between the tuna larvae species, some found preferentially in neritic stations (bullet and Atlantic black skipjack) and others in the oceanic offshore stations (Atlantic bluefin and albacore) have been reported in other Mediterranean areas (Oray & Karakulak, 2005;Alemany et al, 2006Alemany et al, , 2010Reglero et al, 2012;Koched et al, 2012Koched et al, , 2013.…”

“…A recent study by Koched et al(2013) has demonstrated that the area is an important spawning habitat for several tuna species such as the Atlantic bluefin tuna Thunnus thynnus (Linnaeus, 1758), and for other small tuna species (bullet tuna Auxis rochei (Risso, 1810), Atlantic black skipjack Euthynnus alletteratus (Rafinesque, 1810).…”

“…European anchovy Engraulis encrasicolus (Linnaeus, 1758), Sardinella Sardinella aurita (Valenciennes, 1847) (Ktari-Chakroun, 1979;Zarrad et al, 2012aZarrad et al, , 2012b) and on the tuna larvae (Koched et al, 2012(Koched et al, , 2013. However, only two of these studies have actually addressed the whole larval fish assemblage in the eastern coast of Tunisia (Koched et al, 2011;Zarrad et al, 2013).…”

Characterization of the spawning area of tuna species on the northern Tunisian coasts

“…The unsuitability of Atlantic bluefin tuna larvae of more productive coastal waters has also been reported in the Gulf of Mexico (Muhling et al 2013). These hypotheses were reinforced by the results of Koched et al (2013) in the Gulf of Gabes, which revealed the absence of Atlantic bluefin tuna larvae near the islands of Kerkennah and Djerba, placed on the wide continental shelves characterized by shallow depths and high trophic conditions.…”