Imed Jribi

Spatio-temporal distribution of Manta birostris in French Guiana waters

Manta ray ( Manta birostris ) is the largest ray species, but little information is available regarding its biology, distribution and migratory pattern. During an aerial survey conducted in French Guiana waters (South America) in 2006, the observation of several dozen individuals all swimming in the same direction prompted us to develop a research programme on this species as part of an environmental impact assessment for oil drilling. Overall, 117 aerial surveys were performed over 3 years in order to complete a database for this species. In 54 of these flights, a total of 138 individuals were observed. A phenological analysis of this species in French Guiana waters shows a peak presence between July and December, which correlates with sea surface temperature and net primary production in the ocean. The primary production in French Guiana waters is particularly active during this period and could explain the annual pattern for this filter-feeding animal.

Status of cetaceans in Tunisia through analysis of stranding data from 1937 to 2009

Abstract A survey of cetaceans stranded along the Tunisian coastline (2004–2009) and a review of the literature allowed us to record a total number of 132 stranding events from 1937 to 2009. They included two species of balaenopteridae, one species of physeteridae and five species of delphinidae. The common bottlenose dolphin Tursiops truncatus (Montagu, 1821) and the fin whale Balaenoptera physalus (Linnaeus, 1758) were the main stranded species in 83 and 21 stranding cases, respectively, representing 78.78% of all records. Stranding events occurred all the year round, with the highest frequency in spring (21.68%) and summer (50.60%) for the common bottlenose dolphin and in winter for the fin whale (50%). The common bottlenose dolphin was more vulnerable to human and fisheries interaction while the fin whale was more prone to be trapped in shallow waters.

Sex Ratio Estimations of Loggerhead Sea Turtle Hatchlings at Kuriat Islands, Tunisia: Can Minor Nesting Sites Contribute to Compensate Globally Female-Biased Sex Ratio?

Hatchling sex ratios in the loggerhead turtle Caretta caretta were estimated by placing electronic temperature recorders in seven nests at Kuriat islands (Tunisia) during the 2013 nesting season. Based on the mean temperatures during the middle third of the incubation period, and on incubation duration, the sex ratio of hatchlings at Kuriat islands was highly male-biased. Presently, the majority of hatchling sex ratio studies are focused on major nesting areas, whereby the sex ratios are universally believed to be heavily female-biased. Here we present findings from a minor nesting site in the Mediterranean, where the hatchling sex ratio was found to be male-biased, suggesting a potential difference between major and minor nesting sites.

Embryonic Growth Rate Thermal Reaction Norm of Mediterranean Caretta caretta Embryos from Two Different Thermal Habitats, Turkey and Libya

Abstract Ectothermic species are strongly affected by thermal changes. To assess the viability of these species under climate change constraints, we need to quantify the sensitivity of their life history traits to temperature. The loggerhead marine turtle (Caretta caretta) nests regularly in the Oriental Basin of the Mediterranean Sea. The different populations are separated because of time (< 12,000 yrs) and very different thermal habitats; it is hotter on the southern coast (Libya) than on the northern ones (Cyprus, Greece, and Turkey). Patterns of embryo growth response to incubation temperatures have been searched for these 2 populations. We found that both populations have similar thermal reaction norms for embryonic growth rate. This highlights that 12,000 yrs is not enough time for this species to adapt to specific thermal habitats and raises the question of the persistence of these populations in the context of rapid climate change.

Effect of bait on sea turtles bycatch rates in pelagic longlines: An overview

Pelagic longline fishing has been identified as a significant threat to endangered sea turtle populations. Reducing sea turtle bycatch in pelagic longline fisheries, in concert with activities to reduce other anthropogenic mortality sources, may halt and reverse population declines. Here, we examine the effect of bait manipulation as a simple mitigation method that could reduce sea turtle interactions with longline fishing gear. We analyzed laboratory experiments and field trials conducted in the Mediterranean, the northeast Distant Area in the Atlantic and the Western North Pacific. Studies showed that turtles are more likely to feed on squid than on mackerel when both are used simultaneously as bait. The stingray, Dasyatis pastinaca, used as bait, was more effective than mackerel; this ray was vulnerable and stimulated much thought about other species to use as alternative bait. Effective in laboratory conditions with captive turtles, dyed and artificial bait did not seemed to be effective in reducing turtle bycatch in field conditions. Optimal mitigation measure must reduce incidence of hooking of threatened sea turtles to acceptable levels and also offer an economic advantage to fisheries. Studies concerning the effect of bait modification to reduce turtle bycatch highlight the importance of an integrated approach towards sensory deterrents, as both visual and chemical cues are likely to attract sea turtles to longline gear. Further research on the development of sensory-based deterrents can contribute to reduced sea turtle bait interactions and maintain catch rates of target species.