First results on zooplankton community composition and contamination by some persistent organic pollutants in the Gulf of Tadjoura (Djibouti).

The Gulf of Tadjoura is located in the Horn of Africa and is widely recognized as an important site where the zooplanktivorous whale sharks seasonally aggregate from October to February. The surface zooplankton community (0-3m) was weekly sampled from November 2016 to February 2017 in two sites during the whale shark aggregation period. A total of 12 phyla were identified. Copepoda represented the most abundant and diverse group with 29 different genera, and contributed with an average of 82% of the mean zooplankton density of approximately 6600indm-3. During the sampling period, copepods were dominated numerically by Calanoida (3600indm-3), followed by Poicilostomatatoida (1300indm-3). Within the copepods, Paracalanidae, Calanidae, Oncaeidae and Miraciidae were the most common families. The temporal trend in zooplankton biomass at both stations revealed the highest peak in December (41.3±36.4mgm-3), and the lowest in February (6.6±3.3mgm-3). As no information is available on the occurrence of legacy contaminants use and release in this area, analysis revealed the consistent presence of both DDT and PCB residues in zooplankton samples in the Gulf of Tadjoura. Total PCB ranged from approximately 110 to 637ngg-1 d.w., while total DDT from 21 to 80ngg-1 d.w. The proportion of primary DDT in the total residue was higher than DDE and DDD, which strongly suggests that the area might actually be subjected to DDT inputs of the parent compound.

A review of the biology, fisheries and conservation of the whale shark Rhincodon typus.

Although the whale shark Rhincodon typus is the largest extant fish, it was not described until 1828 and by 1986 there were only 320 records of this species. Since then, growth in tourism and marine recreation globally has lead to a significant increase in the number of sightings and several areas with annual occurrences have been identified, spurring a surge of research on the species. Simultaneously, there was a great expansion in targeted R. typus fisheries to supply the Asian restaurant trade, as well as a largely un-quantified by-catch of the species in purse-seine tuna fisheries. Currently R. typus is listed by the IUCN as vulnerable, due mainly to the effects of targeted fishing in two areas. Photo-identification has shown that R. typus form seasonal size and sex segregated feeding aggregations and that a large proportion of fish in these aggregations are philopatric in the broadest sense, tending to return to, or remain near, a particular site. Somewhat conversely, satellite tracking studies have shown that fish from these aggregations can migrate at ocean-basin scales and genetic studies have, to date, found little graphic differentiation globally. Conservation approaches are now informed by observational and environmental studies that have provided insight into the feeding habits of the species and its preferred habitats. Notwithstanding these advances, there remain notable gaps in the knowledge of this species particularly with respect to the life history of neonates and adults who are not found in the feeding aggregations.