Mortality rate of silky sharks ( Carcharhinus falciformis) caught in the tropical tuna purse seine fishery in the Indian Ocean

Scientists aboard French purse seine vessels recorded the number and condition of silky sharks (Carcharhinus falciformis) caught during three fishing cruises in the Indian Ocean. A sample of 31 individuals that showed signs of life were tagged with satellite tags to investigate their postrelease mortality. The majority of individuals (95%) were brought on board using the brailer. Combining the proportion of sharks that were dead (72%) and the mortality rate of those released (48%), the overall mortality rate of brailed individuals was 85%. Few individuals (5%) were not brailed as they were entangled and landed during the hauling process. The survival rate of these individuals was high, with an overall mortality rate of meshed individuals of 18%. The combination of these two categories led to an overall mortality rate of 81%. This high value reflects the harsh conditions encountered by sharks during the purse seine fishing process. Consequently, methods that prevent sharks being brought on board are a priority for future investigations, but good handling practices should also be promoted as they could reduce mortality by at least 19%.Des scientifiques embarqués sur des thoniers senneurs français ont enregistré le nombre ainsi que la condition des requins soyeux (Carcharhinus falciformis) capturés pendant trois campagnes de pêche dans l’océan Indien. Un échantillon de 31 individus, présentant des signes apparents de vie, ont été marqués avec des marques satellites pour estimer leur mortalité après leur remise à l’eau. La majorité des individus (95 %) a été embarquée à bord à l’aide d‘une salabarde. En utilisant la proportion des requins morts (72 %) et le taux de mortalité des individus remis à l’eau (48 %), le taux de mortalité global d’individus a été estimé à 85 %. Quelques individus (5 %) n’ont pas été embarqués au moyen de la salabarde car emmaillés et remontés avec le filet lors du virage. Le taux de survie de ces individus était élevé, ainsi le taux de mortalité global n’était que de 18 %. Pour les deux catégories confondues, le taux de mortalité global s’élève à 81 %. Cette valeur élevée reflète la dureté des conditions rencontrées par les requins pendant le processus de pêche. Par conséquent, les méthodes empêchant la mise à bord des requins devraient constituées la priorité des recherches futures. Cependant la mise en œuvre de bonnes pratiques de manipulations devrait aussi être encouragée car elles permettraient de réduire la mortalité d’au moins 19 %

Collaborative research: Development of a manual on elasmobranch handling and release best practices in tropical tuna purse-seine fisheries

The reduction of by-catch mortality is an objective of the ecosystem approach to fisheries and a request made by consumers. Elasmobranchs, an important component of the French tropical tuna purse seine fishery by-catch, are currently thrown back into the sea. Fishers interact with various types of elasmobranchs that range widely in size, weight and shape, and could pose various degrees of danger to the crew. A diversity of discarding practices within the fleet were reported, some practices were considered suitable, others needed to be adapted and improved and others simply had to be banned. The majority of the crews were likely to improve their handling practices if they were presented with practical suggestions that were quick and easy. Combining scientific observations and empirical knowledge from skippers and crew, a manual, providing appropriate handling practices to ensure crew safety and increase the odds of survival for released animals has been developed and disseminated. Bringing these good practices onto the decks of fishing vessels should contribute to the reduction of the fishing mortality of some vulnerable species. It would be positively viewed by consumers as an act that reduces fishing's footprint on the environment and promoting animal welfare which would improve the image of fishing industry. Mitigation research is by definition an iterative process and different complementary methods must be carried out at different levels of the fishing process to significantly reduce the mortality of the by-catch

Early human impact on soils and hydro-sedimentary systems: Multi-proxy geoarchaeological analyses from La Narse de la Sauvetat (France)

International audienceWe analysed the late-Holocene pedo-sedimentary archives of La Narse de la Sauvetat, a hydromorphic depression in the southern Limagne plain (central France), where chronologically accurate studies are scarce. The multi-proxy geoarchaeological and palaeoenvironmental analysis of two cores from different areas of the basin was carried out through sedimentological, geochemical, micromorphological and malacological investigations. Integration of these datasets supported by a robust radiocarbon-based chronology allowed discussion of socio-environmental interactions and anthropogenic impacts from Late Neolithic to Early Middle Ages. Until the Middle Bronze Age, there was no clear evidence of anthropogenic impact on soils and hydro-sedimentary dynamics of the catchment, but two peaks of high alluvial activity probably related to the 4.2 and 3.5 kyr. BP climate events were first recorded in Limagne. Significant anthropogenic impacts started in the Late Bronze Age with increased erosion of the surrounding volcanic slopes. However, a major threshold was reached c. 2600 cal BP with a sharp increase in the catchment erosion interpreted as resulting from strong anthropogenic environmental changes related to agricultural activities and drainage. This implies an anthropogenic forcing on soils and hydro-sedimentary systems much earlier than was usually considered in Limagne. These impacts then gradually increased during Late Iron Age and Roman periods, but environmental effects were certainly contained by progress in agricultural management. Late Antiquity environmental changes are consistent with regional trend to drainage deterioration in lowlands, but marked asynchrony in this landscape change suggests that societal factors implying differential land management were certainly predominant here

Capability of electronic monitoring system to inform the hauling process of French tuna purse seiners catch

Electronic monitoring systems (EMS) have increasingly been used as an alternative technology to complement onboard observer programs and improve the management of tuna fisheries. EMS was installed on French purse seiners in 2014 in the frame of the OCUP program and pilot studies have shown that the system allows in-depth monitoring of fishing activities by providing information on catch composition and handling on deck and below deck. In this study, we further explore the potential of EMS for monitoring the hauling process of tropical tuna purse seiners' catch from the net to the deck. Using information collected during brailing (number of brailers, timing, fullness) on board 5 vessels of the Indian Ocean during 2018-2019, we evaluate the suitability of EMS as a tool to describe the main trends in brailing operations over 50 fishing sets. Our results indicate a large variability in brailer fullness among fishing sets and a relatively fast loading of the catch onto the deck with brailing operations generally consisting of 4 to 5 brailers transferred on board in less than 15 minutes. Results confirm the potential of EMS for collecting complementary data to monitor brailing operations of tropical tuna purse seiners

Capability of electronic monitoring system to inform the hauling process of French tuna purse seiners catch

Electronic monitoring systems (EMS) have increasingly been used as an alternative technology to complement onboard observer programs and improve the management of tuna fisheries. EMS was installed on French purse seiners in 2014 in the frame of the OCUP program and pilot studies have shown that the system allows in-depth monitoring of fishing activities by providing information on catch composition and handling on deck and below deck. In this study, we further explore the potential of EMS for monitoring the hauling process of tropical tuna purse seiners' catch from the net to the deck. Using information collected during brailing (number of brailers, timing, fullness) on board 5 vessels of the Indian Ocean during 2018-2019, we evaluate the suitability of EMS as a tool to describe the main trends in brailing operations over 50 fishing sets. Our results indicate a large variability in brailer fullness among fishing sets and a relatively fast loading of the catch onto the deck with brailing operations generally consisting of 4 to 5 brailers transferred on board in less than 15 minutes. Results confirm the potential of EMS for collecting complementary data to monitor brailing operations of tropical tuna purse seiners

Early human impact on soils and hydro-sedimentary systems: Multi-proxy geoarchaeological analyses from La Narse de la Sauvetat (France)

International audienceWe analysed the late-Holocene pedo-sedimentary archives of La Narse de la Sauvetat, a hydromorphic depression in the southern Limagne plain (central France), where chronologically accurate studies are scarce. The multi-proxy geoarchaeological and palaeoenvironmental analysis of two cores from different areas of the basin was carried out through sedimentological, geochemical, micromorphological and malacological investigations. Integration of these datasets supported by a robust radiocarbon-based chronology allowed discussion of socio-environmental interactions and anthropogenic impacts from Late Neolithic to Early Middle Ages. Until the Middle Bronze Age, there was no clear evidence of anthropogenic impact on soils and hydro-sedimentary dynamics of the catchment, but two peaks of high alluvial activity probably related to the 4.2 and 3.5 kyr. BP climate events were first recorded in Limagne. Significant anthropogenic impacts started in the Late Bronze Age with increased erosion of the surrounding volcanic slopes. However, a major threshold was reached c. 2600 cal BP with a sharp increase in the catchment erosion interpreted as resulting from strong anthropogenic environmental changes related to agricultural activities and drainage. This implies an anthropogenic forcing on soils and hydro-sedimentary systems much earlier than was usually considered in Limagne. These impacts then gradually increased during Late Iron Age and Roman periods, but environmental effects were certainly contained by progress in agricultural management. Late Antiquity environmental changes are consistent with regional trend to drainage deterioration in lowlands, but marked asynchrony in this landscape change suggests that societal factors implying differential land management were certainly predominant here

Téphras et séquences quaternaires

Journée AFEQ / SGF (6 novembre 2006

ANDES, the high resolution spectrograph for the ELT: science goals, project overview, and future developments

International audienc