|
|
Guyader, O., Robert, B., & Lionel, R. (2017). Assessing the number of moored fishing aggregating devices through aerial surveys: A case study from Guadeloupe. Fish Res., 185, 73–82.
Résumé: Moored fish aggregating devices (MFADs) are increasingly being used in small-scale tropical fisheries to access pelagic fish species that are otherwise difficult to harvest in large numbers. Little attention has yet been paid to monitoring MFADs in coastal areas, however. This is most likely due to the small-scale nature of most fisheries that utilize them and the presumed lower impact of those fisheries on fish stocks and their ecosystems. In this paper, we examined the abundance and density of MFADs around Guadeloupe, using aerial line transect surveys. Estimated MFAD densities were found to be high compared with previously reported densities in this area, especially within the 22-45 km range offshore. We examine and discuss possible reasons for these high densities. The main drivers appear to be the target species dolphinfish (Coryphaena hippurus) and yellowfin tuna (Thunnus albacares) and related fishing behaviour. We present different approaches for reducing and monitoring MFADs densities, including the co-management of MFAD territorial use rights by fishing communities. (C) 2016 Elsevier B.V. All rights reserved.
|
|
|
|
Lopez, J., Moreno, G., Lennert-Cody, C., Maunder, M., Sancristobal, I., Caballero, A., et al. (2017). Environmental preferences of tuna and non-tuna species associated with drifting fish aggregating devices (DFADs) in the Atlantic Ocean, ascertained through fishers' echo-sounder buoys. Deep-Sea Res. Part II-Top. Stud. Oceanogr., 140, 127–138.
Résumé: Understanding the relationship between environmental variables and pelagic species concentrations and dynamics is helpful to improve fishery management, especially in a changing environment. Drifting fish aggregating device (DFAD)-associated tuna and non-tuna biomass data from the fishers' echo-sounder buoys operating in the Atlantic Ocean have been modelled as functions of oceanographic (Sea Surface Temperature, Chlorophyll-a, Salinity, Sea Level Anomaly, Thermocline depth and gradient, Geostrophic current, Total Current, Depth) and DFAD variables (DFAD speed, bearing and soak time) using Generalized Additive Mixed Models (GAMMs). Biological interaction (presence of non-tuna species at DFADs) was also included in the tuna model, and found to be significant at this time scale. All variables were included in the analyses but only some of them were highly significant, and variable significance differed among fish groups. In general, most of the fish biomass distribution was explained by the ocean productivity and DFAD-variables. Indeed, this study revealed different environmental preferences for tunas and non-tuna species and suggested the existence of active habitat selection. This improved assessment of environmental and DFAD effects on tuna and non-tuna catchability in the purse seine tuna fishery will contribute to transfer of better scientific advice to regional tuna commissions for the management and conservation of exploited resources.
|
|
|
|
Maufroy, A., Kaplan, D. M., Bez, N., De Molina, A. D., Murua, H., Floch, L., et al. (2017). Massive increase in the use of drifting Fish Aggregating Devices (dFADs) by tropical tuna purse seine fisheries in the Atlantic and Indian oceans. ICES J. Mar. Sci., 74(1), 215–225.
Résumé: Since the mid-1990s, drifting Fish Aggregating Devices (dFADs), artificial floating objects designed to aggregate fish, have become an important mean by which purse seine fleets catch tropical tunas. Mass deployment of dFADs, as well as the massive use of GPS buoys to track dFADs and natural floating objects, has raised serious concerns for the state of tropical tuna stocks and ecosystem functioning. Here, we combine tracks from a large proportion of the French GPS buoys from the Indian and Atlantic oceans with data from observers aboard French and Spanish purse seiners and French logbook data to estimate the total number of dFADs and GPS buoys used within the main fishing grounds of these two oceans over the period 2007-2013. In the Atlantic Ocean, the total number of dFADs increased from 1175 dFADs active in January 2007 to 8575 dFADs in August 2013. In the Indian Ocean, this number increased from 2250 dFADs in October 2007 to 10 300 dFADs in September 2013. In both oceans, at least a fourfold increase in the number of dFADs was observed over the 7-year study period. Though the relative proportion of natural to artificial floating objects varied over space, with some areas such as the Mozambique Channel and areas adjacent to the mouths of the Niger and Congo rivers being characterized by a relatively high percentage of natural objects, in no region do dFADs represent <50% of the floating objects and the proportion of natural objects has dropped over time as dFAD deployments have increased. Globally, this increased dFAD use represents a major change to the pelagic ecosystem that needs to be closely followed in order to assess its impacts and avoid negative ecosystem consequences.
|
|
|
|
Moreno, G., Dagorn, L., Capello, M., Lopez, J., Filmalter, T., Forget, F., et al. (2016). Fish aggregating devices (FADs) as scientific platforms. Fish Res., 178, 122–129.
Résumé: Fish aggregating devices (FADs) are floating objects used by fishers to aggregate pelagic fish such as tunas, and enhance the catch of these species. Because this is so important for tuna fisheries, nearly 100,000 FADs are deployed by fishers every year in the world's tropical oceans. Fishers use geo-locating buoys to track and maintain these FADs by visiting them regularly, reinforcing them if they are weak or replacing them. Many of these buoys are now equipped with echo-sounders in order to provide remote information on the aggregated biomass. FADs are currently only used for fishing purposes but they can also serve scientific objectives. In this paper, we investigate the potential of these data for improving our knowledge on the ecology of tunas and other pelagic animals as well as to obtain fishery-independent indices of distribution and abundance. These FADs also represent platforms for scientists to deploy scientific instruments, such as electronic tag receivers, cameras and hydrophones. Because FADs naturally aggregate several pelagic species other than tuna, these instrumented FADs can be a unique opportunity to observe pelagic ecosystem dynamics that are not possible from conventional research vessels. The amount of cost-effective data that they can provide would make a significant contribution to the scientific understanding of pelagic ecosystems. This information is vital for improved conservation and management of pelagic fisheries. (C) 2015 Elsevier B.V. All rights reserved.
|
|
|
|
Robert, M., Dagorn, L., Lopez, J., Moreno, G., & Deneubourg, J. L. (2013). Does social behavior influence the dynamics of aggregations formed by tropical tunas around floating objects ? An experimental approach. Journal of Experimental Marine Biology and Ecology, 440, 238–243.
Résumé: Tropical tunas associate with objects floating at the surface of the ocean, a behavior widely exploited by fishers. However, the respective roles played by environmental variables and behavioral processes (e.g., social behavior) in the formation of these aggregations remain elusive. To investigate the role of social behavior in the dynamics of such aggregations, we used the binary choice approach. The experimental design comprised two close and identical anchored fish aggregating devices (FADS) equipped with an echo sounder buoy to monitor the aggregated biomass of tuna under each device. Analysis of the results entailed characterizing whether the aggregated biomass is distributed asymmetrically (indicative of social behavior playing a role in the dynamics) or symmetrically between the two close and identical FADs, and comparing the results with theoretical distributions based on different definitions of basic units (individual fish or small schools). The results suggest that social interactions underlie aggregation processes, which represents a major advance in our understanding of these aggregations, a priority for science-based fishery management. While recognizing the logistical and technical constraints, we encourage the development of experimental studies (e.g., in which animals are presented with controlled situations) to enhance our understanding of the behavior of large pelagic fish.
|
|
