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How much do fish aggregating devices (FADs) modify the floating object environment in the ocean?









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    How much do Fish Aggregating Devices (FADs) modify the floating object environment in the ocean? 2013
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    Natural floating objects (e.g., logs) have always been a component of the habitat of tropical tus. However, the introduction of fish aggregating devices (FADs) modifies this environment. To assess the changes due to the deployment of FADs, we compared the spatial distribution of tural and artificial floating objects (FADs), using data from observers onboard tu purse seine vessels in the Indian Ocean from December 2006 to December 2008. Although tural objects occur more commonly in waters south o f 7°S and FADs are more common in waters north of 7°S, all types of floating objects can be found everywhere. Using different spatial scales (quadrats of size 1° 9 1°, 2° 9 2°, 5° 9 5°, and 10° 9 10°), we computed the proportion of FADs observed in quadrats without t- ural objects. The scale of 2° 9 2° quadrats represented a threshold: distributions of the two types of objects were different at scales smaller than this threshold. The strongest change that has occurred since the introduction of F ADs (besides the increased catches) has been the dramatic increase in the total number of floating objects. Since the introduction of FADs, the number of objects has at least doubled everywhere (except in the Mozambique Channel and Chagos) and in some areas (e.g., Somalia area) the multiplication factor has reached as high as 20 or 40. Our study sets the ranges of values of key parameters of the floating object environment, which are crucial in the design of future experimental studies aimed at investigating the impacts of FADs on the ecology of tus.
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    Anchored fish aggregating devices for artisanal fisheries in Southeast Asia: benefits and risks
    Benefits and risks
    2012
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    For centuries fishers have known that fish are attracted to and congregate around naturally occurring floating objects. They have also learned that by placing their own floating objects in the sea that fish would aggregate around them making catching easier. These man-made objects are called Fish Aggregating Devices or FADs and they can be either drifting or anchored. Since FADs can improve fish catches, governments and national fisheries agencies in the Asia region are examining the merits of u sing anchored FAD programmes. Their policy objectives are typically improved food security through better availability of localized aquatic animal protein, increasing the reliability of income from fishing for artisanal fishers and the creation of employment in coastal areas through fish and aquatic product trading and processing. In the last decade or so, FADs for both artisanal and commercial/industrial fisheries have proliferated in Asia and the Pacific region. In some areas this has caused c oncern about the potential negative impacts on fisheries and the marine environment. This has led environmental and conservation groups to lobby for FAD-free caught tuna, particularly in industrial type tuna fisheries. This book highlights the potential benefits of well co-managed anchored FAD programmes, which can contribute to overall food security. It covers the planning and background research requirements and emphasizes the importance and need for holistic and inclusive community consultati on and monitoring processes and the development of enabling policies. The book also covers the environmental concerns and possible negative ecosystem impacts of unplanned and poorly managed programmes, which inevitably lead to unsustainable resource exploitation and financial and economic losses.
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    Does social behavior influence the dynamics of aggregations formed by tropical tunas around floating objects? An experimental approach 2013
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    Tropical tus associate with objects floating at the surface of the ocean, a behavior widely exploited by fish- ers. 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 dymics of such aggregations, we used the biry choice approach. The experimental design com- prised two close and identical anchored fish aggregating devices (FADs) eq uipped with an echo sounder buoy to monitor the aggregated biomass of tu under each device. Alysis of the results entailed character- izing whether the aggregated biomass is distributed asymmetrically (indicative of social behavior playing a role in the dymics) 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 interact ions underlie aggregation processes, which represents a major advance in our understanding of these aggregations, a priority for science-based fishery magement. While recogniz- ing 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.

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