Related items
Showing items related by metadata.
-
DocumentDoes social behavior influence the dynamics of aggregations formed by tropical tunas around floating objects? An experimental approach 2013
Also available in:
No results found.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. -
MeetingStudy of alternative models of artificial floating objects for tuna fishery (experimental purse-seine campaign in the Indian Ocean) 2005
Also available in:
No results found. -
DocumentHow much do Fish Aggregating Devices (FADs) modify the floating object environment in the ocean? 2013
Also available in:
No results found.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.
Users also downloaded
Showing related downloaded files
No results found.