Echotrace classification and spatial distribution of pelagic fish aggregations around drifting fish aggregating devices (DFAD)

Gala Moreno 1 Erwan Josse 2 Patrice Brehmer 3 Leif Nottestad 4
1 AZTI
2 US Acoustique Halieutique
3 CRHMT - Centre de Recherche Halieutique Méditerranéenne et Tropicale
4 IMR - Institute of marine Research
Abstract : This work presents a method to observe pelagic fish around rifting fish aggregating devices (DFADs). A triple-frequency vertical echosounder was employed to observe fish distributions in the vicinity of DFADs. Surveys were conducted in a star pattern that was centred at the DFADs. The objective of the study was to define a methodology for future acoustic studies. This goal was pursued by (i) studying the spatial distribution of fish aggregations, (ii) developing concepts for the grouping of observed aggregations and (iii) developing specifications for future autonomous acoustic tools. For this purpose 5 cruises were carried out in the western Indian Ocean. The multi-frequency approach proved useful as a means of separating acoustic detections into sound-scattering layers (e. g. plankton and micronekton), fish aggregations and individual fish. Fish target strength (TS) was measured. Four types of aggregations were found near DFADs: ( i) dense structure (ii) medium structure (iii) loose structure and (iv) structure consisting of separated targets. More than 90% of these structures were found within a radius of 400 m and about 75% within 200 m of the DFADs. The spatial configuration of DFAD fish aggregations appeared to be more dynamic compared to aggregations near moored FADs. The spatial distribution and structure of DFAD aggregations have direct implications for their catchability by tuna purse-seiner. We have carried out the first quantitative acoustic recordings around DFADs, and obtained a better understanding of the spatiotemporal dynamics of fish aggregations around DFADs in the Indian Ocean. Based on this knowledge we are now working on specifications for instrumented buoys that are intended as autonomous data recording observatories for such pelagic environments.
Keywords : Drifting Fish Aggregating Devices survey design multi-frequency tuna behaviour schooling behaviour pelagic ecosystem echotrace classification
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Article dans une revue
Aquatic Living Resources, EDP Sciences, 2007, 20 (4), pp.343-356. 〈10.1051/alr:2008015〉
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https://hal.univ-brest.fr/hal-00667992
Contributeur : Catherine Bertignac <>
Soumis le : mercredi 8 février 2012 - 17:21:12
Dernière modification le : samedi 28 février 2015 - 01:07:56

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Gala Moreno, Erwan Josse, Patrice Brehmer, Leif Nottestad. Echotrace classification and spatial distribution of pelagic fish aggregations around drifting fish aggregating devices (DFAD). Aquatic Living Resources, EDP Sciences, 2007, 20 (4), pp.343-356. 〈10.1051/alr:2008015〉. 〈hal-00667992〉

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