Acoustic characterisation of pelagic fish aggregations around moored fish aggregating devices in Martinique (Lesser Antilles)

Type Article
Date 2006-06
Language English
Author(s) Doray MathieuORCID1, 2, Josse Erwan1, Gervain Paul2, Reynal LionelORCID3, Chantrel Josselin3
Affiliation(s) 1 : IRD, US S004, Ctr IRD Bretagne, F-29280 Plouzane, France.
2 : POLKA, F-97100 Basse Terre, Guadeloupe, France.
3 : IFREMER, Lab Ressources Halieut Antilles, F-97321 Le Robert, Martinique, France.
Source Fisheries Research (0165-7836) (Elsevier), 2006-06 , Vol. 82 , N. 1-3 , P. 162-175
DOI 10.1016/j.fishres.2006.06.025
WOS© Times Cited 23
Keyword(s) Lesser Antilles, Tuna, Large pelagic fish, Aggregative behaviour, Shoal density, Target Strength, Acoustics, Fish Aggregating Device
Abstract Sea cruises were conducted for 57 days over 16 months to characterise pelagic fish aggregations around 2 moored fish aggregating devices (FADs) in Martinique (Lesser Antilles). Echosounder surveys run in a star pattern were used in conjunction with obliquely beamed sonar observations. An echo-integration-by-shoal algorithm was implemented to isolate pelagic fish shoals from sound scattering layers and to compute mean morphometric, positional and density parameters. Tree regressions were used to select and classify pelagic fish Target Strengths (TS), with reference to their spatial and temporal characteristics. The main type of pelagic fish aggregation was a large sub-surface aggregation. It was observed during all daytime periods within a radius of 400 m of the FAD. A smaller type of aggregation was observed closer to the surface and to the FAD in 65% of daytime periods. Large scattered fish were observed in 16% of daytime periods. At night, a medium-sized aggregation was detected in the sub-surface in 75% of night-time periods. The sizes of the fish inside the aggregations (determined from TS values) were lower in the small near-surface aggregation than in the large sub-surface aggregation. Mean packing densities of sub-surface medium fish and near-surface small fish aggregations (determined from TS and shoal acoustic density) were respectively 0.2 fish per m3 and 1.3 fish per m3. The acoustic methodology and results are discussed with reference to the characteristics and performance of the echosounder and to the spatial structure of pelagic fish aggregations around moored FADs in Martinique.
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