Size-dependent behavior of tuna in an array of fish aggregating devices (FADs) |
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Authors: | Marianne Robert Laurent Dagorn Jean Louis Deneubourg David Itano Kim Holland |
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Institution: | 1.UMR-212 écosystèmes Marins Exploités (Ifremer-IRD-UM II),Institut de Recherche pour le Développement (IRD),Fishing Port, Victoria, Mahé,Seychelles;2.Unit of Social Ecology-CP 231,Université libre de Bruxelles (ULB),Brussels,Belgium;3.Pelagic Fisheries Research Program,University of Hawaii at Manoa,Honolulu,USA;4.Hawaii Institute of Marine Biology,Kane’ohe,USA |
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Abstract: | Several lines of evidence indicate that aggregations of yellowfin tuna associated with floating objects are more frequently
composed of small animals than larger ones. Also, the diet of small yellowfin tuna caught at anchored fish aggregating devices
(FADs) around Oahu, Hawaii, was found to shift quite rapidly when these fish reached approximately 50 cm FL. In order to test
for ontogenetic changes in aggregation behavior, we tagged and released two distinct size classes of yellowfin tuna in an
array of anchored FADs around Oahu, Hawaii. Twenty-four yellowfin tuna 30–39 cm FL and 16 yellowfin tuna 63–83 cm FL were
tagged with acoustic transmitters and released near anchored FADs equipped with automated acoustic receivers. Fish in the
smaller size class stayed about 2.5 times longer at individual FADs than the larger fish (mean 4.05 days vs. 1.65 days) and
displayed larger horizontal movements within the array. However, the durations of unassociated phases, residence times in
the entire FAD array, percentage of time spent associated with FADs and numbers of movements between FADs did not show any
difference between the two size groups. The observed size-dependent behavior is discussed in terms of physiological abilities,
diet segregation and anti-predator behavior. |
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