Dally Fluctuations in the Presence of Thunnus Albacares and Katsuwonus Pelamis Around Fish Aggregating Devices Anchored in Vanuatu, Oceania
An analysis of the catches and daily observations were carried out on schools of yellowfin tuna, Thunnus albacares and skipjack, Katsuwonus pelamis, between June 1982 and July 1985 from six small-scale fishing boats around five Fish Aggregating Devices (FAD) anchored off Efate in Vanuatu. One of the aims was to investigate daily fluctuations in surface school occurrence. Regularity of observation and time spent on monitoring enabled us to bring to light the more striking behavioral characteristics of aggregated schools. 91% of the total number of catches were skipjacks (K. pelamis) and yellowfins (T. albacares). Mixed schools of skipjack and yellowfin tuna were present within a 500 m range around the rafts just before sunrise, the yellowfin being nearer to the FADs than the skipjack. The abundance and extensiveness of surface schools diminished throughout the day. Towards midday, the highest catches of yellowfin tuna were taken in a circle of 100 m radius around the rafts, whereas an increase of skipjack yields was recorded 1 h before sunset. For both species the proportion of smaller specimens increased from dawn to sunset. K. pelamis did not take an obvious position in relation with the direction of the current, while T. albacares was mostly found in a downstream position.
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Document Type: Research Article
Publication date: 1994-09-01
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