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Spatio-temporal variability of fish assemblages in the Gambia Estuary (West Africa) observed by two vertical hydroacoustic methods: Moored and mobile sampling

Published online by Cambridge University Press:  15 March 2004

Jean Guillard ,
Jean-Jacques Albaret ,
Monique Simier ,
Ibrahima Sow ,
Jean Raffray  and
Luis Tito de Morais
Jean Guillard*
Affiliation:
IRD, Centre de Recherche Halieutique Méditerranéenne et Tropicale, BP 171, 34203 Sète Cedex, France INRA, Station Hydrobiologie Lacustre, UMR CARRTEL, BP 511, 74203 Thonon les bains, France
Jean-Jacques Albaret
Affiliation:
IRD, Centre IRD de Dakar, UR070, BP 1386, Dakar, Sénégal
Monique Simier
Affiliation:
IRD, Centre de Recherche Halieutique Méditerranéenne et Tropicale, BP 171, 34203 Sète Cedex, France
Ibrahima Sow
Affiliation:
CRODT, BP 2241, Dakar, Sénégal
Jean Raffray
Affiliation:
IRD, Centre IRD de Dakar, UR070, BP 1386, Dakar, Sénégal
Luis Tito de Morais
Affiliation:
IRD, Centre IRD de Dakar, UR070, BP 1386, Dakar, Sénégal
*
[email protected]
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Abstract

The Gambia Estuary is one of the last estuaries in West Africa not to have been affected by strong environmental changes and adverse human disturbances. In order to describe the spatio-temporal change in fish biomass in this estuary, and the seasonal changes in fish size classes, five research surveys have been conducted at characteristic periods in the river's water regime and meteorological seasons. The fish assemblages were sampled by two vertical echosounding protocols: mobile surveys (zigzag transects) in the estuary and moored stations. The two sampling methods produced a similar image of the fish assemblages in terms of the distribution of total biomass and target strength distributions. Large fish aggregations were detected in the most marine area at the end of the wet season, and fish biomass increased through the dry season in the upstream zone. Fish were smaller at the beginning of the wet season and they were always larger in downstream areas.

Keywords

Hydro-acousticVertical soundingSplit-beamFishEstuaryGambiaWest Africa
Type
Research Article
Information
Aquatic Living Resources , Volume 17 , Issue 1 , January 2004 , pp. 47 - 55
Copyright
© EDP Sciences, IFREMER, IRD, 2004

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