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Marine Ecology Progress Series

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MEPS 334:263-272 (2007)  -  doi:10.3354/meps334263

Schooling behaviour of small pelagic fish: phenotypic expression of independent stimuli

Patrice Brehmer1,*, François Gerlotto2, Charline Laurent1, Pascal Cotel3, Alina Achury4, Birane Samb5

1Centre de Recherche Halieutique Méditerranéenne et Tropicale (IRD; IFREMER and University of Montpellier II), 1 Avenue Jean Monnet, BP 171, 34203 Sète, France
2Institut de Recherche pour le Développement, c/o Instituto del Mar del Peru, Esq. Gamarra y Gral Valle s/n, Chucuito, La Punta, Callao, Peru
3Institut de Recherche pour le Développement, Sainte Clotilde, 97490, Île de La Réunion, France
4Fundación La Salle, Estación de Investigaciones Marinas Isla Margarita, Isla de Margarita, Punta de Piedras 6318, Venezuela
5Institut Sénégalais de Recherche Agronomique, Centre de Recherche Océanographique de Dakar-Thiaroye, BP 2241, Senegal

ABSTRACT: We compared echo sounder measurements of fish schools on Venezuelan and Senegalese coastal shelves. In both areas Sardinella aurita was the predominant aggregative species; the stocks are known to be genetically independent. Persistent school typology is described by analysing 7 acoustic surveys in Venezuela and comparing with pioneer observations in Senegal. The echo types encountered in both countries were comparable, with S. aurita and their associated species having comparable schooling behaviour. School morphology appears to be more related to species than to global characteristics of their ecosystems, as fish school descriptors were similar for both stocks. Nevertheless, S. aurita may adopt different school morphologies. Differentiation between day and night fish schools was mainly due to morphological variables, as determined by fractal dimension. Echo types were different between day and night in both Venezuela and Senegal. This analysis shows that several independent parameters can influence school morphology. However, although schooling behaviour is temporally highly variable, it shows several constant, typical 2D morphological structures, i.e. echo types. The observation of small pelagic fish schools occurring during the night is not unusual according to the literature, although a strict diurnal schooling behaviour, with scattering during the night, is often reported. Schooling behaviour appears to be a phenotypic expression depending on biotic and abiotic stimuli, intrinsic characteristics and motivation.

KEY WORDS: Behaviour · Diel cycle · Echo type · In situ observations · Phenotypic expression · Schooling · Small pelagic fish

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