title: Fish swimming in schools save energy regardless of their spatial position.
abstract: For animals, being a member of a group provides various advantages, such as reduced vulnerability to predators, increased foraging opportunities and reduced energetic costs of locomotion. In moving groups such as fish schools, there are benefits of group membership for trailing individuals, who can reduce the cost of movement by exploiting the flow patterns generated by the individuals swimming ahead of them. However, whether positions relative to the closest neighbours (e.g. ahead, sided by side or behind) modulate the individual energetic cost of swimming is still unknown. Here, we addressed these questions in grey mulletLiza aurataby measuring tail-beat frequency and amplitude of 15 focal fish, swimming in separate schools, while swimming in isolation and in various positions relative to their closest neighbours, at three speeds. Our results demonstrate that, in a fish school, individuals in any position have reduced costs of swimming, compared to when they swim at the same speed but alone. Although fish swimming behind their neighbours save the most energy, even fish swimming ahead of their nearest neighbour were able to gain a net energetic benefit over swimming in isolation, including those swimming at the front of a school. Interestingly, this energetic saving was greatest at the lowest swimming speed measured in our study. Because any member of a school gains an energetic benefit compared to swimming alone, we suggest that the benefits of membership in moving groups may be more strongly linked to reducing the costs of locomotion than previously appreciated.
authors.affiliation: IAMC-CNR, Institute for the Coastal Marine Environment, National Research Council, Localita' Sa Mardini, 09170 Torregrande, Oristano Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Marras
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow, G12 8QQ Scotland UK.
authors.forename: Shaun S
authors.initials: SS
authors.lastname: Killen
authors.affiliation: Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, Graham Kerr Building, University of Glasgow, Glasgow, G12 8QQ Scotland UK.
authors.forename: Jan
authors.initials: J
authors.lastname: Lindström
authors.affiliation: Ecologie des Systèmes Marins Côtiers, UMR5119, Université Montpellier 2, Place Eugène Bataillon, 34095 Montpellier cedex 5, France.
authors.forename: David J
authors.initials: DJ
authors.lastname: McKenzie
authors.affiliation: Marine Biological Laboratory, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark.
authors.forename: John F
authors.initials: JF
authors.lastname: Steffensen
authors.affiliation: IAMC-CNR, Institute for the Coastal Marine Environment, National Research Council, Localita' Sa Mardini, 09170 Torregrande, Oristano Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Domenici
keywords: Collective behaviour; Ecophysiology; Energetics; Hydrodynamics