Titre du document / Document title

Measurement of the size, shape and structure of Atlantic bluefin tuna schools in the open ocean

Auteur(s) / Author(s)

NEWLANDS Nathaniel K. ⁽¹⁾ ; PORCELLI Tracy A. ⁽²⁾ ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

⁽¹⁾ Ecosystem Modeling-Systems Ecology, Environment, Agriculture and Agri-Food Canada, 5403 1st. Avenue South, P.O. Box 3000, Lethhridge, AB, T1J 4B1, CANADA
⁽²⁾ TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T2A3, CANADA

Résumé / Abstract

How do patterns arise spontaneously in the collective motion of fishes'? What specific advantages are conferred when individuals organize into distinct school formation structures'? Automated methods are increasingly important for the rapid retrieval, conversion and integrated statistical analysis of large sets of data. Here, we apply a semi-automated image analysis to measure the size, shape and structure of schools of Atlantic bluefin tuna (Thunnus thynnus L.) in the open ocean. We approximate their school shape as ellipsoids with boundary edge refinement. The distance between nearest neighbors follows a bi-modal distribution and varies between 0.3 and 0.9 BL, conferring maximum to 35% energetic savings, respectively, based on hydrodynamical considerations. Smallest schools comprise individuals in a linear to diagonal arrangement in the horizontal plane, with largest schools containing individuals arranged according to a diamond-lattice structure. Intermediate-sized schools show significant variation in positional, relative neighbor bearing and directional orientation in the horizontal and vertical dimension. Individuals maintain a fixed number of neighbors at preferred bearing angles, improving their ability to search and detect prey by schooling. In addition, individuals gain energetic advantages necessary to migrate over large distances, while maintaining high sustained swimming speeds. Estimated school packing density lies between theoretical estimates for aggregative and optimum packing of spheres. The trade-off between the hydrodynamical and visual advantage, while affecting school internal structure, also explains the shape of observed formations as a collective trade-off between school compactness and elongation. Future simultaneous tracking of schools and individuals would advance our understanding of survival advantages conferred to individuals through adjustments in school compactness and elongation as schools migrate and search for patchy-distributed prey.

Revue / Journal Title

Fisheries research    ISSN  0165-7836   CODEN FISRDJ 

Source / Source

2008, vol. 91, n^o1, pp. 42-55 [14 page(s) (article)] (3/4 p.)

Langue / Language

Anglais

Editeur / Publisher

Elsevier, Amsterdam, PAYS-BAS  (1981) (Revue)

Mots-clés anglais / English Keywords

Vertebrata

;

Pisces

;

Thunnus thynnus

;

Marine environment

;

Fishery

;

Behavior

;

Pelagic zone

;

Ocean

;

Mots-clés français / French Keywords

Scombridae

;

Vertebrata

;

Pisces

;

Thunnus thynnus

;

Milieu marin

;

Pêcherie

;

Comportement

;

Zone pélagique

;

Océan

;

Mots-clés espagnols / Spanish Keywords

Vertebrata

;

Pisces

;

Thunnus thynnus

;

Medio marino

;

Pesquería

;

Conducta

;

Zona pelágica

;

Océano

;

Mots-clés d'auteur / Author Keywords

Behavior

;

Bluefin tuna

;

Movement

;

Schooling

;

Localisation / Location

INIST-CNRS, Cote INIST : 19360, 35400018305673.0050