Meeting Abstract

93.2  Thursday, Jan. 7  Krill Schooling: Defining the Structure of Antarctic Krill Schools and Swarms MURPHY, D. W.*; WEBSTER, D. R.; KAWAGUCHI, S.; KING, R.; OSBORN, J.; YEN, J.; Georgia Institute of Technology, Atlanta; Georgia Institute of Technology, Atlanta; Australian Antarctic Division, Kingston, Tasmania; Australian Antarctic Division, Kingston, Tasmania; University of Tasmania, Hobart, Tasmania; Georgia Institute of Technology, Atlanta dwmurphy@gatech.edu

Antarctic krill (Euphausia superba) exhibit exceptional aggregative behavior and are known to form schools that may extend for several kilometers in the horizontal direction and for greater than 100 m in the vertical direction. These schools are generally characterized by synchronized and polarized swimming. Proposed benefits for school membership include increased hydrodynamic efficiency (drafting) and improved awareness of external environmental signals, such as those created by prey, predators, or mates. Determining the presence of structure within schools of krill would help to define the adaptive advantage of this behavior. Krill exhibiting both schooling and non-schooling (swarming) behaviors were filmed using a stereophotogrammetric camera system at the Australian Antarctic Division in Hobart, Tasmania. Three-dimensional trajectories of individual krill were then constructed from the image data. For both schooling and swarming krill, animal coordinates at multiple time points were interrogated for school parameters such as density, polarity, nearest neighbor distance, and nearest neighbor position. Preliminary analysis shows a mean nearest neighbor distance of slightly less than one body length (5 cm) and suggests an anisotropic school structure in which nearest neighbor positions are nonrandomly distributed. Previous measurements of flow fields generated by swimming Antarctic krill will be used to address the relationship between the hydrodynamics of krill locomotion and school structure.