Spatial and temporal variability in the structure of aggregations of Antarctic krill (Euphausia superba) around South Georgia, 1997-1999

Cox, Martin J.; Watkins, Jonathan L.; Reid, Keith; Brierley, Andrew S.. 2011 Spatial and temporal variability in the structure of aggregations of Antarctic krill (Euphausia superba) around South Georgia, 1997-1999. ICES Journal of Marine Sciences, 68 (3). 489-498. 10.1093/icesjms/fsq202

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Abstract/Summary

Antarctic krill are important in the South Georgia (548S 358W) marine ecosystem. They form aggregations that vary widely in packing density (,1 to 1000 s of individuals m23), length (tens to thousands of metres), and height (tens of metres). Acoustic surveys are often used to estimate krill biomass and provide data that give insight into aggregation structure. Using dual-frequency (38 and 120 kHz) acoustic data collected during six surveys conducted around South Georgia during the 1997, 1998, and 1999 austral summers, we isolated 2990 aggregations by applying the Shoal Analysis and Patch Estimation System algorithm in Echoview and a krill-length-dependent acoustic identifier (DSv120 – 38). Multivariate cluster (partition) analysis was applied to metrics from each of the aggregations, resulting in three aggregation types with an overall proportional split of 0.28 : 0.28 : 0.44. Types 1 and 3 had low mean densities (,2 g m23), whereas Type 2 had a mean density of 94 g m23. Intersurvey differences were found between the effort-corrected numbers of aggregation types (p ¼ 2.5e26), and between on- and off-continental shelf areas (p ¼ 1.5e27), with a greater number of Type 2 aggregations being found on-shelf. The findings suggest intersurvey variation in krill catchability, with krill being more likely to be caught on-shelf.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1093/icesjms/fsq202
Programmes:	BAS Programmes > Polar Science for Planet Earth (2009 - ) > Ecosystems
ISSN:	1054-3139
NORA Subject Terms:	Marine Sciences Biology and Microbiology Ecology and Environment
Date made live:	16 Mar 2011 14:11 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/13780

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