Identifying patterns in the diet of mackerel icefish (Champsocephalus gunnari) at South Georgia using bootstrapped confidence intervals of a dietary index

Main, Charlotte E.; Collins, Martin A. ORCID: https://orcid.org/0000-0001-7132-8650; Mitchell, Richard; Belchier, Mark. 2009 Identifying patterns in the diet of mackerel icefish (Champsocephalus gunnari) at South Georgia using bootstrapped confidence intervals of a dietary index. Polar Biology, 32 (4). 569-581. https://doi.org/10.1007/s00300-008-0552-7

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Abstract/Summary

Ontogenetic, inter-annual and regional variations in diet were investigated for mackerel icefish, Champsocephalus gunnari, in three successive summer seasons around South Georgia. Stomach contents from 2239 C. gunnari (130-560 mm total length) were examined. A bootstrapping technique was used to calculate confidence intervals for an index of relative importance of prey categories (% IRIDC). Diet varied significantly between years and age classes but there was little regional difference in diet. In general, diet was dominated by krill, Euphausia superba and by the amphipod Themisto gaudichaudii. Smaller (younger) fish tended to prey on a higher proportion of T. gaudichaudii and small euphausiids such as Thysanoessa sp. and took smaller quantities of E. superba. In a season of poor krill availability (summer of 2003-2004) the proportion of krill in the diet, stomach fullness and fish condition (indicated by length-weight relationships) were significantly lower than in the other summer seasons. A large reduction (> 80%) in the estimated annual (2005) biomass of the C. gunnari stock directly followed the season of poor krill availability. This decline was largely because of mortality of 2+ and 3+ fish, which were more krill dependent than 1+ fish. Younger fish appear to have survived, leading to an increase in the estimated population biomass in 2006.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1007/s00300-008-0552-7
Programmes:	BAS Programmes > Other BAS Programmes > Global Science in the Antarctic Context (2005-2009) > DISCOVERY 2010 - Integrating Southern Ocean Ecosystems into the Earth System
ISSN:	07224060
Additional Keywords:	Fish; Channichthyidae;
NORA Subject Terms:	Marine Sciences Biology and Microbiology Ecology and Environment
Date made live:	04 Aug 2010 10:29 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/10207

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