Polar Biology

, 32:569 | Cite as

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

  • Charlotte E. Main
  • Martin A. Collins
  • Richard Mitchell
  • Mark Belchier
Original Paper

Abstract

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.

Keywords

Channichthyidae Dietary index Feeding ecology Krill Euphausia superba Scotia Sea, interannual variability, fish stocks 

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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Charlotte E. Main
    • 1
    • 2
  • Martin A. Collins
    • 1
  • Richard Mitchell
    • 1
  • Mark Belchier
    • 1
  1. 1.British Antarctic SurveyNatural Environment Research CouncilCambridgeUK
  2. 2.Fisheries Research Services, Marine LaboratoryAberdeenScotland, UK

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