Some aspects of the biology and ecology of krill (Euphausia superba) in the Bransfield Strait and Elephant Island, austral summer 2006 (ANTAR XVI)

Abstract

Biological-fishery information from experimental hauls in the multidisciplinary survey on board the R/V Humboldt during the XVI Scientific Expedition from Peru to Antarctic (January 2006) was analyzed. This expedition consisted in two phases: the first was a synoptic prospection in Bransfield strait and surrounded Elephant Island, while the second, it was a small scale experiment between Elephant and Clarence Islands with the aim to relate biotic and abiotic variables with Antarctic krill. The total catch from 19 experimental hauls was 2,699 k, where Antarctic krill Euphausia superba was the most representative (99.37%), followed by jellyfish (0.47%) and others (0.16%), among them: glacial krill Euphausia crystallorophias, Thysanoessa sp., salps, fish larvae’s (Notothenia, Notolepis, Chaenocephalus and Cryodraco), mycthopids and amphipods. The best catches of krill (recorded during the first phase) were associated to major abundance of phytoplankton and zooplankton in the Bransfield Front mainly, at north of King George and Elephant islands. The Antarctic krill in the experimental zone performed vertical migrations, generally it found in the surface at dark hours (22:00-04:00 hrs.) and it deepened during the day (05:00-21:00 hrs.) by reaching approximately until 165 m, between 07:00 and 10:00 hrs. The size structure of E. superba spanned a range 30-63 mm total length (TL) in all the surveyed area, it represented a unimodal distribution in 49 mm TL and average length of 46.1 mm. The adult specimens predominated (>44 mm TL) which corresponding mostly gravid females. No clear stratification of Antarctic krill sizes according to day hours and depth strata exists. Adult and sub-adult individuals (38-44 mm TL) were feeding mainly of diatoms, tintinnids and copepod remains. It has not come to identify changes in the krill diet, sizes, depth strata and catch hours.