A comparison of Antarctic euphausiids sampled by net and from geothermallyheated waters: insights into sampling bias

The Antarctic euphausiids Euphausia superba and E. crystallorophias were sa mpled using aln 8 m(2) rectangular midwater trawl inside the caldera of Dec eption Island. Specimens of the same species were collected on the same day from the strandline and sublittoral fringe within the caldera at a bay whe re these euphausiids had been incapacitated by high temperature geothermall y heated waters. Differences between length frequency distributions of samp les obtained by both methods were investigated once net-caught specimens ha d been subject to the simulated effects of geothermally heated waters. Diff erences between maturity stage/sex ratios for E. superba samples were also assessed. No significant differences between sizes of net-caught or beach-s ampled E. crystallorophias were detected, but significant differences were found between both the sizes and sex/maturity stages for E. super ba sample s. Possible explanations for these differences are discussed.