Provisional invalidation of the eyestalk-band ageing method for Antarctic krill, Euphausia superba Dana, 1850 (Malacostraca: Euphausiacea: Euphausiidae)

An international workshop was held in August and November 2021 to assess the usefulness of a direct-ageing method for Antarctic krill (Euphausia superba, Dana 1850) based on the growth bands observed in thin sections of the eyestalk. Blind counting of eyestalk sections from 53 laboratory-reared krill of known age was done by the developer of the method, as well as blind counting of 35 randomly selected images of these sections by 15 readers from seven different laboratories. The resulting coefficients of variation (CV) and indices of average percentage error (IAPE) indicated that consistency in counting bands in eyestalks can be improved by standardised training of readers, but that the accuracy of the method itself, i.e. the use of the number of bands as an indicator of absolute age, is low. The workshop concluded that further study is required to provide reliable age estimation of Antarctic krill, and that this method, in its current form, not be applied in estimating the age of Antarctic krill.