Length distribution data for subsamples of net trawls collected along the Western Antarctic peninsula during March 2023 on board Maria S. Merian. Samples from the RMT8 net were analysed onboard, in accordance with the CCAMLR RMT8 sampling protocol (http://archive.ccamlr.org/pu/e/sc/ipy/RMT8protocol.pdf). Morphometric measurements of both krill and salps were carried out onboard. For krill species, the length of each individual was measured from the anterior margin of the eye to the tip of the telson, excluding the terminal spines. For salps, the internal body length was measured also in accordance with the CCAMLR RMT8 sampling protocol, with a distinction between solitary and colonial individuals.