In 1992–2023 net surveys, Antarctic krill density did not shift toward the south-west along the Antarctic Peninsula; the KRILLBASE southward shift is in cells north of 60°S

Question: did Antarctic krill (Euphausia superba) density move toward the south-west along the Antarctic Peninsula (AP), as the reported southward contraction and the approximately 1000 km south-west shift predict? Data: 2,881 standardised net tows from US AMLR (north AP, 1992–2011) and Palmer LTER (west AP, 1993–2023), as harmonised by Conroy et al. 2026 (EDI knb-lter-pal.324.1), and KRILLBASE v1.0 (1976–2016). Method: cell fixed-effect models of ln(density + 0.1) with day of year and a night flag, year-permutation and year-bootstrap tests. We wrote the plan before we calculated the trends. Results: in the 18 years with both surveys, the west-minus-north difference changed by +0.13 per decade (95% CI −0.49 to +0.75, p = 0.66). The along-shelf gradient in the west AP changed by −0.018 per 100 km per decade (CI −0.16 to +0.13). There was no significant change for any size class. Density had no trend in either region. The shelf-minus-off-shelf difference was positive in all four tests, but only for large krill in the west AP was it significant (p = 0.023, not adjusted). In KRILLBASE, the density-weighted mean latitude in 30–80°W moved 2.96° south with all hauls and 1.47° south in 35 fixed 2° × 4° cells (CI −3.51 to +0.55). With only the cells south of 60°S, it moved +0.08° (CI −0.85 to +0.79). Thus the KRILLBASE southward signal is in cells north of 60°S. Limits: the north-versus-west test can only detect relative changes larger than about 2.3-fold per decade. It cannot detect a rigid translation of 500 km or less. The data do not cover the Scotia Sea or South Georgia, and we did not test the change there.

Antarctic krill · Euphausia superba · range shift · Antarctic Peninsula · Palmer LTER · US AMLR · KRILLBASE · fixed footprint · southward contraction · Southern Ocean · zooplankton monitoring · null result